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AMME2262-无代写
时间：2023-11-02
THE UNIVERSITY OF SYDNEY,
SCHOOL OF AEROSPACE, MECHANICAL AND MECHATRONIC
ENGINEERING
AMME2262 & AMME9262
Thermal Engineering 1
LABORATORY
NOTES
Engine Laboratory
Page 2 of 30
ENGINE LABORATORY
1. Background:
The objective of this experiment is to familiarise students with an actual spark ignition
engine (more commonly known as a petrol engine), understand its operational
characteristics and highlight the differences between the real engine and the ideal Otto
cycle studied in class. Figure 1 shows the P-v diagrams of an ideal petrol engine cycle at
full and part loads.
Figure 1 Ideal Petrol Engine Cycle
0 → 1 Intake of fresh charge;
1 → 2 Compression of charge;
2 → 3 Constant volume combustion
3 → 4 Expansion, power stroke;
4 → 5 Pressure drop as exhaust valve opens. Like cooling in a closed cycle;
5 → 6 Exhaust stroke;
6 → 0 Intake valve opens, pressure drops at part throttle, rises if
turbo-charged.
Page 3 of 30
2. The Experiment
Aims:
i. Acquire measurements in an operating engine such as the in-cylinder pressure.
ii) Compare experimental measurements to theoretical calculations.
The Equipment:
The TD211/TD212 Small Engine (Petrol and diesel respectively) Test Set is a versatile
engine test set with instrumentation for testing the small single-cylinder engines, normally
used to power lawn mowers, generators, cultivators, pumps and generators.
The Engine Test Set helps students to understand of the most important features of an
engine, including the thermodynamic cycle and performance characteristics.
The engine is mounted and coupled to the Test Set includes a robust hydraulic
dynamometer which is simple in operation. This Dynamometer is cost-effective and
efficient, no large electrical supplies or load resistors are needed because the engine
power is dissipated into the water that passes through the Dynamometer.
The equipment is linked with TecQuipment's Versatile Data Acquisition System
(VDAS). Using the VDAS enables accurate real-time data capture, monitoring and
display, calculation and charting of all relevant parameters on a computer, making
tests quick and reliable.
Page 4 of 30
Test Set Test Procedure - Engine Performance
1. Ensure the engine has sufficient fuel in the tank and it is the correct fuel for the test
engine.
2. Ensure that the exhaust fan is switched on.
3. Slowly pull the starting handle of the Test Engine until you can feel that it has
passed the compression stroke and is easy to turn. Allow the starting handle to
return to its original position.
4. Gently rock the Dynamometer, then press the ‘Press and hold to zero’ button on
the Torque and Speed display. This will zero the Torque reading.
5. Press and hold the ‘Zero airbox pressure’ button on the DPT1 Instrument Module.
Release the button; the differential pressure is now zero.
6. Ensure both valves on the Fuel Gauge are in open position - (turn the valves so that
they are in-line with the fuel pipe).
7. Make sure that fuel has passed down the fuel feed pipe to the Test Engine.
8. Make sure that the computer is operating and has started the TecQuipment
software (VDAS and Engine Cycle Analyser, ECA100).
Page 5 of 30
9. Turn on the water supply to the Dynamometer. Open the control valve by half a
turn. Fully open the water outlet valve. Make sure that water flows through the
Dynamometer.
10. Set the ECA100software to show P – chart. Reset the Engine Cycle Analyzer
and then switch on.
Never use the Dynamometer
without water passing through it. If
you run the Dynamometer with no water flow, its
seals may
break.
CAUTION
11. Start and run the Test Engine as described in the engine manufacturers instructions
and the TecQuipment User Guide provided with the Test Engine.
a) First, move the speed control lever (1) to the "Stop" position.
b) Depending on the possibility or requirement, place the speed control lever in
either the "1/2" or "Start" position. Note: A lower speed setting will cause less
exhaust smoke when starting.
Page 6 of 30
c) Check the speed control.
d) Insert the starting key all the way and turn to position "I". Depending on the
model, the following indicators light up:
I. ▪ Charge control (2)
II. ▪ Oil pressure display (3)
III. ▪ Pre glow display (5)
IV. NOTES:
V. ▪ If the engine temperature display (4) lights up, the cylinder head
temperature is impermissibly high. Do not start the engine; eliminate
the cause.
e) Turn the starting key to position "II".
f) As soon as the engine is running, release the starting key.
I. ▪ The starting key springs back to position "I" and remains in this
position during operation.
II. ▪ The charge control (2) and oil pressure display (3) go out.
III. ▪ The operating display (1) lights up.
12. Allow the engine to reach normal operating temperature. Reset the ECA again.
Two or three attempts may be possible to get it right.
13. Set the Test Engine throttle (or rack) for maximum speed.
14. Adjust the Dynamometer control valve to increase the load on the Test Engine and
decrease its speed to its lowest stable speed. You may need to slightly shut the water
outlet valve and carefully adjust the Control Valve to give the best results.
Page 7 of 30
More water volume in the Dynamometer = more load.
NOTE Water flow removes heat from the Dynamometer.
Never fully close the outlet valve.
Figure 31 Adjust Control and Outlet Valve to Give the Best Results
15. Create a Blank Results Table for the engine as described in the TecQuipment User
Guide supplied with each engine.
16. Use the Dynamometer Control Valve to maintain the engine speed at the lowest
stable speed within +/- 100 rev.min-1. Record the Test Engine fuel consumption.
For the automatic fuel gauge (DVF1):
Allow the fuel gauge to do at least two complete cycles before you record its
calculated flow rate. This gives the best accuracy - one cycle may appear to be
complete, but may have started before your engine speed stabilized. This rule
also applies if you are to use the VDAS.
17. Record all test engine results as described in the blank results Table.
18. Use the water flow through the Dynamometer to allow the engine speed to
increase by approximately 250 rev.min-1. Again, use the Dynamometer Control Valve to
maintain this new speed and record the fuel flow and other results as shown in the Results
Table.
CONTROL VALVE
OUTLET VALVE
Page 8 of 30
19. Repeat for the other speeds (up to the maximum governed engine speed) in steps
of approximately 250 rev.min-1.
Figure 32 To use the AVF1
For 16 mL, start your timer when the level is here
For 16 mL, stop your timer when the level is here
For 8 or 24 mL (8+16), start your timer when the level is here
For 8 mL, stop your timer when the level is here
For 24 mL, stop your timer when the level is here
Shut Down
1. Refer to the Test Engine User Guide for engine stop details. There are three choices of
shutting down the engine:
a. Speed Control Lever - Push the speed control lever (1) all the way to the "STOP"
position. The engine switches off.
Page 9 of 30
b. Stop pin - Press and hold the stop pin (2) until the engine switches off. Release the stop
pin and ensure that it returns to its original position.
c. Electrical - Turn the starting key to position "0".
I. The engine switches off.
II. All indicator lamps go out.
III. Remove the starting key.
2. Close the fuel supply valve.
3. Turn off the Dynamometer water supply.
4. Switch off the electrical supply to the Instrument Frame.
Results Analysis - Engine Performance
1. From your results, calculate the air mass flow rate (the TecQuipment Software can
automatically do this for you) and plot the engine variables against speed. For comparison, it
is better to plot all variables on one chart or several charts of a similar scale. The engine
variables are:
• Engine exhaust temperature
• Torque
• Power
• Air/Fuel ratio
• Specific Fuel Consumption
• Volumetric Efficiency
• Thermal Efficiency
NOTE Ignore the torque (-) sign for your charts.
2. Look at your power and efficiency curves. What is the approximate optimum
performance speed for the engine?
3. For each speed, calculate the Brake Mean Effective Pressure (BMEP). Use the BMEP to
compare the results with other Test Engines.
Notation
Item Symbol Units Actual Value
Coefficient of Discharge for the Orifice Cd 0.6
Page 10 of 30
Calorific Value of Fuel CL J.kg-1
See Table 2.
Specific Heat of Air at Constant Pressure CP J.kg
-1 (1004.5 at low
pressure and room
temperature)
Orifice Diameter d m (See ’Technical
Specifications’ on
page 11)
Ambient Pressure pA Pa
Engine Speed N Rev.min-1
Ambient Air Temperature (at inlet) TA °K
Pressure change Δp Pa
Enthalpy of Air HA W
Combustion Energy of Fuel HF W
Heat Lost to Exhaust
HLE
W
Gas Constant for Air R J.kg-1 K 287 J.kg-1 K
Air Velocity U m.s-1
Air Density
kg.m-3
Mass Flow of Air ·
ma
kg.s-1
Mass Flow of Fuel ·
mf
kg.s-1
Volumetric Efficiency
V
%
Thermal Efficiency
T
%
Brake Mean Effective Pressure (BMEP) bar
Mass and Volume Flow
Many of the calculations need the mass flow of a liquid, but the instruments read volume flow. This is
because the mass flow depends on the density of the liquid, which can vary with temperature. The
relationship between mass and volume of a liquid is:
Mass = Density × Volume
So:
Mass Flow (in kg.s-1) = Density (in kg.m-3) x (Volume Flow (in L.s-1)/1000)
Page 11 of 30
Air Consumption
The Airbox includes an orifice at its inlet. The DPT1 Instrument Module shows the ambient air
pressure (before the orifice) and the air pressure in the Airbox (after the orifice). The difference
in the pressures (Δp) and the air density ( ) will give you the basic airflow velocity (U):
= √
2∆
·
To find the mass flow (ma ) the airflow velocity equation is modified to separate the factors of density
and to include the coefficient of discharge (
C
d) for the orifice and the orifice diameter:
̇ =
2
4
√
2∆
Fuel Consumption
To find the mass fuel consumption, you need the volumetric fuel flow and the fuel density:
Mass Fuel Flow (in kg.s-1) = Fuel Density (kg.m-3) x (Fuel Volume Flow (L.s-1)/1000)
To find the specific fuel consumption (work from the fuel) you need the mass fuel consumption and the
mechanical power developed (measured by the Dynamometer):
Specific Fuel Consumption =
Mass Fuel Consumption x 3600
Mechanical Power/1000
Where:
Specific Fuel Consumption = kg kW.h-1
Mass Fuel Consumption = kg.s-1
Mechanical Power = Watts
Air/Fuel Ratio
This is simply the ratio of the air mass flow against the fuel mass flow:
Air/Fuel Ratio =
Volumetric Efficiency
As shown in Figures 27 and 28, the four-stroke engine makes two revolutions for each swept
volume of air that it uses, but the two-stroke engine only rotates once for each swept volume.
Page 12 of 30
The four-stroke engine piston moves down to draw air/fuel mixture in, then moves up to
compress and combust the mixture. It is then forced down again by the combustion and moves
up to push out the exhaust gases. The four strokes are:
• Fresh Air/Fuel Mixture Drawn In
• Mixture Compressed
• Mixture Ignited
• Exhaust Pushed Out
The two-stroke engine draws in fuel/air mixture and exhaust gas around its crankcase as it moves,
so that each time the piston rises, it is ready for combustion.
(d) Exhaust
Figure 27 The Four-Stroke Cycle
The volumetric efficiency is the ratio of the measured volume of air or gas that enters the engine
against the calculated volume of air that the engine should use. For this, you need to know the
engine capacity, the amount of engine strokes and its speed:
Calculated Volume =
Engine Capacity ×
(Strokes/2) x 60
c)Power (
( a)Induction b)Compression (
Page 13 of 30
Engine capacity is normally given in cc (cubic centimetres) or Litres. You
must NOTEconvert this into cubic metres for the volume calculations.
100 cc = 0.0001 m3
Measured Volume =
̇
× 100
Volumetric Efficiency, =
× 100
(
d
)
E
x
h
a
u
s
t
o
f spent charge. Transfer of crankcase charge to cylinder.
This diagram shows the inlet and outlet ports on one side of the engine for
clarity - they are normally opposing each other (cross-flow).
Figure 28 The Two-Stroke Cycle
(a) Piston rising, compression of mixture.
Crankcase suction.
(b) Piston rising, compression of mixture.
Induction of charge into crankcase.
Page 14 of 30
Heat Energy and Enthalpy
The heat energy of combustion from the fuel (in Watts) is found by the fuel consumption and its calorific
value:
= ̇ × 10
6
The inlet air enthalpy (in Watts) is found from the air mass flow rate and the ambient
temperature:
= ̇ × 10
3
Thermal Efficiency
This is the ratio of the heat energy of combustion from the fuel against the useful mechanical
power developed by the engine:
=
Mechanical Power
× 100
Brake Mean Effective Pressure (BMEP)
This is the average mean pressure in the cylinder that would produce the measured brake output.
This pressure is calculated as the uniform pressure in the cylinder as the piston rises from top to
bottom of each power stroke.
The BMEP is a useful calculation to compare engines of any size.
=
60 x Power x (Strokes/2)
0.1 x Speed x Engine capacity
× 100
Where:
BMEP is in bar Power = Watts
Speed = Rev.min-1
Engine Capacity = Cubic Centimetres (cm3) or cc
Report
Page 15 of 30
Reports should be short and brief but technically sound. There is no pre-set length for the reports
however they should be concise but with clear technical explanations, typically 4-6 pages of text. All
experimental results must be tabulated in an appendix. Calculations can be done using spreadsheets,
Matlab or by hand with sample calculation included. Reports must include a cover page stating all
group members names and SID’s and the date the lab was completed if it was completed in person. All
reports must include the universities plagiarism sheet signed by all group members
( https://web.aeromech.usyd.edu.au//plagiarism/Compliance_Statement.doc ). Reports are due Friday
at 5pm week 13 electronically through Canvas. All members must join a group and submit the report.
Report outline:
1. Aims: list the questions you want to find answers from the experiment.
2. Method: brief outline of the method used.
3. Results: raw and processed results, possibly tabulated in a spreadsheet.
4. Calculations: sample calculations to show how the spreadsheets in (3) work.
5. Analyses: graphs and plots. Make sure you present useful and sensible information. Use your
judgment skills to make decisions of what should be included and the order of importance of each.
6. Discussion: discussion and comment on your results. Give reasons, be rational, be scientific, be
sensible, and be practical.
7. Conclusion: describe your conclusions and state whether all your objectives met. If not, provide
reasons and difficulties
Do not cut and paste articles from any other sources. Use your own words to communicate ideas in
your report. Note that long reports do not attract marks. Reports that attract good marks show
originality, creativity, professionalism, clear communication of ideas, well presented and direct
answers.
Your report should contain discussion, analysis and figures relevant to the following:
1. In-cylinder pressure vs. time
2. in-cylinder pressure vs. volume
3. In-cylinder pressure vs. crank angle
4. A proposed Otto cycle to model the engine
5. A proposed Diesel cycle to model the engine
6. A proposed Dual cycle to model the engine
A report that achieves a high mark will address all of the areas above (1-6) for the different engine
speeds examined. It is advisable is to do at least one speed and one cycle really well, rather
than trying to look at all cycles and all speeds and not really doing any of them in any depth.
Calculations:
-Compare the cycle calculations (temperatures, pressures and power output) with Otto, Diesel and
Dual cycles using constant and variable specific heats.
-Compute the BMEP, thermal efficiency, volumetric efficiency, air to fuel ratio and specific fuel
consumption.
Mark breakdown, 20% presentation, 80% calculations and cycle graphs and analysis.
(temperatures, pressures and power input) with Carnot, ideal vapour compression cycle and actual
vapour compression cycle analysis.
Mark breakdown, 20% presentation, 80% calculations and cycle graphs and analysis.
Page 16 of 30
AMME2262 & AMME9262
Thermal Engineering 1
Refrigerator Laboratory Notes
REFRIGERATOR
1. Background
The objective of this experiment is to familiarise students with the vapour compression
cycle which drives most of the air conditioning and refrigeration processes worldwide.
The experimental rig is sufficiently instrumented to enable students to draw the real cycle
and appreciate the differences that arise between an actual vapour compression cycle
(AVC) , the ideal vapour compression cycle and the Carnot refrigeration cycle. The type
of refrigerant used with the current rig is R134a which is a commonly used refrigerant in
industry for both air conditioning systems and refrigeration systems.
Process cycle
The major components of the vapour compression cycle and the corresponding P-h
diagram for the ideal vapour compression cycle are shown in Figure 1. In the four-
process cycle (evaporation, compression, condensation and throttling), work input from a
compressor pressurises the vapour leaving the evaporator to be fed into the condenser as
superheated vapour. The high pressure condensed liquid leaving the condenser is
throttled to the evaporator pressure by passing it through an expansion valve (capillary
tube or thermal expansion valve).
Figure 1: Vapour compression cycle and the corresponding pressure-enthalpy diagram for
an ideal vapour compression cycle (IVC).
(1)
(4)
(2) (3)
h
P
Q L
Q H
Page 17 of 30
In practice in real devices, the vapour leaves the evaporator in a slightly superheated state,
and the liquid leaves the condenser in a slightly sub-cooled state. In the ideal vapour
compression cycle, assumptions are made so that the evaporator and the condenser
operate isobarically; that the compression is isentropic; and that the throttling occurs at
constant enthalpy
2. The Experiment
Aims
To operate the RA1 refrigeration system and understand the relation between the hardware
components and the refrigeration cycle.
Method
Running the RA1 unit at nominal settings and observing the changes in temperature and
pressure around the system.
Introduction:
The vapour-compression refrigeration system is the most common refrigeration system
used today. RA1 is a computer-controlled vapour-compression refrigeration unit with
automatic recording of appropriate process variables using an integral USB interface
device. This allows the student to gain a thorough understanding of the refrigeration
process by changing the operation of different parts of the process and recording the
response of the complete system.
The compressor is driven by a three-phase electric motor with an inverter drive that
allows operation at different operating speeds. The inverter incorporates Torque Vector
Control and allows the speed and torque of the motor to be measured and logged by the
controlling PC. Temperatures throughout the system and pressure on both sides of the
compressor are measured and logged. The refrigerant flow rate is also measured by a
variable area flowmeter.
The condenser and evaporator both consist of a brazed plate heat exchanger. The water-
cooled condenser and water heated evaporator utilises a large reservoir of water to
minimise changes in water temperature during operation. The use of a reservoir to
recirculate the same water continuously eliminates the need for a permanent mains water
connection or water flowing continuously to drain and isolates the system from
fluctuation in mains water pressure or temperature. The flow of water through each heat
exchanger is independently varied by changing the speed of a gear pump. The speed of
both pumps is set by the operator using the PC.
The unit is self-contained, only requiring connection to an electrical supply and a suitable
PC (not supplied). The unit is supplied with the necessary software and incorporates a
USB computer interface device for connection to a PC.
Page 18 of 30
The water reservoir is designed to stand on the floor. The process components are
mounted on a metal support frame that is designed to stand on top of the reservoir. Self-
sealing quick-release connectors and flexible tubing connect the reservoir to the
refrigeration unit.
RA1 Refrigeration Unit
This equipment uses refrigerant R134a (Also known as: HFC-134a; 1, 1, 1-2
Tetrafluoroethane; Norflurane; Norfluran). This is a common refrigerant introduced to
replace CFC (chlorofluorocarbon) refrigerants such as R-12. R134a is colourless, non-
flammable and non-corrosive with a very faint odour. In the RA1 the refrigerant is
contained within a completely sealed circuit and is safe under normal use as described in
this manual.
Apparatus Setup
The process components of the RA1 Vapour Pressure Refrigeration Unit are mounted on a
metal support frame (1) that is designed to stand on top of a large water reservoir. The
water reservoir is designed to stand on the floor. Self-sealing quick release connectors (4)
and flexible tubing connect the reservoir to the refrigeration unit.
With the exception of the compressor and motor, the important process components are
mounted on a panel (2) at the front of the frame so that the student can clearly observe the
flow path through the process. The components that create the refrigeration process are
detailed below.
The process is fully instrumented to allow all of the important parameters to be measured
so that the performance can be monitored. Temperature sensors T1 to T9 measure the
temperature at every stage of the refrigeration process, including the water entering and
Page 19 of 30
leaving the condenser and evaporator. Pressure sensors P1 and P2 measure the pressure of
the refrigerant before and after the compressor. Water flow through the condenser and
evaporator is measured with electronic flowmeters FM1 and FM2. The refrigerant flow
rate is determined using a variable area flowmeter FM3 (13). A schematic of the
apparatus used is shown in Fig. 5. Suction and delivery pressures are measured by
Bourdon gauges. Flow meters measure water and refrigerant flow rates.
Figure 5: Layout of the Refrigeration rig
Methods
Take 3 sets of readings for the same setting on your refrigeration rig allowing 5-10min
intervals between each set. Take the average of the 3 sets of readings for your analysis.
Equipment Required
RA1 Refrigeration Unit
Compatible PC with Armfield RA1 software
Page 20 of 30
Theory
T – s diagram for the Vapour-Compression Refrigeration Cycle
In this cycle, the refrigerant (R134a) enters the compressor as a vapour and is compressed
and superheated (Points T3 to T4) i.e. it is raised above its saturation temperature.
Supercritical
fluid
Subcooled
liquid
Page 21 of 30
The superheated refrigerant vapour passes through the condenser which first cools and
removes the superheat and then condenses the vapour into liquid by removing latent heat
at constant pressure and temperature (Points T4 to T5). Heat from the refrigerant is
transferred to the stream of water in the condenser.
The liquid refrigerant then passes through the expansion valve (also called a throttle valve)
where it expands and the pressure abruptly decreases, this results in a mixture of liquid
and vapour at a lower temperature and pressure (Points T6 to T7).
The cold liquid/vapour refrigerant mixture then travels through the evaporator and is
heated and completely vaporized by heat transfer from the water in the evaporator (Points
T7 to T3).
The refrigerant vapour exiting the evaporator returns to the compressor inlet to complete
the thermodynamic cycle.
An important measure of the system performance is the Coefficient of Performance (CoP).
This is the ratio of the heat exchanged in the evaporator to the amount of work put into the
system by the compressor. In a refrigeration system, this is typically in the region of 3 to 6
i.e. more heat is exchanged than input by the compressor. The CoP is continuously
calculated from the other system variables and displayed on the mimic diagram.
Equipment Set-Up
Ensure that the equipment has been installed in accordance with the Installation section.
Check that the USB connection is made between the RA1 unit and the PC, and that the
RA1 software is installed and running. Check that the circuit breakers and RCD device at
the rear left of the unit are in the on (up) position. Turn the unit on by pressing the
ON/OFF switch on the unit, then click on the Power On switch on the RA1 software
mimic diagram.
Procedure
1. Set the condenser water pump speed to 50% (this may vary and must achieve 1.5 l/min)
and the evaporator water pump speed to 70% (this may vary and must achieve 5.5
l/min).
2. Check that there is a flow of water through both the condenser and evaporator
indicated by FM1 and FM2 on the mimic diagram.
3. When the water flowing into both condenser and evaporator becomes stable, set the
compressor speed to 50% and click “Compressor On” button on the software. The
compressor will run at 3000rpm for 30 seconds then change to the set speed. Check
that refrigerant flows around the system indicated by the variable area flowmeter FM3
on the RA1 – MKII. Let the system run until the temperatures and pressures are
reasonably stable.
4. Configure the sample options as ‘Automatic / 10 seconds intervals’ and click the “GO”
button to log the current set of readings from the sensors. View graphs of T1, T3 and
T7 on the primary y-axis and P1 and P2 on the secondary y-axis.
5. View the table of results and check that a set of readings has been logged. Save the
result for future reference.
Page 22 of 30
Results
View the table of results. Observe the changes in pressure and temperature throughout the
process and compare them with the T – s diagram shown in the theory above. Observe that
the calculated Coefficient of Performance (COP) is significantly greater than unity
whereby more useful heat is transferred in the evaporator than electrical energy is required
to run the compressor.
Page 23 of 30
Conclusion
These observations should provide a basic understanding of the refrigeration process.
Describe the function of the important parts of the refrigeration process, namely the
compressor, condenser, expansion valve and evaporator and explain the temperature and
pressure changes associated with each.
Observe the value of the Coefficient of Performance obtained and comment on the
magnitude of this value.
The exercises that follow investigate the vapour-compression refrigeration cycle in more
detail and the effect of changes to individual parts of the refrigeration system.
Manual calculation of system performance using refrigerant
properties
Objective
To perform appropriate energy balances and a detailed analysis of the performance of the
refrigeration system.
Method
Using the formulae below and the physical properties of the refrigerant to calculate the
performance of the refrigeration system.
Equipment Required
RA1 Refrigeration Unit
Page 24 of 30
Compatible PC with Armfield RA1 software
Table of refrigerant properties (R134A) See Table of Refrigerant Properties for R134A
(Temperature) and Table of Refrigerant Properties for R134A (Pressure).
Table of Refrigerant Properties for R134A (Temperature)
Page 25 of 30
Table of Refrigerant Properties for R134A (Pressure)
Theory
Some formulas below are useful, some are presented just for reference and are not
needed for the analysis required in the report.
The performance of the refrigeration system can be determined using the following
equations:
Mass Flow Rate
Where: = Mass flow rate of the refrigerant (Kg/s)
R = Flow meter reading (l/hr)
= Density of the refrigerant (1.203 Kg/l)
Page 26 of 30
Work Done on Refrigerant
Where: Work = Work done on refrigerant (Watts)
= Mass flow rate of the refrigerant (kg/s)
h2 = Enthalpy of refrigerant at outlet of compressor (kJ/kg)
h1 = Enthalpy of refrigerant at inlet of compressor (kJ/Kg)
Speed of Compressor
Where: Speed = Speed of the compressor (rpm)
CS = Compressor setting (%)
F = Maximum frequency of motor (Hz)
n = Number of polls in motor
Mechanical Power or Compressor Work
Where: W = Work done by the compressor (Watts)
Speed = Speed of the compressor (rpm)
= Torque of the compressor (Nm)
Compressor Efficiency
Where: W = Work done by the compressor (Watts)
Work = Work on the refrigerant (Watts)
Sensible Heat Change in Condenser
( ) ( )6BPh T h T−
Where: h(T) = enthalpy of a saturated liquid at the given temperature
Page 27 of 30
TBP = Boiling point of refrigerant (K)
T6 = Temperature of refrigerant at outlet of condenser (K)
Heat Removed from Refrigerant
Where: Heatout = Heat removed from the refrigerant (Watts)
= Mass flow rate of the refrigerant (Kg/s)
h3 = Enthalpy of refrigerant at outlet of condenser (kJ/Kg)
h2 = Enthalpy of refrigerant at inlet of condenser (kJ/Kg)
Energy Leaving the Condenser
Where: Qout = Energy removed from the condenser (Watts)
F1 = Water flow rate through condenser (l/min)
T2 = Temperature of water at outlet of condenser (K)
T1 = Temperature of water at inlet of condenser (K)
Condenser Efficiency
Where: Qout = Energy removed from the condenser (Watts)
Heatout = Heat removed from the refrigerant (Watts) Heat
Absorbed
Where: Heatin = Heat absorbed by the refrigerant (Watts)
Page 28 of 30
= Mass flow rate of the refrigerant (Kg/s)
h1 = Enthalpy of refrigerant at outlet of evaporator (kJ/Kg)
h2 = Enthalpy of refrigerant at inlet of evaporator (kJ/Kg)
Energy Entering the Evaporator
Where: Qin = Energy absorbed by the evaporator (Watts)
F2 = Water flow rate through evaporator (l/min)
T8 = Temperature of water at inlet of evaporator (K)
T9 = Temperature of water at outlet of evaporator (K)
Evaporator Efficiency
Where: Qin = Energy absorbed from the evaporator (Watts)
Heatin = Heat absorbed by the refrigerant (Watts)
Coefficient of performance
Coefficient of Performance (COP) is the index used to describe how effectively the
device functions as a sink/source of heat transfer as a result of the work input. COP is
often a function of the difference between the condenser’s and the evaporator’s working
temperatures, and the temperature of their surroundings.
The COP for refrigeration (where cooling effect is desired) is defined as:
COPrefrig = ||
||
Where Qin is the heat input to the evaporator
W is the work input to the compressor
Steady flow energy equation
Page 29 of 30
There are 4 components to the refrigeration cycle: compressor, condenser, evaporator and
throttle. The steady flow energy equation can be applied to every component as a
controlled volume and the system as a whole.
out in
Q W m m − = −
Where Q is the net heat Wis the net work mout
and min are the mass flow rates of fluid
accounts for the enthalpy, kinetic energy and potential energy of the fluid.
Procedure
Use any of the measurements from the previous exercises and analyse the performance
using the above formulae.
Conclusion
Comment on the performance of the individual components in the refrigeration system.
If results are available from different runs at different settings, compare the results
and comment on the changes in system performance.
Page 30 of 30
Report
Reports should be short and brief but technically sound. There is no pre-set length for the reports
however they should be concise but with clear technical explanations, typically 4-6 pages of text. All
experimental results must be tabulated in an appendix. Calculations can be done using spreadsheets,
Matlab or by hand with sample calculation included. Reports must include a cover page stating all
group members names and SID’s and the date the lab was completed if it was completed in person. All
reports must include the universities plagiarism sheet signed by all group members
( https://web.aeromech.usyd.edu.au//plagiarism/Compliance_Statement.doc ). Reports are due Friday
at 5pm week 13 electronically through Canvas. All members must join a group and submit the report.
Report outline:
1. Aims: list the questions you want to find answers from the experiment.
2. Method: brief outline of the method used.
3. Results: raw and processed results, possibly tabulated in a spreadsheet.
4. Calculations: sample calculations to show how the spreadsheets in (3) work.
5. Analyses: graphs and plots. Make sure you present useful and sensible information. Use your
judgment skills to make decisions of what should be included and the order of importance of each.
6. Discussion: discussion and comment on your results. Give reasons, be rational, be scientific, be
sensible, and be practical.
7. Conclusion: describe your conclusions and state whether all your objectives met. If not, provide
reasons and difficulties
Do not cut and paste articles from any other sources. Use your own words to communicate ideas in
your report. Note that long reports do not attract marks. Report that attract good marks show
originality, creativity, professionalism, clear communication of ideas, well presented and direct
answers.
Your report should contain at least 4 graphs:
1. Measured variables (e.g. temperature and pressure) vs. time to show steady operating conditions
have been reached.
2. Carnot cycle
3. Ideal vapour compression cycle
4. Actual vapour compression cycle
Calculations:
-Many quantities are already computed in the program you should confirm all of these calculations in
your report. Analyse each of the four components and where possible (evaporator and condenser)
consider and energy balance over the water and refrigerant component of the heat exchanger.
-Compare the cycle calculations (temperatures, pressures and power input) with Carnot, ideal vapour
compression cycle and actual vapour compression cycle analysis.
Mark breakdown, 20% presentation, 80% calculations and cycle graphs and analysis.
SCHOOL OF AEROSPACE, MECHANICAL AND MECHATRONIC
ENGINEERING
AMME2262 & AMME9262
Thermal Engineering 1
LABORATORY
NOTES
Engine Laboratory
Page 2 of 30
ENGINE LABORATORY
1. Background:
The objective of this experiment is to familiarise students with an actual spark ignition
engine (more commonly known as a petrol engine), understand its operational
characteristics and highlight the differences between the real engine and the ideal Otto
cycle studied in class. Figure 1 shows the P-v diagrams of an ideal petrol engine cycle at
full and part loads.
Figure 1 Ideal Petrol Engine Cycle
0 → 1 Intake of fresh charge;
1 → 2 Compression of charge;
2 → 3 Constant volume combustion
3 → 4 Expansion, power stroke;
4 → 5 Pressure drop as exhaust valve opens. Like cooling in a closed cycle;
5 → 6 Exhaust stroke;
6 → 0 Intake valve opens, pressure drops at part throttle, rises if
turbo-charged.
Page 3 of 30
2. The Experiment
Aims:
i. Acquire measurements in an operating engine such as the in-cylinder pressure.
ii) Compare experimental measurements to theoretical calculations.
The Equipment:
The TD211/TD212 Small Engine (Petrol and diesel respectively) Test Set is a versatile
engine test set with instrumentation for testing the small single-cylinder engines, normally
used to power lawn mowers, generators, cultivators, pumps and generators.
The Engine Test Set helps students to understand of the most important features of an
engine, including the thermodynamic cycle and performance characteristics.
The engine is mounted and coupled to the Test Set includes a robust hydraulic
dynamometer which is simple in operation. This Dynamometer is cost-effective and
efficient, no large electrical supplies or load resistors are needed because the engine
power is dissipated into the water that passes through the Dynamometer.
The equipment is linked with TecQuipment's Versatile Data Acquisition System
(VDAS). Using the VDAS enables accurate real-time data capture, monitoring and
display, calculation and charting of all relevant parameters on a computer, making
tests quick and reliable.
Page 4 of 30
Test Set Test Procedure - Engine Performance
1. Ensure the engine has sufficient fuel in the tank and it is the correct fuel for the test
engine.
2. Ensure that the exhaust fan is switched on.
3. Slowly pull the starting handle of the Test Engine until you can feel that it has
passed the compression stroke and is easy to turn. Allow the starting handle to
return to its original position.
4. Gently rock the Dynamometer, then press the ‘Press and hold to zero’ button on
the Torque and Speed display. This will zero the Torque reading.
5. Press and hold the ‘Zero airbox pressure’ button on the DPT1 Instrument Module.
Release the button; the differential pressure is now zero.
6. Ensure both valves on the Fuel Gauge are in open position - (turn the valves so that
they are in-line with the fuel pipe).
7. Make sure that fuel has passed down the fuel feed pipe to the Test Engine.
8. Make sure that the computer is operating and has started the TecQuipment
software (VDAS and Engine Cycle Analyser, ECA100).
Page 5 of 30
9. Turn on the water supply to the Dynamometer. Open the control valve by half a
turn. Fully open the water outlet valve. Make sure that water flows through the
Dynamometer.
10. Set the ECA100software to show P – chart. Reset the Engine Cycle Analyzer
and then switch on.
Never use the Dynamometer
without water passing through it. If
you run the Dynamometer with no water flow, its
seals may
break.
CAUTION
11. Start and run the Test Engine as described in the engine manufacturers instructions
and the TecQuipment User Guide provided with the Test Engine.
a) First, move the speed control lever (1) to the "Stop" position.
b) Depending on the possibility or requirement, place the speed control lever in
either the "1/2" or "Start" position. Note: A lower speed setting will cause less
exhaust smoke when starting.
Page 6 of 30
c) Check the speed control.
d) Insert the starting key all the way and turn to position "I". Depending on the
model, the following indicators light up:
I. ▪ Charge control (2)
II. ▪ Oil pressure display (3)
III. ▪ Pre glow display (5)
IV. NOTES:
V. ▪ If the engine temperature display (4) lights up, the cylinder head
temperature is impermissibly high. Do not start the engine; eliminate
the cause.
e) Turn the starting key to position "II".
f) As soon as the engine is running, release the starting key.
I. ▪ The starting key springs back to position "I" and remains in this
position during operation.
II. ▪ The charge control (2) and oil pressure display (3) go out.
III. ▪ The operating display (1) lights up.
12. Allow the engine to reach normal operating temperature. Reset the ECA again.
Two or three attempts may be possible to get it right.
13. Set the Test Engine throttle (or rack) for maximum speed.
14. Adjust the Dynamometer control valve to increase the load on the Test Engine and
decrease its speed to its lowest stable speed. You may need to slightly shut the water
outlet valve and carefully adjust the Control Valve to give the best results.
Page 7 of 30
More water volume in the Dynamometer = more load.
NOTE Water flow removes heat from the Dynamometer.
Never fully close the outlet valve.
Figure 31 Adjust Control and Outlet Valve to Give the Best Results
15. Create a Blank Results Table for the engine as described in the TecQuipment User
Guide supplied with each engine.
16. Use the Dynamometer Control Valve to maintain the engine speed at the lowest
stable speed within +/- 100 rev.min-1. Record the Test Engine fuel consumption.
For the automatic fuel gauge (DVF1):
Allow the fuel gauge to do at least two complete cycles before you record its
calculated flow rate. This gives the best accuracy - one cycle may appear to be
complete, but may have started before your engine speed stabilized. This rule
also applies if you are to use the VDAS.
17. Record all test engine results as described in the blank results Table.
18. Use the water flow through the Dynamometer to allow the engine speed to
increase by approximately 250 rev.min-1. Again, use the Dynamometer Control Valve to
maintain this new speed and record the fuel flow and other results as shown in the Results
Table.
CONTROL VALVE
OUTLET VALVE
Page 8 of 30
19. Repeat for the other speeds (up to the maximum governed engine speed) in steps
of approximately 250 rev.min-1.
Figure 32 To use the AVF1
For 16 mL, start your timer when the level is here
For 16 mL, stop your timer when the level is here
For 8 or 24 mL (8+16), start your timer when the level is here
For 8 mL, stop your timer when the level is here
For 24 mL, stop your timer when the level is here
Shut Down
1. Refer to the Test Engine User Guide for engine stop details. There are three choices of
shutting down the engine:
a. Speed Control Lever - Push the speed control lever (1) all the way to the "STOP"
position. The engine switches off.
Page 9 of 30
b. Stop pin - Press and hold the stop pin (2) until the engine switches off. Release the stop
pin and ensure that it returns to its original position.
c. Electrical - Turn the starting key to position "0".
I. The engine switches off.
II. All indicator lamps go out.
III. Remove the starting key.
2. Close the fuel supply valve.
3. Turn off the Dynamometer water supply.
4. Switch off the electrical supply to the Instrument Frame.
Results Analysis - Engine Performance
1. From your results, calculate the air mass flow rate (the TecQuipment Software can
automatically do this for you) and plot the engine variables against speed. For comparison, it
is better to plot all variables on one chart or several charts of a similar scale. The engine
variables are:
• Engine exhaust temperature
• Torque
• Power
• Air/Fuel ratio
• Specific Fuel Consumption
• Volumetric Efficiency
• Thermal Efficiency
NOTE Ignore the torque (-) sign for your charts.
2. Look at your power and efficiency curves. What is the approximate optimum
performance speed for the engine?
3. For each speed, calculate the Brake Mean Effective Pressure (BMEP). Use the BMEP to
compare the results with other Test Engines.
Notation
Item Symbol Units Actual Value
Coefficient of Discharge for the Orifice Cd 0.6
Page 10 of 30
Calorific Value of Fuel CL J.kg-1
See Table 2.
Specific Heat of Air at Constant Pressure CP J.kg
-1 (1004.5 at low
pressure and room
temperature)
Orifice Diameter d m (See ’Technical
Specifications’ on
page 11)
Ambient Pressure pA Pa
Engine Speed N Rev.min-1
Ambient Air Temperature (at inlet) TA °K
Pressure change Δp Pa
Enthalpy of Air HA W
Combustion Energy of Fuel HF W
Heat Lost to Exhaust
HLE
W
Gas Constant for Air R J.kg-1 K 287 J.kg-1 K
Air Velocity U m.s-1
Air Density
kg.m-3
Mass Flow of Air ·
ma
kg.s-1
Mass Flow of Fuel ·
mf
kg.s-1
Volumetric Efficiency
V
%
Thermal Efficiency
T
%
Brake Mean Effective Pressure (BMEP) bar
Mass and Volume Flow
Many of the calculations need the mass flow of a liquid, but the instruments read volume flow. This is
because the mass flow depends on the density of the liquid, which can vary with temperature. The
relationship between mass and volume of a liquid is:
Mass = Density × Volume
So:
Mass Flow (in kg.s-1) = Density (in kg.m-3) x (Volume Flow (in L.s-1)/1000)
Page 11 of 30
Air Consumption
The Airbox includes an orifice at its inlet. The DPT1 Instrument Module shows the ambient air
pressure (before the orifice) and the air pressure in the Airbox (after the orifice). The difference
in the pressures (Δp) and the air density ( ) will give you the basic airflow velocity (U):
= √
2∆
·
To find the mass flow (ma ) the airflow velocity equation is modified to separate the factors of density
and to include the coefficient of discharge (
C
d) for the orifice and the orifice diameter:
̇ =
2
4
√
2∆
Fuel Consumption
To find the mass fuel consumption, you need the volumetric fuel flow and the fuel density:
Mass Fuel Flow (in kg.s-1) = Fuel Density (kg.m-3) x (Fuel Volume Flow (L.s-1)/1000)
To find the specific fuel consumption (work from the fuel) you need the mass fuel consumption and the
mechanical power developed (measured by the Dynamometer):
Specific Fuel Consumption =
Mass Fuel Consumption x 3600
Mechanical Power/1000
Where:
Specific Fuel Consumption = kg kW.h-1
Mass Fuel Consumption = kg.s-1
Mechanical Power = Watts
Air/Fuel Ratio
This is simply the ratio of the air mass flow against the fuel mass flow:
Air/Fuel Ratio =
Volumetric Efficiency
As shown in Figures 27 and 28, the four-stroke engine makes two revolutions for each swept
volume of air that it uses, but the two-stroke engine only rotates once for each swept volume.
Page 12 of 30
The four-stroke engine piston moves down to draw air/fuel mixture in, then moves up to
compress and combust the mixture. It is then forced down again by the combustion and moves
up to push out the exhaust gases. The four strokes are:
• Fresh Air/Fuel Mixture Drawn In
• Mixture Compressed
• Mixture Ignited
• Exhaust Pushed Out
The two-stroke engine draws in fuel/air mixture and exhaust gas around its crankcase as it moves,
so that each time the piston rises, it is ready for combustion.
(d) Exhaust
Figure 27 The Four-Stroke Cycle
The volumetric efficiency is the ratio of the measured volume of air or gas that enters the engine
against the calculated volume of air that the engine should use. For this, you need to know the
engine capacity, the amount of engine strokes and its speed:
Calculated Volume =
Engine Capacity ×
(Strokes/2) x 60
c)Power (
( a)Induction b)Compression (
Page 13 of 30
Engine capacity is normally given in cc (cubic centimetres) or Litres. You
must NOTEconvert this into cubic metres for the volume calculations.
100 cc = 0.0001 m3
Measured Volume =
̇
× 100
Volumetric Efficiency, =
× 100
(
d
)
E
x
h
a
u
s
t
o
f spent charge. Transfer of crankcase charge to cylinder.
This diagram shows the inlet and outlet ports on one side of the engine for
clarity - they are normally opposing each other (cross-flow).
Figure 28 The Two-Stroke Cycle
(a) Piston rising, compression of mixture.
Crankcase suction.
(b) Piston rising, compression of mixture.
Induction of charge into crankcase.
Page 14 of 30
Heat Energy and Enthalpy
The heat energy of combustion from the fuel (in Watts) is found by the fuel consumption and its calorific
value:
= ̇ × 10
6
The inlet air enthalpy (in Watts) is found from the air mass flow rate and the ambient
temperature:
= ̇ × 10
3
Thermal Efficiency
This is the ratio of the heat energy of combustion from the fuel against the useful mechanical
power developed by the engine:
=
Mechanical Power
× 100
Brake Mean Effective Pressure (BMEP)
This is the average mean pressure in the cylinder that would produce the measured brake output.
This pressure is calculated as the uniform pressure in the cylinder as the piston rises from top to
bottom of each power stroke.
The BMEP is a useful calculation to compare engines of any size.
=
60 x Power x (Strokes/2)
0.1 x Speed x Engine capacity
× 100
Where:
BMEP is in bar Power = Watts
Speed = Rev.min-1
Engine Capacity = Cubic Centimetres (cm3) or cc
Report
Page 15 of 30
Reports should be short and brief but technically sound. There is no pre-set length for the reports
however they should be concise but with clear technical explanations, typically 4-6 pages of text. All
experimental results must be tabulated in an appendix. Calculations can be done using spreadsheets,
Matlab or by hand with sample calculation included. Reports must include a cover page stating all
group members names and SID’s and the date the lab was completed if it was completed in person. All
reports must include the universities plagiarism sheet signed by all group members
( https://web.aeromech.usyd.edu.au//plagiarism/Compliance_Statement.doc ). Reports are due Friday
at 5pm week 13 electronically through Canvas. All members must join a group and submit the report.
Report outline:
1. Aims: list the questions you want to find answers from the experiment.
2. Method: brief outline of the method used.
3. Results: raw and processed results, possibly tabulated in a spreadsheet.
4. Calculations: sample calculations to show how the spreadsheets in (3) work.
5. Analyses: graphs and plots. Make sure you present useful and sensible information. Use your
judgment skills to make decisions of what should be included and the order of importance of each.
6. Discussion: discussion and comment on your results. Give reasons, be rational, be scientific, be
sensible, and be practical.
7. Conclusion: describe your conclusions and state whether all your objectives met. If not, provide
reasons and difficulties
Do not cut and paste articles from any other sources. Use your own words to communicate ideas in
your report. Note that long reports do not attract marks. Reports that attract good marks show
originality, creativity, professionalism, clear communication of ideas, well presented and direct
answers.
Your report should contain discussion, analysis and figures relevant to the following:
1. In-cylinder pressure vs. time
2. in-cylinder pressure vs. volume
3. In-cylinder pressure vs. crank angle
4. A proposed Otto cycle to model the engine
5. A proposed Diesel cycle to model the engine
6. A proposed Dual cycle to model the engine
A report that achieves a high mark will address all of the areas above (1-6) for the different engine
speeds examined. It is advisable is to do at least one speed and one cycle really well, rather
than trying to look at all cycles and all speeds and not really doing any of them in any depth.
Calculations:
-Compare the cycle calculations (temperatures, pressures and power output) with Otto, Diesel and
Dual cycles using constant and variable specific heats.
-Compute the BMEP, thermal efficiency, volumetric efficiency, air to fuel ratio and specific fuel
consumption.
Mark breakdown, 20% presentation, 80% calculations and cycle graphs and analysis.
(temperatures, pressures and power input) with Carnot, ideal vapour compression cycle and actual
vapour compression cycle analysis.
Mark breakdown, 20% presentation, 80% calculations and cycle graphs and analysis.
Page 16 of 30
AMME2262 & AMME9262
Thermal Engineering 1
Refrigerator Laboratory Notes
REFRIGERATOR
1. Background
The objective of this experiment is to familiarise students with the vapour compression
cycle which drives most of the air conditioning and refrigeration processes worldwide.
The experimental rig is sufficiently instrumented to enable students to draw the real cycle
and appreciate the differences that arise between an actual vapour compression cycle
(AVC) , the ideal vapour compression cycle and the Carnot refrigeration cycle. The type
of refrigerant used with the current rig is R134a which is a commonly used refrigerant in
industry for both air conditioning systems and refrigeration systems.
Process cycle
The major components of the vapour compression cycle and the corresponding P-h
diagram for the ideal vapour compression cycle are shown in Figure 1. In the four-
process cycle (evaporation, compression, condensation and throttling), work input from a
compressor pressurises the vapour leaving the evaporator to be fed into the condenser as
superheated vapour. The high pressure condensed liquid leaving the condenser is
throttled to the evaporator pressure by passing it through an expansion valve (capillary
tube or thermal expansion valve).
Figure 1: Vapour compression cycle and the corresponding pressure-enthalpy diagram for
an ideal vapour compression cycle (IVC).
(1)
(4)
(2) (3)
h
P
Q L
Q H
Page 17 of 30
In practice in real devices, the vapour leaves the evaporator in a slightly superheated state,
and the liquid leaves the condenser in a slightly sub-cooled state. In the ideal vapour
compression cycle, assumptions are made so that the evaporator and the condenser
operate isobarically; that the compression is isentropic; and that the throttling occurs at
constant enthalpy
2. The Experiment
Aims
To operate the RA1 refrigeration system and understand the relation between the hardware
components and the refrigeration cycle.
Method
Running the RA1 unit at nominal settings and observing the changes in temperature and
pressure around the system.
Introduction:
The vapour-compression refrigeration system is the most common refrigeration system
used today. RA1 is a computer-controlled vapour-compression refrigeration unit with
automatic recording of appropriate process variables using an integral USB interface
device. This allows the student to gain a thorough understanding of the refrigeration
process by changing the operation of different parts of the process and recording the
response of the complete system.
The compressor is driven by a three-phase electric motor with an inverter drive that
allows operation at different operating speeds. The inverter incorporates Torque Vector
Control and allows the speed and torque of the motor to be measured and logged by the
controlling PC. Temperatures throughout the system and pressure on both sides of the
compressor are measured and logged. The refrigerant flow rate is also measured by a
variable area flowmeter.
The condenser and evaporator both consist of a brazed plate heat exchanger. The water-
cooled condenser and water heated evaporator utilises a large reservoir of water to
minimise changes in water temperature during operation. The use of a reservoir to
recirculate the same water continuously eliminates the need for a permanent mains water
connection or water flowing continuously to drain and isolates the system from
fluctuation in mains water pressure or temperature. The flow of water through each heat
exchanger is independently varied by changing the speed of a gear pump. The speed of
both pumps is set by the operator using the PC.
The unit is self-contained, only requiring connection to an electrical supply and a suitable
PC (not supplied). The unit is supplied with the necessary software and incorporates a
USB computer interface device for connection to a PC.
Page 18 of 30
The water reservoir is designed to stand on the floor. The process components are
mounted on a metal support frame that is designed to stand on top of the reservoir. Self-
sealing quick-release connectors and flexible tubing connect the reservoir to the
refrigeration unit.
RA1 Refrigeration Unit
This equipment uses refrigerant R134a (Also known as: HFC-134a; 1, 1, 1-2
Tetrafluoroethane; Norflurane; Norfluran). This is a common refrigerant introduced to
replace CFC (chlorofluorocarbon) refrigerants such as R-12. R134a is colourless, non-
flammable and non-corrosive with a very faint odour. In the RA1 the refrigerant is
contained within a completely sealed circuit and is safe under normal use as described in
this manual.
Apparatus Setup
The process components of the RA1 Vapour Pressure Refrigeration Unit are mounted on a
metal support frame (1) that is designed to stand on top of a large water reservoir. The
water reservoir is designed to stand on the floor. Self-sealing quick release connectors (4)
and flexible tubing connect the reservoir to the refrigeration unit.
With the exception of the compressor and motor, the important process components are
mounted on a panel (2) at the front of the frame so that the student can clearly observe the
flow path through the process. The components that create the refrigeration process are
detailed below.
The process is fully instrumented to allow all of the important parameters to be measured
so that the performance can be monitored. Temperature sensors T1 to T9 measure the
temperature at every stage of the refrigeration process, including the water entering and
Page 19 of 30
leaving the condenser and evaporator. Pressure sensors P1 and P2 measure the pressure of
the refrigerant before and after the compressor. Water flow through the condenser and
evaporator is measured with electronic flowmeters FM1 and FM2. The refrigerant flow
rate is determined using a variable area flowmeter FM3 (13). A schematic of the
apparatus used is shown in Fig. 5. Suction and delivery pressures are measured by
Bourdon gauges. Flow meters measure water and refrigerant flow rates.
Figure 5: Layout of the Refrigeration rig
Methods
Take 3 sets of readings for the same setting on your refrigeration rig allowing 5-10min
intervals between each set. Take the average of the 3 sets of readings for your analysis.
Equipment Required
RA1 Refrigeration Unit
Compatible PC with Armfield RA1 software
Page 20 of 30
Theory
T – s diagram for the Vapour-Compression Refrigeration Cycle
In this cycle, the refrigerant (R134a) enters the compressor as a vapour and is compressed
and superheated (Points T3 to T4) i.e. it is raised above its saturation temperature.
Supercritical
fluid
Subcooled
liquid
Page 21 of 30
The superheated refrigerant vapour passes through the condenser which first cools and
removes the superheat and then condenses the vapour into liquid by removing latent heat
at constant pressure and temperature (Points T4 to T5). Heat from the refrigerant is
transferred to the stream of water in the condenser.
The liquid refrigerant then passes through the expansion valve (also called a throttle valve)
where it expands and the pressure abruptly decreases, this results in a mixture of liquid
and vapour at a lower temperature and pressure (Points T6 to T7).
The cold liquid/vapour refrigerant mixture then travels through the evaporator and is
heated and completely vaporized by heat transfer from the water in the evaporator (Points
T7 to T3).
The refrigerant vapour exiting the evaporator returns to the compressor inlet to complete
the thermodynamic cycle.
An important measure of the system performance is the Coefficient of Performance (CoP).
This is the ratio of the heat exchanged in the evaporator to the amount of work put into the
system by the compressor. In a refrigeration system, this is typically in the region of 3 to 6
i.e. more heat is exchanged than input by the compressor. The CoP is continuously
calculated from the other system variables and displayed on the mimic diagram.
Equipment Set-Up
Ensure that the equipment has been installed in accordance with the Installation section.
Check that the USB connection is made between the RA1 unit and the PC, and that the
RA1 software is installed and running. Check that the circuit breakers and RCD device at
the rear left of the unit are in the on (up) position. Turn the unit on by pressing the
ON/OFF switch on the unit, then click on the Power On switch on the RA1 software
mimic diagram.
Procedure
1. Set the condenser water pump speed to 50% (this may vary and must achieve 1.5 l/min)
and the evaporator water pump speed to 70% (this may vary and must achieve 5.5
l/min).
2. Check that there is a flow of water through both the condenser and evaporator
indicated by FM1 and FM2 on the mimic diagram.
3. When the water flowing into both condenser and evaporator becomes stable, set the
compressor speed to 50% and click “Compressor On” button on the software. The
compressor will run at 3000rpm for 30 seconds then change to the set speed. Check
that refrigerant flows around the system indicated by the variable area flowmeter FM3
on the RA1 – MKII. Let the system run until the temperatures and pressures are
reasonably stable.
4. Configure the sample options as ‘Automatic / 10 seconds intervals’ and click the “GO”
button to log the current set of readings from the sensors. View graphs of T1, T3 and
T7 on the primary y-axis and P1 and P2 on the secondary y-axis.
5. View the table of results and check that a set of readings has been logged. Save the
result for future reference.
Page 22 of 30
Results
View the table of results. Observe the changes in pressure and temperature throughout the
process and compare them with the T – s diagram shown in the theory above. Observe that
the calculated Coefficient of Performance (COP) is significantly greater than unity
whereby more useful heat is transferred in the evaporator than electrical energy is required
to run the compressor.
Page 23 of 30
Conclusion
These observations should provide a basic understanding of the refrigeration process.
Describe the function of the important parts of the refrigeration process, namely the
compressor, condenser, expansion valve and evaporator and explain the temperature and
pressure changes associated with each.
Observe the value of the Coefficient of Performance obtained and comment on the
magnitude of this value.
The exercises that follow investigate the vapour-compression refrigeration cycle in more
detail and the effect of changes to individual parts of the refrigeration system.
Manual calculation of system performance using refrigerant
properties
Objective
To perform appropriate energy balances and a detailed analysis of the performance of the
refrigeration system.
Method
Using the formulae below and the physical properties of the refrigerant to calculate the
performance of the refrigeration system.
Equipment Required
RA1 Refrigeration Unit
Page 24 of 30
Compatible PC with Armfield RA1 software
Table of refrigerant properties (R134A) See Table of Refrigerant Properties for R134A
(Temperature) and Table of Refrigerant Properties for R134A (Pressure).
Table of Refrigerant Properties for R134A (Temperature)
Page 25 of 30
Table of Refrigerant Properties for R134A (Pressure)
Theory
Some formulas below are useful, some are presented just for reference and are not
needed for the analysis required in the report.
The performance of the refrigeration system can be determined using the following
equations:
Mass Flow Rate
Where: = Mass flow rate of the refrigerant (Kg/s)
R = Flow meter reading (l/hr)
= Density of the refrigerant (1.203 Kg/l)
Page 26 of 30
Work Done on Refrigerant
Where: Work = Work done on refrigerant (Watts)
= Mass flow rate of the refrigerant (kg/s)
h2 = Enthalpy of refrigerant at outlet of compressor (kJ/kg)
h1 = Enthalpy of refrigerant at inlet of compressor (kJ/Kg)
Speed of Compressor
Where: Speed = Speed of the compressor (rpm)
CS = Compressor setting (%)
F = Maximum frequency of motor (Hz)
n = Number of polls in motor
Mechanical Power or Compressor Work
Where: W = Work done by the compressor (Watts)
Speed = Speed of the compressor (rpm)
= Torque of the compressor (Nm)
Compressor Efficiency
Where: W = Work done by the compressor (Watts)
Work = Work on the refrigerant (Watts)
Sensible Heat Change in Condenser
( ) ( )6BPh T h T−
Where: h(T) = enthalpy of a saturated liquid at the given temperature
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TBP = Boiling point of refrigerant (K)
T6 = Temperature of refrigerant at outlet of condenser (K)
Heat Removed from Refrigerant
Where: Heatout = Heat removed from the refrigerant (Watts)
= Mass flow rate of the refrigerant (Kg/s)
h3 = Enthalpy of refrigerant at outlet of condenser (kJ/Kg)
h2 = Enthalpy of refrigerant at inlet of condenser (kJ/Kg)
Energy Leaving the Condenser
Where: Qout = Energy removed from the condenser (Watts)
F1 = Water flow rate through condenser (l/min)
T2 = Temperature of water at outlet of condenser (K)
T1 = Temperature of water at inlet of condenser (K)
Condenser Efficiency
Where: Qout = Energy removed from the condenser (Watts)
Heatout = Heat removed from the refrigerant (Watts) Heat
Absorbed
Where: Heatin = Heat absorbed by the refrigerant (Watts)
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= Mass flow rate of the refrigerant (Kg/s)
h1 = Enthalpy of refrigerant at outlet of evaporator (kJ/Kg)
h2 = Enthalpy of refrigerant at inlet of evaporator (kJ/Kg)
Energy Entering the Evaporator
Where: Qin = Energy absorbed by the evaporator (Watts)
F2 = Water flow rate through evaporator (l/min)
T8 = Temperature of water at inlet of evaporator (K)
T9 = Temperature of water at outlet of evaporator (K)
Evaporator Efficiency
Where: Qin = Energy absorbed from the evaporator (Watts)
Heatin = Heat absorbed by the refrigerant (Watts)
Coefficient of performance
Coefficient of Performance (COP) is the index used to describe how effectively the
device functions as a sink/source of heat transfer as a result of the work input. COP is
often a function of the difference between the condenser’s and the evaporator’s working
temperatures, and the temperature of their surroundings.
The COP for refrigeration (where cooling effect is desired) is defined as:
COPrefrig = ||
||
Where Qin is the heat input to the evaporator
W is the work input to the compressor
Steady flow energy equation
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There are 4 components to the refrigeration cycle: compressor, condenser, evaporator and
throttle. The steady flow energy equation can be applied to every component as a
controlled volume and the system as a whole.
out in
Q W m m − = −
Where Q is the net heat Wis the net work mout
and min are the mass flow rates of fluid
accounts for the enthalpy, kinetic energy and potential energy of the fluid.
Procedure
Use any of the measurements from the previous exercises and analyse the performance
using the above formulae.
Conclusion
Comment on the performance of the individual components in the refrigeration system.
If results are available from different runs at different settings, compare the results
and comment on the changes in system performance.
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Report
Reports should be short and brief but technically sound. There is no pre-set length for the reports
however they should be concise but with clear technical explanations, typically 4-6 pages of text. All
experimental results must be tabulated in an appendix. Calculations can be done using spreadsheets,
Matlab or by hand with sample calculation included. Reports must include a cover page stating all
group members names and SID’s and the date the lab was completed if it was completed in person. All
reports must include the universities plagiarism sheet signed by all group members
( https://web.aeromech.usyd.edu.au//plagiarism/Compliance_Statement.doc ). Reports are due Friday
at 5pm week 13 electronically through Canvas. All members must join a group and submit the report.
Report outline:
1. Aims: list the questions you want to find answers from the experiment.
2. Method: brief outline of the method used.
3. Results: raw and processed results, possibly tabulated in a spreadsheet.
4. Calculations: sample calculations to show how the spreadsheets in (3) work.
5. Analyses: graphs and plots. Make sure you present useful and sensible information. Use your
judgment skills to make decisions of what should be included and the order of importance of each.
6. Discussion: discussion and comment on your results. Give reasons, be rational, be scientific, be
sensible, and be practical.
7. Conclusion: describe your conclusions and state whether all your objectives met. If not, provide
reasons and difficulties
Do not cut and paste articles from any other sources. Use your own words to communicate ideas in
your report. Note that long reports do not attract marks. Report that attract good marks show
originality, creativity, professionalism, clear communication of ideas, well presented and direct
answers.
Your report should contain at least 4 graphs:
1. Measured variables (e.g. temperature and pressure) vs. time to show steady operating conditions
have been reached.
2. Carnot cycle
3. Ideal vapour compression cycle
4. Actual vapour compression cycle
Calculations:
-Many quantities are already computed in the program you should confirm all of these calculations in
your report. Analyse each of the four components and where possible (evaporator and condenser)
consider and energy balance over the water and refrigerant component of the heat exchanger.
-Compare the cycle calculations (temperatures, pressures and power input) with Carnot, ideal vapour
compression cycle and actual vapour compression cycle analysis.
Mark breakdown, 20% presentation, 80% calculations and cycle graphs and analysis.
