MEC4408 - Thermodynamics and heat transfer Practical Test 5
(Week 11 – Thursday 4 pm)
TEST DURATION: 90 minutes + 15 minutes (reading and scanning time)
This is an open book test. To complete the question, you may need to refer to property tables,
which can be found in the prescribed text book and are also available through the MEC4408
Moodle page, as well as mathematical tables and any other resources like Matlab,
Mathematica, etc. that you choose to use.
This test consists of one question comprising 100 total marks. Ensure you include all
relevant working in your submission and appropriately reference tables and charts. You are
not required to reference equations.
The marking rubric is as follows:
Assumptions - 15%
Methodology - 65%
Explanation of steps / readability / units - 10%
Final answer - 10%
- Include your name and student ID number at the top of the first page
- Write your answers in pen on plain or ruled A4 paper in a single-column format using
legible writing
- Number the top right corner of each page
- Scan or photograph your work in portrait format, ensuring that the text is legible and
upload as a single PDF file. If you upload as anything other than a PDF your work
will not be marked
Name the PDF file: .pdf .
Upload this SINGLE PDF FILE in portrait format to the Moodle submission box before the
due time. If you encounter technical difficulties, please email henry.shen@monash.edu or
mainak.majumder@monash.edu immediately. Late submissions without appropriate
reasoning will receive a penalty of 10% per minute.
Question 1 (60 marks)
An experimental gas of thermal conductivity kg = 17 W/mK is kept within a spherical
storage tank and generates heat equivalent to = 9.2 x 104 W/m3 by controlled˙
chemical reactions. This storage tank is made from titanium and consists of a shell
with inner and outer radii of ri = 0.4 m and ro = 0.7 m, respectively. The ambient
temperature outside the storage tank is maintained at 22℃ and has a convective heat
transfer coefficient of h = 855 W/m2K.
(Titanium properties: kT = 21.9 W/mK, cp = 522 J/kgK, = 4500 kg/m3)
a) Find an expression for the temperature distribution T(r) in the experimental gas
in terms of ri , kg , and Ti (30)˙
b) Determine the temperature at the inner surface (15)
c) Determine the temperature at the outer surface (15)
Question 2 (40 marks)
Small 6mm × 6mm electronic devices are mounted on a flat motherboard and release
80mW of heat from their surface. The electronic devices are placed one after, such
that they are not touching, but the distance between each device is small enough that
we can assume it to be negligible. Air at 290K is blown over the devices at 15m/s for
the purposes of cooling, and an obstruction is situated at the leading edge of the board
which disrupts the flow, causing the boundary layer to be turbulent.
Estimate the surface temperature of the 6th electronic device from the leading edge,
assume that the devices have negligible height such that they do not disrupt the air
flow.