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(MECH3310)[2011](s)midterm~=3_k^_52585.pdf
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Prepare for the Midterm
Time: March 27, Wednesday, 15:00-16:20 Location: 2306 (student ID ends with an odd number) /2404 (student ID ends with an even number).
Closed book/lecture notes.
Prepare 1 sheet (two sides) of notes on standard A4 paper. Bring a calculator, no laptop or wireless communication device though.
The midterm will cover:
1.
Basic heat rate equations for conduction, convection, and radiation. Although the midterm will predominantly cover conduction, you are expected to solve conduction problems with convection or radiation boundary conditions.

2.
Fouriers law and heat conduction equation. You are expected to know the heat conduction equation - How to simply the general heat conduction equation? How to apply the 1st law to a control volume (surface) in rectangular coordinates? Think carefully about the temperature profiles in a system with heat generation and/or transient changes.

3.
Thermal circuit analogy. You should practice developing circuit analogies for 1D steady state no heat generation problems. Also, go over the derivation of the thermal resistances for conduction and convection in rectangular, cylindrical, and spherical coordinates. Know the basic concept of conduction shape factors, contact resistance, and how to apply to thermal circuit network.

4.
Fin analysis. Go over the derivation of the fin equation, and solutions for infinite and finite fins. What are the assumptions when you derive the fin equation? What is LH, Bi ?

5.
Lumped capacitance model: an extension of the circuit analogy to transient problems. What are the assumptions for this model? What is.Bi. ..What is ...

6.
Semi-infinite solid. You should know the basic concept and solutions of transient process for the constant surface temperature case: How does the transient temperature distribution vary in time and space? What is the surface heat flux?



Practice Midterm I (2011)
1. Consider a plane composite wall that is composed of two materials of A and B: thermal conductivity kA = 0.1 W/mK, thickness LA = 10 mm; thermal conductivity kB = 0.06 W/mK, thickness LB = 15 mm. The contact resistance at the interface between the two materials is Rc = 0.1 m2K/W. Material A adjoins a fluid at T1 = 200C for which convective heat transfer coefficient h1 = 10 W/ m2K, and material B adjoins a fluid at T2 = 30C for which convective heat transfer coefficient h2 = 20 W/ m2K.
(a)
Sketch the temperature distribution qualitatively (no need to calculate the exact values).

(b)
What is the rate of heat transfer through a wall that is 2.5 m high and 3 m wide?



R

2.
A hot air flowing over a spherical thermocouple whose junction is 1 mm in diameter. The properties of the junction are: . = 8500 kg/m3, k = 35 W/mK, cp = 320 J/kgK. It takes 10 s for the thermocouple to read 90 % of the initial temperature difference. Estimate the convection heat transfer coefficient between the junction and the air.