Cork Institute of Technology
Bachelor of Engineering (Honours) in Mechanical Engineering - Stage 3
(NFQ - Level 8)
Autumn 2007
Thermodynamics
(Time: 3 Hours)
Instructions:
Answer Question 1 and any FOUR other
questions.
Examiners: Mr. W. Corr
Mr. P. Clarke
Prof. M. Gilchrist
Q1. (i) Consider a medium in which the heat conduction equation is given in its simplest form as:
0
2
2
2=
∂
∂
+
∂
∂
r
T
r
T
r
• Is heat transfer steady or transient?
• Is heat transfer 1D, 2D, or 3D?
• Is there heat generation within the medium?
• Is the thermal conductivity of the medium constant? (4 marks)
(ii) Consider a cold canned drink left on a dinner table.
Would you model the heat transfer to the drink as one-, two- or three-dimensional?
Would the heat transfer be steady or transient?
Also, which coordinate system would you use to analyze this heat transfer problem, and
where would you place the origin? Explain. (4 marks)
(iii) Consider steady heat transfer through the wall of a room in winter. The convection heat
transfer coefficient at the outer surface of the wall is three times that of the inner surface
as a result of the winds. On which surface of the wall do you think the temperature will be
closer to the surrounding air temperature? Explain. (4 marks)
(iv) Two pin fins are identical, except that the diameter of one of them is twice the diameter of
the other. For which fin will the (a) fin effectiveness, and (b) fin efficiency be higher?
Explain. (4 marks)
(v) What is a graybody? How does it differ from a blackbody? What is a diffuse gray
surface? (4 marks)
