AE2024 Heat Transfer B.E Question Bank : sriengg.com

Name of the College : Srinivasan Engineering College
University : Anna University
Department : Aeronautical Engineering
Degree : B.E
Subject Code/Name : AE2024 Heat Transfer
Year : 3rd
Semester : 6th
Document Type : Question Bank
Website : sriengg.com

Download Model/Sample Question Paper :https://www.pdfquestion.in/uploads/sriengg.com/3220-HT-QB.pdf

Srinivasan AE2024 Heat Transfer Question Paper

Unit- I

1. What is the difference between diffusion and radiation heat transfer ? :
Diffusion heat transfer is due to random molecular motion. Neighboring molecules move randomly and transfer energy between one another – however there is no bulk motion. Radiation heat transfer, on the other hand, is the transport of heat energy by electromagnetic waves.

Related : Srinivasan Engineering College AE2202 Aero Engineering Thermodynamics B.E Question Bank : www.pdfquestion.in/3208.html

All bodies emit thermal radiation. In particular, notice that unlike diffusion, radiation heat transfer does not require a medium and is thus the only mode of heat transfer in space. The time scale for radiative heat transfer is much smaller than diffusive heat transfer.

2. How is natural convection different from forced convection ? :
In natural convection, the movement of the fluid is due entirely to density gradients within the fluid (e.g. hot air rises over cold air). There is no external device or phenomenon which causes fluid motion. In forced convection, the fluid is forced to flow by an external factor – e.g. wind in the atmosphere, a fan blowing air, water being pumped through a pipe. Typically heat transfer under forced convection conditions is higher than natural convection for the same fluid.

3. Define a black surface :
A black surface is defined by three criteria :
**  it absorbs all radiation that is incident on it
**  it emits the maximum energy possible for a given temperature and wavelength of radiation (according to Planck’s law)
**  the radiation emitted by a blackbody is not directional (it is a diffuse emitter) A black surface is the perfect emitter and absorber of radiation. It is an idealized concept (no surface is exactly a black surface), and the characteristics of real surfaces are compared to that of an ideal black surface.

4. What is the range of values for the emissivity of a surface ? :
The emissivity i ranges between 0 and 1.

5. What are the conditions to be satisfied for the application of a thermal circuit ? :
The problem must be a steady state, one-dimensional heat transfer problem.

Unit – II

6. Will the thermal resistance of a rectangular slab be increased or decreased if :
a. the thermal conductivity is increased ? :
b.the cross sectional area is increased ? :
c.the thickness of the slab is increased ? :
a. resistance will decrease
b. resistance will decrease
c. resistance will increase

7. State the condition which must be satisfied to treat the temperature distribution in a fin as one-dimensional :
When ht/k <<1 where h is the convective heat transfer coefficient, t is the thickness of the fin and k is the thermal conductivity of the fin, one can consider that the temperature gradient in the thickness direction is very small and the analysis can be considered as one-dimensional.

8. Define and state the physical interpretation of the Biot number :
The Biot number is given by :
Bi = hL/k
where
h = convective heat transfer coefficient,
k = thermal conductivity
L = characteristic length.
It is a ratio of the temperature drop in the solid material and the temperature dropthe solid and the fluid. So when the Bi <<1 , most of the temperature drop is in the fluid and the solid may be considered isothermal

9. What is a lumped system ? :
A lumped system is one in which the dependence of temperature on position (spatial dependence) is disregarded. That is, temperature is modeled as a function of time only

10. When can the unsteady temperature in a spatial body be considered uniform ? :
When the Biot number is small (Bi << 0.1)