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CHL 471: Tutorial-4 (T_1_AV)

Revisi t ing Heat Transfer Fundamentals 

1. Discuss the mechanism of thermal conduction in gas and solid.

2. Differentiate between thermal conductivity and specific heat capacity. Discuss their

importance in heat transfer operations.

3. In a chemical process industry (CPI), cylindrical geometry for the heat transfer has very

important role. Develop a relation for rate of heat transfer through a composite cylindrical

pipe wall. You may take 3 different material for the composite. Use your own but different

generalized notation for all the materials.

4. Consider a hot fluid at 100 oC is being transported through a 50 m long pipe made up of 3

mm thick, 2.5 cm ID. A 5 cm thick insulation material is wrapped around the pipe to reduce

the rate of heat loss to the atmosphere (25oC). The thermal conductivity of the pipe material

and the insulator is 20 and 0.15 W/m·oC. Find out the rate of heat loss with and without

insulation. State all the assumptions clearly.

5. Discuss and develop a general relation for the critical insulation thickness for a cylindrical

body stating all the relevant assumptions.

6. What is heat transfer coefficient? Explain the reason, why it is always complex to

determine the heat transfer coefficient.

7. What are the fundamental assumptions behind film theory? Does a film really exist in

practice, or is it just an idealization?

8. Is the thermal boundary layer and hydrodynamic boundary layer, in general are different?

What information may be deduced by the ratio of these boundary layer thicknesses?

9. Water is the one of the most important utilities in any CPI. In a particular process water

needs to be transported at 60 oC inside a 30 mm ID, and 1 mm thick wall tube such that

the heat transfer coefficient is 3500 W/m2·oC. The outside of the tube losses heat by free

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convection with heat transfer coefficient of 8 W/m2·oC. Calculate the overall heat transfer

coefficient and heat loss per unit length to surrounding, which is at 25oC. The thermal

conductivity of the pipe material is 15 W/m· oC.

10. What is the difference between Nusselt and Biot number?

11. What is the philosophical basis of the heat transfer analogies and underlying purpose?

12. Does boiling water have higher heat transfer coefficient, or condensing steam? Why?

13. What is the concept of LMTD? What are the underlying assumptions? How do you get the

log in your expressions?

14. In general, are heat transfer coefficients during phase change larger or smaller than heat

transfer coefficient without phase change? Why?

15. Discuss boiling phenomenon with the help of boiling curve.