GTU B.Tech 2020 Winter Question Papers || Gujarat Technological University
Subject Code:3140503 Date:11/02/2021
Subject Name:Heat Transfer
Time:02:30 PM TO 04:30 PM Total Marks:56
Enrolment No.
GUJARAT TECHNOLOGICAL UNIVERSITY
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BE- SEMESTER-IV (NEW) EXAMINATION - WINTER 2020Subject Code:3140503 Date:11/02/2021
Subject Name:Heat Transfer
Time:02:30 PM TO 04:30 PM Total Marks:56
Instructions:
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- Attempt any FOUR questions out of EIGHT questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
| Marks | |
|---|---|
| Q.1 (a) Distinguish between the conduction, convection and radiation modes of heat transfer. | 03 |
| (b) A furnace wall is made up of steel plate 10 mm thick (k= 62.8 kJ/m-hr-deg) lined on inside with silica bricks 150 mm thick (k=7.32 kJ/m-hr-deg) and on the outside with magnesia bricks 200 mm thick (k= 18.84 kJ/m-hr-deg). The inside and outside surfaces of the wall are at temperature 650 °C and 125 °C respectively. Make calculations for the heat loss from unit area of the wall. | 04 |
| (c) Derive equation for heat transfer by conduction through hollow cylinder. Also mention assumptions made for it. | 07 |
| Q.2 (a) Discuss the physical significance of (i) Reynolds Number (ii) Prandtl number. | 03 |
| (b) Set up the relationship between local heat transfer coefficient and average heat transfer coefficient for flow past a stationary flat plate. | 04 |
| (c) Calculate the rate of heat loss from a human body which may be considered as a vertical cylinder 30 cm in diameter and 175 cm high in still air at 15 °C. The skin temperature is 35 °C and emissivity at the skin surface is 0.4. Neglect sweating and effect of clothing. The thermo-physical properties of air at 25 °C are: ?=15.53 x 10-6 m2/s; k= 0.0263 W/m-deg; Pr=0.7 Use the following correlation Nu =0.13(Gr x Pr)0.33 | 07 |
| Q.3 (a) Explain the concepts of critical insulation. How do you decide the thickness of insulation for electric wires? | 03 |
| (b) Explain the terms absorptivity, reflectivity and transmissivity of radiant energy. How are they related to each other for a black body and opaque body? | 04 |
| (c) What is boiling and when does occurs? Explain pool boiling. How does it differ from forced convection boiling? | 07 |
| Q.4 (a) How the thermal conductivity of metals varies with temperature and pressure? | 03 |
| (b) State and prove Stefan Boltzman law relating to thermal radiation and temperature of a radiating body. | 04 |
| (c) What is condensation and when does occurs? How does film-wise condensation differ from drop-wise condensation? Which type has a higher heat transfer film coefficient and point out the reason thereof? | 07 |
| Q.5 (a) When can we consider heat exchanger as compact heat exchanger? | 03 |
| (b) Explain the concept of NTU for heat exchangers. | 04 |
| (c) Derive equation for LMTD for parallel flow heat exchanger. Also state necessary assumptions made for it. | 07 |
| Q.6 (a) List at least eight important parts of shell & tube heat exchanger. | 03 |
| (b) What do you mean by “fouling” in heat exchangers? What is the effect of it on performance of heat exchangers? | 04 |
| (c) Calculate the surface area required for a heat exchanger which has to cool 55,000 kg/hr of alcohol from 66 °C to 40 °C using 40,000 kg/hr of water entering at 5 °C. Assume that U based on the outer area is 580 W/m2 K. Specific heat of alcohol is 3.76 kJ/kg K and that of water is 4.18 kJ/kg K. Consider counter flow tube and shell arrangement. | 07 |
| Q.7 (a) How does evaporation differ from distillation? | 03 |
| (b) Mention any four characteristics of solutions to be considered before selecting the evaporator? | 04 |
| (c) What are the various types of evaporators? Draw neat sketch of Calandria type evaporator and briefly explain its construction and working. | 07 |
| Q.8 (a) Why evaporators generally operate under vacuum? | 03 |
| (b) When will you select plate type evaporators? Explain construction & working of it. | 04 |
| (c) Discuss various methods of feeding in multiple effect evaporators with their relative merits and demerits. | 07 |
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