P08AU46 Heat Transfer B.E Model Question Paper : pescemandya.org

Name of the College : P.E.S College of Engineering
University : Visvesvaraya Technological University
Department : Automobile Engineering
Subject Code/Name : P08AU46/Heat Transfer
Year : July 2010
Degree : B.E
Sem : IV
Website : pescemandya.org
Document Type : Model Question Paper

Download Model/Sample Question Paper : https://www.pdfquestion.in/uploads/pescemandya.org/4667-qp.pdf

PES Heat Transfer Model Question Paper

Fourth Semester B.E. Degree Examination, July 2010
( P08AU46)
Time : 3 Hrs Max. Marks : 100

Related : P.E.S College Engineering P08AU44 Theory of Machines–I B.E Model Question Paper : www.pdfquestion.in/4669.html

Instructions

Note:
1. Answer any FIVE full questions.
2. All questions carry equal marks.
3. Assume suitable data wherever necessary.
4. Use pf heat transfer data book is permitted.

PART A

1. (a) Explain the different modes of heat transfer. (8 Marks)
(b) Derive the general heat conduction equation in cylindrical coordinates. (12 Marks)

2. (a) Explain:
i) Thermal conductivity ii) Thermal diffusivity (4 Marks)
(b) Derive expression for radial heat transfer and temperature distribution along the radius of a hollow cylinder whose inside and outside surfaces are maintained at steady state temperature Tl and T2 respectively and constant thermal conductivity.
Also obtain expression for overall heat transfer co-efficient based on inner radius. (10 Marks)
(c) Derive an expression for critical thickness of insulation of a cylinder and explain the significance of critical thickness of insulation. (6 Marks)

3. (a) Derive an expression for temperature distribution and heat flow in a fin of finite length with an adiabatic end. (8 Marks)

(b) An electronic semi conductor device generates 38 x 10-3kcal/hr of heat. To keep the surface temperature at the upper safe limit of 75°0, it is desired that the generated heat should be dissipated to the surrounding environment which is at 30°0. The task is accomplished by attaching aluminium fins 0.5mm2 square and 10mm to the surface. Workout the numbers of fins if thermal conductivity of fin material is 165kcal/m-nOK and the heat transfer co-efficient is 10.75kcal/m2nok. Neglect the heat loss from the tip of the fin. (12marks)

4. (a) what are biot and Fourier numbers? Explain their physical significance. (8marks)
(b) Aluminium sphere of mass 5.5 kg and initially at a temperature of 290 0C is suddenly immersed in a fluid at 15 0 C. The convective heat transfer co efficient is 58w/m2K. Estimate the time required for the sphere to reach 95oC, using lumped heat capacity method of analysis. Take properties of aluminium density 2700kg/m 3 =900J/kg K=205w/mk. (12marks)

PART B

5 a) Using dimensional analysis obtain a relation between dimensionless numbers in forced convection. (8marks)

b) A light oil with 20° C inlet temperature flows at a rate of 600 kg/min through 5 cm ID pipe which is enclosed by a jacket containing condensing steam at 150° C if the pipe is 10m long, find the outlet temperature of the oil. The properties of oil at 85° C are:
p = 8~0 Kg/m3, Cp = 2.09 kJ/Kg K
K = 0.502 kJ/m-hr °C, v = 3.6 x 10-6 m2/se (12marks)

6. a) What is the significance of the following dimensionless numbers?
i) Reynolds iii) Nusselt ii) Prandtl iv) Grashoff. (10marks)

b) Considering the body of a mass as a cylinder of 30 cm diameter and 160 m height. If the temperature of the body is to be maintained at 36.5° C, find out the amount of heat generated in the body of a mass per hour. Temperature of surrounding is 13.50 C. (10marks)

7. (a) Obtain an expression for the mean temperature difference for a counter flow heat exchanger. (8 Marks)

(b) An economizer is to be purchased for a power plant. The unit is to be large enough to heat 7.5kg/s of water from 71 to 182°C. There are 26kg/s of flue gases (Cp = 1.0kJ/kg.k) available at 426°C. Estimate
1) The outlet temperature of the flue gases.
2) The heat transfer area required for a counter flow arrangement if the overall heat transfer coefficient is 57W/m2 oK (12 Marks)

8. (a) State and prove Kirchoff’s law of radiation. (8 Marks)
(b) Explain the concept of view factor as applied to radiation heat transfer. (4 Marks)
(c) Derive an expression to calculate the net rate of heat transfer between two black surfaces. (8 Marks)