GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-V (NEW) EXAMINATION - WINTER 2018
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Subject Code:2151909 Date:27/11/2018Subject Name:Heat Transfer
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
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2. Make suitable assumptions wherever necessary.3. Figures to the right indicate full marks.
4. Use of air table, steam table, heat exchanger chart is permitted.
MARKS
Q.1 (a) What is insulation? State its six applications in engineering field. 03
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(b) It is observed that the intensity of the radiation emitted by the sun is maximum at a wavelength of 0.5 µm. Assuming the sun to be black body. Calculate its surface temperature and emissive power. 04(c) Saturated steam at 120 °C is condensing on the outer tube surface of a single pass heat exchanger. The overall heat transfer coefficient is 1800 W/m² K. Determines the surface area of a heat exchanger capable of heating 1000 kg/h of water from 20 °C to 90 °C. Also calculate the rate of condensation of steam. Assume latent heat of steam is 2200 KJ/Kg. 07
Q.2 (a) What is dimensional analysis? Explain dimensional homogeneity. 03
(b) A copper pipe (temperature 55 °C) is kept in atmosphere (temperature 35 °C). The length and diameter of pipe is 1m and 50 mm respectively. The air velocity is 3 m/s. use the co-relation Nu= 0.0239 (Re)0.8 , Calculate heat loss from the pipe. 04
(c) Derive the two dimensional energy equation for thermal boundary layer over a flat plate. 07
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OR
(c) By dimensional analysis, show that for force convection Nusselt Number is a function of Reynold Number and Prandtl Number. 07
Q.3 (a) Explain film wise condensation. 03
(b) Emissivity of two large parallel plates maintained at 800 °C and 300 °C are 0.3 and 0.5 respectively. Find the net radiant heat exchange per square meter for these plates. 04
(c) Derive equation of net heat transfer by radiation between two infinite parallel plates. 07
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OR
Q.3 (a) Define shape factor. What is shape factor with respect to itself if the surface is concave, convex or flat? 03
(b) Differentiate between 1. Subcooled and saturated boiling 2. Nucleate and film boiling 04
(c) State and prove Kirchof’s law of radiation. Derive Wein’s displacement law. 07
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Q.4 (a) What is difference between heat transfer and thermodynamics? 03
(b) What is fouling? State the causes of fouling. 04
State the limitations of LMTD method. What is heat pipe?
(c) Derive equation of LMTD for counter flow heat exchanger. 07
OR
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Q.4 (a) Which are the basic laws governing the heat transfer. State any one. 03
(b) What is compact, multipass and regenerator type heat exchanger? State six application of heat exchanger in the field of engineering. 04
(c) Derive equation of effectiveness for parallel flow heat exchanger. 07
Q.5 (a) What is Fourier’s law of heat conduction? State its assumptions. 03
(b) A steel pipe (k=35 W/m K) with inner diameter 50 mm and outer diameter 60 mm is insulated using insulation material having (K=0.055 W/m.K). The temperature interface between pipe and insulation is 573 K, while the temperature on outside of insulation must not exceed 343 K, with permissible heat loss of 700 W/m. calculate (1) the minimum thickness of insulation and (2) the temperature of inside surface of pipe. 04
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(c) Derive expression for temperature distribution and heat dissipation in a straight infinitely long fin of rectangular profile. 07OR
Q.5 (a) Define fin efficiency. Explain the situation, when addition of fin to a surface is not useful. 03
(b) A steel rod (K= 54 W/ m K) with a cross section of an equilateral triangle (each side 5 mm) is 80 mm long. It is attached to a furnace wall which is maintained at a temperature of 400 °C. The surrounding is at 50 °C and surface conductance is 90 W/m²K. Calculate the heat dissipated by the rod. Assume tip of the rod is insulated. 04
(c) Derive expression for temperature distribution, under one dimensional steady state heat conduction for the hollow cylinder. 07
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