JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year HEAT TRANSFER Previous Question Paper (February - 2023 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
What are the applications of heat transfer?
Answer
Heat transfer applications include power generation (boilers, condensers), refrigeration and air conditioning systems, heat exchangers in chemical processing, cooling of electronic components, and thermal management in aerospace and automotive engines.
What do you understand by initial and boundary conditions?
Answer
Initial conditions define the temperature distribution within a system at the starting time (t=0). Boundary conditions specify the thermal state (temperature, heat flux, or convection) at the surfaces of the system for all time t > 0, which are necessary to solve the heat conduction equation.
What is meant by Lumped heat analysis? Explain with the help of an example.
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Define Fin efficiency and fin effectiveness.
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State Buckingham π- theorem.
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What are the advantages and limitations of dimensional analysis?
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What is fouling factor? Explain.
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Define Grashoff Number and Stanton Number.
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What is condensation? How does it occur?
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Write the use and importance of Plank’s Law.
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Part B
With relevant examples, explain mechanism of conduction, convection and radiation.
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Explain clearly basic laws of heat transfer.
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A Stainless steel plate is of 2 cm thick is maintained at a temperature of 550° C at one face and 50° C on the other. The thermal conductivity of stainless steel at 300° C is 19.1 W/m K. Calculate the heat transferred through the material per unit area.
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In what way is the science of heat transfer different from thermodynamics? Explain.
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Explain why the conductivity of metals decreases and conductivity of insulating material increases with increases in temperature.
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A metallic plate, 3cm thick is maintained at 400°C on one side and 100°C on the other side. How much heat is transferred through the plate? Take k for the metallic plate as k=370 W/m-K.
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Discuss briefly thermal and hydrodynamic boundary layer and obtain Reynold’s analogy in forced convection.
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A plate 20 cm height and 1m wide is placed in air at 20°C. If the surface of the plate is maintained at 100°C calculate the boundary layer thickness and local heat transfer coefficient at 10cm from the leading edge. Also calculate the average heat transfer coefficient over the entire length of the plate.
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Describe Buckingham’s method of π-terms to formulate a dimensionally homogenous equation.
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A flat plate 1m wide and 1.5 m long is to be maintained at 90°C in air when free stream temperature is 10°C. Determine the velocity at which air must flow over the plate so that the rate of energy dissipation from the plate is 3.75 kW.
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Air at 27°C and 1 atm flows over a flat plate at a speed of 2m/s. Calculate the boundary layer thickness at a distance of 20 and 40 cm from the leading edge of the plate. Calculate the mass flow which enters the boundary layer between x= 20 cms and x = 40 cms. The viscosity of the air is at 27°C is 1.85 × 10-5 kg/m s. Assume the unit depth in the z- direction.
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A flat electrical heater of 0.4 m × 0.4 m size is placed vertically in still air at 20°C. The heat generated is 1200 W/m2. Determine the value of convective heat transfer co-efficient and the average plate temperature.
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Explain Grashoff number significance in natural convective heat transfer.
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A Counter flow heat exchanger consisting of two concentric flow passages is used for heating 1200 kg/hr of oil (specific heat=2.1kJ/kgK) from an initial temperature of 27°C. The oil is flowing through the inner pipe and the convective heat transfer coefficient on the oil side is 750 W/m2K. The inner and outer radii of the inner pipe are 12 mm and 15 mm and the thermal conductivity of the pipe materials is 350 W/mK. The oil is heated by hot water supplied at the rate of 400 kg/hr at the inlet temperature of 92°C. The waterside heat transfer coefficient is 1470 W/m2K. The length of the heat exchanger is 9 m. What are the terminal temperatures of the two fluids?
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A drying plant needs hot air at 135°C. This is obtained by passing 2.45 kg/Sec of atmospheric air at 1 bar pressure and 27°C over tubes through which hot glycerin is circulated. The tubes have 20mm diameter, 1.5mm thickness, with a thermal conductivity of the material of the tube 50 W/m-K. The hot glycerin enters at 210°C and leaves at 305°C. Assuming counter flow, Find:
Overall heat transfer coefficient
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Total heating surface.
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i) Distinguish between a black body and grey body.
ii) Prove that intensity of radiation is given by Ib = Eb/π.
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State and explain Kirchoff’s identity. What are the conditions under which it is applicable?
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