JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II PROCESS HEAT TRANSFER Previous Question Paper (May - 2019 - R13)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
Write the equation for conduction heat transfer through a cylinder?
Answer
The rate of steady-state heat conduction through a hollow cylinder of length L, inner radius r1, and outer radius r2 with thermal conductivity k is given by:
Write the difference between conduction and convection?
Answer
Conduction is the transfer of heat through stationary matter by physical contact of atoms or molecules, whereas convection is the transfer of heat by the actual physical movement of a fluid (liquid or gas). Conduction occurs in solids, liquids, and gases, while convection is restricted to fluids and involves the bulk motion of the medium.
What is the difference between counter flow and cross flow?
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How do you find fouling factors? Explain.
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What is the physical significance of Prandtl number?
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Explain thermal boundary layer.
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Define black and gray body.
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What is Kirchhoff’s law?
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What is NTU method?
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Define the capacity and economy of an evaporator.
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Part B
Define the terms thermal conductivity, thermal resistance, thermal conductance?
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Derive the equation for steady-state heat transfer through a cylinder.
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A steam pipeline, 150/160 mm in diameter, is covered with a layer of insulating material of thickness 50 mm. The thermal conductivity of the pipe is 50 W/m K and that of the insulating material is 0.08 W/m K. The temperature inside the pipeline is 120 ℃, and that of the outside surface of the insulation is 40 ℃. Calculate the rate of heat loss per 1 m length of the pipeline.
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Discuss the advantages of counter-current flow over parallel flow in heat exchangers, explain these using graphs.
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Water enters a two-fluid heat exchanger at 55℃ and leaves at 85℃. Hot gases enter at 305℃ and leaves at 160℃. If the total heat transfer area is 500 m2 and the overall heat transfer coefficient is 600 kcal/hr m2 ℃, determine the total heat transferred per hour for parallel flow of the two fluids.
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Explain the difference between individual and overall heat transfer coefficient?
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What is LMTD? Explain its advantages and limitations?
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Determine the heat transfer coefficient for water flowing in a tube of 16 mm diameter at a velocity of 3 m/s. The temperature of the tube is 24℃, and the water enters at 80℃ and leaves at 36℃. Use the Dittus-Boelter equation
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Toluene is being condensed at 110℃ on the outside of 19mm 16 BWG copper condenser tubes through which cooling water is flowing at an average temperature of 27℃. Individual heat transfer coefficients for cooling water(hi), toluene(ho) are 1135, 2840 W/m2 ℃, respectively. Neglecting resistance of the tube wall, what is the tube wall temperature? The inner and outer diameters of the tube are 0.620 in, 0.750 in, respectively.
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Derive the equation for natural convection to air from vertical shapes.
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A laboratory water bath has an immersed horizontal heating element, 2.54 cm in diameter and 30 cm in length, with a power input of 500 W. If the bulk water temperature is 38℃ and heat transfer occurs by free convection only, calculate the surface temperature of the heater?
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Explain the following terms:
- Pool boiling
- Calandrias
- Subcooled boiling
- Leidenfrost point
- Film boiling.
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Explain about different methods of feeding in multiple effect evaporators with neat Figures.
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Estimate the heat transfer area for an exchanger to cool an organic liquid from 105℃ to 50℃. The hot liquid will flow at a rate of 10,000 kg/hr and will be cooled by using circulating foul water containing some salt. The cooling water will leave at 40℃. It is proposed to use one shell pass and two tube pass heat exchanger for the above duty. Cooling water inlet temperature = 25℃, heat capacity for water = 4.2 kJ/kg℃, heat capacity for hot liquid = 2.84 kJ/kg℃, Ft, the temperature correction for the design will be 0.85. The recommended overall heat transfer coefficient U will be 600 W/m2 ℃.
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