JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II PROCESS HEAT TRANSFER Previous Question Paper (December - 2017 - 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.
Part A
Write the equation for unsteady state heat conduction.
Answer
The general heat conduction equation for unsteady state in three dimensions is given by:
What is the effect of T, P on thermal conductivity?
Answer
Thermal conductivity (k) generally increases with temperature for most gases and liquids, but decreases with temperature for most pure metals. The effect of pressure is negligible for solids and liquids, but for gases, thermal conductivity is largely independent of pressure at moderate ranges, though it increases at very high pressures.
How you find the critical radius of insulation of a cylinder?
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Write the limitations of LMTD.
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What is the physical significance of Nusselt number?
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What is significance of Stanton number?
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What is Plank’s law?
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What is Grashof’s number?
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What is calandrias?
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What is vapor recompression?
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Part B
Derive the unsteady state one dimensional conduction equation in a solid slab?
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A flat slab of plastic initially at 21oC is placed between two platens at 121oC. The slab is 2.54 cm thick. i) How long will it take to heat the slab to an average temperature of 99oC? ii) How much heat will be transferred to the plastic during this time per square metre of surface? Density of the solid= 900 kg/m3, k=0.13 W/moC, CP= 1.67 J/goC, NF0= 0.52.
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Derive the equation for steady-state heat transfer through a spherical shell of inner radius r1 and outer radius r2.
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Define the terms ‘thermal diffusivity’ ‘Fourier’s law’ and ‘penetration distance’.
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Explain the concept of critical insulation thickness.
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A copper wire, 5.2 mm in diameter, is insulated with a layer of PVC of thermal conductivity k = 0.43 W/ moC. The wire carries current, and its temperature is 60oC. The film coefficient at the outer surface of the insulation is 11.35 W/m2 oC. Calculate the critical insulation thickness.
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Define the terms ‘heat flux’, mixing-cup stream temperature.
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Water enters a two-fluid heat exchanger at 55oC and leaves at 85oC. Hot gases enter at 305oC and leaves at 160oC. If the total heat transfer area is 500 m2 and the overall heat transfer coefficient is 600 kcal/hr m2 oC, determine the total heat transferred per hour for parallel flow and counter flow of the two fluids.
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Define hydrodynamic and thermal boundary layer.
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Differentiate between Reynolds and Prandtl analogy. What is the significance of Colburn j-factor?
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Air at 70oC and essentially atmospheric pressure is flowing through a 15 cm × 10 cm rectangular duct at a velocity of 12 m/s. If the wall temperature of the duct is 32oC, and the length of the duct is 50 m, calculate the drop in the air temperature?
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Write brief note on the following: a) Monochromatic radiating power b) Monochromatic emissivity c) Stefan-Boltzmann law d) Cosine law e) Wien’s displacement law.
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A shell and tube steam condenser is to be constructed of 2.5 cm OD, 2.2 cm ID, single pass horizontal tube with steam condensing at 54oC on the outside of the tubes. The cooling water enters at 20oC and leaves at 36oC at a flow rate of 1 kg/s. The heat transfer coefficient for the condensation of steam is 7900 W/m2 oC. Calculate the tube length. If the latent heat of condensation is 2454 kJ/kg, calculate the condensation rate per tube. The properties of water are as follows: Specific heat 4180 J/kgoC, viscosity 0.86×10-3 kg/ms, thermal Conductivity 0.61 W/moC. The heat transfer coefficient for turbulent flow in pipe may be determined by
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What is extended surface equipment? Discuss about different types of extended surfaces with neat figures.
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Derive the equation to calculate fin efficiency.
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A continuous single effect evaporator is to be fed with 600 kg/hr of a solution containing 5% wt. The feed is at a temperature of 310 K. It is to be concentrated to a solution of 8 wt% solute. The evaporation is at atmospheric pressure of 51.33 kPa. What will be the requirement for the evaporator? Saturated steam is applied at 163.6 kPa for heating. The overall heat transfer coefficient = 1763 W/m2 K.
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