SOME IMPORTANT QUESTION OF HMT FOR UPTU

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 1. A 120mm diameter apple (density=990 kg/m3, c=4170 J/kg0C, k=0.58 W/m0C), approximately spherical in shape is taken from a 250 C environment and placed in a refrigerator where temperature is 60 C and average convective heat transfer coefficient over the plate surface is 12.8W/m2 0C. Determine the temperature at the centre of the apple after a period of 2 hours.

 2. Explain the following
(i) Gray Bodies
(ii) Diffuse Emitter
(iii) Emissivity

 3. Calculate the net radiant heat exchange per m2 for two large parallel plates at temperatures of 4270C and 270C respectively. ε (hot plate= 0.9) and ε (cold plate= 0.6). If a polished aluminium shield is placed between them, find the percentage reduction in the heat transfer. ε (shield)= 0.4

 4. Two parallel plates are at temperatures T1 and T2 and have emissivities ε1 = 0.8 and ε2 = 0.5. A radiation shield having the same emmisivity ε3  both sides is placed between the plates. Calculate the emissivity ε3  of the shield in order to reduce the radiation loss from the system to one-tenth of that without the shield.


 5. Discuss Fick’s law of diffusion. Derive the expression for steady state equimolar counter diffusion.

 6. (i) Discuss the various regimes of saturated pool boiling.
(ii) Differentiate between the mechanism of filmwise and dropwise condensation.

 7. Derive expression for effectiveness of parallel flow heat exchanger in terms of NTU.

 8.A concentric tube heat exchanger uses water, which is available at 150 C to cool ethylene glycol from 1000C to 600C. The water and glycol flow rates are same at 5 kg/s. Determine the effectiveness of heat exchanger.
        Take:   Cp(water) = 4178 J/kg.K
                    Cp (ethylene glycol) = 2650 J/kg.K
    Can you comment, whether the heat exchanger is working in parallel flow or counter flow or counter flow modes of operation.


 9. Derive the following expression
         (Q)n–shields            = (R) without shield =  1  
         (Q)without shields   = (R) n–shield =         n+1


 10. Derive expression for effectiveness of parallel flow heat exchanger in terms of NTU.


 11. 16.5 Kg/s of the product at 6500C (Cp = 3.55kJ/Kg0C), in a chemical plant, are to be used to heat 20.5 Kg/s of the incoming fluid from 1000C (Cp = 4.2 Kj/Kg 0C). If the overall heat transfer coefficient is 0.95 KW/m2 0C and the installed heat transfer surface is 44m2, calculate the fluid outlet temperatures for the counter-flow and parallel flow arrangements.

 12. Steam condenses at atmospheric pressure on the external surface of the tubes of a steam condenser. The tubes are 12 in number and each is 30 mm in diameter and 10 m long. The outlet and inlet temperatures of the cooling water flowing inside the tubes are 600C and 250C respectively. If the flow rate is 1.1 Kg/s, Latent heat of steam at atmospheric pressure = 2257 kj/Kg. Calculate the following.
(i) The rate of condensation of steam
(ii) The mean overall heat transfer coefficient based on the inner surface area.
(iii) The number of transfer units
(iv) The effectiveness of the condenser.

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