Heat Transfer

31. A graph between _________ is called Wilson plot.

1. (1/U) Vs. (1/v^0.8)
2. (1/v^0.8) Vs. U
3. v^0.8 Vs . U
4. (1/U) Vs. (1/V)

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32. A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case,

1. The cooling rate will be the same for the two spheres and hence the two spheres will have equal temperatures at any instant
2. Both the spheres will emit equal amount of radiation per unit time in the beginning
3. Both will absorb equal amount of radiation from the surrounding in the beginning
4. Both (B) & (C)

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33. A hot body will radiate heat most rapidly, if its surface is

1. White & rough
2. Black & rough
3. White & polished
4. Black & polished

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34. A hot liquid is kept in a big room. The logarithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly a/an

1. Ellipse
2. Straight line
3. Parabola
4. Circular arc

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35. A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time

1. t = 283 s
2. t = 356 s
3. t = 400 s
4. t = 800 s

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36. A measure of the extent to which viscous heating is important relative to the heat flow resulting from the impressed temperature difference is represented by the _________ number.

1. Condensation
2. Grashoff
3. Stanton
4. Brinkman

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37. A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m³ and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m².K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is

1. 555
2. 55.5
3. 0.55
4. 0.15

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38. A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m².K. The Biot number is

1. 5.6
2. 0.025
3. 3.5
4. 0.0035

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39. A multiple effect evaporator as compared to a single effect evaporator of the same capacity has

1. Lower heat transfer area
2. Lower steam economy
3. Higher steam economy
4. Higher solute concentration in the product

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40. A multiple effect evaporator has a capacity to process 4000 kg of solid caustic soda per day, when it is concentrating from 10% to 25% solids. The water evaporated in kg per day is

1. 6000
2. 24000
3. 60000
4. 48000

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