Heat Transfer

41. A perfect black body is a perfect _________ of radiation.

1. Absorber
2. Emitter
3. Both (A) & (B)
4. Neither (A) nor (B)

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42. A process stream of dilute aqueous solution flowing at the rate of10 Kg.s^-1 is to be heated. Steam condensate at 95°C is available for heating purpose, also at a rate of 10 Kg.s^-1. A 1 - 1 shell and tube heat exchanger is available. The best arrangement is

1. Counter flow with process stream on shell side
2. Counter flow with process stream on tube side
3. Parallel flow with process stream on shell side
4. Parallel flow with process stream on tube side

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43. A single pass air heater is connected to a two pass unit. For the air flow rate and other conditions remaining the same, the film heat transfer co-efficient for air will vary in the ratio of

1. 2
2. 2^0.8
3. 2^0.2
4. 2^0.5

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44. A sphere of radius 'r₁' is enclosed in a sphere of radius 'r₂'. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is

1. 0
2. r₂/(r₁+r₂)
3. 1
4. (r₁/r₂)2

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45. A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions? Assume that the conductive heat transfer co-efficient is infinitely large.

1. 5 minutes
2. 10 minutes
3. 20 minutes
4. 40 minutes

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46. A tank painted with which of the following coloured paints, would heat up maximum by radiation from sun?

1. Yellow paint
2. White paint
3. Black paint
4. Grey paint

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47. A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of material A is twice that of B. Under the equilibrium, the temperature difference across the wall is 36°C. The temperature difference across the layer A is _________ °C.

1. 6
2. 12
3. 18
4. 24

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48. Absorptivity and reflectivity of a perfect black body are respectively

1. 1 and 0
2. 0 and 1
3. 1 and ∞
4. 0 and 0.5

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49. Absorptivity of a perfect black body is unity. Which of the following has maximum absorptivity?

1. Aluminium foil
2. Refractory bricks
3. Iron plate
4. Coke breeze

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50. According to Reynolds analogy, Stanton number is equal to (where, f = Fanning friction factor)

1. 2f
2. ƒ
3. ƒ/2
4. ƒ/4

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