Question 41 : Which of the following has the minimum absorptivity ?
1. Coal dust
2. Refractory bricks
3. Iron plates
4. Aluminium foil
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Question 42 : A black body when hot, emits heat radiation of __________ wavelengths.
1. large
2. small
3. one fixed
4. all
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Question 43 : Which of the following has the lowest overall heat transfer co-efficient ?
1. Molten sodium
2. Air
3. Water
4. Dowtherm
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Question 44 : The rate of heat transfer is a product of overall heat transfer co-efficient, the difference in temperature and the
1. heating volume
2. Nusselt number
3. none of these
4. heat transfer area
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Question 45 : Heat exchangers operating, when the asymptotic range is reached,
1. results in making part of the heating surface inactive
2. provide very large heat transfer co-efficient
3. results in abruptly increased velocity.
4. none of these.
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Question 46 : Boiling point elevation of an ideal solution
1. increases rapidly with temperature rise.
2. decreases rapidly with temperature rise
3. in independent of pressure.
4. both in independent of pressure. and decreases rapidly with temperature rise
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Question 47 : In case of a shell and tube heat exchanger, the minimum and maximum baffle spacing is respectively (where, D = inside diameter of the shell)
1. D/4 and 2 D
2. D/2 and 2 D
3. D/5 and D
4. D and 2 D
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Question 48 : In a gas-liquid shell and tube heat exchanger, the
1. gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature.
2. gases to be heated/cooled is normally routed through the shell side, because the corrosion caused by the cooling water or steam condensate remain localised to the tubes.
3. presence of a non-condensible gas decreases the condensing film co-efficient.
4. all 'a', 'b' & 'c'
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Question 49 : In case of heat transfer by conduction in a hollow cylinder, __________ mean area is used to calculate the heat transfer rate.
1. geometric
2. arithmetic
3. logarithmic
4. either (a), (b) or (c)
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Question 50 : For __________ Prandtl number values, the heat conduction will be negligible in the buffer zone.
1. high
2. extremely low
3. no
4. low
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