Q. 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

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Q. Intermittant tube cleaning is possible to be done in case of a __________ evaporator.

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Q. Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is

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Q. Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for

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Q. Overall heat transfer co-efficient for cooling of hydrocarbons by water is about

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Q. For concentrating an aqueous solution of a material like anhydrous Na₂SO₄, whose solubility decreases with rise in temperature, the most suitable evaporator is a __________ evaporator.

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Q. Circulation pump is located below the evaporater to

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Q. The statement that "maximum wavelength of radiation is inversly proportional to the temperature" is __________ law.

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Q. Steam condensate is recovered by steam traps and recycled for use as boiler feed water, because of its low

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Q. Duhring rule is important in solving problems on

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Q. In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to (where, D = inside diameter of shell)

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Q. Multiple effect evaporation is generally recommended, when the

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Q. The inside heat transfer co-efficient in case of turbulent flow of liquid in the tube side in a 1-2 shell and tube heat exchanger is increased by __________ times, when the number of tube passes is increased to 8.

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Q. __________ heat exchanger is the most suitable, when the temperature of shell side fluid is much higher than that of tube side.

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Q. The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as

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Q. If air (a non-condensing gas) is present in a condensing vapor stream, it will __________ the condensation rate of vapor.

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Q. Prandtl and Reynold's analogies are identical for Prandtl number value of

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Q. The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid

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Q. In evaporators, lowering the feed temperature

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Q. Unsteady state heat conduction occurs, when

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