GATE CH Heat Transfer PYQs & Answers — Page 6

Questions 51–57 of 57. Imported answers require independent review unless marked reviewed.

Vapour bubbles are formed in the nucleate boiling regime at a frequency of 10 bubbles per second per nucleation site. There are 100 nucleation sites per m² of heating area. The latent heat of vaporization and the density of vapour under the operating condition are 1000 kJ/kg and 1 kg/m³ respectively. The diameter of each bubble is 10⁻³ m. Assume that the entire heat supplied is used for vapour generation. The heat flux (in Watt per m² of heating area) is ______________ (rounded off to third decimal place).

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A hot liquid is to be cooled in a 1-1 shell and tube heat exchanger from 80 °C to 50 °C. Cooling water enters the tube side at 30 °C, and exits at 45 °C. The properties of the liquids are constant. Also, the overall heat transfer coefficient is same for counter-current and co-current modes. The percentage saving in heat transfer area for counter-current option with respect to the area of co-current option is __________ (rounded off to third decimal place).

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The one-dimensional unsteady heat conduction equation is

where

– temperature,

– time,

– radial position,

– thermal conductivity,

– density, and

– specific heat.

For the cylindrical coordinate system, the value of

in the above equation is

Your answerChoose one option.

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In a heat exchanger, the inner diameter of a tube is 25 mm and its outer diameter is 30 mm. The overall heat transfer coefficient based on the inner area is 360 W/m²·°C. Then, the overall heat transfer coefficient based on the outer area, rounded to the nearest integer, is ______ W/m²·°C.

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Let

be the spectral blackbody radiation intensity per unit wavelength about the wavelength

. The blackbody radiation intensity emitted by a blackbody over all wavelengths is

Your answerChoose one option.

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A fluid flows over a heated horizontal plate maintained at temperature

. The bulk temperature of the fluid is

. The temperature profile in the thermal boundary layer is given by:

Here,

is the vertical distance from the plate,

is the thickness of the thermal boundary layer and

is the thermal conductivity of the fluid. The local heat transfer coefficient is given by

Your answerChoose one option.

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In nucleate boiling, the pressure inside a bubble is higher than the pressure of the surrounding liquid. Assuming that both the liquid and vapour are saturated, the temperature of the liquid will ALWAYS be

Your answerChoose one option.

at 100 °C

lower than the temperature of the vapour

equal to the temperature of the vapour

higher than the temperature of the vapour

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GATE CH Heat Transfer PYQs

Question 36

Question 55

Question 12

Question 13

Question 39

Question 40

Question 41