GATE ME Heat-Transfer PYQs & Answers — Page 4

Questions 31–40 of 54. Imported answers require independent review unless marked reviewed.

In a concentric tube counter-flow heat exchanger, hot oil enters at 102°C and leaves at 65°C. Cold water enters at 25°C and leaves at 42°C. The log mean temperature difference (LMTD) is __________ °C (round off to one decimal place).

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A small metal bead (radius 0.5 mm), initially at 100°C, when placed in a stream of fluid at 20°C, attains a temperature of 28°C in 4.35 seconds. The density and specific heat of the metal are 8500 kg/m³ and 400 J/kg.K, respectively. If the bead is considered as a lumped system, the convective heat transfer coefficient (in W/m².K) between the metal bead and the fluid stream is

Your answerChoose one option.

283.3

299.8

149.9

449.7

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The spectral distribution of radiation from a black body at

K has a maximum at wavelength

. The body cools down to temperature

. If the wavelength corresponding to the maximum of the spectral distribution at

is 1.2 times of the original wavelength

, then the temperature

is ______ K (round off to the nearest integer).

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Water flows through a tube of 3 cm internal diameter and length 20 m. The outside surface of the tube is heated electrically so that it is subjected to uniform heat flux circumferentially and axially. The mean inlet and exit temperatures of the water are 10°C and 70°C, respectively. The mass flow rate of the water is 720 kg/h. Disregard the thermal resistance of the tube wall. The internal heat transfer coefficient is 1697 W/m

·K. Take specific heat

of water as 4.179 kJ/kg·K. The inner surface temperature at the exit section of the tube is ______ °C (round off to one decimal place).

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For a hydrodynamically and thermally fully developed laminar flow through a circular pipe of constant cross-section, the Nusselt number at constant wall heat flux (

) and that at constant wall temperature (

) are related as

Your answerChoose one option.

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Sphere 1 with a diameter of 0.1 m is completely enclosed by another sphere 2 of diameter 0.4 m. The view factor

Your answerChoose one option.

0.0625

0.25

0.5

1.0

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A slender rod of length

, diameter

(

) and thermal conductivity

is joined with another rod of identical dimensions, but of thermal conductivity

, to form a composite cylindrical rod of length

. The heat transfer in radial direction and contact resistance are negligible. The effective thermal conductivity of the composite rod is

Your answerChoose one option.

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One-dimensional steady state heat conduction takes place through a solid whose cross-sectional area varies linearly in the direction of heat transfer. Assume there is no heat generation in the solid and the thermal conductivity of the material is constant and independent of temperature. The temperature distribution in the solid is

Your answerChoose one option.

Linear

Quadratic

Logarithmic

Exponential

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A thin vertical flat plate of height

, and infinite width perpendicular to the plane of the figure, is losing heat to the surroundings by natural convection. The temperatures of the plate and the surroundings, and the properties of the surrounding fluid, are constant. The relationship between the average Nusselt and Rayleigh numbers is given as

, where

is a constant. The length scales for Nusselt and Rayleigh numbers are the height of the plate. The height of the plate is increased to

keeping all other factors constant.

Diagram for Mechanical Engineering question 24

If the average heat transfer coefficient for the first plate is

and that for the second plate is

, the value of the ratio

is ____________.

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The wall of a constant diameter pipe of length 1 m is heated uniformly with flux

by wrapping a heater coil around it. The flow at the inlet to the pipe is hydrodynamically fully developed. The fluid is incompressible and the flow is assumed to be laminar and steady all through the pipe. The bulk temperature of the fluid is equal to 0 °C at the inlet and 50 °C at the exit. The wall temperatures are measured at three locations, P, Q and R, as shown in the figure. The flow thermally develops after some distance from the inlet. The following measurements are made:

Point	P	Q	R
Wall Temp (°C)	50	80	90

Among the locations P, Q and R, the flow is thermally developed at

Your answerChoose one option.

P, Q and R

P and Q only

Q and R only

R only

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GATE ME Heat-Transfer PYQs

Question 25

Question 34

Question 50

Question 51

Question 9

Question 10

Question 11

Question 11

Question 24

Question 32