GATE ME topic:heat-transfer PYQs & Answers

Questions 1–10 of 62. Imported answers require independent review unless marked reviewed.

A sphere of radius 5 mm is initially in equilibrium at 400 °C in a furnace. It is suddenly removed from the furnace and dipped in a well-stirred water bath at 20 °C, with a convection heat transfer coefficient of 500 W/(m²K). For the given range of temperatures, the thermophysical properties of the material of the sphere are: density

kg/m³, thermal conductivity

W/(mK), and specific heat

J/(kg K). Neglecting radiation heat transfer, the time required for the centre of the sphere to cool from 400 °C to 50 °C is ______ seconds (rounded off to 2 decimal places).

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A very long fin of a uniform square cross-section is replaced by another very long fin of a uniform circular cross-section of the same material. Assume uniform and identical heat transfer coefficient for both the fins. If the diameter of the circular fin is equal to the side length of the square fin, then the ratio of heat transfer rates before and after the replacement is

Your answerChoose one option.

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Two rectangular surfaces both having 1 m² area are placed perpendicular to each other with a common edge. One surface is hot, having a temperature of 1000 K and emissivity of 0.4, while the other is insulated and in radiant balance with a large surrounding room at 300 K. If the fraction of radiation leaving the hot surface which reaches the cold face is 0.2, then the equivalent overall resistance for the radiation heat loss from the hot surface is ______ m⁻² (rounded off to 2 decimal places).

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Convective heat transfer coefficients for Fluid 1 and Fluid 2 in a heat exchanger, as shown in the figure below, are 50 W/(m²K) and 80 W/(m²K), respectively. The inner tube is made of a material which has a thermal conductivity 386 W/(m K) for the given range of temperatures in the heat exchanger. The length of the heat exchanging surface, the inside radius of the inner tube, and thickness of the inner tube are 1 m, 10 mm, and 1 mm, respectively. Considering no heat exchange between the outer tube and the surrounding, the heat transfer rate for the heat exchanger is ______ W (rounded off to 1 decimal place).

Diagram for Mechanical Engineering question 55

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Let a spherical block of ice at

be exposed to atmospheric air at

with the gravitational direction as shown in the figure below. What will be the overall direction of air flow in this situation?

Diagram for Mechanical Engineering question 15

Your answerChoose one option.

Upward

Downward

NO motion

Sideward

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During a welding operation, thermal power of 2500 W is incident normally on a metallic surface. As shown in the figure below (figure is NOT to scale), the heated area is circular. Out of the incident power, 85% of the power is absorbed within a circle of radius 5 mm while 65% is absorbed within an inner concentric circle of radius 3 mm. The power density in the shaded area is __________ W m

(rounded off to 2 decimal places).

Diagram for Mechanical Engineering question 33

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Consider a cylindrical furnace of 5 m diameter and 5 m length with bottom, top and curved surfaces maintained at uniform temperatures of 800 K, 1500 K and 500 K, respectively. The view factor between the bottom and top surfaces,

is 0.2. The magnitude of net radiation heat transfer rate between the bottom surface and the curved surface is __________ kW (rounded off to 1 decimal place). All surfaces of the furnace can be assumed as black. The Stefan-Boltzmann constant,

Diagram for Mechanical Engineering question 48

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Water enters a tube of diameter, D = 60 mm with mass flow rate of 0.01 kg s

as shown in the figure below. The inlet mean temperature is

K and the uniform heat flux at the surface of the tube is 2000 W m

. For the exit mean temperature of

K, the length of the tube, L is ________ m (rounded off to 1 decimal place).

Use the specific heat of water as 4181 J kg

Diagram for Mechanical Engineering question 51

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A plane, solid slab of thickness

, shown in the figure, has thermal conductivity

that varies with the spatial coordinate

, where

and

are positive constants (

). The slab walls are maintained at fixed temperatures of

and

. The slab has no internal heat sources. Considering one-dimensional heat transfer, which one of the following plots qualitatively depicts the steady-state temperature distribution within the slab?