GATE PI concept:heat-transfer PYQs & Answers — Exam Papers

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Questions 1–7 of 7. Imported answers require independent review unless marked reviewed.

Topic practice 7 questionsPage 1 of 1

The left-hand side of a 20 cm thick wall is maintained at 25 °C. The right-hand side of the wall is exposed to hot air at 50 °C. There is no heat generation inside the wall and its thermal conductivity is 100 W/m·K. The convective heat transfer coefficient is 50 W/m²·K. Under steady state condition, the temperature (in °C) of the right-hand side surface of the wall is__________. (Rounded off to one decimal place)

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Mild steel plates are welded to make butt joints by arc weld with 85% heat transfer efficiency ignoring other losses. The first weld joint is made by selecting arc voltage of 30 V and current of 180 A with a welding speed of 6 mm/s. Using identical plates, a second weld joint is made with the same arc voltage and a welding speed of 8 mm/s. If both the welds have the same heat input, then the welding current (in A) for the second weld joint is ________. (Answer in integer)

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Two plane parallel surfaces exchange heat by thermal radiation. A radiation shield is placed in between at equal distance from the two surfaces to reduce heat transfer. All surfaces are black with infinite length and width. The ratio of heat transfer rate between surfaces with and without radiation shield is

Your answerChoose one option.

A.

B.

C.

D.

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Water flows through a pipe of diameter 0.02 m. The Reynolds number of the flow is 100. The pipe is heated from outside with a uniform heat flux. The flow and heat transfer in the pipe are steady and fully developed. The thermal conductivity of water is 0.66 W/(m-K). The convective heat transfer coefficient, in W/(m²-K), is _____ (round off to 2 decimal places).

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In an arc welding process, the DC power source characteristic is linear with an open circuit voltage of 60 V and short circuit current of 600 A. The heat required for melting a metal during the welding is 10 J/mm³, and the heat transfer and melting efficiencies are 80% and 25%, respectively. If the weld cross-sectional area of 20 mm² is made using the maximum arc power, then the required welding speed in mm/s is ________. [round off to one decimal place]

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A steel ball of 12 mm diameter is heated to 1225 K. It is slowly cooled in air to a temperature of 475 K. During the cooling process, the ambient temperature is 325 K and the heat transfer coefficient is 30 W/m

-K. Assume the density of steel is 7800 kg/m

and the specific heat is 600 J/kg-K. Using the lumped capacitance method of analysis, the calculated time for the required cooling (rounded off to one decimal place) in seconds is __________.

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The heat transfer efficiency in arc welding of a plate using a current of 250 A at 20 V is 90%. The heat required to melt the material is 10 J/mm³. If the cross-sectional area of the weld joint is 30 mm² and the travel speed is 5 mm/s, the melting efficiency (in %) is ______ (round off to 2 decimal places)

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