UPSC Mechanical Engineering PYQs 2019 | Vaidra

1Medium20 marks

With the help of continuity, momentum and energy equations, obtain an expression for Mach number after a normal shock in terms of the Mach number before the shock.

2Medium10 marks

A furnace wall consists of 200 mm inner layer of refractory brick (k = 1.52 W/m-K), 8 mm thick steel plate (k = 45 W/m-K) and outer layer of 100 mm thick insulation brick (k = 0.138 W/m-K). The inner wall of the furnace is maintained at 1150 °C, while the outer wall of the insulation brick is at 40 °C. Calculate the heat transfer through the wall. What is the temperature at the junction of steel plate and outer insulation brick wall?

3Medium10 marks

A Carnot refrigeration cycle is operating between the minimum and maximum temperatures of -8 °C and 20 °C respectively. The refrigerant used in the cycle is R-134a and the cycle is operating in the saturated liquid-vapour region. The mass of the refrigerant is 0.8 kg and the refrigerant is saturated liquid at the end of heat rejection process. The net work input to the cycle is 15 kJ. Determine the fraction of the mass of the refrigerant that vaporizes during the heat addition process. Given

h_{fg}\text{ at } -8\text{ °C} = 204.59\text{ kJ/kg}

h_{fg}\text{ at } 20\text{ °C} = 180.33\text{ kJ/kg}

Mechanical Engineering UPSC PYQ 2019

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