Thermodynamics GATE 2019, Set-2

  • 1. For a simple compressible system, v , s , p and T are specific volume, specific entropy, pressure and temperature, respectively. As per Maxwell’s relations, \(\large \left ( \frac{\partial v}{\partial s} \right )_{p}\) is equal to

    (A) \(\large \left ( \frac{\partial s}{\partial T} \right )_{p}\)

    (B) \(\large \left ( \frac{\partial p}{\partial v} \right )_{T}\)

    (C) \(\large -\left ( \frac{\partial T}{\partial v} \right )_{p}\)

    (D) \(\large \left ( \frac{\partial T}{\partial p} \right )_{s}\)

    Answer

    2. Which one of the following modifications of the simple ideal Rankine cycle increases the thermal efficiency and reduces the moisture content of the steam at the turbine outlet?

    (A) Increasing the boiler pressure.

    (B) Decreasing the boiler pressure.

    (C) Increasing the turbine inlet temperature.

    (D) Decreasing the condenser pressure.

    Answer

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  • 3. Water flowing at the rate of 1 kg/s through a system is heated using an electric heater such that the specific enthalpy of the water increases by 2.50 kJ/kg and the specific entropy increases by 0.007 kJ/kg·K. The power input to the electric heater is 2.50 kW. There is no other work or heat interaction between the system and the surroundings. Assuming an ambient temperature of 300 K, the irreversibility rate of the system is ______ kW (round off to two decimal places).

    Answer

    4. An air standard Otto cycle has thermal efficiency of 0.5 and the mean effective pressure of the cycle is 1000 kPa. For air, assume specific heat ratio γ = 1.4 and specific gas constant R = 0.287 kJ/kg·K. If the pressure and temperature at the beginning of the compression stroke are 100 kPa and 300 K, respectively, then the specific net work output of the cycle is ______ kJ/kg (round off to two decimal places).

    Answer

    5. The figure shows a heat engine (HE) working between two reservoirs. The amount of heat (Q2) rejected by the heat engine is drawn by a heat pump (HP). The heat pump receives the entire work output (W) of the heat engine. If temperatures, T1 > T3 > T2 , then the relation between the efficiency (η ) of the heat engine and the coefficient of performance (COP) of the heat pump is

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    (A) COP = η

    (B) COP = 1 + η

    (C) COP = η– 1

    (D) COP = η -1 – 1

    Answer

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