JNTU
JNTU B.Tech II THERMODYNAMICS Previous Question Paper (November/December - 2017 - R13)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit.
Part A
Show that heat is a path function.
Answer
Heat is a path function because the amount of heat transferred depends on the specific path taken between two equilibrium states, not just the states themselves. Since heat is not a state variable, its differential is inexact (δQ), and the integral of heat transfer between two states depends on the process trajectory.
Show that energy is a property of a system.
Answer
Energy is a property because it depends only on the state of the system and not on the history or path taken to reach that state. For any cycle, the net change in energy is zero, meaning the cyclic integral of the differential of energy is zero, which is the mathematical condition for a point function or property.
What are the causes of irreversibility of a process?
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Why is the second law called a directional law of nature?
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What do you understand by the degree of superheat and the degree of subcooling?
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Show that for an ideal gas,
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How is the partial pressure in a gas mixture related to the mole fraction?
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What is an adiabatic saturation process?
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Why is the COP of a gas cycle refrigeration system low?
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Define m.e.p.
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Part B
A gas of mass 1.5 kg undergoes a quasi-static expansion which follows a relationship
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A reciprocating air compressor takes in 2 m3/min at 0.11 MPa, 20°C which it delivers at 1.5 MPa, 111°C to an after cooler where the air is cooled at constant pressure to 25°C. The power absorbed by the compressor is 4.15 kW. Determine the heat transfer in (a) the compressor, and (b) the cooler. State your assumptions.
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Using an engine of 30% thermal efficiency to drive a refrigerator having a COP of 5, what is the heat input into the engine for each MJ removed from the cold body by the refrigerator? If this system is used as a heat pump, how many MJ of heat would be available for heating for each MJ of heat input to the engine?
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A block of iron weighing 100 kg and having a temperature of 100°C is immersed in 50 kg of water at a temperature of 20°C, what will be the change of entropy of the combined system of iron and water? Specific heats of iron and water are 0.45 kJ/kg K and 4.18 kJ/kg K respectively.
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A rigid closed tank of volume 3 m3 contains 5 kg of wet steam at a pressure of 200 kPa. The tank is heated until the steam becomes dry saturated. Determine the final pressure and the heat transfer to the tank.
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Write down the van der Waals equation of state. How does it differ from the ideal gas equation of state? What is force of cohesion? What is co-volume?
0.5 kg of helium and 0.5 kg of nitrogen are mixed at 20°C and at a total pressure of 100 kPa. Find (a) the volume of the mixture, (b) the partial volumes of the components, (c) the partial pressures of the components, (d) the mole fractions of the components, (e) the specific heats cp and cv of the mixture, and (f) the gas constant of the mixture.
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A gaseous mixture consists of 1 kg of oxygen and 2 kg of nitrogen at a pressure of 150 kPa and a temperature of 20°C. Determine the changes in internal energy, enthalpy and entropy of the mixture when the mixture is heated to a temperature of 100°C (a) at constant volume, and (b) at constant pressure.
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Explain what do you understand by evaporative cooling.
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Calculate the amount of heat removed per kg of dry air if the initial condition of air is 35°C, 70% RH, and the final condition is 25°C, 60% RH.
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Explain the effect of superheat and subcooling on the vapour compression cycle.
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What do you understand by dry and wet compression? Which is preferred and why?
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An engine working on the Otto cycle has an air standard cycle efficiency of 56% and rejects 544 kJ/kg of air. The pressure and temperature of air at the beginning of compression are 0.1 MPa and 60°C respectively. Compute (a) the compression ratio of the engine (b) the work done per kg of air, (c) the pressure and temperature at the end of compression, and (d) maximum pressure in the cycle.
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