JNTU B.Tech III THERMODYNAMICS AND REFRIGERATION SYSTEMS Previous Question Paper (November/December - 2018 - R15)

Define a pure substance.

Explain the concept of temperature measurement method used before 1954.

What do you mean by the term ‘Entropy’?

What is economizer in a steam generation? What are the advantages of economizer?

Define mean effective pressure.

Write down the classification of IC Engines.

Define ton of refrigeration.

Differentiate clearly between open and closed air refrigeration systems.

What are the functions of an absorber in an absorption system?

List out various psychrometric process on a psychrometric chart.

Explain the other forms of work transfer.

A cyclic heat engine operates between a source temperature of 900°C and a sink temperature of 30°C. What is the least rate of heat rejection per kW net output of the engine?

Establish the equivalence of Kelvin-Planck and Clausius statements.

The properties of a system, during a reversible constant pressure non-flow process at p = 1.6 bar, changed from v1 = 0.3 m³/kg, T1=25°C to v2 = 0.55 m³/kg, T2=260°C. The specific heat of the fluid is given by C_p = (1.5 + T/45) kJ/kg°C, where T is in °C. Determine: (i) Heat added/kg; (ii) Work done/kg; (iii) Change in Internal energy/kg; (iv) Change in enthalpy/kg.

Derive an expression for entropy change of a closed system for the polytropic process?

Air at 20°C and 1.05 bar occupies 0.025 m³. The air is heated at constant volume until the pressure is 4.5 bar, and then cooled at constant pressure back to original temperature. Calculate: (i) The net heat flow from the air; (ii) The net entropy change. Sketch the process on T-s diagram.

With a neat sketch, explain the working principle of Babcock-Wilcox boiler.

A fluid undergoes a reversible adiabatic compression from 0.5 MPa, 0.2 m³ to 0.05 m³ according to the law, pv^1.3=constant. Determine the change in enthalpy, internal energy and entropy, and the heat transfer and work transfer during the process.

Explain the working principle of a four – stroke CI engine with a neat sketch.

Derive an expression for efficiency of an Otto cycle with a neat diagram.

Define the figure of merit related to thermo – electric refrigeration system and explain its effect on COP of the system.

A dense air refrigeration machine operates on reversed Brayton cycle and is required for 10 tonnes of refrigeration capacity. The cooler pressure is 4.5 bar and refrigerator pressure is 1.5 bar. The air is cooled in the cooler to a temperature of 50°C and the temperature of air at inlet to the compressor is -20°C. For an ideal cycle, determine the following: (i) COP of the system; (ii) Mass of air circulated per minute; (iii) Theoretical piston displacement of the compressor; (iv) Net power per ton of refrigeration. Show the cycle on p-V and T – S diagrams. Take C_p = 1.07 kJ/kg-K.

With a neat sketch, explain an air refrigerator working on a reversed Carnot cycle.

A dense air refrigeration cycle operates between pressures of 4 bar and 16 bar. The air temperature after heat rejection to surroundings is 37°C, and air temperature at exit to refrigerator is 7°C, the isentropic efficiencies of turbine and compressor are 0.85 and 0.8 respectively. Determine compressor and turbine work per TR, COP and HP/TR. γ = 1.4 and C_p = 1.005 kJ/Kg K.

Explain the Ozone depletion. What happens when ozone layer is depleted?

An air refrigerator used for food storage, provides 50 TR. The temperature of air entering the compressor is 7°C and the temperature before entering into the expander is 27°C. Assuming a 70% mechanical efficiency find: (i) Actual COP; and (ii) The power required to run the compressor. The quantity of air circulated in the system is 100 kg/min. The compression and expansion follow the law pv^1.3=Constant. Take γ=1.4; C_p=1 kJ/kg K.

Explain with reference to T-s diagram, the stages involved in vapour compression refrigeration process of refrigeration. Establish an expression for the coefficient of performance.

Explain with the help of neat sketches, vapour absorption cycle for refrigeration. How is it different from vapour compression refrigeration system?

Define relative humidity, specific humidity, and dew-point temperature and describe a theoretical method for determining their values.

A vapour compression refrigerator works between the pressures 4.9 bar and 1.9 bar. The vapour is superheated at the end of compression, its temperature being 25°C. The liquid is cooled to 9°C before throttling. The vapour is 95% dry before compression. Calculate the coefficient of performance and refrigerating effect per kg of the working substance circulated. Given: (At 1.9 bar: Tsat = -15°C, hf = 21.67, hfg = 161.41; At 4.9 bar: Tsat = 14.45°C, hf = 49.07, hfg = 147.80).