JNTU B.Tech III THERMODYNAMICS AND REFRIGERATION SYSTEMS Previous Question Paper (November/December - 2017 - R15)

Define a quasi – static process.

State and explain the zeroth law of thermodynamics.

State Clausius theorem.

What do you understand by entropy principle?

Define Indicated thermal Efficiency.

Explain the working principle of dynamometer with a sketch.

What is a refrigeration?

What is the difference between a refrigerator and a heat pump?

Define Coefficient of Performance of a refrigerator.

What is sub cooling and super heating?

Define heat engine, heat pump and refrigerator with neat sketches. Write down an expression for performance of the above three types of cycles.

During flight, the air speed of a turbojet engine is 250 m/s. ambient air temperature is -14°C. Gas temperature at outlet of nozzle is 610°C. Corresponding enthalpy values for air and gas are respectively 250 and 900 kJ/kg. Fuel air ratio is 0.0180. Chemical energy of fuel is 45 MJ/kg. Owing to incomplete combustion 6% of chemical energy is not released in the reaction. Heat loss from the engine is 21 kJ/kg of air. Calculate the velocity of the exhaust air.

Derive an expression for Steady Flow Energy Equation (SFEE).

A reversible engine operates between two reservoirs at temperatures of 600°C and 40°C. The engine drives a reversible refrigerator which operates between reservoirs of 40°C and -20°C. The heat transfer to the heat engine is 2000 kJ and the net work output for the combined engine refrigerator is 360 kJ. Calculate the heat transfer to the refrigerator and the net heat transfer to the reservoir at 40°C.

State and prove Carnot’s theorem.

One kg of ice at -5°C is exposed to the atmosphere which is at 20°C. The ice melts and comes into thermal equilibrium with the atmosphere. (i) Determine the entropy increase of the universe. (ii) What is the minimum amount of work necessary to convert the water back into ice at -5°C? Cp of ice is 2.093 kJ/kgK and the latent heat of fusion of ice is 333.3 kJ/kg.

Why mountings and accessories are required for steam generation? List out some mountings and accessories.

Explain the working principle of Locomotive boiler with a suitable sketch.

Derive an expression for thermal efficiency of a diesel engine.

A single cylinder four-stroke diesel engine running at 1800 rpm. Has a bore of 85 mm and a stroke of 110 mm. It takes 0.56 kg of air per minute and develops a brake power output of 6 kW while the air-fuel ratio is 20:1. The calorific value of the fuel used is 42550 kJ/kg, and the ambient air density is 1.18 kg/m³. Calculate: i) The volumetric efficiency ii) Brake specific fuel consumption.

What is an indicator diagram? Explain the working principle of an indicator diagram.

An engine of 250 mm bore and 375 mm stroke works on Otto cycle. The clearance volume is 0.00263 m³. The initial pressure and temperature are 1 bar and 50°C. If the maximum pressure is limited to 25 bar, find the following: i) The air standard efficiency of the cycle ii) The mean effective pressure for the cycle. Assume the ideal conditions.

Prove that the performance factor of a Bell-Coleman cycle refrigeration system is given by COP = T2 / (T3 - T2). Where T2 and T3 are the temperatures of air at the inlet and discharge of compressor respectively. Explain, with a neat sketch, the working of this cycle.

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 Cp = 1.07 kJ/kg-K (for dense air).

Write down the applications of refrigeration? And explain the dry ice refrigeration.

The capacity of a refrigerator is 200 TR when working between -6°C and 25°C. Determine the mass of ice produced per day from water at 25°C. Also find the power required to drive the unit. Assume that the cycle operates on reversed Carnot cycle and latent heat of ice is 335 kJ/kg.

Explain the effect of superheating of vapour before compression with the help of T-s and p-h diagrams in vapour compression systems.

Draw a neat diagram of the simple ammonia – water absorption refrigeration system and explain its working.

Show the vapour compression cycle on ‘Temperature-Entropy’ (T-s) diagram for the following cases: i) When the vapour is dry and saturated at the end of compression. ii) When the vapour is superheated after compression. iii) When the vapour is wet after compression.

Define the following terms: i) Specific humidity ii) Relative humidity iii) Dew point temperature.