Thermodynamics university questions 2015

This post help you for the mechanical engineering student who is going to write thermodynamics exam.Here important repeated 2 marks and 16 marks of unit 1 is given. 

Anna University Chennai

Regulation 2013

Thermodynamics                                                

  UNIT-1    

 PART-A

      
1. What is Perpetual motion machine of the second kind? 

2. State Carnot theorem.

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

4. Give the criteria of reversibility, irreversbility and impossibility of a thermodynamic cycle.

5. Explain the throttling process. 

6. Define Clausius statement. 

7. What are the assumptions made on heat engine?

8. What is meant by reversible process?

9. Define available energy and unavailable energy.

10. What are the important characteristics of entropy?

                                                    PART-B                

1. A heat pump working on the Carnot cycle takes in heat from a reservoir at 5 C and delivers heat to a reservoir at 60 C. A heat engine is driven by a source at 840 C and rejects heat to a reservoir at 60 C. The reversible heat engine, in addition to driving the heat pump, also drives a machine that absorbs 30 kW. If the heat pump extracts 17 kJ/s from the 5 C reservoir, determine (1) the rate of heat supply from the 840 C source, and (2) the rate of heat rejection to the 60 C sink.

2.If the required input to run the pump is developed by a reversible engine which receives heat at 380 C and rejects heat to atmosphere, then determine the overall C.O. P. of the system. 

3.A heat engine operating between two reservoirs at 100 K and 300 K is used to drive heat pump which extracts heat from the reservoir at 300 K at a rate twice that at which engine rejects heat to it. If the efficiency of the engine is 40% of the maximum possible and the co-efficient of performance of the heat pump is 50% of the maximum possible, make calculations for the temperature of the reservoir to which the heat pump rejects heat. Also work out the rate of heat rejection from the heat pump if the rate of supply of heat to the engine is 50 kW. 

4. One kg of ice at -5 C is exposed to atmosphere which is at 20 C. The ice melts and comes into contact 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 he water back into ice at -5 C? Cp of ice is 2.093 kJ / kg K and the latent heat of fusion of ice is 333. kJ / kg. 

5. A Carnot heat engine receives heat from a reservoir at 1173 K at a rate of 800kJ/min and rejects the waste heat to the ambient air at 300 K. The entire work output of the heat engine is used to drive a refrigerator that removes heat from the refrigerated space at 268K and transfers it to the same ambient air at 300 K. Determine the maximum rate of heat removal from the refrigerated space and the total rate of heat rejection to the ambient air. 

6.        An ideal gas of 0.12 m3 is allowed to expand isentropically from 300kPa and 120 C to 100 kPa. 5 kJ of heat is then transferred to the gas at constant pressure. Calculate the change in entropy for each process. Assume γ = 1.4 and Cp=1.0035 kJ/kg.K. If these two processes are replaced by a reversible polytropic expansion, find the index of expansion between original and final states. What will be the total changes in entropy?

7.A Carnot heat engine receives 650 kJ of heat from a source of unknown temperature and rejects 250kJ of it to a sink at 297 K. Determine the temperature of the source and the thermal efficiency of the heat engine. 

8. Determine the rate of power loss due to irreversibility in a heat engine operating between temperatures of 1800 K and 300 K. Engine delivers 2 MW of power when heat is added at the rate 

of 5 MW. 

9.A reversible heat engine operates between two reservoirs at 827 C and 27 C. Engine drives a Carnot refrigerator maintaining - 13 C and rejecting heat to reservoir at 27 C. Heat input to the engine is 2000 kJ and the net work available is 300 kJ. How much heat is transferred to refrigerant and total heat rejected to reservoir at 27 C? If the efficiency of the heat engine and COP of the refrigerator are each 40% of their maximum values, determine heat transfer to the refrigerator and also heat rejected to the reservoir at 27 C. Show that the efficiency of a reversible engine operating between two given constant temperatures is the maximum. 

10.Derive an expression for the change in entropy of a perfect gas during polytropic process in terms of T1 and T2. 

11. In a Carnot heat engine 50g of air acts as the working substance. The peak cycle temperature is 930K and the maximum pressure is 8.4x103 kPa. The heat addition per cycle is 4.2 kJ. Determine the maximum cylinder volume if the minimum temperature during the cycle is 315 K.