Thermodynamics important questions bank

 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-5   Part - A

                                     Answer all the questions             

1. Define degree of saturation. 

2. Differentiate absolute humidity and relative humidity.

3. Define dew point depression.

4. What is meant by adiabatic saturation temperature?

5. What is psychrometer? 

6.What is humidification and dehumidification?

7. Define sensible heat and latent heat.

8. What are the important psychrometric processes?

9. State Helmholtz function.

10. What are the assumptions made in Vanderwaal’s equation of state? 

                                                  Part - B                 

1. 30 m3/ min of moist air at 15 C DBT and 13 C WBT are mixed with 12m3/min of moist air at 25 C DBT and 18 C WBT. Determine DBT and WBT of the mixture assuming the barometric pressure is one atmosphere. 

2.For the atmospheric air at room temperature of 30 C and relative humidity of 60% Determine partial pressure of air, humidity ratio, dew point temperature, density and enthalpy of mixture.

3. Atmospheric air at 1.0132 bar has a DBT of 32◦C and a WBT of 26◦C. Find (i) the partial pressure of water vapour (ii)the specific humidity (iii) the dew point temperature (iv) the relative humidity (v) the degree of saturation (vi)the density of the air in the mixture (vii) the density of the vapour in the mixture (viii) the enthalpy of the mixture. 

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 the water back into ice at -5 C? Cp of ice is 2.093 kJ / kg K and the latent heat of fusion of ice.

5.A sample of moist air at 1 atm and 25 C has a moisture content of 0.01% by volume. Determine  the  humidity  ratio,  the  partial  pressure  of  water  vapour,  the  degree  of saturation, the relative humidity and the dew point temperature.

6. Air at 20 C, 40% R.H is mixed with air at 40 C, 40% R.H in the ratio of (former) 1:2 (later) on dry basis. Determine the final condition of air.

7. One kg of air at 40 C dry bulb temperature and 50% relative humidity is mixed with 2 kg of air at 20 C dry bulb temperature and 20 C dew point temperature. Calculate the temperature and specific humidity of the mixture. 

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. An air-water vapour mixture enters an air- conditioning unit at a pressure of 1.0 bar, 38 C DBT, and a relative humidity of 75%. The mass of dry air entering is 1 kg/s. The air- vapour mixture leaves the air-conditioning unit at 1.0 bar, 18 C, 85% relative humidity. The moisture condensed leaves at 18 C. Determine the heat transfer rate for the process. 

10. Atmospheric air at 1.0132 bar has 20 C DBT and 65% RH. Find the humidity ratio, wet bulb temperature, dew point temperature, degree of saturation, enthalpy of the mixture, and density of air and density of vapour in the mixture. 

11. In a laboratory test, a sling psychrometer recorded dry bulb and wet bulb temperatures as 303 K and 298 K respectively. Calculate (i) vapour pressure (ii) relative humidity (iii) specific humidity (iv)Degree of saturation (v) dew point temperature (vi) enthalpy of the mixture. 

12.1 kg of air at 40 C DBT and 50% relative humidity is mixed with 2 kg of air at 20 C DBT and 20 C dew point temperature. Calculate the specific humidity, enthalpy and the dry bulb temperature of the mixture.

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.