Anna University November/December 2011

ME2202 — ENGINEERING THERMODYNAMICS

(Regulation 2010)

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 ´ 2 = 20 marks)

(Regulation 2010)

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 ´ 2 = 20 marks)

1. Explain the following terms :

(a) Process (b) cycle.

2. Define internal energy.

3. What do you mean by the term ‘entropy’?

4. What is a temperature entropy diagram?

5. Draw a p-T (pressure-temperature) diagram for a pure substance.

6. Explain comparison between Rankine cycle and Carnot cycle.

7. Explain compressibility factor.

8. Write the Maxwell’s equation.

9. Define dry bulb temperature.

10. Explain adiabatic mixing of two substances.

PART B — (5 ´ 16 = 80 marks)

11. (a) 10 kg of fluid per minute goes through a reversible steady flow process. The properties of fluid at the inlet are 1 P = 1.5 bar, 1 r = 26 kg/m3, 1 v = 110 m/s and 1 u = 910 kJ/kg and at the exit are 2 P = 5.5 bar, 2 r = 5.5 kg/m3 2 v = 190 m/s and 2 k = 710 kJ/kg. During the passage, the fluid rejects 55 kJ/s and rises through 55 m. Determine : (i) the change in enthalpy (h) (ii) work done during the process (w).

Or

Or

(b) A system contain 0.2 m3 of a gas at a pressure of 4 bar and 150°C. It is expanded adiabatically till the pressure falls to 1 bar. The gas is then heated at a constant pressure till its enthalpy increases by 100 kJ. Determine the total work done. Take p c = 1 kJ/kgK and v c = 0.714 kJ/kgK. (16)

12. (a) A reversible heat pump is used to maintain a temperature of 0°C in a refrigerator when it rejects the heat to the surroundings at 27°C . If the heat removal rate from the refrigerator is 1500 kJ/min. Determine the C.O.P of the machine and work input required. If the required input to

run the pump is developed by a reversible engine which receives heat at 400°C and rejects heat to atmosphere, then determine the over all C.O.P of the system. (16)

Or

(b) A reversible engine is supplied with heat from two constant temperature sources at 900K and 600K and rejects heat to a constant temperature sink at 300K. If the engine executes a numbers of complete cycles while developing 100 kW, and rejecting 3600 kJ of heat per minute. Determine

the heat supplied by each source per minute and efficiency of the engine. (16)

13. (a) One kg of steam at 10 bar exists at the following conditions (i) wet and 0.8 dry (ii) dry and saturated and (iii) at a temperature of 199.9°C. Determine the enthalpy, specific volume, density, internal energy and entropy in each case. Take ps c = 2.25 kJ/kg. (16)

Or

(b) A Rankine cycle works between 40 bar and 0.2 bar with saturated steam at turbine inlet. Determine the cycle efficiency and the ratio of pump work and turbine work. (16)

14. (a) A certain ideal gas has R = 290 J/kg k and g = 1.35 (i) Determine the values of p c and v c . (ii) The mass of the gas it is filled in a vessel of 0.5 m3 capacity till the pressure inside becomes 4 bar gauge and the temperature is 27°C (iii) if 40 kJ of heat is given to the vessel when the vessel is closed, determine the resulting temperature and pressure. Take the atmospheric pressure = 100 kPa. (16)

Or

(b) A container of 3m3 capacity contains 10 kg of CO2 at 27°C. Estimate the pressure exerted by CO2 by using.

(i) Perfect gas equation.

(ii) Vander Waal’s equation.

(iii) Beattie Bridgeman equation. (16)

15. (a) It is required to design an air conditioning plant for a small office room for following winter conditions. Outdoor conditions = 14°C DBT and 10°C WBT Required conditions = 20° C DBT and 60% R.H Amount of air circulation 0.30 m3/min/person. Seating capacity of office = 60 The required condition is achieved first by heating and then by adiabatic humidifying.

Determine the following :

(i) Heating capacity of the coil in kW and the surface temperature required if the by pass factor of coil is 0.4.

(ii) The capacity of the humidifier. (16)

Or

(b) Saturated air at 20°C at a rate of 70 m3/min is mixed adiabatically with the outside air at 35°C and 50% relative humidity at a rate 30 m3/min. Assuming that the mixing process occurs at a pressure of 1 atm, determine the specific humidity, the relative humidity, the dry bulb temperature, and the volume flow rate of the mixture. (16)