Gujarat Technological University 2010-4th Sem B.E Mechanical Engineering , Mechanical , Subject ame :Engineering Thermodynamics - Question Paper
Instructions:
1. Attempt all ques..
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of molier chart and steam tables is permitted
GUJARAT TECHNOLOGICAL UNIVERSITY
B.E Sem-IV Examination June 2010
Seat No. Enrolment No.
Subject code: 141903 Subject Name :Engineering Thermodynamics Date: 17 / 06 /2010 Time: 10.30 am - 01.00 pm
Total Marks: 70
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of molier chart and steam tables is permitted
Q.1 (a) Describe the phase change process of water using a T-V diagram. 04
1. A tube of bicycle filled with air
2. A jet engine in flight
3. water pump
4. car battery
5. An Electric geyser
6. Thermos flask
(c ) Air at a temperature of 15C passes through a heat exchanger at velocity of 30 m/s 07 where temperature is raised to 800C. It then enters a turbine with same velocity of 30m/s and expands until temperature falls to 650C. On leaving the turbine the air is taken at velocity of 60m/s to a nozzle where it expands until the temperature has fallen to 500C, If the air flow rate is 2kg/s, calculate (a) rate of heat transfer to air in the heat exchanger, (b) power output from turbine assuming no heat loss and (c) velocity at exit from the nozzle. Assuming no heat loss.
Q.2 (a) Define following terms: Kelvin Plank statement, Third law of Thermodynamics, 04 Thermodynamic temperature scale, Exergy
(b) Derive Maxwells thermodynamics relation and explain their importance in 03 thermodynamics.
(c ) A reversed carnot cycle operates at either a refrigerator or heat pump. In either case, 07 the power input is 20.8 kW. Calculate the quantity of heat extracted from the cold body for either type of machine. In both case 3500 kJ/min heat is delivered by the machine. In case of the refrigerator the heat is transferred to the surroundings while in case of heat pump, the space is to be heated. What is their respective coefficient of performances? If the temperature of cold body is 0C for the refrigerator and 5C for heat pump what will be respective temperatures of surrounding for refrigerator and heated space for heat pump? What reduction in heat rejection temperatures would be achieved by doubling the COP for same cold body temperature?
OR
(c) A volume of 0.14 m3 of air at 1 bar and 90C is compressed to 0.014m3 according 07 to the law pv13= C . Heat is then added at constant volume the pressure is 66 bar. Determine (a) Heat exchange with cylinder walls during compression and (b) Change of entropy during each portion of the process. Assume y=1.4 and R=286 J/Kg K
Q.3 (a) With usual notations prove that 05Q/T <=0
04
03
(b) Explain following terms: Flow work, critical point, triple point.
(c ) 10 Kg of water undergoes transformation from initial saturated vapour at 150 C, 07 velocity of 25 m/s and elevation of 10 m to saturated liquid at 20C, velocity of 10m/s and elevation of 3m. determine the availability of for initial state, final state and change if availability considering environment to be taken at 0.1 MPa and 25C C and g=9.8 m/s2
OR
Q.3 (a) Show that entropy of universe during mixing of flow fluid always increases. 04
(c) Two Kg of air at 500 KPa, 80C expands adiabatically in a closed system until its 07 volume is doubled and its temperature becomes equal to that of surrounding which
is at 100 kPa, 5 C . For this process, determine (a) maximum work, (b) Change in availability and irreversibility , for air take Cv =0.718 kJ/Kg K, R=0.287 kJ/Kg K
(b) An engine uses 6.5 Kg of oil per hour of calorific value of 30,000 kJ/Kg. If the 03 Brake power of engine is 22 kW and mechanical efficiency is 85% calculate (a) indicate thermal efficiency (b) Brake thermal efficiency (c)Specific fuel consumption in Kg/B.P/hr.
(c ) A carnot cycle works on steam between the pressure limits of 7 MPa and 7KPa. 07 Determine the thermal efficiency, turbine work and compression work per kg of steam.
OR
Q.4 (a) With suitable T-S diagram explain methods of improving efficiency of Rankine 04 cycle.
(b) In an Otto cycle the temperature at the beginning and end of the isentropic 03 compression are 316K and 596K respectively. Determine the air standard efficiency and compression ratio.
(c) Explain briefly the Otto cycle with help of P-V and T-S diagram and derive an 07 expression for deal efficiency of Otto Cycle.
Q.5 (a) Explain following terms: Excess air, Adiabitic flame temperature, Enthalpy of 04 formation,
(c) A vessel of volume 0.4 m3 consists of 0.45 Kg of carbon monoxide and 1 kg of air 07 at 15C. Calculate the partial pressure of each constituents and total pressure in the vessel. The partial pressure of each constituent and total pressure in the vessel. The
air contains 23.3% oxygen and 76.6% nitrogen by mass. Take the molar mass of carbon monoxide, oxygen and nitrogen as 28, 32 and 28Kg/ K mole, respectively.
OR
Q.5 (a) Write down Vanderwalls equation of state. How does it differ from ideal gas 04 equation?
(c ) How are fuels classified? List advantages and disadvantages of solid fuels over 07 liquid fuel.
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