Question Paper: Engineering Thermodynamics : Question Paper Dec 2016 - Mechanical Engineering (Semester 3) | Gujarat Technological University (GTU)
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## Engineering Thermodynamics - Dec 2016

### Mechanical Engineering (Semester 3)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.
1(a) The equation $\left ( p+a/v^2 \right )\left ( v-b \right )=R$/ is known as
a) Maxwell's equation b) Van der Wall's equation c) Avogadro's equation d) Real gas equation
(1 marks)
1(b) If a gas is heated against a pressure keeping the volume constant, then work done will be equal to
a) Positive b) Negative c) Zero d) Between zero to infinity
(1 marks)
1(c) An ineventor claims that his heat engine has the following specification: Power developed -50 kW, Fuel Burned per hour - 3kg, Heating value of fuel-75000 kJ per keg Temperature limits - (627°C and 27°C), His heat engine is
a) Reality b) Impossible c) Costly d) Cheaper.
(1 marks)
1(d) The constant volume cycle is also called
a) Carnot cycle b) Braton cycle c) Diesel cycle d) Otto cycle
(1 marks)
1(e) Thermal power plants works on
a) Carnot cycle b) Joule cycle c) Brayton cycle d) Rankine cycle
(1 marks)
1(f) Gas turbines work on
a) Constant volume cycle b) Constant temperature cycle c) Constant pressure cycle d) Dual combustion cycle
(1 marks)
1(g) Triple point a pure substance on P-V diagram is represented by a
a) Point b) Line c) Curve d) Triangle
(1 marks)
1(h) Which of the following is the unit entropy?
a) J/kg K b) J/K c) Nm/kg sec d) j/kg
(1 marks)
1(i) For same compression ratio and for same heat added
a) Otto cycle is more efficient than diesel cycle b) Diesel cycle is more efficient than Otto cycle c) Efficiency depends on other factors d) None of the above
(1 marks)
1(j) The contents of a well-insulated tank are heated by a resistor of 23Ω in which 10A current is following. Consider the tank along with its contents as a thermodynamic system. The work done by the system and the heat transfer to the system are positive. The rates of heat (Q),work (W) and change in internal energy (δU) during the process in kW are
a) Q=0, W=2.3, δU=+2.3 b) Q = + 2.3, W=0, δU = +2.3 c) Q = -2.3, W=0, δU=-2.3 d) Q =0, W=+2.3, δU =-2.3
(1 marks)
1(k) Heat and Work are
a) Intensive Property b) Extensive Property c) Point function d) Path function
(1 marks)
1(l) All reversible engines operating between two fixed temperatures have _________ efficiency.(1 marks) 1(m) Justify: Complete conversion of high grade energy to low grade energy is possible but the reverse is not true(1 marks) 1(n) What are the causes of irreversibility?(1 marks) 2(a) A domestic refrigerator is loaded with food and the door closed. During a certain period the machine consumes 1kW h of energy and the internal energy of the system drops by 5000kJ. Find the net heat transfer for the system.(3 marks) 2(b) A reversible heat engine operates between two reservoirs at temperatures of 600 °C and 40°C. The engine drives a reversible refrigerator which operates between reservoirs at temperature of 40°C and -20°C. The heat transfer to the heat engine is 2000kJ and the net work output of the combined engine refrigerator plant is 360kJ. Evaluate the heat transfer to the refrigerant and the net heat transferred to the reservoir at 40°C(4 marks)

### Solve any one question.Q2(c) &Q2(d)

2(c) State the SFEE for a single stream inlet and single stream leaving a control volume and explain the various terms in it. Also write SFEE for following Applications: 1) Coolin Tower 2) Centrifugal pump 3) Expansion valve of refrigerator.(7 marks) 2(d) Evaluate the following statements: 1) Heat pump provides a thermodynamic advantage over direct heating.
2) Kelvin tenperature scale is independent of the peculiar characteristics of any particular substance.
(7 marks)

### solve any one question Q.3(a,b,c) &Q4(a,b,c)

3(a) Justify: For the same compression ration and work capacity, Brayton cycle is more suitable than Otto cycle in gas turbine power plants(3 marks) 3(b) Explain using p-v and T-s diagram, which of the two cycles - Otto cycle and Diesel cycle, will have higher efficiency for a given maximum pressure and temperature in the cycle?(4 marks) 3(c) In an air standard Diesel cycle, the compression ration is 16, and at the beginning of isentropic compression, the temperature is 15°C and the pressure is 0.1MPa. Heat is added until the temperature at the end of the constant pressure process is 1480°C. Calculate a) the cut-off ratio, b) the heat supplied per kg of air, and c) the cycle efficieny.(7 marks) 4(a) Why steam power plants are popular than gas turbine plant in electric power generation?(3 marks) 4(b) What do you understand by the mean temperature of heat addition? For a given T2, show how the Rankine cycle efficiency depends on the mean temperature of heat addition.(4 marks) 4(c) In a single heater regenrative cycle the steam enters the turbine at 30 bar , 400 °C and the exhaust pressure is 0.1 bar. The feed water heater is direct contact type which operates at 5 bar. Find a) efficiency b) steam rate and c) mean temperature of heat addition with regeneration. Neglect pump work.(7 marks)

### solve any one question Q.5(a,b,c) &Q6(a,b,c)

5(a) What do you understand by steam rate and heat rate ? What are their units?(3 marks) 5(b) What is the effect of regeneration? On the 1) Specific output, b) mean temperature of heat addition c ) cycle efficiency and d) steam rate(4 marks) 5(c) Determine work required to compress steam isentropically from 1 bar to 10 bar, assuming that at the initial state the steam exists as a) saturated liquid and b) saturated vapor. Neglect changes in kinetic energy and potential energy. What conclusion do you derive from this example?(7 marks) 6(a) What is an equation of state ? State its different type and which type is focused in the present subject.(3 marks) 6(b) A cylinder of 0.1m3 volume is filled with 0.727 kg of C8H18 at 427.85 K. Assuming that C8 H18 obeys Van der walls equation of state, calculate the pressure of the gas in the cylinder. The Van der walls Constant a and b for C8 H18 are 3.789 Pa(m3/mol)2 and 2.37 10-4m<supp>3/mol, respectively.</supp>(4 marks) 6(c) What is entropy principle? With the help of it prove that adiabatic mixing of two fluids is irreversible.(7 marks) 7(a) What is an ideal gas equation? What assumption are made in deriving the ideal gas equation of state from kinetic theory of gas?(3 marks) 7(b) State the law of corresponding states and define the compressibility factor and explain its significance.(4 marks) 7(c) Calculate the available energy in 40 kg of water at 75°C with respect to the surrounding at 5°C, the pressure of water being 1 atm.(7 marks)