Question Paper: Thermodynamics Question Paper - Jun 18 - Mechanical Engineering (Semester 3) - Jawaharlal Nehru Technological University (JNTUH)
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## Thermodynamics - Jun 18

### Mechanical Engineering (Semester 3)

Total marks: 80
Total time: 3 Hours
INSTRUCTIONS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Draw neat diagrams wherever necessary.

PART- A (25MARKS)

1.a. What are the positive and negative work interactions?
(2 marks) 00

1.b. what is a Quasi static process?
(3 marks) 00

1.c. Define enthalpy. How is it related to internal energy?
(2 marks) 00

1.d. Why is the performance of the heat pump or a refrigerator not measured in terms of thermal efficiency, but in the term of COP?
(3 marks) 00

1.e. What do you understand by triple point?
(2 marks) 00

1.f. Define an ideal gas. What is universal gas constant?
(3 marks) 00

1.g. What is specific humidity and relative humidity?
(2 marks) 00

1.h. Explain mole fraction, volume fraction.
(3 marks) 00

1.i. What is a ton of refrigeration?
(2 marks) 00

1.j. What is an air standard cycle? Why are such cycle conceived?
(3 marks) 00

PART- B (25MARKS)

2.a. Why does free expansion has zero work transfer?
(5 marks) 00

2.b. A new scale N of temperature is divided in such a way that the freezing point of the ice 100°N and the boiling point is 400°N. What is the temperature reading on the new scale when the temperature is 160°C? At which temperature both the Celsius and the new temperature scale reading would be the same.
(5 marks) 00

OR

3.a. Explain the working of constant volume gas thermometer.
(5 marks) 00

3.b. 2kg of gas at the pressure of 1.5 bar, occupies a volume of 2.5 m³. If this gas compresses isothermally is 1/3 times the initial volume, find initial, find temperature, work done, heat transfer.
(5 marks) 00

4.a. Discuss the significance of Gibbs and helmholtz functions.
(5 marks) 00

4.b. Two blocks of metal, each having a mass of 10 kg and having a specific heat of 0.4 kj/kg.K, are the temperature of 40°C. A reversible refrigerator receives heat from one block and rejects heat to the other. Calculate the work required to cause a temperature difference of 100°C between the two blocks .
(5 marks) 00

5.a. State and prove clausius theorem
(5 marks) 00

5.b. A reversible heat engine operates between two reservoirs at temperature of 600°C and 40°C. The engine drives a reversible refrigerator which operate between reserve water temperature 40°C and -20°C the heat transfer to the heat engine is 2000KJ at the net work output of the combined engine refrigerator planet is 300 kJ. Evaluate the heat transfer to the refrigerator and heat transfer to the reservoir at 40°C.
(5 marks) 00

6.a. What is the critical state? Explain the term critical pressure, critical volume, and critical temperature of water?
(5 marks) 00

6.b. extreme pressure of holding capacity containes a mixture of saturated water and Saturated stream of 250°C. The mass of liquid present in 1 ton.Determine (i)quality (ii) specific volume (iii)specific enthalpy; (iv) specific entropy and (v) specific internal energy of steam.
(5 marks) 00

OR

7.a. Write short notes on "mollier diagram". Why do isobars on the mollier diagram diverge from one another?
(5 marks) 00

7.b. A pressure cooker holding 2 kg of stream fibre and 90% dry is being colled slowly. What quantity of heat has been extracted to reduce the stream quality down to 60%? Also calculate the pressure and temperature of the stream that remain in the pressure cooker after the heat rejection.
(5 marks) 00

8.a. Compare the contrast the gravimetric and volumetric analysis.
(5 marks) 00

8.b. A sling psychrometer reads 39°C dry bulb temperature at 35°C wet bulb Temperature find the humidity ratio, Relative humidity, dew point temperature, specific volume, and enthalpy of air.
(5 marks) 00

OR

9.a. Explain the following: I)heating and dehumidification ii) cooling and dehumidification.
(5 marks) 00

9.b. 100m3 of air per min at 40DBT and 15% relative humidity is passed through adiabatic humidifier. The air coming out 25°C DBT and 20°C WBT. Find: I) Dew point temperature ii) Relative humidity iii) Water carried by the air per min.
(5 marks) 00

10.a. Drive an expression for thermal efficiency of Otto cycle.
(5 marks) 00

10.b. An engine works on a diesel cycle with inlet pressure and temperature of 1 bar and 17°C. The pressure at the end of the adiabatic compression is 35 bar. The ratio of expression, i.e. constant pressure heat addition is 5. Calculate the heat addition, heat rejection and efficiency of cycle. Assume r=1.4, Cp=1.005KJ/kgk CV=0.717 KJ/kgk.
(5 marks) 00

OR

11.a. Explain the working of Bell- Coleman cycle.
(5 marks) 00

11.b. Explain the working of the Atkinson cycle.
(5 marks) 00