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Thermodynamics Question Paper - Dec 15 - Mechanical Engineering (Semester 3) - Jawaharlal Nehru Technological University (JNTUH)

## Thermodynamics - Dec 15

### 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.**Discuss the microscopic and microscopic point of view of thermody namics.

**1.b.**Explain the term - state, path, process and cyclic process.

**1.c.**What are the limitations of first law? Explain.

**1.d.**Show the equivalence of Celsius and Kelvin statement of second law of thermodynamics.

**1.e.**What is the vender walls equation of state? What are the limitation? Discuss.

**1.f.**Discuss the various methods for determining the dynes fraction of steam with relative merits and demerits.

**1.g.**Discuss Dalton's law of partial pressure.

**1.h.**bIs it possible to have equal value of DBT and WBT?

**1.i.**What do you mean by air standard cycle and what are assumption in air standard cycles?

**1.j.**List the main elements of vapour compression refrigeration system.

PART- B (25MARKS)

**2.a.**Distinguish between closed system, open system, and semi closed system.

**2.b.**If the temperature scale is granduated according to the equation l = 100 + 3t, where t is the temperature reading on the scale of t1 is the Celsius temperature find the freezing as well as boiling point of the thermodynamic substance.

**2.c.**Verify the first law of thermodynamics used joule's experiment.

OR

**3.a.**At the speed of 50 km/h the residence of motion of a car is 900 N. Neglecting looses. Calculate the power of engine of the car of which speed. Determine also the engine developing power.

**3.b.**A household refrigerator contain fresh food and it is closed. 1kWh of electric energy is consumed in Colling the food and internal energy of the system decrease by 500 kJ as the temperature drop. Find the magnitude and sign of the heat transfer for the process. Assume the entire refrigerator and it's contents as system.

**4.a.**A cornet engine with and efficiency of 40 percent receive 400 kj/h from a high temperature source and reject heat to sink at 26.7°C. What is the power output of the engine and the temperature of source in °C?

**4.b.**all spontaneous processes and reversble. Explain.

**4.c.**An inverter claim to have device which receive 100W of energy as he puts out only 750W of electric power. The rest of the energy is put out as electric work and dissipated outside his device by friction. Discuss the validity of the claims.

OR

**5.a.**During a cyclic process, total interaction happen to be positive. Does it violate that Celsius in equality? Explain it.

**5.b.**The efficiency of a carnot engine rejecting her to a cooling found at 27°C is 30 percent the cooling found received 13.91 kw. calculate the power of the engine and the source temperature.

**6.a.**What is the physical significance of compressibility factor? Discuss its significance.

**6.b.**A method cylinder of 0.5m³ contain gas at 10 MPa and 298K. Determine the mass of methane gas I'm the cylinder by based using ideal gas law and compressibility chart.

OR

**7.a.**What do you mean by superheated vapour? What is the difference between saturated vapour and superheated vapour? Discuss.

**7.b.**Calculate the external work of evaporation, internal energy of one kg of steam at a pressure of 13bar when the screen is (i) 0.8 dry (ii) dry saturated. TYPE_QUESTION_HERE

**8.a.**What do you mean by mass fraction of specific in mixture? How is it different from mole fraction? Discuss.

**8.b.**A rigid insulated tank of volume 50 liters containing 40% H2 and 60% ch4 gas by volume is connected to a high pressure H2 gas pipeline at 3MPa and 300k by opening the value. The gas mixture is allowed to fill this tank until it attains pressure of 3MPa at 300k then this tank was discounted from the pipeline and isolated .Estimate the mass fraction of final mixture.

OR

**9.a.**Does mixture of ideal gases behave like an ideal gas? Explain with the help of an example.

**9.b.**The DBT of atmospheric air is 26.7°C and the relative humidity is 30% find the value of humidity ratio and the partial pressure of water vapour if the total pressure is 1.103 bar. What is the dew point?

**10.a.**How many parameters do we need to describe an ideal simple brayton cycle completely?

**10.b.**A simple ideal brayton cycle uses air as working fluid and have a pressure ratio of 12. If the air temperature in the enterence of the compressor and turbine are at 300k and 1300 k respectively determine (i)the air temperature at the compressor exit and back work ratio and (ii) thermal efficiency assume constant specific heat at room temperature.

OR

**11.a.**Why is Higher air fuel ratio by mass basis is used in the case of gas turbine energy?

**11.b.**In an ideal vapour compression refrigeration system the refrigerator R-12 enter the compressor as the saturated liquid at -16°C with volumetric fow rate of 1m¹/min. The refrigerator leave the concert dress at 36°C. 10 bar Calculate (i) the compressor power (ii) the refrigerator capacity in tons and (iii) the coefficient of performance

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