# KTU B.TECH S3 MODEL QUESTIONS Thermodynamics

**THIRD SEMESTER B.TECH DEGREE EXAMINATION JANUARY 2017**

**ME 205: THERMODYNAMICS**

**Time:**

**3 Hrs Marks: 100**

__PART A__
(

**Answer any Three**)**1. a)**Derive the expression for work transfer and heat transfer in a polytropic process.

**(8 marks)**

**b)**Classify the following properties of a system as extensive or intensive: volume, pressure, energy and density.

**(2 marks)**

**2.**A gas expands in a piston–cylinder assembly from p1 = 8 bar, V1 = 0.02 m3 to p2 = 2 bar in a process during which the relation between pressure and volume is pV1.2 = constant. The mass of the gas is 0.25 kg. If the specific internal energy of the gas decreases by 55 kJ/kg during the process, determine the heat transfer, in kJ. Kinetic and potential energy effects are negligible.

**3.**Derive the steady flow energy equation, stating all the assumptions.

**4.**Air enters a compressor operating at steady state at a pressure of 1 bar, a temperature of 290 K, and a velocity of 6 m/s through an inlet with an area of 0.1 m2. At the exit, the pressure is 7 bar, the temperature is 450 K, and the velocity is 2 m/s. Heat transfer from the compressor to its surroundings occurs at a rate of 180 kJ/min. Employing the ideal gas model, calculate the power input to the compressor, in kW.

__PART B__
(

**Answer any Three**)**5.**State the Kelvin-Plank and Clausius statements of second law of thermodynamics and prove their equivalence.

**6.**0.5 kg of air at 1 bar and 47 °C is compressed in a piston-cylinder assembly to 4 bar and 127°C by doing 5 kJ of work when the surrounding temperature is 27°C. (Cp of air is 1.005 kJ/kgK, R =0.287 kJ/kgK)

Determine:

**i)**the entropy change of air**ii)**the entropy change of the surroundings, and

**iii)**the entropy change of the universe.

**7.**Sketch and explain the P-V diagram for a pure substance and show the isotherms and constant quality lines on it.

**8.**A mass of 8 kg of helium undergoes a process from an initial state of 3 m3/kg and 15°C to a final state of 0.5 m3/kg and 80°C. Assuming the surroundings to be at 25°C and 100 kPa, determine the increase in the useful work potential of the helium during this process. The gas constant of helium is R = 2.0769 kJ/kg.K, The constant volume specific heat of helium is cv = 3.1156 kJ/kg.K

__PART C__
(

**Answer any Four**)**9.**A 3.27m3 tank contains 100 kg of nitrogen at 175 K. Determine the pressure in the tank, using (a) the ideal-gas equation and (b) the van der Waals equation. Compare your results with the actual value of 1505 kPa. (R = 0.2968 kPa·m3/kg·K, M = 28.013 kg/kmol, Tcr = 126.2 K, Pcr = 3.39 MPa).

**10.**Explain Joule Thomson effect. What do you mean by inversion temperature?

**1**

**1.**

**12.**Write notes on real gas mixtures.

**13.**Sketch and explain a psychrometric chart showing constant volume and constant enthalpy lines. Also explain the cooling, heating, humidifying and dehumidifying processes.

**14.**An insulated rigid tank of volume 1m3 is divided into two chambers by a partition. One chamber of volume 0.7 m3 contains helium at 20 bar and 400 K while the other chamber contains Nitrogen at 10 bar and 500 K. The partition is removed and the gases are allowed to mix. Calculate

**i)**the change in entropy of Helium and Nitrogen, and

**ii)**the total entropy change for Nitrogen: Cp = 1.039 kJ/kg K, Cv = 0.742 kJ/ kg K for Helium: Cp = 5.19 kJ/kg K, Cv = 3.12 kJ/ kg K

**15.**Explain Dalton’s law of additive pressures. Does this law hold exactly for ideal-gas mixtures? How about non-ideal gas mixtures?

## 0 comments