Third Semester B.E. Degree Examination, May/June 2010/ Basic Thermodynamics·

Note: 1. Answer any FIVEfull questions, selectingat least TWO questions from each part.

2. Use of thermodynamics data handbook is permitted.

1 a. What are intensive, extensive and specific extensive properties? Give examples of each.(06 Marks)

b. What is a quasi static process? What is its characteristic feature? (04 Marks)c. A thermometer is calibrated with ice and steam points as fixed points referred to as oOe and

1000e respectively. The equation used to establish the scale is t = alogex + bi) Determine the constants 'a' and 'b' in terms of ice point (XI) and stam point (xs).

10ge(~Jii) Show that tOe = 100 XI (08 Marks)

[Og,( :: Jd. Define thermodynamic equilibrium. (02 Marks)

2 a. Does heat transfer inevitably cause a temperature rise? What is the other cause for rise intemperatUre? (05 Marks)

b. Defme thermodynamic work. Briefly explain, what is displacement work. (07 Marks)c. A mass of gas is compressed in a quasistatic process from 80 Kpa; 0.1 m3 to 0.4 MPa,

0.03 m3. Assuming that the pressure and volume are related by PVn = constant, find thework interaction during the process. Is it a work producing system or work absorbingsystem? (08 Marks)

3 a. State and explain the first law of thermodynamics for a closed system undergoing a cycle.What is PMM1? (07 Marks)

b. During one cycle, the working fluid in an engine engages in two work interactions: 15 kJ tothe fluid and 44 kJ from the fluid. There are three heat interactions, two of which are known:75 kJ to the fluid and 40 kJ from the fluid. Evaluate the magnitude and direction of the thirdheat transfer. (04 Marks)

c. At the inlet to a certain nozzle, the enthalpy of the fluid passing is 3000 kJ/kg and the

velocity is 60 mls. At the discharge end, the enthalpy is 2762 kJ . The nozzle is horizontalkg

and there is negligible heat loss from it.i) Find the velocity at the exit from the nozzle.ii) If the inlet area is 0.1 m2 and specific volume at inlet is 0.187 m3/kg, find the mass

flow rate.iii) If the specific volume at the nozzle exit is 0.498 m3/kg, find the exit area of the nozzle.

(09 Marks)

4 a. Establish the equivalence of Kelvin - Planck and Clausius statements of second law ofthermodynamics. (08 Marks)

b. A source 'X' can supply energy at a rate of 11000 kJ/minute at 320°C. A second source 'Y'can supply energy at a rate of 110000 kJ/minute at 60°C. Which source 'X' or 'Y' wouldyou choose, to supply energy to an ideal reversible engine, that is to produce a large amountof power, if the temperature of surroundings is 4°C? (08 Marks)

c. What do you understand by a reversible and an irreversible process? What are the causes ofirreversibility of a process? (04 Marks)

5 a. Define entropy. Show that entropy is a property of the system. (08 Marks)b. Define the terms, available and unavailable energy. (02 Marks)c. One kg of ice at _5°C is exposed to the atmosphere, which is at 20°C. The ice melts and

comes into thermal equilibrium with the atmosphere. Determine the entropy increase of the

universe. Take Cp of ice = 2.093~ and latent of fusion of ice = 334 kJ/kg. (10 Marks)kgK

6 a. 25 kg of water at 95°C is mixed with 35 kg of water at 35°C, the pressure being taken asconstant and temperature of the surroundings being 15°C. Calculate decrease in availableenergy of the system. (10 Marks)

b. Define the terms: i) Useful work; ii) Reversible work; iii) Irreversibility. (06 Marks)c. Define first law efficiency and second law efficiency. How these efficiencies can be

improved? (04 Marks)

7 a. What do you understand by the term "degree of superheat" of steam? Show that drynessfraction of a sample of steam measured using combined separating and throttling calorimeteris given by X = Xl X2, where,X =Dryness fraction of steam in steam mainXl = Dryness fraction of steam as measured by using separating calorimeter.X2 =Dryness fraction of steam as measured using throttling calorimeter. (10 Marks)

b. A pressure cooker contains 1.5 kg of steam at 5 bar and 0.9 dryness when the gas wasswitched off. Determine the quantity of heat rejected by the pressure cooker when thepressure in the cooker falls to 1 bar. (10 Marks)

8 a. Under what conditions the behaviour of a real gas approaches closely that of an ideal gas?Write van der waal's equation for a real gas. (06 Marks)

b. A gas at a pressure of 1.4 MN/m2 and 360°C is expanded adiabatically to a pressure of

100 k~ . The gas is then heated at constant volume until it attains 360°C when its pressurem

is found to be 220 kN/m2. Finally it is compressed isothermally to the original pressure of

1.4 ~. Sketch the process on P-V and T-S diagrams. For 0.23 kg of gas, evaluate them

following: work transfer, heat transfer, change in internal energy and change in entropyduring each process. Assume the following data for the gas:Cp = 1.005 kJ/kg KCv = 0.718 kJ/kg KR = 0.287 kJ/kg Ky = 1.4 (14 Marks)