JNTU II B.Tech I Semester Supplimentary Examinations, November 2008

JNTU II B.Tech I Semester Supplimentary Examinations, November 2008

THERMODYNAMICS

( Common to Mechanical Engineering and Automobile Engineering)

SET-1

 

1. A gas undergoes two processes that are in series. The first process is an expansion

that is carried out according to the law PV = constant, and the second process is a Constant pressure process that returns the gas to the initial volume of the first process. The start of the first process is at 400 KPa and 0.025 m3 with the expansion to 200 KPa. Sketch the process on a P-V diagram, and determine the work of the combined process.

 

2. (a) List any five physical properties of matter which can be used for the measurement of temperature

(b) State the concept of temperature and quality of temperature

(c) In a general compression process, 2 kJ of mechanical work is supplied to 5 kg of working substance, and 800 J of heat is rejected to the cooling jacket. Calculate the change in specific internal energy.

 

3. Two kg of air at 500 KPa, 800C expands adiabatically in a closed system until its volume is doubled and its temperature becomes equal to that of the surroundings which is at 100 KPa, 50C. For this process, determine

(a) the maximum work

(b) the change in availability and

(c) the irreversibility for air,

take Cv = 0.718 KJ/Kg-K and R = 0.287 KJ/Kg-K.

 

4. (a) Describe the process of formation of steam and give its graphical representation

(b) Steam enters an engine at a pressure 10 bar absolute and 2500C. It is exhausted at 0.2 bar. The steam at exhaust is 0.9 dry. Find

i. Drop in enthalpy

ii. Change in enthalpy.

 

5. (a) Write down the Vander Waal’s equation of state. How does it differ from the ideal gas equation of state?

(b) A mass of air is initially at 2600C and 700 Kpa and occupies 0.028m3. The

air is expanded at constant pressure to 0.084m3.Apolytropic process with n= 1.5 is then carried out, followed by a constant temperature process, which completes a cycle. All the processes are reversible

i. Sketch the cycle in the P-V &T-S planes

ii. Find heat received & rejected in the cycle

iii. Find ? of the cycle.

 

6. (a) Define

i. Humidification

ii. Dehumidification

iii. sensible heating

(b) Avessel of 6m3  capacity contains two gases ?A? and ?B? in proportion of 45% respectively at 300C.If the value of ?R? for the gases is 0.288 Kj /kg. k and 0.295 Kj /kg. K and if the total weight of the mixture is 2 kg, calculate

i. Partial presser

ii. The mean value of ?R? for the mixture.

 

7. (a) Explain the dual combustion cycle. Derive an expression for the efficiency of dual cycle.

(b) Which air-standard cycle is used in I.C. Engines? Explain the differences between Otto cycle and Dual cycle.

 

8. (a) Explain the important components of a simple vapour compression refrigeration system. Also discuss the functions of each component.

(b) Discuss the effect of sub cooling on C.O.P.of the vapour compression refrigeration cycle. Would you derive large sub cooling and why?

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