Engineering Thermodynamics


A piston and cylinder machine contains a fluid system which passes through a complete cycle of four processes. During a cycle, the sum of all heat transfers is -170kJ. The system completes 100 cycles per min. Complete the following table showing the method for each item, and compute the net rate of work output in kW.

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|Process |Q (kJ/min) |W (kJ/min) |?E (kJ/min) | |a-b |0 |2,170 |- | |b-c |21,000 |0 |- | |c-d |-2,100 |- |-36,600 | |d-a |- |- |- | P. K. Nag Pg. No. 66) 2. Air at 1. 02 bar, 22? C, initially occupying a cylinder volume of 0. 015 m3 is compressed reversibly and adiabatically by a piston to a pressure of 6.

8 bar. Calculate : (i) the final temperature, (ii) the final volume & (iii) the work done. (Ans: T2=507. 25 K, V2= 0.

003869, W=24. 513kJ) 3. Air at 30? C and 1 bar is compressed reversibly and polytropically from 5m3 to 1m3 . Calculate the final temperature, pressure and also the work done and heat transfer if the index of compression is 1, 1. and 0. 9 respectively. Assume Cp=1.

005kJ/kgK and Cv=0. 7178 kJ/kgK. 4. 2m3 of H2 at a pressure of 1 bar and 20? C is compressed isentropically to 4 bar. The same gas is expanded isothermally restored to o9riginal volume by constant volume heat rejection process.

Determine: i) Pressure, Volume and Temperature at each end of the process. ii) Heat added during isothermal process. iii) Heat rejected during constant volume process. iv) Change in internal energy during each process. Take R=4. 206 kJ/kgK, Cp=14.

5 kJ/kgK. 5. 1 kg of air at 1 bar and 300 K is compressed adiabatically till its pressure becomes 5 times the original pressure.

Then it is expanded at constant pressure and finally cooled at constant volume to return to its original conditions. Calculate: (a) Heat Transfer (b) Internal Energy. For each process and for the cycle.

Represent the process on p-V and T-S diagrams. Take Cv= 0. 718 kJ/kgK and ? =1.

4. 6. A certain quantity of air initially at a pressure of a 8 bar and 280? C has a volume of 0. 035 m3.It undergoes a cycle consisting of the following processes: 1) Expands at constant pressure to 0. 1m3. 2) Follows polytropic process with n=1. 4 and 3) A constant temperature process which completes the cycle.

Evaluate the Heat received and rejected in the cycle and cycle efficiency. 7. A centrifugal air compressor compresses air at the rate of 0.

7m3/s from 85kPa to 650 kPa. The initial specific volume is 0. 35 m3/kg and final specific volume 0. 1 m3/kg. If the suction line diameter is 10 cm and the discharge line diameter 6. 5 cm . Determine (a) the change in flow of work, (b)the mass flow rate & (c) the change in velocity. 8.

A small nozzle is used for water at 40? C. The inlet pressure is 700 kPa and discharge pressure is 100kPa. Assuming adiabatic process, calculate the exit velocity. For an exit area of 0. 3cm2, calculate the flow rate in lit/min.

Density of water at 40? C is 1000 kg/m3. 9. Derive the steady flow energy equation in detail.

10. Tabulate the corresponding formulae for all the non flow process.

Author: Leonard Warren


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