Winter 2015 Thermodynamics Question Paper

***********

GUJARAT TECHNOLOGICAL UNIVERSITY
DIPLOMA ENGINEERING – SEMESTER – III • EXAMINATION – WINTER 2015
Subject Code: 3331902 Date: 04- 12- 2015
Subject Name: Thermodynamics
Time: 10:30 AM TO 01:00 PM Total Marks: 70

Instructions:
1. Attempt all questions.
2. Make Suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of programmable & Communication aids are strictly prohibited.
5. Use of only simple calculator is permitted in Mathematics.
6. English version is authentic.

************

Q.1 Answer any seven out of ten. 14

1. Explain cut-off ratio.

2. List types of boundary.

3. Define enthalpy and write its unit in S.I. system.

4. Write steady flow energy equation.

5. Represent isentropic process on P-V and T-S diagram.

6. Write statement of Boyle’s law and Charle’s law.

7. Write concept of reversibility and irreversibility of thermodynamics.

8. State application of Otto cycle.

9. Write equation of COP for reversed brayton cycle.

10. Define heat and work.

Q.2 (a) Define thermodynamic system with example. 03

OR

(a) Explain how SFEE is applied to turbine. 03

(b) Derive expression of work done during isothermal process. 03

OR

(b) Explain universal gas constant (Ru). 03

(c) Prove that internal energy is a point function. 04

OR

(c) Explain first law of thermodynamics with help of joule’s experiment. 04

(d) In a gas turbine, air enters with velocity 220 m/s and enthalpy 5678 KJ/Kg with steady mass flow rate of 3.6 Kg/Sec. Gas exits from the system at velocity 170 m/s and enthalpy 4560 KJ/Kg. If 54 KJ/Kg heat is wasted into the surroundings, find power developed by the gas turbine. 04

OR

(d) 2 kg. of gas enclosed in a closed vessel heated from 2 bar to 5 bar. The initial temperature of gas is 27oC. Find 1] final temperature 2] change in internal energy. Take Cv = 0.72 KJ/Kg K. 04

Q.3 (a) Derive characteristics equation for ideal gas. 03

OR

(a) Draw P-V and T-S diagram for... (1) Isobaric process (2) Isochoric process. 03

(b) Derive Cp - Cv = R with usual notations. 03

OR

(b) Derive equation of work done in isentropic process. 03

(c) In an engine, working on diesel cycle, compression ratio is 15 and fuel is cut off at 5% of stroke length, find air standard efficiency. Take γ = 1.4 04

OR

(c) Draw the diesel cycle on P-V and T-S diagram and write the equation of air standard efficiency of diesel engine. 04

(d) Differentiate process and cycle. 04

OR

(d) Draw the dual cycle on P-V and T-S diagram and explain its processes. 04

Q.4 (a) Derive general energy equation for first law of thermodynamics. 03

OR

(a) Derive equation of COP for reversed Carnot cycle for refrigeration purpose. 03

(b) Deduce the equivalence between Kelvin-plank and clausius statements at second law of thermodynamics on the basis of diagrammatic representation. 04

OR

(b) One Carnot engine receives 1200 KJ/min heat energy from the reservoir of 350oC temperature and rejects heat energy to the sink of 25oC temperature. Find thermal efficiency and work done. 04

(c) Derive equation for air standard efficiency of brayton cycle. 07

Q.5 (a) In one Otto cycle engine clearance volume is 30% of its swept volume. Find air standard cycle efficiency. Take γ = 1.4 04

(b) Define 1] heat engine 2] heat source 3] refrigerator 4] heat reservoir. 04

(c) Define. 1] Specific heat at constant pressure (Cp) 2] specific heat at constant volume (Cv). 03

(d) State limitations of first law of thermodynamics. 03

************