GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-1V (NEW) EXAMINATION - WINTER 2018
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Subject Code: 2143406 Date: 22/11/2018
Subject Name: Thermo Dynamics and Thermal Eng.
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) Write a short note on p-T (Pressure — Temperature) diagram for pure substance. 03
(b) Differentiate between open system, closed system and an isolated system. 04
(c) A fluid system, contained in a piston and cylinder machine, passes through a complete cycle of four processes. The sum of all heat transferred during a cycle is — 340 kJ. The system completes 200 cycles per min.
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Complete the following table showing the method for each item, and compute the net rate of work output in kW.
Process Q(KJ/min) W(KJ/min) dU(KJ/min)
1-2 0 4340 -
2-3 42000 -
3-4 -73200 -
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Q.2 (a) State kelvin plank statement and Clausius statement for 2nd law of thermodynamics 03
(b) Write a short note on modified Rankine cycle. 04
(c) State the methods of increasing the thermal efficiency of a Rankine cycle. 07
OR
(c) Explain Constant Pressure or Diesel Cycle also find the air Standard efficiency of Diesel Cycle. 07
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Q.3 (a) Define Thermal efficiency, Relative efficiency & Volumetric efficiency. 03
(b) Derive the Maxwell relations and explain their importance in thermodynamics. 04
(c) Derive and Explain Clausius-Clapeyron Equation with p-T Diagram 07
OR
Q.3 (a) Differentiate between the energy and exergy. 03
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(b) Write short note on entropy. 04
(c) Define the Joule Thomson coefficient. State the conditions for cooling effect, heating effect and neither cooling nor heating effect. 07
Q.4 (a) Define Available and Unavailable energy. 03
(b) Write a short note on Gibbs-Dalton law 04
(c) Show that for pV? = Constant for Reversible Adiabatic Process 07
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OR
Q.4 (a) Differentiate between ideal and real gases. 03
(b) Write a short note on Compressibility chart 04
(c) 8Kg of air at 650 K and 5.5 bar pressure is enclosed in a closed system. If the atmospheric temperature and pressure are 300 K and 1 bar respectively, determine:
The availability if the system goes through the ideal work producing process.
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The availability and effectiveness if the air is cooled at constant pressure to atmospheric temperature without bringing it to complete dead state. Take cp= 0.718 kJ/Kg K; cv= 1.005 kJ/Kg K
Q.5 (a) Derive the mathematical expression for the Critical insulation thickness. 07
(b) The inner surface of a plane brick wall is at 60°C and the outer surface is at 35°C. Calculate the rate of heat transfer per m2 of surface area of the wall, which is 220 mm thick. The thermal conductivity of the brick is 0.51 W/m°C.
OR
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(a) Define black body, white body & gray body. 03
(b) Differentiate free convection and force Convection. 04
(c) Using Clausius - Clapeyron’s equation, estimate the enthalpy of vaporization. 07
The following data is given : At 200°C : vg= 0.1274 m3/kg ; vf =0.001157 m3/kg; (dp/dT = 32 kPa/K)
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