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Subject Code: 131404
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GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- III(OLD) EXAMINATION - SUMMER 2019
Date: 11/06/2019
Subject Name: Food Engineering Thermodynamics
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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) Differentiate between ideal and real gases. 07
(b) A container of 1000 liter contains CO2 gas at 6 atmosphere pressure and 27 °C. Calculate the mass of gas in kg. Assume ideal gas behaviour. [Take R = 8.314 J/mol K] 07
Q.2
(a) What is Van der Waals gas equation? Hundred kilogram of N2 gas is stored in a 20 liter sealed container at 7 °C. Calculate the pressure of the gas in kPa using compressibility factor of z=0.88. [Take M =28 and R = 8.314 J/mole K] 07
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(b) Explain Zero™ law of thermodynamics. List different types of thermometers and explain the principle of operation of any one. 07
OR
(a) Define enthalpy and specific heats Cp and Cv. Prove that Cp - Cv = R for ideal gases. The temperature of 5 kg of a gas held in a rigid cylinder was increased from 24 °C to 37°C by adding 45 kJ of heat externally. Calculate the work done and the change in internal energy of the system. [Take Cv = 745 J/kg K] 07
(b) Explain Joule—Kelvin coefficient specifying its importance. 07
Q.3
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(a) State first law of thermodynamics. Prove that the work done by an ideal gas undergoing a reversible adiabatic process is given by W = (P1V1 - P2V2) / (1-?) = mR(T1-T2) / (1-?). 07
(b) What is turbine? Write down SFEE for a fluid stream entering and leaving a system in terms of work and energy transfer per unit mass. Steam is flowing through a horizontal nozzle in steady state. The inlet and outlet conditions given are: INLET: h1 =3200 kJ/kg, V1 =110 m/s, A1 =0.11 m², v1 = 0.2 m³/kg OUTLET: h2 = 2900 kJ/kg, v2 = 0.51 m³/kg. Calculate (i) Exit velocity in m/s (ii) Mass flow rate of steam in kg/s (iii) Exit area of the nozzle in m² 07
OR
(a) For a 2-phase Liquid-Vapour system in thermal equilibrium, prove that: dP/dT = L / (T(V2-V1)) 07
(b) Derive an expression for the work done by an ideal gas undergoing a reversible adiabatic process. Ten kilogram of an ideal gas at 200 °C and 20 bar pressure expands isentropically through a volume ratio of 5:1. Calculate the work done during the process in kJ. [Take Cp = 1.025 kJ/kgK, Cv = 0.714 kJ/kgK] 07
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Q.4
(a) Define thermodynamic degrees of freedom and state Gibb’s phase rule. Explain different types of thermodynamic equilibrium. Calculate the thermodynamic degrees of freedom of pure water at its critical point. 07
(b) Explain the following: (i) Second law of thermodynamics (ii) Clausius inequality (iii) PMM1 And PMM2 07
OR
(a) Explain Carnot theorems. A heat engine operating between two constant temperature reservoirs at 600 K and 400 K is producing a net steady work output of 24 kW. If the thermal efficiency of the engine is 80% of the maximum possible efficiency, calculate heat input to the engine and heat rejection in kW. 07
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(b) With the help of schematic diagram explain the operation of a heat engine and refrigerator A refrigerator is operating between 1 °C and 30 °C at a COP of 50 % of the maximum possible COP. If the net cooling effect generated is 2 kW, calculate the power requirement. 07
Q.5
(a) Prove the following: (i) (?T/?P)H = - (?H/?P)T / Cp (ii) (?P/?V)T (?V/?T)P (?T/?P)V = -1 07
(b) Draw a neat labeled P-v diagram of a pure substance (water) showing its various states. Determine the following using steam tables for saturated steam at 10 bar pressure: (i) Saturation temperature in °C (ii) Entropy in kJ/kg K (iii) Latent heat of vaporization in kJ/kg (iv) Specific volume in m³/kg 07
OR
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(a) The weather report on a particular summer day in Anand states the following: Atmospheric pressure = 1.01325 bar Atmospheric temperature =42 °C & Relative humidity = 60%. Using Psychrometric Chart find out the following: (i) Dry Bulb Temperature (DBT) (ii) Wet Bulb Temperature (WBT) (iii) Absolute humidity (iv) Mass of moist air (v) Dew point temperature (vi) Specific volume (vii) Specific enthalpy 07
(b) Draw and explain phase diagram of water on a T-s diagram. 07
Q.5
(a) Using Steam Tables determine the following for saturated steam at 160 °C: (i) Specific enthalpy (ii) Latent heat of vaporization (iii) Density (iv) Specific entropy (v) Saturation pressure in kPa 07
(b) Define the following in relation to moist air: i. Dry bulb temperature ii. Wet bulb temperature iii. Adiabatic saturation temperature iv. Relative humidity v. Absolute humidity vi. Sensible heating vii. Dehumidification 07
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