Download GTU BE/B.Tech 2019 Winter 3rd Sem New 2131404 Food Engineering Thermodynamics Question Paper

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GUJARAT TECHNOLOGICAL UNIVERSITY

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Subject Code: 2131404

BE - SEMESTER- III (New) EXAMINATION — WINTER 2019

Subject Name: Food Engineering Thermodynamics

Time: 02:30 PM TO 05:00 PM

Instructions:

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1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Standard Steam Tables and normal range Psychrometric Chart can be used

Q.1

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1. Why gases deviate from ideal behavior? A 50 liters capacity vessel contains CO₂ gas at 77 °C and 3 bar pressure. Calculate the mass of CO₂ in kilogram. [03]
2. Two kilogram of methane gas was injected into a 100 liter vessel containing nitrogen at 0.9 bar absolute pressure and 27 °C under isothermal conditions. Calculate the partial pressure of methane gas and the total pressure in the container in bar. [M = 16 g/mol] [04]
3. Answer the following: [07]
   1. Explain the law of corresponding states.
   2. Write Van der Waal’s gas equation and give SI units.
   3. Define open system.

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   4. If vacuum is 600 mmHg, calculate absolute pressure in kPa.
   5. Calculate the specific gas constant for a gas mixture containing 80% N₂ and 20% O₂ by weight.
   6. Name different types of thermometers.
   7. Show that C_p—C_v= R for ideal gases.

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Q.2

1. State Zeroth law of thermodynamics. Discuss different temperature scales and their interrelationships. [03]
2. Ten kilogram of O₂ gas is heated reversibly at constant pressure from an initial state of [T = 330 K, P= 1.6 bar] until its volume doubles. Calculate [04]
   1. The expanded work in kJ
   2. Change in internal energy and enthalpy in kJ.
   [Take Cp = 35J/mol K, R = 8.314 J/mol k]

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3. State first law of thermodynamics for a closed system. Ten kilogram of an ideal gas at 113 °C and 8 bar pressure expands isentropically four times its initial volume. Calculate the work done during the process in kJ. [07] [Cp = 1.005 kJ/kgK, Cv=0.715 kl/kgK]

OR

Q.3

1. Derive SFEE for a fluid stream entering and leaving a turbine in terms of work and energy transfer per unit mass. Specify the assumptions made. [03]
2. What is Gibb’s phase rule? Calculate the degrees of freedom of water at its triple point. [04]

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3. Calculate the approximate pressure at which water would boil at 180 °C. It is known that water boils at 100 °C at 1.01325 bar. [Take R = 8.314 J/mol K, hg (at 100 °C) = 2258 kJ/kg] [07]

Q.3

1. Explain Joule-Kelvin effect with the help of a T-P diagram. [03]

OR

1. What is Gibb’s phase rule? Calculate the degrees of freedom of water at its critical point. [03]

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Date: 03/12/2019

Total Marks: 70

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Q.4

1. Prove that for any gas undergoing a throttling process, the Joule-Kelvin coefficient is given by µ = (?T/?P)_h [04]

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2. Explain Carnot cycle showing all the state points and explain the significance of this cycle. [07]

Q.4

1. Explain the following: [03]
   1. Clausius inequality.
   2. Thermal reservoirs

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2. Explain Kelvin-Plank and Clausius statements of second law of thermodynamics & prove that they are in fact equivalent. [04]

OR

1. Explain the concept and importance of available and unavailable energy [03]
2. Prove that §(dQ/T) < 0; for any cyclic irreversible process. [04]

Q.5

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1. Explain Clausius statement of second law of thermodynamics. A heat pump is operating between — 5°C and 25 °C. It delivers a COP which is 50% of the maximum possible COP. If it is delivering 55kW of heat into the warm room, calculate the power requirement to drive the unit. [07]

Q.5

1. Prove that specific humidity of moist air is given by ?= 0.622 [p_v/(P-P_v)] [03]
2. The weather report on a certain date was recorded as given below: [04]
   1. Atmospheric pressure = 760 mm Hg
   2. Ambient Temperature = 38 °C

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   3. RH=60%
   Using Psychrometric Chart, calculate the DPT, WBT, Specific enthalpy and absolute humidity of the atmospheric air.

1. Explain P-V and T-s phase diagram of a pure substance (water). Using Steam Tables determine the following for saturated steam at 2MPa pressure: [07]
   1. Saturation temperature in °C
   2. Entropy in kJ/kg K
   3. Latent heat of vaporization in kJ/kg

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   4. Specific volume in m³/kg

OR

1. Define the following terms for moist air: [03]
   1. Wet bulb temperature
   2. Relative humidity

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   3. Dry bulb temperature
2. Air at a certain place is at 40 °C and has a barometric pressure of 1 bar. If p_w of water vapours present in the air is 20 mm Hg, calculate the following: [04]
   1. DBT
   2. Specific humidity
   3. Relative humidity

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   4. DPT
3. Explain phase diagram of a pure substance (water) on a P-v diagram. Ten kg of wet steam at 120 °C containing 80% of dry steam is allowed to completely condense to water at 92 °C. Calculate the amount of heat released in kJ. [07]

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