Food Engineering Thermodynamics — Summer 2019

Why do gases deviate from ideal behaviour? Ten kilogram of CH is injected into a 110 liter vessel containing oxygen at 2 bar absolute pressure and 13 oC. Calculate the partial pressure of methane gas and the total pressure in the container in kPa assuming isothermal process.

Write down Van der Waal’s equation of state for real gases. Hundred kg of N2 gas is stored in a 100 liter closed container at – 23 oC. Calculate the pressure of the gas in kPa using Van der Waal’s gas equation. Take a = 0.137 Pa (m3/mole)2, b = 3.86 x 10-5 m3/mole, R = 8.314 J/mole K

Answer the following:

State law of corresponding states. (ii) If vacuum is 600 torr, calculate absolute pressure in kPa. (iii) Write SI unit and dimensions of universal gas constant. (iv) Calculate the specific gas constant of Ogas.2

Differentiate between cyclic and reversible process with an example. (vi) Define ideal gas. (vii) Show that C – C = p v1 _R07 for ideal gases.

Exp lain Zeroth law of thermodynamics. List various types of thermometers and briefly explain the working principle constant volume type of thermometer.

Define flow work. Steam is steadily flowing through a turbine with inlet and outlet conditions given as: INLET CONDITION h = 3250 kJ/kg, v = 0.07 m3/kg, P = 60 bar, t = 550 oC OUTLET CONDITION h = 3230 kJ/kg, v = 0.08 m3/kg, P = 50 bar, t = 480 oC The heat loss due to poor body insulation is 16 kJ/kg. Calculate the steam inlet and outlet velocities in m/s and steam flow rate in kg/s. Assume that turbine inlet and outlet points are at the same elevation.

Explain first law of thermodynamics. Prove that   P V Constant for an ideal gas undergoing a reversible adiabatic process.The temperature of 10 kg of a gas held in a rigid cylinder was increased from 5 oC to 25 oC by adding 55 kJ of heat. Calculate the work done and the change in internal energy of the system. [C = 742 J/kg K] v

Define control volume. Derive SFEE for a stream of fluid entering and leaving a nozzle in terms of work and energy transfer per unit mass and state the assumptions made.

For a 2-phase Liquid-Vapour system in thermal equilibrium, prove that: l n  P P2   h R fg  T1  T1 03 .

Explain different types of thermodynamic equilibria and state their conditions of stability.

Explain Joule-Kelvin effect. Prove that for a gas undergoing a throttling process, the Joule-Kelvin coefficient is given by j, T  C1 P  T    v T  P  v 07 

Define entropy. Arefrigerator is operating between -5oC and 35 oC at a COP of 60% of the maximum possible COP. If the refrigeration effect is 5TR, calculate the power requirement and the heat it has to reject to the ambient.

What is Gibb’s phase rule?

Calculate the maximum number of phases in which a 2- component mixture can exist in equilibrium with each other. (ii) Calculate the degrees of freedom of water at its triple point.

Explain the following: (i) Carnot cycle (ii) Thermal reservoirs

Explain Carnot theorems. Aheat engine is operating between two constant temperature reservoirs at 650 Kand 270 K. The engine produces a net steady work output of 10 HP. If the thermal efficiency of the engine is 60% of the Carnot efficiency, calculate heat input to the engine and heat rejection in kW.

Explain Kelvin-Plank and Clausius statements of second law of thermodynamics. Aheat engine produces 100 kW of power when operating between two thermal reservoirs maintained at 700°Cand 70oC. The thermal efficiency of the engine is 50% of the maximum possible. Determine

The engine efficiency. (ii) Rate of heat input to the engine. (iii) Heat rejected.

Explain the following in related perspective:

Clausius inequality (ii) Available and unavailable energy

Define relative humidity. Prove that specific humidity of moist air is given by  0 . 6 2  p o p  w p w 03  .

Air at a certain place having a barometric pressure of 755 torr has a temperature of 25 oC. If the partial vapour pressure of water vapours present in unsaturated air is 24 mm Hg, calculate the following:

Specific humidity (ii) Specific enthalpy (iii) Relative humidity (iv) Dew point temperature

Explain phase diagram of water on a P-Vdiagram showing various states. Define and indicate the location of triple point. Using standard Steam Tables determine the following for saturated steam at 200 oC:

Saturation pressure in kPa (ii) Entropy in kJ/kg K (iii) Enthalpy of saturated steam in kJ/kg (iv) Specific volume m3/kg

Define the following in relation to moist air:

Wet bulb temperature (ii) Specific humidity (iii) Dehumidification