Chemical Thermodynamics

Questions & Answers

2. Water initially at 155°C is contained in a piston- cylinder assembly. The water undergoes a process to the corresponding saturated vapor state, during which the piston moves freely in the cylinder. There is no heat transfer with the surroundings. If the change of state is brought about by the action of a paddle wheel, determine the net work per unit mass in kJ/kg and the amount of entropy produced per unit mass in kJ/kg. [MO2]


4.13 Refrigerant 134a enters the evaporator of a refrigeration system operating at steady state at -4°C and quality of 20% at a velocity of 7 m/s. At the exit, the refrigerant is a saturated vapor at a temperature of -4°C. The evaporator flow channel has constant diameter. If the mass flow rate of the entering refrigerant is 0.1 kg/s, determine a. the diameter of the evaporator flow channel, in cm. b. the velocity at the exit, in m/s.


4.14 WP Figure P4.14 provides steady-state data for water vapor flowing through a piping configuration. At each exit, the volumetric flow rate, pressure, and temperature are equal. Determine the mass flow rate at the inlet and exits, each in kg/s.


1. Consider an ordinary vapor compression cycle with a condenser at 40°C, an evaporator at -20°C, and R134a as the working fluid. The compressor is 75.% efficient. For each kg of R134a circulated, determine the amount of cooling, the heat rejected, the work, and the COP.


2. Draw the cycle from problem 1 on (a) a temperature-entropy diagram and (b) a pressure-enthalpy diagram. For each diagram, include a curve for the phase envelope, labels for each step, and an additional cycle in which the compressor is 60.% efficient.


3. Carbon monoxide is compressed reversibly and adiabatically in a piston-cylinder from 1.0 bar and 75°C to 47 bar. a. Use the Peng-Robinson equation of state to determine the amount of work performed on the gas. b. How much work would be required for an ideal gas? c. Explain the reasons for the differences between (a) and (b) based on interactions between the gas molecules.


9. Refrigerant 134a at p₁ = 30 lbf/in², T₁ = 40°F enters a compressor at a steady state with a mass flow rate of 300 lb/h and exits as saturated vapor at p2 = 160 lbf/in². Heat transfer occurs from the compressor to its surroundings, which are at To = 40°F. Changes in kinetic and potential energy can be ignored. The power input to the compressor is 3 hp. Determine the heat transfer rate for the compressor, in Btu/hr, and the entropy production rate for the compressor, in Btu/hr.°R. [MO3, MO7]


2. Which fluid will have a more negative internal energy departure function: water at 375°C and 2.3 bar or water at 100°C and 1.6 bar? Explain.


ques1


1. Water, initially a saturated liquid at 160°C, is contained in a pistol-cylinder assembly. The water undergoes a process to the corresponding saturated vapor state, during which the piston moves freely in the cylinder. If the change of state is brought about by heating the water as it undergoes an internally reversible process at constant pressure and temperature, determine the work and heat transfer per unit mass in kJ/kg. [MO1]


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