
a)
The rate of dehumidification.
a)

Answer to Problem 132RP
The mass flow rate of condensate water is
Explanation of Solution
Write the expression to obtain the vapor pressure at inlet conditions
Here, saturation pressure of water at
Write the expression to obtain the atmospheric pressure of an ideal gas mixture
Here, dry air partial pressure at state 1 is
Write the expression to obtain the specific volume of duct
Here, inlet temperature is
Write the expression to obtain the specific humidity
Here, total pressure at state 1 is
Write the expression to obtain the enthalpy at state 1
Here, specific heat of air is
Write the expression to obtain the vapor pressure at second inlet conditions
Here, saturation pressure of water at
Write the expression to obtain the specific humidity
Here, total pressure at state 2 is
Write the expression to obtain the enthalpy at state 2
Here, initial condition of enthalpy at saturation vapor at state 2 is
Write the expression to obtain the mass flow rate of dry air
Here, volume flow rate is
Apply the water mass balance equation to the combined cooling and dehumidification section.
Here, initial and final mass flow rate of dry air is
Conclusion:
Refer Table A-4, “Saturated water – Temperature table”, obtain the properties of water at a temperature of
Substitute 4.247 kPa for
Refer Table A-5, “Saturated water – Pressure table”, obtain the properties of water at a pressure of
Rewrite Equation (II) and substitute 90 kPa for
Convert the unit of
Refer Table A-2, “Ideal gas specific heats of various common gases”, obtain the value of
Substitute
Substitute 2.973 kPa for
Substitute
Refer Table A-4, “Saturated water – Temperature table”, obtain the properties of water at a temperature of
Substitute 2.3392 kPa for
Substitute 2.3392 kPa for
Substitute
Substitute
Substitute
Thus, the mass flow rate of condensate water is
b)
The rate of heat transfer.
b)

Answer to Problem 132RP
The rate of heat transfer of air stream is
Explanation of Solution
Apply the energy balance equation to the combined cooling and dehumidification section.
Here, the amount of energy rate required for cooling coils is
Conclusion:
Refer Table A-4, “Saturated water – Temperature table”, obtain the value of enthalpy at saturation liquid
Substitute
Thus, rate of heat transfer of air stream is
c)
The mass flow rate of the refrigerant.
c)

Answer to Problem 132RP
The mass flow rate of the refrigerant is
Explanation of Solution
Write the expression to obtain the inlet enthalpy of the refrigerant
Here, enthalpy evaporation is
Write the expression to obtain the mass flow rate of a refrigerant
Here, heat lost by the air is
Conclusion:
Refer Table A-12, “Saturated refrigerant 134a – Pressure table”, obtain the properties of refrigerant 134a at a pressure of 700 kPa.
Substitute
Refer Table A-12, “Saturated refrigerant 134a – Pressure table”, obtain the value of
Substitute
Thus, the mass flow rate of the refrigerant is
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Chapter 14 Solutions
Thermodynamics: An Engineering Approach
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