
a)
The rate of heat transfer of air stream.
a)

Answer to Problem 83P
The rate of heat transfer of air stream is
Explanation of Solution
Write the expression to obtain the vapor pressure of air
Here, saturated pressure is
Write the expression to obtain the atmospheric pressure of an ideal gas mixture
Here, vapor pressure at state 1 is
Write the expression to obtain the specific volume of circular duct
Here, inlet temperature is
Write the expression to obtain the specific humidity
Write the expression to obtain the enthalpy at state 1
Here, specific heat of air is
Write the expression to obtain the exit vapor pressure of air
Here, saturated pressure is
Write the expression to obtain the atmospheric pressure of an ideal gas mixture
Here, vapor pressure at state 2 is
Write the expression to obtain the specific volume of circular duct
Here, final temperature is
Write the expression to obtain the specific humidity
Write the expression to obtain the enthalpy at state 2
Here, specific heat of air is
Write the expression to obtain the volume flow rate
Here, diameter is D, and velocity of air is
Write the expression to obtain the mass flow rate of dry air through the cooling section
Here, volume flow rate of air entering the cooling section 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
Apply the water 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-4E, “Saturated water – Temperature table”, write the value of saturation pressure of liquid
Substitute 0.69904 psia for
Refer Table A-5E, “Saturated water – Temperature table”, obtain the properties of water at a temperature of
Rewrite Equation (II) and substitute 14.4 psia for
Convert the unit of
Refer the Table “Ideal gas specific heats of various common gases”, write the value of
Substitute
The mass flow rate of dry air remains constant, but the amount of moisture in the air decreases due to the dehumidification
Substitute 0.42 psia for
Refer Table A-4E, “Saturated water – Temperature table”, write the value of
Refer the Table “Ideal gas specific heats of various common gases”, write the value of
Substitute
Refer Table A-4E, “Saturated water – Temperature table”, write the value of saturated pressure
Substitute 0.36 psia for
Rewrite Equation (VII) and substitute 14.4 psia for
Convert the unit of
Substitute
Substitute 0.36 psia for
Refer Table A-4E, “Saturated water – Temperature table”, write the value of
Substitute
Refer Table A-4E, “Saturated water – Temperature table”, write the value of enthalpy at saturation liquid
Substitute 1 ft for D and
Substitute
Substitute
Substitute
Thus, rate of heat transfer of air stream is
b)
The mass flow rate of cooling water.
b)

Answer to Problem 83P
The mass flow rate of cooling water is
Explanation of Solution
Write the expression to obtain the mass flow rate of cooling water
Here, specific heat of water is
Conclusion:
Substitute
Thus, the mass flow rate of cooling water is
c)
The exit velocity of the airstream.
c)

Answer to Problem 83P
The exit velocity is
Explanation of Solution
Apply the conservation of mass of dry air to calculate exit velocity
Conclusion:
Substitute
Thus, the exit velocity is
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Chapter 14 Solutions
Thermodynamics: An Engineering Approach
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