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Thermodynamics: An Engineering Approach, 4/e

Yunus A. Çengel, University of Nevada, Reno
Michael A. Boles, North Carolina State University

Gas-Vapor Mixtures and Air-Conditioning

Multiple Choice Quiz

Answer all the questions


1	What is the specific humidity of air at 150 kPa whose dry bulb temperature is 20 °C and relative humidity is 70%?
		A)	0.000981 kg-wv/kg-da
		B)	0.00382 kg-wv/kg-da
		C)	0.00514 kg-wv/kg-da
		D)	0.00686 kg-wv/kg-da


2	Using saturated liquid water and 0 °C as the reference state, what is the specific enthalpy of humid air at 120 kPa, 20 °C, and 50% relative humidity?
		A)	32.71 kJ/kg-da
		B)	35.63 kJ/kg-da
		C)	38.93 kJ/kg-da
		D)	41.72 kJ/kg-da


3	What is the dew-point temperature of humid air at 200 kPa, 30 °C, and 55% relative humidity?
		A)	10 °C
		B)	15 °C
		C)	20 °C
		D)	25 °C


4	Humid air at 150 kPa, 30 °C, and 80% relative humidity undergoes an isobaric cooling process until its temperature is 25 °C. Will any liquid condensate form during this process?
		A)	Yes
		B)	No
		C)	Not applicable
		D)	Not applicable


5	Humid air is cooled, dehumidified and reheated during an isobaric process. Which one of the psychometric charts below correctly depicts these processes?
		A)	a
		B)	b
		C)	c
		D)	d


6	One-hundred cubic meters per minute of humid air at 101 kPa, 35 °C, 40% relative humidity is cooled to 25 °C in a constant pressure process. The cooling rate for this process is:
		A)	9.3 kW
		B)	17.8 kW
		C)	20.2 kW
		D)	22.3 kW


7	Saturated humid air at 101 kPa, 20 °C is heated to 35 °C during an isobaric process. What is the final relative humidity of this air?
		A)	42%
		B)	53%
		C)	68%
		D)	75%


8	Humid air at 101 kPa, 35 °C, 80% relative humidity is conditioned to 101 kPa, 25 °C, 50% relative humidity. How much condensate is formed during this process?
		A)	0.0087 kg/kg-da
		B)	0.0168 kg/kg-da
		C)	0.0193 kg/kg-da
		D)	0.0231 kg/kg-da


9	Humid air at 101 kPa, 35 °C, 80% relative humidity is conditioned to 101 kPa, 25 °C, 50% relative humidity. How much heat must be removed to accomplish this when the condensate leaves the system at 25 °C?
		A)	41.7 kJ/kg-da
		B)	46.7 kJ/kg-da
		C)	52.3 kJ/kg-da
		D)	57.5 kJ/kg-da


10	A standard atmospheric pressure cooling tower uses humid air at 30 °C, 60% relative humidity to cool liquid water from 55 °C to 40 °C. Saturated humid air leaves this tower at 35 °C. How much make-up water must be supplied to this tower?
		A)	0.0206 kg/kg-da
		B)	0.0313 kg/kg-da
		C)	0.0347 kg/kg-da
		D)	0.0404 kg/kg-da

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