1 kg of moist air at 60% R.H., 30oC is cooled at a constant pressure of 100 kPa to a final temperature of 5oC. For the initial state determine the (a) specific humidity, (b) dew point temperature, and (c) amount of moisture in air. For the process, determine (d) the amount of condensate. (e) What-if-Scenario: How would the answer in part (d) change if the pressure were 200 kPa. [Manual Solution] [TEST Solution] Click on the image to animate!
Answers: (a) 0.0163, (b) 21.4oC, (c) 0.016 kg, (d) 0.011 kg, (e) 0.0053 kg

 

1 m3 of moist air at 50% R.H., 25oC, and 100 kPa is compressed in a constant temperature process. Determine (a) the final volume, and (b) pressure at which air becomes saturated, and (c) the mass of water vapor in air at the end of the process. (d) What-if-Scenario: How would the answer in part (b) change if the final volume were one tenth of the original volume? [Manual Solution] [TEST Solution]
Answers: (a) 0.5m3, (b) 200 kPa, (c) 0.0115 kg, (d) 0.0092 kg

 

Moist air enters a duct at 100 kPa, 35oC, 30% R. H. with a volumetric flow rate of 100 m3/min. The mixture is cooled and both the condensate and mixture leave at 10oC. For steady state operation, determine the (a) rate of heat transfer in tons, (b) mass flow rate of the condensate in kg/min. (c) What-if-Scenario: How would the answer in part (b) change if the relative humidity at the inlet were 95%? [Manual Solution] [TEST Solution]
Click on the image to animate!
Answers: (a) -17.4 ton, (b) 0.033 kg/min, (c) -48.02 ton

 

In the closed process described in Ex. 11-2, determine the (a) work and (b) heat transfer. [Manual Solution] [TEST Solution]
Answers: (a,b) -69.31 kJ

 

The dry- and wet-bulb temperatures of air in a room at 101 kPa are measured with a sling psychrometer to be 30oC and 15oC respectively. Determine the (a) specific humidity, (b) relative humidity, and (c) enthalpy of the air in the room. [Manual Solution] [TEST Solution]
Answers: (a) 0.0045 kg H2O/kg d.a., (b) 17.07%, (c) 41.65 kJ/kg

 

Use psychrometric chart at 1 atm to answer parts (a)-(d) of Ex. 11-1. (e) Also evaluate the heat transfer during the cooling process. [Manual Solution] [TEST Solution]
Answers: (a) 17 g H2O/kg d.a., (b) 21oC, (c) 0.017 kg, (d) 0.013 kg, (e) -52.1 kJ

 

An air-conditioning system is to take outdoor air at 5oC, 30% R. H. at a steady rate of 50 m3/min and to condition it to 25oC and 50% R.H. The air is first heated in a heating section and then humidified by spraying liquid water at 25oC. Assuming a constant pressure of 1 atm everywhere in the system, determine the (a) heating rate, (b) the mass flow rate of water in kg/min. (c) What-if-Scenario: How would the answers change if saturated steam were used for humidification instead? [Manual Solution] [TEST Solution] 		Click on the image to animate!
Answers: (a)44.2 kW, (b) 0.532 kg/min , (c) 0.525 kg/min

 

An air-conditioning system is to take outdoor air at 30oC, 90% R. H. at a steady rate of 20 m3/min and to condition it to 15oC. The condensate also leaves at 15oC. Assuming a constant pressure of 1 atm everywhere in the system, determine (a) the cooling rate in kJ/min, (b) moisture removal rate in kg/min. (c) What-if-Scenario: How would the answers change if the outdoor air had a R.H. of 50%? [Manual Solution] [TEST Solution]
Answers: (a) -18.1 kW, (b) 0.525 kg/min, (c) -8.27 kW

 

A swamp cooler takes outdoor air at 100 kPa, 30oC, 10% R. H. at a steady rate of 20 m3/min. At the exit the relative humidity is 90%. Determine (a) the exit temperature, and (b) the rate of water consumption. (c) What-if-Scenario: How would the answers change if the outdoor air had a R.H. of 50%? [Manual Solution] [TEST Solution] 		Click on the image to animate!
Answers: (a) 13.97oC, (b) 0.147 kgmin, (c) 23.1oC

 

A saturated stream of air at 30oC with a volume flow rate of 50 m3/min mixes with a stream of cooled air consisting of a flow rate of 25 m3/min at 15oC and 30% R.H. Assuming the total pressure to remain constant at 1 atm, determine (a) the exit temperature, and (b) relative humidity. (c) How would the volume flow rate of the cooler stream change if the desired relative humidity at the exit were 65 %? [Manual Solution] [TEST Solution] 		Click on the image to animate!
Answers: (a) 25oC, (b) 95%

 

Warm water leaving the condenser of a power plant enters a wet cooling tower at 35oC with a mass flow rate of 120 kg/s. The water is cooled to 20oC by the counter-flow air which enters at 15oC, 50% R.H, and leaves at 30oC, 90% R.H. Neglecting the power input to the fan, determine the volume flow rate of air at the (a) inlet and (b) exit, and (c) mass flow rate of the makeup water. (d) What-if-Scenario: How would the answer in part (a) change if the air left the cooling tower at saturated condition? [Manual Solution] [TEST Solution] 		Click on the image to animate!
Answers: (a) 99m3/sec, (b) 108m3/sec, (c) 2.3 kg/s, (d) 108.4 kg/s

 

 

Copyright 1998-: Subrata Bhattacharjee