METBD 330: Thermodynamics

Homework for Gas-Vapor Mixtures (HVAC)

  1. Determine the mass of dry air and the water vapor contained in a 120 m3 room at 98 kPa, 23oC, and 50% relative humidity.

Answers: 136.4 kg, 1.25 kg 

  1. The air in a room has a dry-bulb temperature of 22oC and a wet-bulb temperature of 16oC. If the pressure is 100 kPa (not on the chart), find: the specific humidity, the relative humidity, and the dew-point temp.

Answers: 0.0091 kg H2O/kg dry air, 54.1%, 12.4oC

  1. (Simple cooling) Air enters a 40 cm diameter cooling section at 1 atm., 32oC, and 30% relative humidity at 18 m/s. Heat is removed from the air at a rate of 1200 kJ/min. Determine the exit temperature, the exit relative humidity of the air, and the exit velocity.

Answers: 24.4oC, 46.6 %, 17.6 m/s

  1. (Heating with Humidification) Air at 1 atm., 15oC, and 60% relative humidity is first heated to 20oC in a heating section and then humidified by introducing water vapor (steam). The air leaves the humidifying section at 25oC and 65% relative humidity. Determine the amount of steam added to the air (in kg H2O/kg dry air), and the amount of heat transfer to the air in the heating section (in kJ/kg dry air).

Answers: 0.0065 kg H2O/kg dry air, 5.1 kJ/kg dry air

  1. (Cooling with De-humidification) Air enters a window air conditioner at 1 atm., 32oC, and 70% relative humidity at a rate of 8 m3/min., and it leaves as saturated air at 12oC. Part of the moisture in the air (which condenses during the process) is also removed at 12oC. Determine the rates of heat and moisture removal from the air.

Answers: 462.4 kJ/min, 0.112 kg/min