Note: You may use a psychrometric chart for any of the problems below. However, any property value looked up from the chart must be explicitly noted. For example: "enthalpy h=30 Btu/lbma using psych chart" 2.1 A5m x 5mx 3 m room contains moist air at 25 °C, 100 kPa and relative humidity of 75 percent. Find: (a) partial pressure of dry air in kPa (b) the specific humidity (c) enthalpy of the mixture, per unit mass of dry air (d) mass (in kg) of dry air and water vapor in the room. 2.2 A 1 lb sample of moist air at 70 °F, 14.7 psia and 70 % relative humidity is slowly cooled to 40 °F while keeping the pressure constant. Determine the (a) initial humidity ratio, (b) the dew point temperature, and (c) the mass of vapor that has condensed out when temperature reaches 40 °F. 2.3 Air enters a 40-cm diameter cooling section at 1 atm, 32 °C, and 30 percent relative humidity at 18 m/s. Heat is removed from the air at a rate of 1200 kJ/min. The specific humidity of air remains constant through the cooling process. Determine (a) the exit temperature, (b) the exit relative humidity of the air, and (c) the exit velocity. 2.4 A heating and humidification system operates at atmospheric pressure. As shown in the figure, air is first heated and then humidified by wet steam at 100 °C (saturated water vapor, hw = 2.6757 kJ/g) (assuming adiabatic humidification). Air enters the heating section at 15° C and 60% relative humidity at a rate of 30 m³/min, and leaves the humidifying section at 25 °C and 50% relative humidity. Dry air and water vapor are considered as ideal gases. The psychrometric chart (SI units) may be used to determine the properties of air at various states. Determine: Sat. vapor 100°C Heating coils Humidifier 15°C 60% AIR 25°C 50% 30 m³/min P=1 atm 2 3 (a) The temperature and relative humidity of air when it leaves the heating section; (b) The rate of heat transfer in the heating section; (c) The rate at which water is added to the air in the humidifying section. 2.5 Conditions in one zone of a dual-duct conditioning system are to be maintained at 75 °F and 50% relative humidity (RH). The cold deck air is at 52 °F and 90% RH, while the hot deck air (outdoor air) is at 90 °F and 20% RH. The sensible heat factor for the zone is 0.65. Assume sea level pressure. In what proportion must the warm and cold air be mixed to satisfy the space condition? If the total zone load is 6×10³ But/hr, what is the total volume flow rate of air supplied to the zone? Sketch the states and processes on a psychrometric chart.