Question

A sample of moist air has a relative humidity and dew point of 60% and 5 °C, respectively. Find the air dry bulb temperature and humidity ratio. Assume the sample exists at atmospheric pressure. (0.0056, 13 °C)

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Answer 1

Ta-Dry bulb temperature (DBT) in °C Tw-Wet bulb temperature (WBT) in °C Topt-Dew Point temperature (DPT) in °C P-Atmospheric pressure Ps- Saturation pressure corresponding to DBT Pw-Pressure corresponding to WBT Given data: Relative humidity (%) 0 = p = 60% = 0.6 Tapt = 5 °C P = Patm = 1.01325 bar Find: Dry bulb temperature (Ta) Humidity ratio (w) Solution: P = 1.01325 bar Read partial pressure of water vapor (PD) at saturation temperature (Tapt = 5°C) from steam tables Po = 0.0087258 bar Relative humidity(Ø) 0.0087258 0.6 = - = P = 0.014543 bar Read temperature corresponding to saturation pressure (Ps) from saturated steam tables i.e @Ps = 0.014543 bar corresponding temperature =12.547 °C Ta(DBT) = 12.547 °C ~ 13 °C Humidity ratio(w): = PS (Ps) DBT (Pw) WBT (Po) DPT W = 0.622_lv P-P, 0.0087258 w = 0.622 x = 0.005831 1.01325 – 0.0087258 w = 0.005831 kg of water vapor /kg of dry air