Question

Example 5: Ambient air at 38°C db-temperature and 20°C wb- temperature enters an evaporative cooler with a dry air mass flow rate of 0.75 kg/s. The pressure is constant at 95 kPa. The air leaves at a db-temperature of 25°C. Calculate (i) the relative humidity of the air at inlet, (ii) the relative humidity of the air at exit, (iii) the rate of flow of water to the cooler, and (iv) the saturation effectiveness of the cooler.

Answer 1

MASS low sq A Levesat DBT- 2s 'c. the follouwing data e obtained som bhe steam tables 1 233 KPa, hy, 25374 kjlkj At the wet bulb Tempesatuse the velative homidity 0,622 φ Pgw' (t) 0 622 x 2 337 9S 2 337 at the wet buib Tempesatose and the d'y buib Tempesstose ase vel' Ew ' bstitu tinj rumesicol vqlves in the qbove evtion we have Hence : O. 0082 4

0622 624 95-6-624 φ C) he sefose the selative humiaity at the nied 0 00 82 4 Assume the udates çesayed ·n ihe humidities is at the wb7 he Inioming a ,that is at eo'c The Jo ve Sn.nJ swation 4 the humidifies :s given hr substituting we ha ve me Numer,C9, V4've nence o.ol3s The Homidity is given 0322 ) These fose the seiq tve humidity atthe oute (tti) The mass Flouw 5ate & wates is given by mw (o-) My .: 0.75 (0.0135-0.00824 is Ch atsstien Etfectiveness the humidifis 38-25 38-20 9iven by t- t2 e1:12%