Water is often cooled by evaporation into the air, using a cooling tower. Incoming hot water is sprayed into the air where a portion is evaporated, lowering the temperature of the remaining water by 10 to15C. (Evaporation of 1 kg of water provides sufficient cooling to lower the temperature of approximately 56 kg of liquid water by 10C.) Consider water entering a cooling tower at 40C and leaving at 30C. Air enters at 25C with a relative humidity of 40% and exits at 34C with 90% rh. For a water flow rate of 50 kg/s, and sufficient evaporation to meet the above conditions, determine the required air flow rate (kg/s) through the cooling tower.