In a certain industrial dryer 4 kg/h of water is to be removed from a moist material. The drying is accomplished by passing air over this material. Air with a dry bulb temperature of 19°C and a relative humidity of 20 percent is preheated to 50°C and passed over the moist material. It leaves with a dry bulb temperature of 40°C and a relative humidity of 80 percent. Determine the mass flow rate of dry air required for this process.