Specific heat capacity of dry air and water vapour are 1.005 and 1.88 kJ kg-1 K-1, respectively. In an energy conserving system, 1 kg s-1 air at 300C with constant absolute humidity of 0.02 kg water (kg dry air)-1 is heated up to 650C. Water at the wet bulb temperature of air is then sprayed into the air so that the final temperature of the air-water vapour mixture is 400C. Latent heat of vapourization of water at 700C and 400C are 2334 and 2407 kJ kg-1, respectively. The thermal energy supplied per second during heating in kW is