4. In an industrial drying process, 1 kg/s of a wet solid is dried from a water content of 30% to 10% by weight. This is achieved by passing heated air over the solid in a countercurrent mode. Air enters at 50C with a humidity of 0.002kg water/kg dry air and leaves with a humidity of 0.013kg water/kg dry air. Total recirculation of the air is used so all moisture picked up by the air must be removed by cooling the