Experimental investigations on the performance of a cross flow air heated humidifier

A horizontal cross flow air heated humidifier is designed for three modes of heating. It is tested to investigate its performance in terms of its ability to effectively humidify air. The system investigated in this study has both the humidifier and the heater(s) integrated in one unit. Special low pressuredrop nozzles are used to spray water such that they provide a fine mist, thus they break a liquid to tiny droplets to increase the surface area for better heat and mass transfer between the hot air and sprayed water. Several attempts to improve system performance are made. For example, the effect of adding packing material to further increase heat and mass transfer surface area is attempted. Another attempt is by having an interstage heating such that a heating coil (basically a heat exchanger where hot water is circulated in a closed loop) is placed after a first-stage sprayer to heat the air again such that its ability to absorb more moisture increases as it is passed through a second-stage sprayer. A mist eliminator is placed at the exit of the humidifier to make sure water droplets are not allowed to leave the humidifier with the exit humid air stream. Performance parameters used in the analysis include the temperature and humidity of the exit air stream in addition to the humidifier effectiveness that is considered one of the crucial parameters in designing a HDH desalination system. A comparison between different modification to the humidifier are made to select the mode that results in the closest exit air stream to saturation condition and the highest humidifier effectiveness. Adding the packing material showed insignificant improvement to the humidifier performance. On the other hand, the interstage heating is believed to be effective in increasing the unit effectiveness.