Experimental Investigation on Spray Cooling Using Saline Water

Natural draft dry cooling towers (NDDCTs) are a type of cooling technology used in thermal power plants, including geothermal power plants. Interest from industry in this technology is increasing due to its water saving potential. However, the cooling performance of NDDCTs is inherently negatively impacted by high ambient temperatures. Among all existing solutions to this issue, inlet airflow precooling using water sprays is thought to be a good method to reduce the impact of high ambient temperature on the performance of NDDCTs. In previous studies, spraying of saline water obtained from water sources such as coal seam gas wells (as a by-product) was shown not only to save valuable freshwater resources but also to provide the further possibility of increasing the evaporation rate of water droplets, thereby shortening the wet length (distance) required for the spraying system. However, this benefit has not been verified. To address this knowledge gap, three different water sources were experimentally examined in the current study, viz. fresh, artificial simulated saline water, and real coal seam gas well water. Spraying using these three types of water was compared based on tests in a wind tunnel using a specific type of nozzle. The results confirmed an increase in the cooling efficiency of the spraying system when saline water was selected as the water source. However, the cooling efficiency may be more influenced by the nozzle orientation with respect to the airflow. On the other hand, spraying of saline water resulted in considerable deposition of solid particles from the water droplets in the airflow at 4.5m downstream of the nozzle after only 2h of spraying, although no significant nozzle clogging was observed even after the total of 50h of testing. This effect could potentially cause fouling and corrosion on heat exchanger surfaces.