Operating principle of the Hybrid Dry Cooler

The hybrid dry cooler combines two well-known methods of heat transfer: First, dry cooling and second, evaporative cooling. The warm process fluid is transported by a pump (6) in an enclosed primary cooling circuit (1) from the heat source (5) via the inlet flange (2) to the finned heat exchangers (3), leaving the heat exchangers via the outlet flange (4)  und  back to the heat source. In an induced draft cross-flow process, the warm process fluid and the cool air (11) taken in by the fan (12) meet in the heat exchangers. In this case, pure dry cooling takes place. In cool weather conditions and at night, this process is often sufficient. High outside temperatures, on the other hand, can cause a loss of effect for which dry cooling cannot compensate. The hybrid cooler uses the principle of evaporation in order to achieve a clear increase in capacity. A pump standing in the water basin (9) conveys water via a wetting circuit (7) to the upper end of the heat exchanger. The heat exchanger is evenly wetted by the water flowing down. The air flowing past causes the water to evaporate on the fin surface, taking warmth from the fin and thus from the process fluid. The water level falls as the water evaporates. To protect the wetting pump, however, the water level should not fall below a particular level. Water is therefore added via a fresh water valve (8). Because of the evaporation and the addition of fresh water, the water gradually becomes thicker, i.e. the salts dissolved in the water become more concentrated. In order to avoid an over-concentration of these salts, the thickened water is removed from the circuit via a blow down valve (10). Cooling capacity: 35 to 365 evaporative tons under nominal operating conditions (cooling water FW temp. IN/OUT 95/85°F, wet bulb temp. 78°F.)