The working principle and performance of evaporative condenser

Evaporative condenser is a water-cooled condenser and cooling tower integrated structure of equipment, its main role is to condense the hot refrigerant gas discharged by the compressor into saturated liquid. The refrigerant flows in the evaporative condenser tube, the surface of the tube is covered by a thin layer of water film, and the cooling air flows in the outer layer of the tube, which includes two parts: mass transfer heat and convective heat transfer, which is a complex process with heat and mass exchange. The cooling water is sent to the upper part of the condensing coil by the circulating pump, and sprayed to the outer surface of the condensing tube group through the nozzle to form a water film and flow downward. When the water in the middle of the water film evaporates, the heat is absorbed and the high-temperature and high-pressure refrigerant steam in the tube is condensed into a liquid. The air enters from below the box, flows upward along the lower part of the condensing tube group, and carries away the water vapor outside the condenser tube. When the temperature of the air is lower than the water temperature, it can also play a certain cooling role. The unevaporated water still returns to the tank bottom pool, and the float ball valve is used to maintain a certain water level, and the cycle works accordingly.

It can be seen that in the evaporative condenser, the heat of the refrigerant steam is transferred to the air through the water film through the wall of the heat exchange coil. The heat and mass transfer process of evaporative condenser consists of two parts, namely, the temperature difference between the refrigerant and the water film, and the temperature difference and mass concentration difference between the water film and the air. Here the water film (formation, scouring, thickness and distribution) is the key to the performance of the evaporative condenser.

The heat transfer effect of evaporative condenser is compared with that of air-cooled condenser, and the condensing temperature is relatively low, because the condensing capacity of air-cooled condenser is limited by the dry bulb temperature of the environment, and the condensing temperature of evaporative condenser can be close to the wet bulb temperature of the environment, and the wet bulb temperature is usually 8℃ lower than the dry bulb temperature, so the condensing temperature is lower, and the heat transfer effect is greatly superior to that of air-cooled condenser. Compared with the water-cooled condenser with a cooling tower, the evaporative condenser mainly relies on the latent heat of water evaporation to carry away the condensing heat load due to the completion of the heat transfer and mass transfer exchange between the refrigerant and the cooling water, especially the condensation temperature in summer is low, and the water consumption is greatly reduced. In theory, the water consumption is only 5-10% of the water-cooled type, and in fact, it is only about 15%. Therefore, the whole device has compact structure, small volume and small footprint.

The use of evaporative condenser reduces the condensing temperature of the refrigeration system, so the input power of the compressor is reduced, and the total power consumption of the condenser is also significantly reduced, so obvious energy saving can be achieved. Because the condensation temperature increases by 1℃, the power consumption per unit cooling capacity will increase by 3-3.5%. Many test reports show that under the same conditions, if evaporative condenser is used, the energy consumption of refrigeration unit can be reduced by about 10%.