The basic principles and categories of cooling towers

　　A cooling tower is a device that uses the contact (direct or indirect) of air and water to cool water. It uses water as a circulating coolant, absorbs heat from a system and discharges it into the atmosphere, thereby reducing the temperature in the tower and making equipment that can be recycled for cooling water.

　　Wuxi Deep Sea Heat Transfer Technology Co., Ltd. In the wet cooling tower, the temperature of the hot water is high, and the temperature of the air flowing over the water surface is low. The water transfers the heat to the air, which is carried away by the air and dissipated into the atmosphere. There are three forms of heat dissipation:

　　① Touch heat dissipation;

　　② Evaporative heat dissipation;

　　③ Radiation heat dissipation.

　　The cooling tower mainly relies on the first two kinds of heat dissipation, and the radiation heat dissipation is very small, so it should not be ignored.

　　Evaporative heat dissipation principle

　　Evaporative heat dissipation is accomplished through material exchange, that is, through the continuous diffusion of water molecules into the air. Water molecules have different energies, and the average energy is determined by the water temperature. Some water molecules with large kinetic energy near the water surface overcome the attraction of adjacent water molecules and escape from the water surface and become water vapor. As the water molecules with large energy escape, the water body near the water surface energy is reduced.

　　Therefore, the water temperature decreases, which is evaporation and heat dissipation. It is generally believed that the evaporated water molecules first form a thin layer of saturated air on the surface of the water, whose temperature is the same as the temperature of the water surface, and then the speed of the diffusion of water vapor from the saturated layer to the atmosphere depends on The difference between the water vapor pressure of the saturated layer and the water vapor pressure of the atmosphere, that is, Dolton's law, can be represented by the following figure.

　　1. The basic structure of cooling tower

　　Brackets and Towers: External Supports

　　Packing: Provide the largest possible heat exchange area for water and air

　　Cooling water tank: located at the bottom of the cooling tower, receiving cooling water

　　Water collector: recovers the water droplets taken away by the air flow

　　Air inlet: cooling tower air inlet

　　Sprinkler device: spray cooling water

　　Fan: supply air to the cooling tower

　　Axial fans are used in induced draft cooling towers.

　　Axial/Centrifugal fans are used in forced draft cooling towers.

　　Cooling tower shutters: average intake airflow; retains moisture in the tower.

　　2. Types of cooling towers and their advantages and disadvantages

　　Natural ventilation cooling tower: The hot air with lower density flows out from the top of the cooling tower, and the cold air with higher density enters the cooling tower from the bottom of the tower to fill, no fan is needed, and the concrete tower is less than 200 m, which is used for cooling of large heat.

　　Mechanical ventilation cooling tower: The high-power fan forces the heat exchange between the air and the circulating water, and the water film on the surface of the filler can exchange heat with the air to the maximum extent; there are many factors that determine the cooling efficiency, and there are various cooling capacity options. Cooling towers work simultaneously.

　　The air is blown into the vent by the centrifugal fan; advantages: it is suitable for the tower body with large airflow resistance; the centrifugal fan has relatively low noise.

　　Counter-current cooling tower: The cooling water is sprayed on the filler and flows down into the cooling water tank. Air is forced in from the bottom, and in the packing, it contacts with water to evaporate part of the cooling water, thereby reducing the water temperature.

　　Induced draft cooling tower: There are cross-flow induced draft cooling tower and counter-flow induced draft cooling tower. The advantage is that the degree of backflow is lower than that of forced draft cooling towers; the operating cost of fans is less than that of forced draft cooling towers. The disadvantage is that the mechanical transmission of the fan and the motor requires a waterproof design.

　　Induced draft cooling tower The hot water enters the cooling tower from the top, the air is forcedly induced by the fan, and enters the cooling tower from the bottom; the forced induction fan is used. The cooling water enters from the top and flows through the packing layer; the air enters from one or both sides, and the fan is induced to make the air flow laterally through the packing layer.