High performance and cost-effective materials for water-saving and defogging modules in cooling towers to solve whitening and cooling problems

The water distributor of the cooling tower is a key component in the cooling tower. Its function is to evenly distribute water onto the cooling tower packing, increase the water air contact interface, vaporize a portion of the water, carry away heat, and reduce the water temperature. It is necessary to conduct in-depth research on the impact of its low cost on the cooling efficiency of the cooling tower. There are many types of cooling tower water distributors, including orifice plate type, exhaust pipe type, overflow type, cooling tower nozzle type, etc., and the rotary cooling tower water distributor is widely used.

Working principle of cooling tower water distributor

The cooling water flows into the cooling tower water pipe through the inlet pipe, and then forms a water flow through the spray hole on the cooling tower water pipe, which is sprinkled on the cooling tower packing. Due to the relatively small diameter of the spray hole, the water flow has a certain speed. According to the principle of force and reaction force, the cooling tower water pipe is rotated by the force opposite to the direction of the water flow, causing the water flow to continuously distribute on the cooling tower packing. The cooling tower water distributor may seem simple, but the determination of various parameters is very important, and there is a certain logical relationship between the parameters.

Principles for determining various parameters

1Determination of the spray hole diameter of the cooling tower water pipe:In theory, the smaller the diameter and number of spray holes, the better the uniformity of water distribution. However, if the spray hole is too small, it is easy to block and difficult to process. The size should be ≥ 0.003m, and the flow rate should also be comprehensively considered.

2Determination of orifice flow rate:The flow rate of the spray holes in both large and small cooling towers should be approximately the same value. Because the orifice velocity is too small, the reaction force is too small, the rotation speed will be very small or even stop, the orifice velocity is too large, the fluid Friction loss energy is large, the spraying is uneven, and water mist will also be generated, generally 0.8-2.5m/s is appropriate.

3Determination of the number of holes:The cooling water volume L is known, divided by the average flow rate of each nozzle to obtain the number of openings n on the water distributor. But the positions of each spray hole have not been determined yet, and the flow rate cannot be calculated. Note that the change in nozzle flow rate is approximately linear, so take the flow rate at half the radius of the branch pipe as the average flow rate uO 'and calculate the number of nozzle holes. Due to the different flow rates of each spray hole, the final number of spray holes may not be equal to this value, but is determined by the calculation process of each spray hole position. This is an initial value for calculation.

 fourDetermination of the cross-sectional area of the cooling tower water pipe:The cross-sectional area of the cooling tower water distribution pipe is closely related to the uniformity of water distribution. If the cross-sectional area is too small, it will affect the flow rate of the spray holes at both ends of the cooling tower water pipe; If the cross-sectional area is too large, it will increase the mass of rotating parts, reduce the rotational speed, and increase wear. Because the flow rate is a vector that can be superimposed, it is assumed that the flow rate of the nozzle of the cooling tower distributor is the superposition of the normal flow rate and the force release flow rate. The meaning of normal flow rate is the design method for the orifice flow rate of a fixed porous liquid distributor or for a smaller diameter liquid distributor with uniform orifice flow rate (without considering centrifugal force conditions).

The main content can be summarized as follows: to ensure equal flow rate of each nozzle, two points must be met simultaneously.

(1) Each nozzle should have sufficient resistance, and the greater the resistance, the more uniform the flow rate of the nozzle;

(2) The cross-sectional area of the water distribution pipe should be greater than the sum of the cross-sectional areas of each spray hole, and the larger the ratio, the more uniform the flow rate of the spray. By taking the cross-sectional area of the water distribution pipe as three times the sum of the cross-sectional areas of each spray hole, the normal flow rate can be uniform.

5. Determination of the hole position on the water distribution pipe: Generally, equal spacing holes are used for the water distribution pipe of the cooling tower. This method of opening holes causes uneven spraying. The unit area flow rate at the center of the filling material is too high, and the unit area flow rate at both ends is too low. This is because the cooling tower is cylindrical, and the cross-sectional area is proportional to the square of the diameter. The design method for the opening position of the water distributor when the flow rate of the spray hole is equal, but this method is not suitable for the situation of the water distributor in the cooling tower, because the cross-sectional area of the cooling tower is large and the centrifugal force of the water distributor cannot be ignored. Here, it is necessary to establish a calculation method for the opening position of the nozzle flow rate changing with centrifugal force. The optimization basis is to ensure that the spraying area of each small hole is equal, and the circular ring area on both sides of each nozzle is also equal, achieving uniform spraying with equal area.

6. Determination of rotational speed: If the rotational speed is too low, it will affect the quality of water distribution and easily cause stalling; When the speed is ≥ 40r/min, water droplets will splash around. It is generally recommended to use 20-30r/min.