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The water collector of a foam metal cooling tower

Cooling towers are commonly used devices for discharging waste heat and they typically use air to cool circulating water through either counterflow or crossflow direct contact heat dissipation where the hot water to be cooled comes into direct contact with the cool air. The hot and humid air, which absorbs heat from the water, is then discharged from the top of the tower, carrying small droplets of circulating water, known as drift. Drift contains various non-biodegradable water treatment chemicals and soluble salts (salt content is present in seawater cooling tower drift), which can have adverse effects on the environment and human health.

Copper Foam 1 (11)

The efficiency of droplet collection and pressure drop are the most important performance indicators of the water collector, and they are primarily related to the two-phase flow of gas and liquid inside the collector. The droplet collection efficiency refers to the ability of the collector to capture and retain the water droplets carried by the air. A higher collection efficiency means that a larger percentage of the droplets will be captured and prevented from being released into the environment. On the other hand, the pressure drop is a measure of the resistance encountered by the air and water flow as they pass through the collector. A lower pressure drop is desirable as it indicates less energy is required to drive the flow, resulting in lower operating costs.

Typically, PVC water collectors are made by arranging PVC folding plates in a certain pattern. The adjacent plates form curved channels, which allow for the rapid removal of liquid droplets by taking advantage of the varying properties of gas and liquid. On the other hand, foam metal water collectors rely on their distinctive structural design to achieve an effective filtering effect. When combined with the inertial effect, this design ensures a uniform distribution of gas throughout the water collector, resulting in fewer vortices and a better collection efficiency for small liquid droplets. Additionally, this design minimizes the likelihood of entrainment, making it less prone to carry along unwanted substances.

By comparing the results of the simulated gas-phase flow, pressure drop, and liquid droplet collection efficiency inside the foam metal and PVC water collectors, the following conclusions can be drawn:

  • The internal gas in the channel of the foam metal water collector can circulate with the gas in the adjacent channel. The liquid droplets carried in the circulating gas are removed through the filtering effect of the foam metal. At the same time, the liquid droplets in the channel are removed using the principle of inertia. The foam metal water collector adopts a combination of filtering and inertia methods to remove small liquid droplets from the air, ensuring a cleaner and purer gas flow.
  • The foam metal water collector is designed to optimize the distribution of airflow within its channels. Unlike a conventional PVC water collector, the foam metal water collector ensures a more even distribution of airflow throughout each channel and minimizes the chances of the liquid film being disrupted, which is crucial for efficient separation processes. This is achieved through the use of foam sheets that allow the gases in the adjacent channels to interact with the airflow within each channel. As a result, the range of low-pressure areas and high-speed regions is reduced, leading to a more uniform airflow distribution. Furthermore, the foam metal water collector also helps in reducing entrainment. Entrainment refers to the unwanted carryover of liquid droplets or particles with the gas stream. By promoting a more uniform airflow distribution, the foam metal water collector minimizes the occurrence of entrainment, leading to cleaner gas streams. Moreover, the enhanced airflow distribution provided by the foam metal water collector allows for an increased operational limit. The improved distribution ensures that the water collector can handle higher gas flow rates without compromising its performance. This expanded operational limit is beneficial in various applications where higher gas flow rates are required.
Copper Foam
Copper Foam
  • At low gas velocities, the foam metal collector has a higher droplet collection efficiency for droplets within the calculated particle size range compared to the ordinary PVC collector. This is because at lower gas velocities, the droplets have less inertia and are more easily carried along with the gas flow, being entrained to the outlet. The foam metal collector not only collects small droplets based on the principle of inertia, but also removes them through the filtration principle, resulting in a higher overall droplet collection efficiency compared to the ordinary collector. As the gas velocity increases, the inertia of the droplets also increases, leading to more large droplets being collected by the collector. It can be observed that the two types of collectors gradually approach each other in terms of the collection efficiency for large droplets. Due to the combined effect of collecting small droplets based on the principle of inertia and removing them through the filtration principle, the foam metal collector exhibits a higher droplet collection efficiency compared to the ordinary collector. The filtration effect of the foam metal substrate can cause a change in the droplet particle size range in the cooling tower collector, resulting in an increase in the average particle size and consequently improving the collection efficiency.

Copper Foam 1 (6)

  • The properties of foam metal have an impact on the pressure drop of foam metal, resulting in a higher-pressure drop compared to a regular PVC drain. This is because within the foam metal drain, the flow of gas reaches a balance between the losses due to turning resistance and foam metal filtration. Due to the high porosity and large surface area of foam metal, gas experiences significant losses while passing through the foam metal. The pressure drop can be reduced by adjusting parameters such as the thickness, porosity, and PPI (pores per inch) of the foam metal.
Picture of Lu

Lu

Our materials research team from Tsinghua University postdoctoral researcher lin and Harbin Institute of Technology researcher Mu, Nanjing University of Technology researcher Wei, they share their expertise in foam metal materials article.

About HGP

WE were established in 2003, located in the Gaoxin Zone of Guangdong-Guangxi Cooperation Special Experimental Zone, covering an area of 70 mu, with a plant of about 30,000 square meters, with more than 170 employees, is an advanced new material technology enterprise integrating research and development, production and sales.

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