Scaling of the condenser heat exchange tubes is indeed a common problem during the operation of chiller units. The formation of these scaling substances is complex and diverse, mainly related to the quality of cooling water, temperature conditions, and the operating status of the system. Below, we will explore in detail the mechanism of scale formation and its impact on heat conduction.
Causes of scaling formation
1. Formation of Hard Scale
Hard scale is mainly caused by the precipitation and deposition of calcium and magnesium salts dissolved in cooling water on the heat exchange surface after heating. When hard water containing high concentrations of calcium and magnesium ions is used as a cooling medium, as the water flows through the copper tubes in the condenser, the water temperature increases, resulting in a decrease in solubility. Carbonate ions combine with calcium and magnesium ions to form insoluble compounds such as calcium carbonate or magnesium hydroxide, which adhere to the heat exchange surface inside the condenser. Especially at the bend of the heat exchange tube, local changes in flow velocity can easily cause mineral precipitation, thereby accelerating the scaling process. Therefore, if conditions permit, it is recommended to remove calcium and magnesium ions through pre-treatment to slow down the scaling rate and maintain regular cleaning and maintenance.
2. Accumulation of biological sludge
In addition to chemical composition, sediment and microorganisms (such as algae) carried by natural water sources may also become part of the dirt. These particulate matter will gradually deposit in areas with slow water flow, forming a biofilm. As time goes by, this layer of film will become thicker and thicker, which not only reduces heat transfer efficiency, but may also cause pipeline blockage or even physical damage. To prevent this situation from happening, an effective filtering device can be installed at the inlet to intercept larger suspended solids, thereby reducing the generation of biological sludge.
3. Scaling intensifies under the influence of temperature
Excessive return water temperature is also one of the important factors that promote the formation of scale. According to relevant information, when the cooling water temperature exceeds 40 ° C, the formation of scale will become easier. This is because higher water temperatures reduce the solubility of certain salts in water, causing them to precipitate from the solution and adhere to metal surfaces. In addition, high temperature environments can accelerate the rate of chemical reactions, further promoting the occurrence of scaling phenomena.
The impact on heat conduction
As a poor conductor, scaling significantly increases the thermal resistance along the heat transfer path, leading to a significant decrease in heat transfer efficiency. Research has shown that different types of scaling can reduce heat exchange efficiency by 10% to 50%. Specifically, the presence of a fouling layer hinders the transfer of heat from the refrigerant to the outside world, forcing the system to consume more energy to maintain the same cooling effect. At the same time, as the thickness of the scale layer increases, the cross-sectional area of the flow inside the heat transfer tube will also decrease accordingly, increasing the water flow resistance and affecting the flow performance of the cooling water.
Cleaning method
There are usually two main cleaning methods for the above-mentioned issues: chemical cleaning and physical cleaning.
chemical cleaning
This method involves using specific acidic or alkaline solutions to dissolve and remove dirt. For example, an appropriate amount of acidic cleaning solution can be added to the cooling water system, and the circulation pump can be started to keep the cleaning solution flowing for 12 to 24 hours, continuously flushing the pipe wall until the dirt is completely removed. Afterwards, neutralize with alkaline solution to ensure that all residual chemicals are thoroughly washed away. Although chemical cleaning can effectively remove stubborn stains, it may cause slight corrosion to copper pipes, and the resulting waste liquid needs to be properly disposed of to avoid environmental pollution.
Physical cleaning
In contrast, physical cleaning uses mechanical means to directly act on the surface of dirt, such as using soft shaft brush cleaning technology. This method relies on a high-speed rotating nylon brush to penetrate deep into the copper tube of the condenser, using friction to peel off the attached material, and finally rinsing it clean with water. This method does not require the addition of any chemical agents, reducing its impact on the environment while also avoiding potential risks of metal corrosion. However, for particularly hard or tightly adhered scale layers, relying solely on physical cleaning may not achieve the desired effect. In this case, it may be considered to implement chemical pretreatment first and then follow up with physical cleaning steps to improve overall cleaning efficiency.
In summary, prevention is better than cure. Good water quality management and appropriate maintenance measures can greatly delay or even prevent scaling, ensuring the long-term stable and efficient operation of chiller units.
