What are the causes of fouling?
(1) The flow velocity of the fluid. Thefluid flow rate can be affected by the influence of heat and mass transfer and mechanical force, which is very complicated. In fact, the effect of flow rate on different types of fouling is different, and the influence degree on the scaling of different types of heat exchange equipment is also different. In heat exchangers, the flow rate effect on fouling should also consider its effect on fouling and scale erosion. For all types of fouling, the increase in erosion rate is more pronounced than the rate of fouling due to increased flow rate. Therefore, the growth rate of dirt decreases as the flow rate increases. However, in actual operation, the increase of the flow rate will increase the energy consumption. Therefore, the flow rate is not as high as possible, and should be considered in terms of energy consumption and dirt.
(2) Fluid properties. The fluid properties include the nature of the fluid itself and the nature of the various materials that are insoluble or entrained by the fluid. In the cooling water system, the water quality characteristics play a key role in the deposition of dirt. If salt and other substances are contained, it may crystallize due to changes in temperature or concentration; if it contains insoluble gas, it will affect the corrosion of the metal surface; if it contains microorganisms and nutrients It also has an effect on biofouling.
(3) The temperature of the heat transfer wall. The fluid temperature and its heat transfer coefficient determine the interface temperature. The rate of chemical reaction depends on the temperature, and the biofouling also depends on the temperature. The temperature increase of the fluid leads to an increase in the rate of chemical reaction and the rate of biofouling, thereby affecting the amount of fouling deposited, resulting in an increase in the growth rate of the fouling.
(4) Parameters of heat exchange equipment. First, the heat exchange surface material: usually the fouling situation has a great relationship with the material. Studies have found that copper alloy materials inhibit biofouling. For other commonly used carbon steels and stainless steels, scaling is only affected by the deposition of corrosion products, and if non-metallic materials such as graphite or ceramics with good corrosion resistance are used, scaling is less likely to occur. The second is the state of the heat exchange surface: the surface quality of the heat transfer surface material will affect the formation and deposition of dirt, and the greater surface roughness, the more favorable for formation and deposition of dirt. Third, the heat exchanger structure: experience shows that plate heat exchanger and spiral plate heat exchanger have better anti-scaling performance than shell-and-tube heat exchanger.