Regarding the cleaning coefficient and dirt coefficient

I would like to know the answer to this question as well; the teachers who designed the heat exchangers before also gave only vague responses. I hope for some guidance. . .

It is clear that the fouling factor must be taken into account in any operating condition (even for gases that have been purified or distilled water). The fouling coefficient (generally referred to in the appendix of GB151) is a parameter that must be included when considering the heat transfer coefficient under actual operating conditions. Typically, process designers of heat exchangers do not use the cleaning coefficient mentioned by the original poster (\"the ratio of the heat transfer coefficient under dirty conditions to that under clean conditions\")), but rather introduce the parameter of the clean heat transfer coefficient, which corresponds to both the heat transfer coefficient under actual operation (taking into account the fouling factor) and the design heat transfer coefficient. Only the heat transfer coefficient that takes into account the fouling factor is the parameter that reflects the actual heat exchange capacity of the equipment; the clean heat transfer coefficient has no practical value for operational purposes and generally serves only as a reference value. Therefore, the heat transfer coefficients provided by designers of heat exchange equipment generally take the fouling coefficient into account. Now we can address the last question: due to factors related to the actual operating conditions on site, as well as various commercial considerations, many manufacturers do not choose this value based on the standards set in GB151. In my nearly sixteen or seventeen years of experience, I have reviewed many design parameter sheets, including those provided by major brands. In many cases, the dirt coefficient is set very low, or even to 0, in order to achieve a high heat transfer coefficient. This is because it is assumed that the party providing the process parameters may have exaggerated those values, or that the desired outcome can be achieved through other adjustments during actual operation. Thus, this phenomenon is quite common. Regarding the final question specifically, those who are interested may wish to take a look at the calculation documents for plate heat exchangers to see how the fouling coefficient is determined. Either they will tell you that my type of heat exchanger is special and doesn’t tend to accumulate scale, so there’s no need to consider a fouling factor, or they will mention that there are measures in place for removing scale or that water softening is used, etc. What’s certain is that, regardless of the type of heat transfer element, scale will inevitably accumulate on it; it may be present in small amounts in some cases, but it’s impossible for it not to be there. Whether it’s plate-type, tubular, or finned heat transfer elements, heat exchangers are all static devices and therefore do not have the ability to remove scale automatically (I’ve personally experienced a situation where a manufacturer of corrugated tubes claimed that such tubes had automatic scale-removal capabilities, and as a result they ignored my advice to treat the water problem as a temporary solution and opted for corrugated tubes; one can imagine what happens – those tubes become unusable after just a year). So for the last question, I’ll keep it brief; everyone should have an idea in mind by now.