Fouling is the deposition of unwanted materials, such as scale, suspended solids, insoluble salts, and even algae on the internal surfaces of the heat exchanger. Fouling occurs in all industries and most heat exchangers. It represents a resistance to fluid flow and heat transfer, which increases the pressure drop and reduces the efficiency of the heat exchanger. Fouling can occur because of the fluids being handled and their constituents in combination with the operating conditions such as temperature and velocity. There are different types of fouling, including:

• Biological fouling: caused by the growth of organisms, such as algae, within the fluid that deposit onto the surfaces of the heat exchanger.

• Corrosion fouling: occurs when impurities in the water change the composition of the heat exchangers metal surfaces, degrading the metal and often making it more susceptible to fouling.

• Particulate fouling: caused by accumulating suspended solids or particles, such as dirt, sand, sediments, and organic materials, in the process fluid.

Fouling prevention for heat exchangers is typically focused around the heat exchanger itself, but the fouling and heat exchanger performance can be affected by system characteristics that are present both before and after the heat exchanger. The best method to reduce fouling is to keep it from happening in the first place by utilizing a heat exchanger that is properly sized for the application, giving adequate velocities, surface area, and temperature splits. Fouling detection typically occurs by physical inspection or by monitoring system performance. Physical inspection includes measuring the foulings thickness on plates, pipes, or tubes. Cleaning processes include mechanical cleaning, chemical cleaning, and high-pressure water jetting.