Why Spiral Heat Exchanger is Better…………….? Self Cleaning Effect The spiral exchanger, with a single flow channel and pure countercurrent flow, produces flow path with high shear rates and high turbulence. At fluid velocities that would normally be in laminar flow in other types of heat-transfer equipment, the SHE is in fully developed turbulent flow. The continuously curving flow channel produces an intense scrubbing effect that prevents fouling deposits from forming. [If fouling starts to build up anywhere in the channel, the local cross-sectional area for the flow will be reduced at that position. As a consequence, the local velocity will be higher than in the rest of the channel. The shear rate between the liquid and the solid fouling will increase in proportion to the velocity squared and will cause a scrubbing effect that helps to remove the fouling. This phenomenon is often referred to as the self-cleaning effect] The resulting overall heat transfer coefficient is 10% to 50% higher than in comparable shell-and-tube heat exchangers. In a multiple channel heat exchanger such as an S&T, partial plugging of one tube will, due to the law of least resistance, lead to higher flow in the other tubes. The plugged tube will see a smaller flow that may not be sufficient to scrub it clean. A snowballing effect will result as more and more tubes become plugged, and the effective heat transfer area decreases rapidly.