When handling viscous fluids in laminar flow, empty tubes allow significant gradients in velocity and temperature to develop. This can lead to thermal degradation of the process fluid at the tube wall as well as a wide residence time distribution in the process, both of which result in poor product quality. Heat exchangers with static mixer elements inside the tubes can overcome these operating problems and limitations.
Benefits of Static Mixer ElementsStatic mixer elements eliminate the thermal and velocity gradients found in open tubes and produce uniform fluid characteristics throughout the heat exchanger. The mixing elements' helical shape causes process fluid to constantly move from the center of the tube out to the tube wall and back again. This results in rapid blending of the fluid stream, thereby eliminating thermal gradients. The flow disruption also flattens out the velocity distribution so that it closely approaches plug flow, resulting in a more uniform thermal history for the process fluid. The shape of static mixer elements offers little obstruction to flow and can produce these benefits with minimal pressure loss through the exchanger.
Constant surface renewal significantly reduces the thermal boundary layer, so the tube-side heat transfer coefficient is increased. In addition, mixing elements can be attached to the tube wall via vacuum brazing. This creates an internally finned, enhanced surface heat exchanger that further boosts the heat transfer rates. This combination of features results in a heat exchanger that can be used effectively with fluids with a wide range of viscosities.
Heat exchangers employing static mixers often are used in the man-made fibers industry to remove the heat generated by high purity inline filters. The units also are used throughout the adhesives industry to cool products prior to pelletizing and to significantly boost production rates over conventional equipment. Static mixer elements provide benefits to both of these industries and can benefit your process by eliminating the thermal and velocity gradients found in open tubes.
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