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.
No Leakage Risk
The single flow channel of the spiral heat exchanger eliminates leakage and bypassing streams common in shell-and-tube equipment (such as shell-to-baffle or tube-to-baffle leakage). The unit’s single flow passage also eliminates flow plugging caused by mal-distribution and entrance/exit problems, which allows for easy handling of viscous materials.
No Dead Zones
Since there are no sharp turns or corners in the flow channel, eddying and stagnant areas are reduced or eliminated. This has the added benefit of reducing potential problems commonly caused by erosion. The spiral’s thicker gauge material minimizes possible erosion and corrosion effects.
Higher Heat Transfer Rates
In liquid-liquid duties, one liquid enters the SHE in the center and spirals to the periphery, where it exits through a connection welded to the shell. The other fluid enters through a peripheral connection and exits through a center connection. The flow is practically 100% counter-current, which allows a high degree of heat recovery. The studs and the curvature of the single channel help to promote turbulence and thus heat transfer, which gives the SHE up to twice the heat transfer coefficient compared to the S&T.
The high heat transfer rate in combination with the spiraling channel makes the SHE very compact in terms of m2/m3 and offers a small installed footprint. In addition, the service footprint is significantly smaller than for an S&T, which requires space for removing the bonnets, rodding the tubes or even extracting the tubes.
High Vacuum Applications to Highly Viscous Fluids
The single flow channel & reduced fouling results in achieving very low pressure drops in vacuum operations which is not possible by the normal S&T Heat Exchangers since they have minimum pressure drop restrictions.
Efficient handling of highly viscous fluids such as oils, greases, fluids containing solids, thick slurries, pastes, paints, fruit pulps, fibrous materials, etc. is also possible with compact Heat Exchanger size, minimum fouling & maintenance. A standard S&T tends to foul & chock due to smaller tube passages for fluids & requires frequent cleaning adding up to maintenance time & cost.