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How does finned tube enhance heat transfer?

As flat fin heat exchanger is simple and convenient in structure and manufacture, durable in use and good in applicability, so far, the heat exchanger widely used in Refrigeration Engineering (such as evaporator of ammonia cooling fan, surface air cooler, etc.) still widely uses rectangular flat fin as expansion surface. 

Heat transfer characteristics of fins

Rectangular flat fin has the advantages of simple and compact structure, convenient defrosting, easy manufacturing and so on. At the same time, because it only depends on increasing the heat transfer area to enhance the heat transfer, the effect is poor, especially in the heat exchanger with phase change heat transfer of fluid in the tube and forced flow heat transfer of air outside the tube, the heat resistance of the air side is still the main heat resistance in the whole process despite the addition of fins.

Corrugated fins are widely used in air conditioning and refrigeration because they can increase the length of air passage and mix the air flow sufficiently. Corrugated fins can change the direction of air flow, greatly increase the area of air heat transfer and enhance the fluid disturbance. 

Because of the formation and separation of vortices, the continuous development of the heat boundary layer is reduced or damaged, the characteristics are effectively strengthened, and at the same time, a large loss of resistance is brought, but the increase of heat transfer is greater than the increase of resistance. 

Under the wet condition, the resistance of the slotted fins increases more, and the air volume of the system decreases. At this time, the corrugated fin heat exchanger can be considered, and the fin spacing should not be too small.

 

Murphy finned tubes heat exchanger

 

Heat transfer enhancement solutions

In the research of heat transfer enhancement on the surface of stainless steel fin tube by laser welding, Murphy experts put forward various methods of enhancement, mainly including the following: first, to enhance the turbulence intensity on the air side, the purpose of heat transfer enhancement can be achieved by constantly changing the flow direction of the air flow, mainly by stamping the fins into corrugations, resulting in the type of corrugation fins. 

The second is to use the discontinuous fin surface to gradually disconnect the fin surface along the air flow direction, so as to prevent the development of the air laminar boundary layer on the fin surface, make the boundary layer continuously damaged on each surface, and form a new boundary layer on the next punching strip, and constantly use the leading edge effect of the punching strip to achieve the purpose of strengthening heat exchange. 

There are slat fins, louver fins, etc. belonging to this kind of finsCorrugated fins are widely used in air conditioning and refrigeration because they can increase the length of air passage and mix the air flow sufficiently. Corrugated fins can change the direction of air flow, greatly increase the area of air heat transfer and enhance the fluid disturbance. 

Because of the formation and separation of vortices, the continuous development of the heat boundary layer is reduced or damaged, the heat transfer characteristics are effectively strengthened, and at the same time, a large loss of resistance is brought, but the increase of heat transfer is greater than the increase of resistance. Under the wet condition, the resistance of the slotted fins increases more, and the air volume of the system decreases. At this time, the corrugated fin heat exchanger can be considered, and the fin spacing should not be too small.

For more details about heat transfer please contact us. We can provide customized products according to your individual needs.

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