Heat exchange – Tubular structure – With discrete heat transfer means
Patent
1989-06-29
1991-03-05
Schwadron, Martin P.
Heat exchange
Tubular structure
With discrete heat transfer means
165151, 165181, F28F 130
Patent
active
049970364
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is directed to a heat exchanger tube with flat lateral ribs spaced uniformly from each other in longitudinal direction.
In order to improve the heat exchange conditions at the transverse ribs, turbulators (vortex or turbulence generators) projecting at right angles from the surfaces of the lateral ribs have been provided, which turbulators protrude into fluid flow. These turbulators have a rectangular cross-section. They are stamped out of the material of the lateral ribs and are subsequently bent over or folded. The direction of their extent runs parallel to the direction of the fluid flow.
The heat exchange conditions can be distinctly improved by these turbulators compared to transverse ribs without projections. The disadvantage however is an overproportionate pressure loss as compared to the improved heat transfer.
SUMMARY OF THE INVENTION
The invention is based upon the task of taking all necessary measures permitted to avoid an overproportional rise of the pressure loss at improved heat transfer conditions.
In accordance with the present invention, the heat exchanger tube has turbulators or longitudinal vortex generators projecting from the rib plane by approximately 90.degree.. The turbulators are essentially triangularly shaped with unequal sides and extend at an angle with respect to the fluid flow direction. The turbulators are provided in a distributed arrangement at an angle with respect to the tube longitudinal plane which extends through the tube axis as well as parallel to the fluid flow direction. The turbulators have parting lines which rise in fluid flow direction as well as in the direction of the tube surface.
Because of such a special design and arrangement of the turbulators the fluid is twisted downstream of them viewed in flow direction and indeed in such a manner that longitudinal vortices or longitudinal turbulence is generated there. The boundary layer adjacent to the ribs, which essentially constitutes the thermal resistance can, so-to-speak, be rolled over with a relatively minor energy expenditure with the help of these longitudinal vortices. Herein the warm or cold fluid layers near the ribs are continuously replaced by the cold or warm fluid layers remote from the ribs by the generated pronounced rotation of the flow perpendicularly to the fluid flow direction. The longitudinal vortices, extremely low in friction, cause downstream of the turbulators regions with locally considerably improved heat transfer conditions, so that overall the heat transfer coefficient is clearly increased without a simultaneous rise of the pressure loss.
The turbulators in the invention develop their advantageous effects with any cross-section of heat exchanger tubes. This means they can be used with round elliptical or wedge-shaped ribbed tubes.
An especially intensive longitudinal vortex is generated downstream of each turbulator because the parting line of each turbulator rises in fluid flow direction. The longitudinal vortex extends far into the fluid flow.
Another improvement of the basic concept of the invention resides in the fact that the turbulators are arranged to be offset with respect to each other in the fluid flow direction as well as transversely to the fluid flow direction.
The offset or stagger is arranged herein in such a manner that the longitudinal vortices do not influence each other in a disadvantageous manner. Since the parting line of each turbulator also tilts in the direction of the tube outer surface, the heat passage between the fluid flowing in the tube and the fluid flowing around the ribbed tube is improved.
In this connection it was seen during in house experiments that the heat transfer can be further improved when the angle between the turbulators and the tube longitudinal plane is 10-30.degree., preferably approximately 15.degree..
In accordance with a preferred embodiment of the turbulators the ratio of the length of the turbulators to the maximum height thereof is approximately 3:2 to 3:1, preferably 3:1.75. This de
REFERENCES:
patent: 1743861 (1930-01-01), Modine
patent: 3976126 (1976-08-01), Ruff
Paikert Paul
Schulze Heinrich
Flanigan Allen J.
Gea Luftkuhlergesellschaft Happel GmbH & Co.
Schwadron Martin P.
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