Heat exchanger with dimpled bypass channel

Details Heat exchanger with dimpled bypass channel Heat exchanger with dimpled bypass channel

2000-02-29

2001-04-24

Flanigan, Allen (Department: 3743)

Heat exchange

With adjustor for heat, or exchange material, flow

Branched flow

C165S153000, C165S916000

Reexamination Certificate

active

06220340

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to heat exchangers, and in particular, to heat exchangers with built-in bypass channels to provide some flow through the heat exchanger under all operating conditions.
FIELD OF THE INVENTION
Where heat exchangers are used to cool oils, such as engine or transmission oils in automotive applications, the heat exchangers usually have to be connected into the flow circuit at all times, even where the ambient temperature is such that no oil cooling is required. Usually, the engine or transmission includes some type of pump to produce oil pressure for lubrication, and the pump or oil pressure produced thereby causes the oil to be circulated through the heat exchanger to be returned to a sump and the inlet of the pump. Under cold ambient conditions, the oil becomes very viscous, sometimes even like a gel, and under these conditions, the flow resistance through the heat exchanger is so great that little or no oil flows through the heat exchanger until the oil warms up. The result is that return flow to the transmission or engine is substantially reduced in cold conditions to the point where the transmission or engine can become starved of lubricating oil causing damage, or the oil inside the engine or transmission can become overheated before the heat exchanger becomes operational, in which case damage to the engine or transmission often ensues.
One way of overcoming these difficulties is to provide a pipe or tube that allows the flow to bypass the heat exchanger in cold flow conditions. Sometimes a bypass channel or conduit is incorporated right into the heat exchanger between the inlet and outlet of the heat exchanger. The bypass conduit has low flow resistance, even under cold ambient conditions, so that some bypass or short circuit flow can be established before any damage is done, as mentioned above. Usually these bypass channels are straight or plain tubes to minimize cold flow resistance therethrough, and while such bypass channels provide the necessary cold flow, they have a deleterious effect in that when the oil heats up and the viscosity drops, excessive flow passes through the bypass channels and the ability of the heat exchanger to dissipate heat is reduced. In order to compensate for this, the heat exchanger must be made much larger than would otherwise be the case. This is undesirable, because it increases costs, and often there is insufficient room available to fit a larger heat exchanger into an engine compartment or the like.
The present invention attempts to overcome these difficulties by providing a dimpled bypass channel in the heat exchanger, the dimples having a height, width and spacing to produce a desired cold flow resistance to permit cold flow, but also an increasing hot flow resistance as the temperature of the fluid in the bypass channel increases.
SUMMARY OF THE INVENTION
According to the invention, there is provided a heat exchanger comprising a plurality of stacked tubular members defining flow passages therethrough. The tubular members have raised peripheral end portions defining respective inlet and outlet openings, so that in the stacked tubular members, the respective inlet and outlet openings communicate to define inlet and outlet manifolds. The tubular members have a predetermined internal cold flow resistance. A bypass conduit is attached to the stacked tubular members. The bypass conduit has opposite end portions and a tubular intermediate wall extending therebetween defining a bypass channel. The opposite end portions of the bypass conduit define, respectively, a fluid inlet and a fluid outlet, the inlet and outlet communicating with the respective inlet and outlet manifolds for the flow of fluid through the bypass channel. The intermediate wall has a plurality of longitudinally spaced-apart, inwardly disposed, mating dimples formed therein. The mating dimples define flow restrictions between the mating dimples and adjacent areas of the intermediate wall. The mating dimples have a predetermined height and transverse width such that the cold flow resistance past the flow restrictions is less than the predetermined internal cold flow resistance of the tubular members. Also, the mating dimples are spaced apart such that the hot flow resistance pass the dimples increases as the temperature of the fluid in the bypass channel increases.


REFERENCES:
patent: 4443188 (1984-04-01), Buhler
patent: 5575329 (1996-11-01), So et al.
patent: 5797450 (1998-08-01), Kawabe et al.
patent: 5875834 (1999-03-01), Brooks
patent: 5906237 (1999-05-01), Aikawa
patent: 5950715 (1999-09-01), Jonsson et al.
patent: 564761 (1993-10-01), None

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