SPECIFICATIONAir cooled heat exchanger unitThis invention relates to an air cooled heatexchanger unit comprising two air cooled heatexchangers having their chambers through whichthe cooling air flows arranged one behind theother.
Air cooled heat exchanger units of this type arerequired when, for example, in a propellercompressor it is necessary to provide a very spacesaving arrangement for installing both the aircooled heat exchanger for cooling a mixture of oiland air and the air cooled heat exchanger forcooling the compressed air from which the oil hasbeen separated. In such a case, two heatexchangers having very different coolingcapacities (the heat exchanger for cooling the oilrequires only about one third of the coolingcapacity required in the heat exchanger for coolingthe oil-air mixture) are arranged one behind theother so that the stream of cooling air flows firstthrough the heat exchanger for the oil-air mixture and then through the heat exchanger for the oil.
The cross-sections of the cooling air through flowchambers of these two heat exchangers must beequal because the cooling air would otherwiseseek the path of least resistance and flow onlythrough that part of the cross-section of thecooling air through flow chamber of the first coolerto which the through flow chamber of the secondcooler is not adjacent.
Another example of an air cooled heatexchanger unit requiring two air cooled heatexchangers having their cooling airflow chambersarranged one behind the other for reasons ofspace is found in hydraulically operating machinessuch as dredgers or the like, where hydraulic oil iscooled in the first heat exchanger and the transmission oil for the automatic transmission inthe second heat exchanger. Here again, verydifferent cooling capacities are required for thetwo heat exchangers.
Since air cooled heat exchanger units of thetype mentioned above frequently require verydifferent cooling capacities for the two heatexchangers, it follows that the heat exchanger for the smaller cooling capacity must be designed fora cooling capacity which is much too great for thepurpose because its through flow chamber forcooling air must, for the reason stated above,extend over the whole cross section of the coolingair flow chamber of that heat exchanger which isrequired to have the greater cooling capacity.
Since the costs of a heat exchanger depend among other things on its cooling capacity, an aircooled heat exchanger unit constructed in thismanner would therefore carry a much greater cost than would be necessary purely for the cooling capacity required.
It is an object of the present invention toprovide an air cooled heat exchanger unit of the type defined above, in which the two air cooledheat exchangers only have the cooling capacitynecessary for the use to which they are put, so that they can be manufactured at a substantially lower cost than the known air cooled heat exchanger units.
To solve this problem in accordance with the invention in an air cooled heat exchanger unit having two air cooled heat exchangers, the crosssections of the cooling air through flow chambers of the two heat exchangers differ, and that part of the cross-section of the flow chamber of larger cross section which does not communicate with the trough-flow chamber of smaller cross-section is provided with an air flow retarder extending over this whole portion of the cross-section of the flow chamber of larger cross-section and having substantially the same coefficient of resistance, based on the unit surface area of the cross section, as the flow chamber of smaller cross section of the other heat exchanger.This air flow retarder has the effect that the flow chamber of the heat exchanger unit has the same flow resistance at every point of its cross section so that the air flow is everywhere uniform, thus ensuring that the previously calculated amount of cooling air will also flow through the heat exchanger having the smaller cooling capacity.
The airflow retarder used for this purpose may be formed in any known manner.
In one particularly inexpensive and yet effective embodiment, the air flow retarder is in the form of a perforated plate. The coefficient of resistance of this plate can be adapted to every purpose for which it is used by suitable choice of the size and arrangement of the perforations.
The invention is described in detail below with reference to an embodiment illustrated by way of example in the drawing.
The drawing shows a perspective view of the embodiment, with the perforated plate partly broken away.
The air cooled heat exchanger unit illustrated in the drawing comprises a first air cooled heat exchanger with relatively large cooling capacity, indicated by the reference numeral 1, and a second air cooled heat exchanger with substantially smaller cooling capacity generally indicated by the reference numeral 2. Both heat exchangers 1 and 2 have parallel flat tubes 3 and 4 spaced apart, the two ends of the tubes opening into collecting chambers 5 and 6 which communicate with connecting pipes 7 and 8 for the fluids to be cooled.
The spaces 9 between the flat tubes 3 of the heat exchanger 1 together form the through flow chamber for the cooling air of the first heat exchanger 1. The totality of spaces 11 between the flat tubes 4 of the heat exchanger 6 constitutes the cooling air through flow chamber of the second heat exchanger 2.
The two heat exchangers 1 and 2 are so connected, as shown in the drawing, that some of the spaces 9 of the first heat exchanger 1 communicate with the spaces 11 of the second heat exchanger 2. This heat exchanger unit is installed in position so that the stream of cooling air is directed perpendicularly to the flow of the media to be cooled in the flat tubes 3 and 4 andparallel to the broad walls. In the example illustrated, the air stream first flows through the spaces 9 of the first heat exchanger 1 and then through the spaces 11 of the second heat exchanger 2. Corrugated strips 1 2 are provided in the spaces 9 and 11 to increase the heat exchanging surface areas.
In order to ensure that the coefficient of resistance, based on a unit surface area of the cross section of the cooling air through-flow chamber, which is perpendicular to the stream of cooling air, will be substantially the same in every part of the heat exchanger unit so that the air flow will be uniform through all the spaces 9 and 11, those flow spaces 9 of the heat exchanger which do not communicate with the flow spaces 11 are covered by a perforated plate 13 which has substantially the same coefficient of resistance, based on the unit surface area of cross section of cooling air, as the flow chamber of the second heat exchanger 2 formed by the spaces 11.
The perforated plate 3 ensures that when the heat exchanger unit is in operation, the cooling air flows uniformly through all the flow spaces 9 and 11 of both heat exchangers 1 and 2 inspite of the fact that the through-flow chambers are only partly arranged one behind the other.