US2437287A - Heat exchange apparatus - Google Patents

Description

Max:119 194s; J.E.WOODS 2,431,281

HEAT EXCHANGE APPARATUS Filed Dem- 15, 1943 Patented Mar. 9, 1948 v I HEAT EXCHANGE APPARATUS John E. Woods, Brooklinc, Mass., assignor, by mesne assignments, to Standard-Thomson Corporation, Boston, Mass, a corporation of Delaware Application December 15, 1943, Serial No. 514,383

2 Claims. (Cl. 257-2) 'apparatus of the thin The present invention relates to heat exchange apparatus and thermostatic control devices therefor, and is more particularly concerned with control devices for radiators, oil coolers, and other heat exchange apparatus or the types suitable ior use in aircraft.

Oil coolers and similar heat exchange apparatus for aircraft are usually mounted in ducts extending through the wing. The heat exoperating range. As applied to heat exchange tube type, the control members are in the form 01' tips applied to the individual tubes.

Other features of the invention consist of certain novel features of construction and combinations oi parts hereinafter described. in the speciflcation and particularly claimed in the claims.

In the accompanying drawings, Fig. 1 is a section through a portion 01' a heat exchanger changer has channels for. flow of the fluid to be 1 illustrating the application of individual concooled and channels for flow of cooling liquid, trol devices according to the present invention. the two sets 01' channels being in heat exchange the control devices being shown in closed posirelation.- In one widely used. form oi unit,.the tion; Fig. 2 is an end view of oneof the conchannels for the, flow oi cooling fluid will com-- trol devices; Fig. 3 is a sectional view of the rear prise thin-wall, closely spaced tubes, whilethe part of the heat exchanger shown in Fig. l; but channels for the flow of fluid to be cooled comwith the control devices open; Fig. 4 is a view prise the external inter-tube spaces. illustrating the manufacture of the control mem- In connection with heat exchange apparat bers; Fig. 5 isv an end view of one of the control for aircraft, shutters are fr quently provid d to devices in open position; and Fig. 6 is a sectional diminish the flow of air through the cooling chanelevation of a modified arrangement. nels at low temperatures. In oil coolers espec- Fig. 1 illustrates a heat exchanger of the genially, vproper'control under cold conditions preeral type described in my Patent No. 2,298,996, sents a serious problem, since at high altitudes comprising closely spaced thin-wall tubes 4, 1 under low power conditions, the oil congeals mounted at opposite ends in a rear header plate in the inter-tube spaces 01' the cooler. In order 6 and a front header plate 8. As an example, one to free the oil, special warm-jackets with therconstruction employs tubes .210" in diameter mostatically controlled valves are provided in the and about .006" in wall thickness, spaced about oil circulating system. It is also important to I .260" on centers. Some units have 3000 or more shut oil! or at least diminish the flow of cooling tubes. At the front-ends the tubes may be exfluid through the tubes until the temperature 80 panded,.as indicated 'at l0 and as described in rises to the normal operating range. my patent. The tubes project slightly through The use of shutters for controlling the flow the rear header, as indicated at I l, The tubes 01' air is attended with a number 01 difficulties. are suitably secured to the headers by soldering, The shutters are ordinarily operated manually, by brazing as described in my patent, or in any and therefore do not respond accurately to tem- 5 other suitable manner. perature conditions within the unit. For con.- As is customary in devices .of this kind,the enstructional reasons, they are usually placed at tire unit is enclosed in a tank or casing having the end of the duct where the air, emerging from suitable inlet and outlet ports for introducing the duct, enters the air stream. Hence, any theoil into the spaces between the tubes 4. The changes in shutter position are likely to intro- 40 unit is placed in the cooling duct or the plane duce aerodynamic disturbances which affect the in such a direction that the air flows through drag on the airplane. Furthermore, congealed the tubes in the direction 01' the arrow. In the oil in the cooler thaws out progressively from end of each'tube isprovideda, control member one point to another, and hence the flow of air in the form of a tip, indicated generally at I 4. should be controlled independently through dii- Each tip is formed from bendable thermostatic ferent sections 01 the cooler, an operation which I, material such as bimetal. The tips are preferis impossible with the conventional shutter. ably formed by stamping them out of a sheet or According to the present invention, the coolbimetal, as illustrated in Fig. 3, each member ing fluid channels are provided at the'rear of the having a tab l8 so thatfthe member may be unit with individual temperature controlled clorolled up, with a cylindrical base portion, and sure devices. These devices operate to close the soldered or welded by the overlapping tab it. As cooling fluid channels when the temperature of shown in Fig. 3, the member H in flatform is the air is below the normal operating range and provided with a series of petals I8 of such shape to open them as the temperature approaches the that the petals are in close contact in the completed tip when the metal is at low temperatures.

At higher temperatures the metal bends and the petals open outwardly as shown in Fig. 3. The tips are slipped over the protruding ends l2 of the tubes and are secured in position by soldering, or by means of an adhesive lacquer.

At low temperatures, the control members are closed, as shown in Figs. 1 and 2, substantially blocking the air flow through the tubes except for inconsequential leakage between the petals l8. In an oil cooler, this represents the condition in which the oil is at low temperature, so that the air in the tubes 4 is not heated. As th oil thaws out and and increases in temperature, the air is warmed in its passage through the tubes 4 and the warm air passing over the petals l8 causes them to bend outwardly, thereby opening the passage. The amount of opening of the petals is determined by the air temperature. The thermostat characteristics are determined by the fact that the control members should be fully open as indicated by Fig. 3 for normal operating temperatures.

It will be observed that the controls are applied to the individual tubes whereby the control members operate in response to the air flow through their respective tubes. Since the oil necessarily warms up at different rates in the different sections of the cooler, the air temperatures are proper for the different conditions existing in different parts of the unit.

Attention is directed to one important feature of the device. It will be observed from Fig. 3 that if the petals open more than indicated, the petals of adjacent tubes will engage one another and thus limit the extent of opening movement. Except for this feature, the petals of one control member might, under overheating conditions, expand sufficiently to block the passage of air through an adjacent tube or tubes. According to this invention, the tubes are fully open for normal operating temperatures and all higher temperatures.

In the arrangement shown in Fig. 6, a thermostatic member 20 is placed internally of each tube, preferably at about the middle of the tube. This arrangement is important from aerodynamic considerations.

The cooling air upon engaging the front ends of the tubes has some turbulence imparted to it. This turbulence, although it increases the pressure drop, is advantageous in enhancing the heat transfer. In the case of the plain tube unit, as the air progresses along the tube, the turbulence tends to damp out, so that at some intermediate point, the flow becomes laminar, or nearly so. The laminar flow in the remaining travel through the tube contributes little to the heat exchange.

According to the construction in Fig. 6, the thermostatic member 20 in an intermediate portion of the tube obstructs the flow slightly, even when wide open, and thus introduces some turbulence. The turbulence thus introduced improves the heat transfer, although with some unavoidable increase in pressure drop.

It will be understood that the requirements of high heat transfer and low pressure drop are inconsistent and that an improvement in heat transfer is usually accompanied by an increased pressure drop. However, according to the present invention the obstruction of the passage by use of the inserted members is a minimum because the petals, when open, conform to the inside walls of the tube. Hence the turbulence is no more than necessary to prevent the occurrence of laminar flow from the place occupied by the control member to the rear of the tube.

In manufacture, each control member has its base portion coated with adhesive lacquer and is inserted a definite distance into the tube. The petals open and close under temperature changes as in the construction previously described.

Although the invention has been illustrated and described as embodied in a header-type heat exchanger using thin-wall tubes, it will be understood that the invention is not limited to this construction but is applicable to the use of bendable thermostatic leaf members arranged at the rear of individual cooling fluid channels of other types of units.

Having thus described my invention, I claim:

1. In an aircraft oil cooler having tubes for the flow of cooling fluid therethrough, control devices applied to individual tubes at the rear thereof and having bendable thermostatic leaves operating to close the channels at low temperatures and to open for substantially unrestricted flow at normal and higher temperatures, adjacent control devices opening outwardly to engage one another to limit the extent of movement at excessive temperatures.

, 2. In an aircraft oil cooler having tubes for flow of cooling fluid, control devices for individual tubes at the rear thereof, each device comprising a tip of bendable thermostatic material and having petals capable of closing together at low temperatures and opening outwardly at higher temperatures, the petals of adjacent control devices opening outwardly for engagement with one another to limit the extent of movement at excessive temperatures.

JOHN E. WOODS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,189,786 Byrnes July 4, 1916 1,459,318 Birdsall June 19, 1923 1,864,052 Dykeman June 21, 1932 1,766,608 Crews June 24, 1930 FOREIGN PATENTS Number Country Date 257,593 Great Britain Aug. 14, 1926 510,960 Germany Oct. 24, 1930 Certificate of Correction Patent No. 2,437,287. March 9, 1948.

JOHN E. WOODS It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 1, line 11, for the word liquid readflm'd; line 14, strike out will line 26, for Warm-jackets read warmup jackets; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the PatentvOffice.

Signed and sealed this 18th day of May, A. D. 1948.

.THOMAS F.- MURPHY,

Assistant Oomrntssz'oner of Patents.

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