US3191673A - Sectionalized heat-exchanger core-unit - Google Patents

Description

VF. M. YouNG SECTIONALIZED HEAT-EXCHANGER CORE-UNIT Filed April 25. 1962 im@ N INVENTOR. FRED M. YOUNG United States Patent O 3,191,675 SECTIONALIZED HEAT-EXCHANGER CORE-UNIT Fred M. Young, Racine, Wis., assignor to Young Radiator Company, Racine, Wis., a corporation of Wisconsin Filed Apr. 25, 1962, Ser. No. 190,085 4 Claims. (Cl. 165-151) This invention relates to steam-fed heat-exchangers the parts of which are formed of metals having materially different heat-expanison coei'lcients.

In the construction of heat exchangers, of the herein shown type, the core unit is made of a battery of parallel, closely-spaced tubes, mounting closely-spaced thin metal ns, and spanning and supporting spaced hollow headers, usually one piece. The holes in the ns are formed with perimetrical collars into which the tubes are mechanically expanded. The collars on one iin abut the adjacent fin which results in the formation of a double-wall of continuous metal for heat transfer. The tubes are bonded at the ends to the headers by scientifically-timed electrical induction.

Obtaining the best possible heat transfer for such heat exchangers requires the tubes and tins to be made from non-ferrous metal whereas the overall rigidity of the heatexchanger requires the headers to be made from ferrous metal. Gver the years the best non-ferrous metal for the tubes has been found to be copper, copper alloys, brass and/or a brass-like metal known as Admiralty. More recently the fins have been made of aluminum.

When this type of heat-exchanger is used with steam, the thermal-expanison differential of these non-ferrous and ferrous metals makes, for the manufacturer, the problem of so structuring the units as to prevent rupturing of the tubes and/ or the bonds between the tubes and the headers. Also, there has been the problem of the warping or crawling of the ns along the tubes. A Standard Hand Book indicates that under temperature changes from 70 F. to 600 F. steel expands 7.2 l06 inches per inch per degree Fahrenheit, copper expands 10.1 X 106 inches per inch per degree Fahrenheit, Admiralty metal expands 11.2 106 inches per inch degree Fahrenheit, and aluminum expands 14.2 106 inches per inch per degree Fahrenheit.

This problem of ruptured tubes and/or bonds and the distortion or displacement of the fins results from the fact that in this type of heat exchanger there is a constant on and ott operation under thermostatic control determined by the temperature demands of the space that is beingheated by these units.

Depending upon the weather conditions, these on and olf periods may vary in frequency from to 20 a day. Moreover, with steam pressures ranging from 0 to 150 p.s.i. there is a consequent temperature change in the heat-exchanger ranging from 70 F. to 366 F.

Recent carefully-controlled tests, with heat-exchangers of this type, i.e., steel headers, copper or copper-alloy tubes .and aluminum fins, have shown that the ruptures of the tubes or the bonds, almost without exception, occur with the outside tubes at the ends of the headers, always at or near the tube-header joint, and, as a rule, on the wall of the tube nearest the center of the unit.

It has long been known that the incident of such ruptures could be materially reduced, if not eliminated, by making these non-ferrous metal tubes of a heavier gage material than that which the economy of manufacture and the efficiency of heat transfer respectively demand. It also has been known that aluminum iins reduce the costs of production and increase the heat-transfer efciency. However, the expansion differential between the ferrous headers and the tins made of aluminum have created an additional problem of having the fins become warped and crawl along the tubes where the heat-exchangers have been used with steam heat.

The main objects of this invention, therefore, are to provide an improved structuring of the core unit for hightemperature heat-exchangers to permit the formation of the tubes and Iins of non-ferrous metals having the highest heat-transfer capacity consistent with the requisite tensile strength; to provide an improved heat-exchanger core-unit of this kind made in multiple sections with the tubes of all sections bonded to the opposed supporting headers; and to provide animproved heat-exchanger of this construction permitting the core-unit tubes and fins to be formed of non-ferrous metals of differing expansion coetlicients having the highest heat-transfer capacity with an inherent tensile strength requisite to make the heatexchanger as durable as those heretofore obtained with more expensive materials and having less heat transfer capacity.

In the adaptation shown in the accompanying drawings;

FIG.- l is a perspective view of a conventional-type heat-exchanger with portions thereof broken away to more clearly show the over-all construction and assembly of the core unit and the headers and the position of the air-flow accessories;

FIG. 2 is a vertical sectional View of the same taken on the plane of the line 2-2 of FIG. 1; and

FIG. 3 is a horizontal sectional view of the same taken on the plane of the line 3 3 of FIG. 2.

The essential concept of this invention involves forming the finned-tube core in multiple sections to permit structuring the fins and headers from metals of differing expansion coefiicients and highest heat-transfer capacity consistent with a tensile strength sufficient for lasting durability of the heat-exchanger over an optimum life use.

A heat-exchanger 5, of the particular type herein shown, incorporates a core unit 6 which, embodying the foregoing concept, comprises a pair of headers 7 and 8 spanned by and supported on a battery of tubes 9 multiple groups of which mount portions of a transverse series of closely-spaced parallel tins 10. As can be clearly seen from FIG. 3, the tubes 9 are located in staggered rows.

The heat-exchanger 5, as herein shown, in the industry is referred to as a unit heater. It is connected to a steam supply line most often in an over-head location for heating large open spaces, such as factories.

For such a heat-exchanger 5 the core-unit 6 is mounted on a shroud 11 having a shelf 12 for the support of a motor-driven fan 13 and the arrangement of adjustable louvres 14. The headers 7 and 8 are formed with steam supply and return tappings 16 and 17 (FIG. 2). Such unit-heaters generally are guaranteed for use with p.s.i. saturated steam. In normal operation, however, the heat exchanger 5 operates with steam pressure between 2 and 50 p.s.i. and steam temperatures of between 219 F. and 298 F., with air entering at around 65 F. and discharged at up to 298 F.

As heretofore noted, it has been the practice over the years to structure these core-units 6 with cast steel headers 7 and 8 and with the tubes 9 and the ns 10 formed of non-ferrous metal. All too often, in the past, manufacturers of such unit heaters have had too many develop leaks after a very short period of normal use. As a rule these leaks occur at the header joint of the extreme side tubes. For the manufacturer who has formed the fins of aluminum there has been the added problem of the top and/ or bottom series of ns 10 warping and/or crawling into irregular-spaced position on the tubes 9.

After a long series of tests with continuing failures in various moditications designed to remedy these twin problems of tube-joint rupture and/or iin distortion, a final archers 39 series of experiments were made with core-units 6 sectionalized as best shown in FIG. 3. With the headers cast steel, the tubes of brass of minimal wall thickness, and tins of aluminum, tests showed no leaks and less n distortion after the equivalent of 38 years of normal use.

The core-unit 6, herein shown, is just such a unit. The headers 7 and 8 :are cast steel with brass tubes 9 brazed to the headers 7 and 8 by scientifically-timed electrical induction and the tubes 9 mechanically expanded in the iin collars 20 of the aluminum tins '10, all of which is illustrated most clearly in FIG. 2.

As shown in FIG. 3, the core-unit 6 is divided into three sections by pairs of cuts 18 and 19 formed vertically of the coreunit between tubes 9 at points approximately one-third the width of the core-unit 6. Although these three core sections might be fabricated separately and subsequently bonded to the headers 7 and 8, the present practice is to assemble the tubes 9 and tins lil as heretofore they have been assembled for the conventional unit heater. After bonding the tube ends yto the headers 7 and 8 in the conventional manner, a saw is used to sever the stack of tins 10 as shown by the cuts 18 and 19. The cuts 18 and 19 leave the ends yof the severed fins inclined between the tubes. Y

A plurality of heat-exchangers 5, having their core units 6 structured in the above-described manner are branched olf from a steam supply line. A conventional thermostat is connected to control each unit heater to prevent overheating or underheating and keep fuel costs to a minimum.

The aforesaid series of tests have led to theories to account for the operational causes for ruptured joints of the side tubes 9 to the headers 7 and 8, when the core units were not sectionalized, :and for the absence or" ruptures with the sectionalized core units, as herein shown.

The relatively lower expansion coefficient of the steel headers 7 and 8, plus their wall thickness and their opposed arrangement, establishes a condition of considerable stability bordering on rigidity :as compared to the interposed linned tubes. Hence the headers, when heated, have a tendency to resist the faster-expanding thin-wall tubes 9 and the thin-tins 1t). The result must be that the tubes 9 will buckle. Concurrently, the ins 1li tend to expand lengthwise thereof, radially of the tubes 9. Ob-

viously, such expanding tins lil tend to create radial pressures on the tubes 9 supplementing their tendencyto buckle. Undoubtedly, this radial pressure against the tubes tends to increase outwardly along the longitudinally-expanding fins 10. This accumulating pressure `of tube buckling and iin expansion, it is believed, results in such a strain on the extreme side tubes 9, at the opposite ends of the headers 7 and 8, as to cause the rupturing of the tube bonds to the headers, as hereinbefore explained.

In sectionalizing the ns 10, by the cuts 18 and 19, it is believed the above-mentioned transverse expansion strains Vfrom the middle section of the core unit are not communicated to the opposite end sections of the core-unit 6.

Cil

Rather, it seems reasonable to assume that in a core-unit 6, structured as herein shown and explained, the transverse expansion strains, limited to two outer sections of the core 6, have been so materially reduced as to preclude pressures of the magnitude that have heretofore occurred with the non-sectionalized core unit. For that reason, therefore, a sectionalized core-unit, as herein shown and described, is free of the incident of ruptured joints of the side tubes 9 and the respective headers 7 and 8. Moreover, such sectionalizing of the fins reduces the tendency of their buckling and/or crawling, as has been the case with the non-sectionalized unit.

Variations and modifications in the details or structure of arrangement of the parts may be resorted to within the spirit of the appended claims.

l claim: Y

1. A heat-exchanger core-unit, for use in a steam-heating system which is subject to constantly uctuating pressures and temperatures, comprising:

(a) a pair of headers, each of one piece, elongated,

having a single chamber of rectangular cross-section,

(b) a battery of tubes in multiple staggered rows bonded at their ends to the respective headers and disposing the headers in vertically-spaced relationship with fluid ow in one direction between the two headers, and

' (c) a vertical series of transverse fins divided into multiple vertical groups approximately of the same length radially of the tubes, and embracing approxi- Y mately the same number of tubes with the opposedlyspaced ends of the groups of tins disposed in common vertical planes extending throughout the entire distance between the headers and with said ends being inclined between the staggered tubes and sufficiently spaced to avoid buckling of said tins.

2. A heat-exchanger as set forth in claim 1 wherein the materials for the headers, the tubes and the 'lins are respectively of dilerent expansion coefficients and tensile strengths.

3. A heat-exchanger core-unit as set forth in claim 1 wherein the headers are formed of a ferrous metal and the tubes and tins are formed of non-ferrous metal.

4. A heat-exchanger as set forth in claim 1 wherein the headers are formed of steel, the tubes are formed of copper or copper alloy, and the ns are formed of aluminum.

References Cited by the Examiner UNITED STATES PATENTS 1,841,361 1/32 Bulkeley Y 165-74 1,893,270 1/33 Caldwell l65--l5l 2,226,243 12/40 Herz 165-151 FOREIGN PATENTS 320,889 5 57 Switzerland.

ROBERT A. OLEARY, Primary Examiner.

CHARLES SUKALO, Examiner.

Claims (1)

1. A HEAT-EXCHANGER CORE-UNIT, FOR USE IN A STEAM-HEATING SYSTEM WHICH IS SUBJECTED TO CONSTANTLY FLUCTUATING PRESSURES AND TEMPERATURES, COMPRISING: (A) A PAIR OF HEADERS, EACH OF ONE PIECE, ELONGATED, HAVING A SINGLE CHAMBER AND RECTANGULAR CROSS-SECTION, (B) A BATTERY OF TUBES IN MULTIPLE STAGGERED ROWS BONDED AT THEIR ENDS TO THE RESPECTIVE HEADERS AND DISPOSING THE HEADERS IN VERTICALLY-SPACED RELATIONSHIP WITH FLUID FLOW IN ONE DIRECTION BETWEEN THE TWO HEADERS, AND (C) A VERTICAL SERIES OF TRANSVERSE FINS DIVIDED INTO MULTIPLE VERTICAL GROUPS APPROXIMATELY OF THE SAME LENGTH RADIALLY OF THE TUBES, AND EMBRACING APPROXIMATELY THE SAME NUMBER OF TUBES WITH THE OPPOSITELYSPACED ENDS OF THE GROUPS OF FINS DISPOSED IN COMMON VERTICAL PLANES EXTENDING THROUGHOUT THE ENTIRE DISTANCE BETWEEN THE HEADERS AND WITH SAID ENDS BEING INCLINED BETWEEN THE STAGGERED TUBES AND SUFFICIENTLY SPACED TO AVOID BUCKLING OF SAID FINS.

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