CA1317772C

CA1317772C - Condenser with small hydraulic diameter flow path

Info

Publication number: CA1317772C
Application number: CA000518329A
Authority: CA
Inventors: Leon A. Guntly; Jack C. Dudley
Original assignee: Modine Manufacturing Co
Current assignee: Modine Manufacturing Co
Priority date: 1985-10-02
Filing date: 1986-09-16
Publication date: 1993-05-18
Anticipated expiration: 2010-05-18
Also published as: EP0583851A2; ATE145051T1; EP0583851A3; EP0219974A2; ATE160441T1; KR880004284A; JPH0587752B2; DE3650658T2; MX167593B; EP0219974B1; DE3650648D1; DE3650658D1; ES2002789A6; KR950007282B1; BR8604768A; JPS62175588A; EP0219974A3; EP0583851B1; DE3650648T2

Abstract

Abstract An improved condenser for use in air conditioning or refrigeration systems. A pair of spaced headers have a plurality of tubes extending in hydraulic parallel between them and each tube defines a plurality of hydraulically parallel, fluid flow paths between the headers. Each of the fluid flow paths has a hydraulic diameter in the range of about 0.015 to about 0.07 inches.

Description

13177~ ~

Index 750 CONDENSER WITH SMALL
~YDRAULIC ~EAMETER ~OW PAT~

Field of the Invention This invention relates to condensers, and ~ore particu-5 ' larly, to condenser6 ~uch ~8 ~re u~ed in nir conditioning orrerrigeration ~y~te~s for condensing a refrigerant.

~ackaround of ~he Invention Many condensPr6 employed in ~ir c~nditioning or refriger&tion ~y~tems ~t the pre~ent time utilize one or more 6erpentine conduit6 on the vapor side. In ~rder to prevent the ~xistence 2f ~n overly high pressure differential ~rom the vapor inlet to the outlet, which would necessarily increase 8y8tem energy r~quirements, the flow passages with~n æuch tu~es ~re ~ rel~tively large 6ize to avoid high re6istance t~ the flow of vApor and/or conden~ate.
Thi6, ln turn, ~eans thAt the air ~ide of the tubes will be relatively large ln ~lze. The relatively large size of the tube6 on the ~ir gide results in a relatively large portion of the frontal are~ of the air ~de being bl~cXed by the tube and le65 area available ln which ~ir ~ide ~ins may be dispo~ed to enhance heat tr~n~fer.

1 3 ~L 7 YjJ Y~ 2 As a consequence, to maintain a desired rate of heat transfer the air side pressure drop will become undeslrably large and a commensurately undesirably large system eneryy requirement in moving the necessary volume of air through the air side of the condenser will result.
The present invention is directed to overcoming the above problems.
Summary of the Invention Generally the invention seeks to provide a new and improved condenser for use preferably ln air conditioning or refrigerant systems. More specifically, the invention seeks to provide such a condenser wherein the condenser has a lesser frontal area on the air side that is blocked by tubes allowing an increase in the air side heat exchange surface area without increasing air side pressure drop and without increasing vapor and/or condensate side pressure drop.
The invention in one claimed aspect provides a condenser comprising a pair of spaced headers, one of the headers having a vapor inlet, one of the headers having a condensate outlet and a condenser tube extending between the headers and in fluid communication with each of the headers. The tube defines a plurality of hydraulically parallel fluid flow paths between the headers, each of the fluid flow paths having a hydraulic diameter in the range of about 0.015 to 0.040 inches, the hydraulic diameter being defined as the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path.
Another aspect of the invention provides a condenser comprising a pair of spaced headers, one of the headers having a vapor inlet, one of the headers having a condensate outlet and a plurality of tubes extending in hydraulic parallel between the headers, each in fluid communication with each of the headers. The tubes define a plurality of discrete hydraulically parallel fluid flow paths be-tween the headers, each of the fluicl flow paths having a hydraulic diameter in the range of about 0.015 to 0.040 inches, the hydraulic diameter being defined as the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path.
Further, the invention comprehends a condenser comprising a pair of spaced headers including a vapor inlet and a condensate outlet and a plurality of tubes extending in hydraulic parallel between the headers, each in fluid 1~7~7;~

communication with each of the headers. I'he tubes define a plurality of discrete, hydraulically parallel fluid flow paths between the headers, each flow path having a non-circular, nominally triangular cross-section to define a plurality of crevices for each such flow path. Each of the fluid flow paths has a hydraulic diameter in the range of about 0.015 to 0.040 inches, the hydraulic diameter being the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the coxresponding flow path.
Still further the invention provides a condenser comprising a pair of spaced, generally cylindrical, tubes defining headers, one of the header tubes having a vapor inlet and one of the header tubes having a condensate outlet, the header tubes each having a series of elongated slots with the slots on one header tube facing the slots on the other header tube. A plurality of flattened tubes having opposed ends, extend in hydraulic parallel between the headers, the ends of the flattened tubes being disposed in corresponding ones of the slots to be in fluid communication with each of the header tubes. An undulating insert is in each of the flattened tubes to define a plurality of hydraulically parallel flow paths within each flattened tube between the header tubes. Each of the fluid flow paths has a hydraulic diameter in the range of about 0.015 to 0.040 inches, the hydraulic diameter being defined as the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path. Fins extend between the exteriors of adjacent ones of the flattened tubes.
The invention further still provides a condenser comprising a pair of spaced headers including a vapor inlet and a condensate outlet. A plurality of tubes extend in hydraulic parallel between the headers, each in fluid communication with each of the headers, the tubes having a plurality of fluid flow paths between the headers and each flow path having a non-circular, nominally triangular cross-section to define a plurality of crevices for each such flow pathO The tubes are flattened tubes and each of the fluid flow paths has a hydraulic diameter in the range of about 0.015 inches to 0.040 inches, the hydraulic diarneter being the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path. The fluid flow paths are defined by an undulating spacer with each of the tubes having elongated crests on each side thereof and .~

13 ~ 7 l 7 ~.

bonded to the interior wall of the associated tube along substantially their entire length by being brazed thereto.
A further aspect of the invention comprehends a condenser for a refrigerant in a cooling system comprising a pair of spaced, generally parallel, elongated tubes defining headers with a vapor inlet in one of the tubes and a condensate outlet from one of the tubes. The header tubes each have a series of elongated generally parallel slots with the slots in the series on one header tube aligned with and facing the slots in the series on the other header tube. A tube row defined by a plurality of straight tubes of flat cross-section and with flat side walls and having opposed ends extend in parallel between the header tubes, the ends of the flat cross-section tubes being disposed in corresponding aligned ones of the slots and in fluid communication with the interiors of the header tubes, at least some of the tubes being in hydraulic parallel with each other. Web means are within the flat cross-section tubes and extend between and are joined to the flat side walls at spaced intervals to (a) define a plurality of hydraulically parallel flow paths within each flat cross-section tube that extend between the header tubes, to (b) absorb forces resulting from internal pressure within the condenser and tending to expand the flat cross-section tubes, and to (c) conduct heat between both the flat sides and fluid in the flow paths. The flow paths are of relatively small hydraulic diameter defined as the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path. Serpentine fins incapable of supporting the flat cross-section tubes against substantial internal pressure ex-tend between facing flat side walls of adjacent flat cross-section tubes.
In a preferred embodiment, there are a plurality of such tubes extending between the headers in hydraulic parallel with each other in sufficient number as to avoid high resistance to condensate and/or vapor flow.

13~7772 The invention con-templates that the tubes be fla-ttened tubes.

In a highly preferred embodiment, the invention contemplates that the plurality of flow paths in each tube be defined by an undulating spacer contained within the tubes.

Fins may be disposed on the exterior of the condenser tube and extend between the exteriors of adjacent ones of the condenser tubes.

The invention contemplates that the headers be defined by generally cylindrical tubes having facing openings, such as slots, for receiving respective ends of -the condenser tubes.

Other aspects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.

Description of the Drawings Fig. 1 is an exploded, perspective view of a condenser made according to the invention;
Fig. 2 is a fragmentary, enlarged, cross-sectional view of a condenser tube that may be employed in the invention;
Fig. 2A is an enlarged cross-sectional view of a section of the condenser tube;
Fig. 3 is a graph of the predicted performance of condensers with the same face area, some made in a prior art design and others made according to the invention, plotting heat transfer against cavity (hydraulic) diameter;
Fig. 4 is a graph comparing the present invention with the prior art construction showing air flow through each versus (a) the rate of heat transfer, (b) the refrigerant flow rate, and (c) the refrigerant pressure drop;
Fig. 5 is a further graph comparing the prior art construction with a condenser made according to the invention on the basis of air velocity versus the heat ~ 3 ~ 7 rJ rl j~

Index 750 transfer per pound of ~aterinl employed ln ~aking up the core of e~ch; ~nd Fig. 6 ~ a further graph comparin~ ~he prlor ~rt con6truction with the present lnventlon by plotting air velocity ver6us pressure drop across the ~ir 6ide of the condenser.

~escriptlon of_~he Prefer~L~mbod:iment An exemplary embodiment of n condenser ~ade ~ccording to the invention iB lllustrated in Flg. 1 and i~ ~een to include opposed, ~paced, generally parallel ~eader~ 10 ~nd 12. Accordlng to the invention, the headers 10 and 12 are preferably made up from generAlly cylindrical tubing. On their f~cing 6ides, they are provided with n series of generally parallel slot~ or open~ngs 14 for receipt of corresponding ends 16 and 18 of conden~er tube~ 20.
Preferably, between the 810t~ 14, in the area ~hown at 22, each of the headers 10 and 12 i provided with ~ some-what ~pherical dome to l~prove re6istance to pressure as explnined more fully in the commonly ~6~igned, copending application of Sapersteln et al, entltled ~eat Exchanger"
Canadian Application Serial No. 502,~27, filed February 19, 1986.
The he~der 10 has one end closed by ~ c~p 24 br~zed or welded thereto. Brazed or welded to ~he oppo6~te end 16 fitting 26 to whlch ~ tube 28 ~y be connected.
The lower end of the header 12 lg closed by a welded or bra~ed cap 30 61milar to the cap 24 while it~ upper ~nd is provided with a welded or brRzed ~n place fittlng 32.
~epending upon the orlent~tion of the condenoer, one of the ~lttings 26 and 32 ~erves ~ ~ vapor inlet ~hilo ~he other ~erve~ n~ a conden6ate outlet. For the oxl~nt~tion~ ~hown in Fig. 1, the ~ltting 26 wll~ ~erve ~ onden~ate outlet.

~L 3 ~. 7 ~

Index 750 A plur~lity of the tube~ 20 ~xtend between the header6 10 and 12 and are in fluid communic~tion therewith. The - tubes 20 are gevmetrically in parallel with ~ach other ~nd ~ydraul~cally ln parallel ~B well. Di~posed b~tween adja-cent ones o~ the tube~ 20 ar~ ~erpentine ~ine 34 ~lthoughpl~te fins could be u6ed if de6ired. Upper and lower ch~nnel6 36 ~nd 3B extend between and are bonded by any suitable ~ean~ to the headerE 10 and 12 t~ provide rigidity to the eystem.
A6 can be 6een ln Fig. 1, ~ach o~ the tubes 20 i~ a flatt2ned tube and within its interlor include~ an undu-lating ~pacer 40.
In cro~ section, the spacer 40 appear~ ~5 ~hown in Fig. 2 and it will ~e fieen that alternating crests are in csntact ~long their ~ntir~ length with the interior wall ~2 or the tube 20 and bonded thereto by fillets 44 of 601der or braze ~etal. As ~ con~equence, a plurality of ~ub~tantially ai6cret~ hydraulicdlly p~rallel fluid ~low path~ 46, 48, 50, 52, 54, 56; 5B and 60 are provided within ~ach o~ the tubes 20. ~hat iB to aay, ~her~ rtually no flui~ com~uni~
~tion fro~ on~ ~f ~uch ~low path5 to the ~d~a~ent flow paths on ~ach ~idQ. ThiY ~ ctlv*ly ~n~ that o~ch of ~he ~all~ ~parating adiacsnt ~luid ~low p~th~ 46, ~8~ 50, 52, ~4, 56, 5~ ~nd 60 ~r~ ~on~d t~ ~o~h o~ o~ ~he flat~
t~n~a tube 20 ~lon~ ~h~ir ~ntir~ l~n~th. A~ a eonseguence, er~ i~ no g~p th~t ~uld b3 ~ill2d ~y ~lu~ ~ith a l~er ~her~al co~duct~Yity. as a r~ult, ~at tr~n~ar Pro~ ~he 21uid VlA th~ W~ QParAt1n~ ~he ~rlou~ ~lu~ ~low paths Identl~ pr~vlo~ly to ~h~ ~xt~r~or ~ thæ tube 1~ ~xi-0 ~iz~. In ~dit~o~, lt 1~ ~el~ov~ th~t ~ r~t~ w paths3~ th~ Q ~ntlono~ t~k~ a~v~ntage og ~lr~blo ~oct~ of h~at tr~n~r ~aus~ ~y ~ur~c~ ton~ion ~no~n~

7 rJ 7 2 Index 75~

A econd adv~ntage r~6ide6 ln the ~ct ~he conden6ers ~uoh a~ that o~ the prssent lnv~ntion are ~ploysd on the ~utlQt ~lda o~ a compressor and khere~ore ~ro ~ub~cted to ~xtr~mely high pras~ur~. Conventionally, thi~ high pre~6ure ~ill be appliQ~ to the lnterior o~ the tUb~B 20. Where so-called ~plate" ~ins ~re ut~ ed ln lieu of the erpen-tlne flns 3~ lllustrat~d ln the dr~wing6, ~he same tend to confine ths tubes 20 ~nd ~upport them again~t the lnternal pres6ure o~ployed ln a condenser epplication. Conversely, ~erpentins rins ~uch A8 tho6e shown ~t 34 are lncapable of ~upporting the tube~ 20 agAln~t ~ubstantlal intern~l pres-~ure. Accordlng to ~he ~nvention, however, the deslred ~upport ~n a ~erpentlne ~ln heat ~xchanger ~ 6 aCCO~pll6hed by the ~act that the ~pacer 40 and th~ cre6t thereof 16 bonded along lts ontlr~ l~ngth ~n the int~rior ~all 42 of ~ch tube 20. Thi~ bond re6ult~ ln varlous part~ of the ~pacer ~0 being placed $n ten~ion when the tube 20 16 pre6surlzed to ~bsorb the ~orce rQ~ulting rrom internal pressure wlthin ths tube 2~ t~nding to ~xpand ~he tube 20.
A highly preEerred means by which the tubes 20 with accomp~
anying inserts 40 may be formed is disclosed in the commonly assigned application of Saperstein et al, entitled l'Method of Making a Heat Exchangerll, Canadian Serial No. 527,933, filed January 22, 1987.
According to the invention, each of the flow paths 48, 50, 52, 54, 56 and 58, and to the extent possible depending upon the shape of the insert 40, the flow paths 46 and 60 as J ~ 2 Index 750 well, have ~ hydraulic dia~eter in the rang¢ of about 0.015 to 0.040 1nc~e~ ven ~urr~nt ~ bly t~hnlqu~ ~ncwn in ~ e art, ~ hydraulic dia~eter o~ approxl~t~ly a. 035 inches opti~i~c~ ultlm~t~ h~at trRna~r o~f~cl~n~y ~n~ o~ee of con~truction. Hydraulic di~mçt~er is a~ conventionally de~in~d, namely, the cro~s-sectional ~rea o~ ~ach of the flow p~ths ~ultiplied by four and in turn divided by the wetted perimeter of the corresponding flow path.
~h~ valU~8 0~ hydr~uli~ ~lameter given ~re for cvn-~ene~rs ln R-12 ~yst~m6. 80~ewhat difrer~nt ~lue~ might be xpect~d ln oy6t~s u~ing a ~i~fer~nt re~rlgerant.
Within that range, ~t i~ desirable to ~ake the tube dimension a~ross the direotion of air flow through ~he core as ~all a~ possible. This in turn will provide more frontal area ln which ~ins, 6uch ~ the ~in 34, ~ay be disposed in the core without adversely lncreasing air ~ide pressure drop to ~btain a better rate of heat trans~r. In some in6tances, by mini~zing tube width, one or more ~dditional rows of the tubes can be included.
In thi~ ~onnection, the pre~erred embodi~ent contem-plates that tubes wlth ~eparate ~pacer~ 6u~h a~ ~llu trated in Fig. 2 be ~mployed ~fi oppo~ed to ~xtrude~ tube having pa~sages of t~e requ~6ite hydraulic d~a~eter. Current extrusion technique~ that are ~conomically feaslble at the pre~ent ~or large scale ~anufacture ~ oonden~r~ generally r~sult in a tube wall ~hiCkn~6B ~hat i~ greater ~han ~ha~
that ~6 r~guired to ~upp~rt ~ glven pre~6ure u6ing ~ tube and ~pacer ~6 di~clo~ed herein. A6 a consequence/ ~he over~ll tube width of ~uch extrud~d tubes i~ $~mewhat ~ 30 greAter ~Qr ~ given hydraul~c ~iameter ~han a tube and ~pacer co~bina~ion, which i8 unde6irhble ~or the r~asons ~t~ted l~mediately preceding. Noneth~le~6, ~h2 invention 13177~

contemplates the use of extruded tubes having passages with a hydraulic diameter within the stated range.

It is also desirable -that the ratio of the outside tube periphery to the wetted periphery within -the tube be made as small as possible so long as the flow path does not beco~e sufficiently small that the refrigerant cannot readily pass therethrough. This will lessen the resistance to heat transfer on the vapor and/or conduit side.

In addition to the utilization of a relatively small hydraulic diameter for the flow paths as mentioned previously, each of the flow paths preferably has at least one crevice preferably extending along the entire length of the flow path, but at least along a substantial part of that portion of the flow path that is exposed to vapor. As is apparent from Figs. 2 and 2A, the use of the undulating spacer 40 provides two to three such crevices for each flow path. Looking at Figure 2A for example, at the flow path 52, the spacer 40 has one crest 70 bonded to an upper side 72 of the tube 20 as indicated by the presence of the fillets 44 and adjacent crests 74 and 76 bonded to the lower side 78 of the tube 20. One such crevice is generally designated 80 and is located at the juncture of the crest 74 and the tube side 78. A second such crevice is generally designated 82 and is located at the juncture of the crest 76 and the tube side 78. It will be seen that both the crevices 80 and 82 are quite well defined as crevices notwithstanding the fact that they are partially filled by respective fillets 44 of braze material.

133.77r.?'?

A less well defined crevice (perphaps a semi-crevice) is generally designated 84 and i3 in fact defined by the concave curved part of the insert crest 70.
The crevices 80 and 82 are separated by a relatively flat area 86 and similar relatively flat areas 88 and 90 respectively separate crevices 82 and 84 and the crevices 80 and 84. These crevices unexpectedly increase heat transf~r from vapor ~lowing in the flow passages to both the spacer 40 and the tube 20. The mechanism by which improved heat 10 transfer is believed to occur is as follows. It is known that the equilibrium vapor pressure above a liguid surface is dependent upon the curvature o~ the surface. As a result, the local liquid pressure on a concave liquid surface is less than the local vapor pressure. There~ore, a 15 pressure gradient will exist across the interface of the vapor and the liquid. The magnitude o~ the pressure differential will depend upon the curvature of the interface.
Applying the foregoing to Fig. 2A, it will be considered 20 that the surface tension o~ the condensing refrigerant within a flow passage such as the flow passage 52 will result in bodies 92 of condensed refrigerant in the crevices 80 and 82 having generally similar concave surfaces 94. In addition, a lesser body of condensed refrigerant 96 will 25 accu~ulate in the semi crevice 8~ and will have a somewhat larger radius of curvature for its surface 98. At the same time, at the relatively flat areas 86, 88 and 90, there will be a very thin film of conde~sed refrigerant having essenti-ally no curved surface whatsoeverO As a conseguence~ the 30 liquid pressure at a generally central point A on the flat surface 90, for example, will be approximately equal ko the vapor pressure within the flow path center and greater than the pressure at point B in the condensate body 92 or point C

~L3~7~

in the condensate body 96. As a result the film will flow bidirectionally as indicated by an arrow 100 to the areas of lesser pressure, namely, the body 92 in the crevice 80 and the ~ody 96. Similar action will occur in the flak areas 86 and 88 for the same reasons.
Th~ls the film of condensed refrigeran-t in the areas 86, 88 and 90 will be thinned as the condensate flows to and collects in the crevices. This thinned film provides less resistance to heat transfer from the vapor to the tube 20 or spacer 40 than the film in a conventionally shaped flow passage. As a consequence, the local heat transfer rate is dramatically increased over a circul~r passage with the same hydraulic diameter because of the very high heat transfer rate at the flat areas 86, 88 and 90.
As the two-phase mixture flows down a flow path, the crevices increasingly fill and the collecting streams of condensate eventually merge, leaving a core of vapor. As flow continues, the vapor core will continue ko shrink until finally surface tension causes the liquid to collapse upon itself forming intermittent liquid slugs, separated by small elongated vapor bubbles which will be pushed down the passage by the liquid slugs and which will rapidly collapse as condensation continues to occur. The small hydraulic diameters that are employed allow the various flow paths to completely fill with condensed refrigerant due to capillary forces. Unexpectedly this renders operation of the conden-ser independent of gravity, which is to say that it will operate successfully in virtually any attitude. In summary then, the sm~ll crevices create significant surface tension forces which otherwise would not exist and which promote thinning of the vapor ~ilm at other areas on the interior of the flow passages to enhance heat transfer.

~ 3 ~ 7 ~ 7 '~

A number of advantages of the invention will be apparent from the data illustrated in Figs. 3 - 6 inclusive and -from the following discussion. Fig. 3, for example, on the righthand side, plots the heat transfer rate against the cavity or hydrau]ic diameter in inches at air flows varying from 450 to 3200 standard cubic feet per minute for production condenser cores made by the assignee of the instant application.

To the left of such data are computer generated curves based on a heat transfer model for a core made according to the present invention, the model constructed using empirically obtained data. Various points on the curves have been confirmed by actual tests. The curves designated "A" represent heat transfer at the stated air flows for a core such as shown in Fig. 1 having a frontal area of two square feet utilizing tubes approximately 24 inches long and having a 0.015 inch tube wall thickness, a 0.532 tube major dimension, 110F. inlet air, 180F. inlet temperature and 235 psig pressure for R-12 and assuming 2F. of subcooling of the exiting refrigerant after condensation. The core was provided with 18 fins per inch between tubes and the fins were 0.625 inches by 0.540 inches by 0.006 inches.

The curves designated "B" show the same relationship for an otherwise identical core but wherein the length of the flow path in each tube was doubled i.e. the number of 1 3 ~ r~ r~ ~rj1'~

Index 750 tubes W~8 h~lved and tub2 len~th wa~ doubled. A6 can be ~ppreciat~d ~ro~ ~lg. 3, heat tran6fer ~B ~dvant~ u~ly and ~ ~u~st~nt~ally ~ncrea~ed ln the range of hydraullc d$~meters of about 0.015 inche6 to about 0.040 inches through the u e of the inv¢ntion with some vari~nce depending upon air flow.
Turning now to Fig6. 4, actual te6t data ~or a core made according to the ~nvention and h~vlng the dimensions ~tated in T~ble 1 ~elow 16 corparld agalnst actual test data for n conden~er core designated by the assiynee of the present application a~ 2803". The data ~r the conven-tional core i6 likewi6e ~i~ted in Table 1 belcw.
Both the ~ore ~ade ~ccording to ~he ~nvention ~nd the conventional core have the ~ame design p~int which ~ s shown in Fig. 4, ~ heat trzn6fer r~te of 26,000 BTU per hour at ~n air ~low of 1800 ~tandard cubic ~eet per ~inute. The actual observed equivalence of the two cores occurred at 2B,000 BTU per hour and 2,000 ætandard cubic feet per minute; and those par~meter~ may be utilized for comparative purposes.
Viewing ~ir6t the curves "D" ~nd ~E" for the prior ~rt condenser and the ~ubjeet invention respectively $t will be appreciated that r~friger~nt ~low ~or elther i~ ~omparable over a wide range of a$r flow v~lues. For this test, ~nd tho~e $11ustrated el~where in F~ 4-6, R-12 ~as applied 25 to the oondenser inlet ~t 235 p~ig at 180~F. ~he exiting refri~erant was 6ubcool~d 2F. Inlet ~ir temper~ture to the conden6er ~a~ 110F.
The greater re~rigerant ~ide pre~ure drop ~croes a conventional core than tha~ acro~ a core ~ade according ~o -- 30 the invention ~uggests ~ greater Qxpenditure o~ ~nergy by ~he compre6~0r in the ~onvention~l ~y~tem than ~n the one ~de according t:o the ~ub~ect invention ~ well.

~ 3 ~
Index 750 Curves ~F" ~nd "G", again ~or the prior art oonden er and the conden~er oP the ~ubject invention, ~ p~CtiVely, ~how c~mparable heat tr n~fer r~te~ over the ~e range of ~ir ~loW8.
Curves ~H'I ~nd ~J" respectively Por the conventional condenser and the ~ondenser of the~ 6ub~ect invention illus-trate ~ Gonsiderable dlfference in the pre~ure drop of the refriger~nt acro6s ~he conden6er. This demonstrates one advantage of the invention. ~ecauce o~ the lesser pressure drop acros6 the condenser when ~ade w cording to the inven-tion, the average temperature of the refr~gerant, whether in vapor form or in the form of conden6at~ wlll be higher than with the conventional conden6er. A6 ~ con~e~uence, ~or the same ~nlet air temperature, a greater te~perature ~ifferen-tial will exist which, according to Fourierls law, willenhance the rate of heat transfer.
There will al60 be a le~ser air 6ide pressure drop in a core made according to the lnven~ion than with the conven-tional core. This i5 due to two f~ctor~, namely, the le~ser depth of the core and the greater ~reP ~low area not blocked by tube~; ~nd ~uch ln turn will ~ave on the ~an energy required to direct the de6~r~d ~ir flow rate ~hrough ~he core. Y~t, a~ ~hown by the curves ~F" and ~G" ~he heat tranGfer rate re~ain~ entially the ~a~e.
It ha~ al60 been deter~ined that a core ~ade ~ccording to the ~nventlon, ~hen compared wit~ the ~onventional ~ore, hold6 l~s re~rigerant. ~hus, th~ ~ore o~ t~e inventi~n reduces the ~y~te~ reguirement ~or re~rigera~ imilarly, there i~ er ~pace required for inst~llation o~ the inventive core bec~use o~ ~t~ le6~er depth.
A~ ~an be ~en ~r~m the table, and in con6ider~tion with the da~a ~hown ln Fig. ~, it will be ~ppr~ci~t~d th~t a ~ore ~ade according to the invent~on c~n ~ ~ade o~

~ 3 ~ 7 ~

Index 750 con6ider~bly le6ser weight than H convention~l core. Thus, Fig. ~ compares, ~t various ~ir velociti~5, the heat tran~er rate per pound o~ core o~ the conventional condenæer (ourve "X") versu~ heat tran~er per pound of core ,~ _ ~ a conden~er ~ade According to the invention (curve "Ll').
Thu6, Fig. S demon6trates a oon~iderable weight savings in a sy~tem ~ay be obtained without ~acriflcing heat tran6ferability by UBing the core o~ the present lnvention.

13~7~

Index 750 TABI E
CONDENSER CORE PHYSICAL PROPERTIES
FOR FIGS. 3 AND 4 CURRENT
PRODUCTIONPRESENT
CORE EROPERT~_S lE2803 INVENTION
Depth (in. ) . 938 .540 Heights (in. ) 12 . 27612 . 00 Length (in.) 24.13 23.259 Face Area (ft.2) 2.057 1.938 Weighk (lbs) 5 . 6822 . 057 Ratio out~ide surfAce 4 . 478 5 . 391 inGide sur~ace FIN PROPER~IES

Fin Rows 13 21 Fin ThicXne~s (in. ) . 008 . 004 Fin Height (in.) .7502 .S018 Free Flow Area (ft2) 1.444 1.554 5urface Area (ft2) 37.110 33.389 Hydraulic Di meter (in. ) .1304 .091 Fin Weight (lbs. ) 2.163 O9g3 ~UBE PROPERT~ES
No . Circuits ~ ~ 0 25 Tube Rows 14 20 Tube ThicXness (in.) ~1~7 .075 Tube Wall (in. ) . 027 . 015 q~e Length (ft. ) 15.168 2 . 047 Free Flow Area- ~in.2) ol556 ~3209 30 Hydrauli~ Diameter (in. ) . 07871 . 0302 Out6ide Tube Sur~ace (ft2) 4 . 431 3 . 494 ~ ide Tube Surface (ft2) 9.276 6.842 Tube Weight (lb~ . ) 3 . 519 1. 064 . .~

~ ~ ~ r~ 7 !

Index 750 ~ig. 6, in s:urve "M" th.3reon, illu~trate5 the air side pres~ur. drop ~or a conv~ntional core for varit:~us air ~'lows.
Curve ~N" illu~trate~ the ~ir ei.de pre6sure dlrop 3Eor the 7r core of the present invention. It will be appr~ciated that the air ~ide pressure drop, and t~hus fan energy, i~ reduced when a core ~nade ~ccording to the invention i6 utilized.

Claims

1. A condenser comprising:
a pair of spaced headers;
one of said headers having a vapor inlet;
one of said headers having a condensate outlet; and a plurality of tubes extending in hydraulic parallel between said headers, each in fluid communication with each of said headers;
said tubes defining a plurality of discrete hydraulically parallel fluid flow paths between said headers;
each of said fluid flow paths having a hydraulic diameter in the range of about 0.015 to 0.040 inches, the hydraulic diameter defined as the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path.

2. The condenser of claim 1 wherein each of said tubes defines a plurality of said flow paths.

3. The condenser of claim 2 wherein said tubes are flattened tubes and the plurality of flow paths in each tube is defined by an undulating spacer contained within the tube.

4. A condenser comprising:
a pair of spaced headers;
one of said headers having a vapor inlet;
one of said headers having a condensate outlet; and a condenser tube extending between said headers and in fluid communication with each of said headers;

said tube defining a plurality of hydraulically parallel fluid flow paths between said headers;
each of said fluid flow paths having a hydraulic diameter in the range of about 0.015 to 0.040 inches, the hydraulic diameter being defined as the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path.

5. The condenser of claim 4 wherein there are a plurality of said condenser tubes, each extending between and in fluid communication with said headers, each of said tubes and their respective fluid flow paths being in hydraulic parallel with each other.

6. The condenser of claim 5 further including fins on the exterior of said condenser tubes.

7. The condenser of claim 5 further including fins extending between the exteriors of adjacent ones of said condenser tubes.

8. The condenser of claim 5 wherein said headers are defined by generally cylindrical tubes and having facing openings for receiving respective ends of said condenser tubes.

9. A condenser comprising:
a pair of spaced, generally cylindrical, tubes defining headers;
one of said header tubes having a vapor inlet;
one of said header tubes having a condensate outlet;
said header tubes each having a series of elongated slots, the slots on one header tube facing the slots on the other header tube;

Index 750 a plurality of flattened tubes having opposed ends extending in hydraulic parallel between said headers, the ends of said flattened tubes being disposed in corresponding ones of said slots to be in fluid communication with each of said header tubes;
an undulating insert in each of said flattened tubes to define a plurality of hydraulically parallel flow paths within each flattened tube between said header tubes;
each of said fluid flow paths having a hydraulic diameter in the range of about 0.015 to 0.040 inches, the hydraulic diameter defined as the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path; and fins extending between the exteriors of adjacent ones of said flattened tubes.

10. A condenser for a refrigerant in a cooling system comprising:
a pair of spaced, generally parallel, elongated tubes defining headers;
a vapor inlet in one of said tubes;
a condensate outlet from one of said tubes;
said header tubes each having a series of elongated generally parallel slots with the slots in the series on one header tube aligned with and facing the slots in the series on the other header tube;
a tube row defined by a plurality of straight tubes of flat cross-section and with flat side walls and having opposed ends extending in parallel between said header tubes, the ends of said flat cross-section tubes being disposed in corresponding aligned ones of said slots and in fluid communication with the interiors of said header tubes, at least some of said tubes being in hydraulic parallel with each other;
web means within said flat cross-section tubes and extending between and joined to the flat side walls at spaced intervals to (a) define a plurality of hydraulically parallel flow paths within each flat cross-section tube that extend between said header tubes;
to (b) absorb forces resulting from internal pressure within said condenser and tending to expand the flat cross-section tubes;

and to (c) conduct heat between both said flat sides and fluid in said flow paths, said flow paths being of relatively small hydraulic diameter defined as the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path; and serpentine fins incapable of supporting said flat cross-section tubes against substantial internal pressure extending between facing flat side walls of adjacent flat cross-section tubes.

11. The condenser of claim 10 wherein said web means are defined by undulating spacers within each flat cross-section tube and having crests with alternating crests bonded to opposite flat side walls.

12. The condenser of claim 10 wherein said web means further define at least one elongated crevice in each of said flow paths extending along the length thereof.

13. The condenser of claim 12 wherein there are a plurality of said crevices for at least some of said flow paths.

14. The condenser of claim 13 wherein the hydraulic diameter of substantially each of said flow paths is no more than about 0.040 inches.

15. A condenser for a refrigerant such as R-12 comprising:
a pair of spaced, generally cylindrical tubes defining headers;
one of said header tubes having a vapor inlet;
one of said header tubes having a condensate outlet;
said header tubes each having a series of elongated slots, the slots on one header tube facing the slots of the other header tube;
a plurality of straight, flattened tubes having opposed ends extending in parallel between said headers, the ends of said flattened tubes being disposed in corresponding ones of said slots and in fluid communication with each of said header tubes;
an undulating insert in each of said flattened tubes defining a plurality of flow paths within each flattened tube between said header tubes, said insert having crests on opposite sides thereof, said crests being bonded along their entire length to the corresponding tube to provide said discrete flow paths and to absorb forces resulting from internal pressure within the tubes and tending to expand the tube;
each of said fluid flow paths having a hydraulic diameter in the range of 0.015 to 0.040 inches where hydraulic diameter is defined as the cross-sectional area of the corresponding flow path multiplied by four (4) and divided by the wetted perimeter of the corresponding flow path; and serpentine fins extending between the exterior of adjacent ones of said flattened tubes.

16. A condenser comprising:
a pair of spaced headers arranged to have a vapor inlet and a condensate outlet;
a plurality of tubes extending in hydraulic parallel between said headers, each in fluid communication with each of said headers:
said tubes defining a plurality of discrete hydraulically parallel capillary fluid flow paths between said headers;
each of said fluid flow paths being non-circular in cross-section and having an elongated crevice extending along the length thereof.

17. The condenser of claim 16 wherein the plurality of flow paths in each said tube is defined by an undulating spacer contained within the tube and wherein each of said flow paths has a plurality of said crevices, said undulating spacer having crests in bonded abutment with the interior of the tube and together with the interior of the tube, defining said crevices on either side of the point of said abutment.

18. The condenser of claim 16 wherein each of said flow paths has a nominally triangular cross-section.

19. The condenser of claim 16 wherein the hydraulic diameter of each of said flow paths is sufficiently small that surface tension in condensate in said crevice will create an area of relatively lower pressure thus causing a pressure differential whereby condensate in a film elsewhere in said flow path will flow by operation of said pressure differential to said crevice.

20. The condenser of claim 19 wherein said hydraulic diameter is in the range of about 0.015 to 0.040 inches, said hydraulic diameter being the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path.

21. A condenser comprising:
a pair of spaced headers including a vapor inlet and a condensate outlet;
a plurality of tubes extending in hydraulic parallel between said headers, each in fluid communication with each of said headers;
said tubes defining a plurality of discrete, hydraulically parallel fluid flow paths between said headers, each said flow path having a non-circular, nominally triangular cross-section to define a plurality of crevices for each such flow path;
each of said fluid flow paths having a hydraulic diameter in the range of about 00015 to 0.040 inches, said hydraulic diameter being the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path.

22. A condenser for a refrigerant in a cooling system comprising:
a pair of spaced, generally parallel, elongated headers;
a vapor inlet in one of said headers;
a condensate outlet from one of said headers;
said headers each having a series of elongated generally parallel slots with the slots in the series on the one header aligned with and facing the slots in the series on the other header;
a tube row defined by a plurality of straight tubes of flat cross-section and with flat side walls and having opposed ends extending in parallel between said headers, the ends of said flat cross-section tubes being disposed in corresponding aligned ones of said slots and in fluid communication with the interiors of said headers, at least some of said tubes being in hydraulic parallel with each other;
web means within said flat cross-section tubes and extending between and joined to the flat side walls at spaced intervals to (a) define a plurality of flow paths within each flat cross-section tube that extend between said headers;
to (b) absorb forces resulting from internal pressure within said condenser and tending to expand the flat cross-section tubes;
and to (c) conduct heat between both said flat sides and fluid in said flow paths, said flow paths being of relatively small hydraulic diameter defined as the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path; and serpentine fins incapable of supporting said flat cross-section tubes against substantial internal pressure extending between facing flat side walls of adjacent flat cross-section tubes.

23. The condenser of claim 22 wherein said web means are defined by undulating spacers within each flat cross-section tube and having crests with alternating crests bonded to opposite flat side walls.

24. The condenser of claim 22 wherein said web means further define at least one elongated crevice in each of said flow paths extending along the length thereof.

25. The condenser of claim 24 wherein there are a plurality of said crevices for at least some of said flow paths.

26. The condenser of claim 25 wherein the hydraulic diameter of substantially each of said flow paths is no more than about 0.040 inches.

27. A condenser comprising:
a pair of spaced headers including a vapor inlet and a condensate outlet;
a plurality of tubes extending in hydraulic parallel between said headers, each in fluid communication with each of said headers;
said tubes having a plurality of fluid flow paths between said headers, each said flow path having a non-circular, nominally triangular cross-section to define a plurality of crevices for each such flow path;
said tubes being flattened tubes;
each of said fluid flow paths having a hydraulic diameter in the range of about 0.015 inches to 0.040 inches, said hydraulic diameter being the cross-sectional area of the corresponding flow path multiplied by four and divided by the wetted perimeter of the corresponding flow path; and said fluid flow paths being defined by an undulating spacer with each of said tubes having elongated crests on each side thereof and bonded to the interior wall of the associated tube along substantially their entire length by being brazed thereto.