CA1215352A - Helicoidally finned tubes - Google Patents
Helicoidally finned tubesInfo
- Publication number
- CA1215352A CA1215352A CA000425391A CA425391A CA1215352A CA 1215352 A CA1215352 A CA 1215352A CA 000425391 A CA000425391 A CA 000425391A CA 425391 A CA425391 A CA 425391A CA 1215352 A CA1215352 A CA 1215352A
- Authority
- CA
- Canada
- Prior art keywords
- ripples
- turns
- helical
- tubular member
- fins
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Abstract
ABSTRACT OF THE DISCLOSURE
A helicoidally finned tube is provided for use mainly in heat exchangers. The tube comprises a cylindrical tubular member which carries or is integral with a helical member the turns of which form the fins of the tube.
The fins are provided with ripples which extend from the outer rim of the fins inwardly and the depth of which diminishes toward the tube center. The ripples serve for baffling a cooling medium inwardly to hotter parts of the tube thereby improving its heat transfer performance.
(Fig. 4)
A helicoidally finned tube is provided for use mainly in heat exchangers. The tube comprises a cylindrical tubular member which carries or is integral with a helical member the turns of which form the fins of the tube.
The fins are provided with ripples which extend from the outer rim of the fins inwardly and the depth of which diminishes toward the tube center. The ripples serve for baffling a cooling medium inwardly to hotter parts of the tube thereby improving its heat transfer performance.
(Fig. 4)
Description
3LZlS352 This invention relates to helicoidally finned tubes and more particularly to heat exchanger tubes of such type.
As is known, heat transfer between fluids of different heat transf~r coefficients is obtained, among other things, by means of helicoidally finned tubes which consist of an inner tubu-lar member and an outer helical member. The turns of the helical member form the fins of the tubes. The fluid of greater heat transfer coefficient such as liquids or condensing vapours flows in the tubular member. The fluid of smaller heat transfer coefficient such as gases or air flows between the turns - the fins - of the helical member at right angles to the longitudinal or principal axis of the tubular member and, thus, to the finned tube itself.
Helicoidally finned tubes having solid helical surfaces the plane of the turns of which is at right angle to the axis of the tubular member are already known. Such geometry permits the adaption of simple manufacturing methods which consist either in winding and fixing a band of rectangular or L-shaped cross sectional area onto the tubular member or in die-rolling helical ribs from the body thereof. In the latter case the turns of the helical member have outwardly diminishing cross sectional areas which means outwardly increasing gaps between the fins. In either case heat transfer is uneven along the radial extension of the fins, which is undesirable for thermodynamic reasons because it results in relatively low mean temperature changes in the external fluids as will immediately be explained:
~Z~53S2 If, for instance, the tubular member has a fluid flowing in it which is warmer than that air, the temperature of the fins decreases with increasing distance from the tubular member. At the same time the flow rate of air increases in the same direction because in the gaps between the fins less air will flow in the proximity of the tubular member than farther out. This is due to the increasing flow resistances met by the external fluid.
Namely, the flow path of the air is longer in central regions of the fins than at the periphery thereof. In addition, air flowing at the foot of the fins contacts the outer surface of the tubular member, in contrast to the air flowing at the periphery where it sweeps only the side surfaces of the fins. Such difference is even more prominent with tubes having die-rolled fins where besides a radial and outwards decrease of flow path lengths, also the gaps between ad~acent fins widen towards the periphery thereby augmenting the cross sectional flow area of air and diminishing the flow resistance thereagainst.
Thus, air flow in the gaps between adjacent fins is uneven which is responsible for the already mentioned low values of the mean temperature change in the air passed over the fluid.
It has been recognized that an economical increase in the performance of helicoidally finned tubes could be obtained if the bulk of the external fluid sweeping the tube would be forced to flow in the proximity of the hot tubular member rather than at the relatively cold periphery of the turns of the helical member.
Furthermore, it has been recognized that such inward shift of the flow area of air could simply be obtained by solid '.~
" ~ ~
~2~53~2 fins the shape of which is other than planar. More particularly, if the fins were provided with ripples the depth of which decreased in an inward direction, also the flow resistance to be met by the external fluid would vary in a similar manner which would mean that more fluid would flow in the proximity of the tubular member than at the outer periphery of the helical member.
Where the ripples were deeper, the fluid flow might even part from the fin surface. Then eddies would form behind the ripples. On the one hand, such eddies would increase the flow resistance and, thereby, the baffling effect. On the other hand, they would cause a detachment of the boundary layers sweeping the fin surfaces and, thereby, entail an increase of the heat transfer coefficient of the peripheral portions of the fins. The total effect would be an increase of the mean temperature change of the fluid along the whole radial length of the turns of the finned tube.
Such heat exchanger tubes with peripherally rippled fins have been disclosed in U.S. 2,667,337. A continuous helical fin is provided with gentle corrugations near the outer edge of the fin~ The corrugations extend radially inwardly up -to the approxi-mate midpoint between inner and outer edges. Thereby the zone ofthe fin adjoining the corrugated area is undistorted to provide for unobstructed flow of air adjacent the tube while the corru-gated area produces a turbulent scrubbing action of the air which accounts for an additional thermal transfer.
A similar heat exchanger tube is described in U.S.
As is known, heat transfer between fluids of different heat transf~r coefficients is obtained, among other things, by means of helicoidally finned tubes which consist of an inner tubu-lar member and an outer helical member. The turns of the helical member form the fins of the tubes. The fluid of greater heat transfer coefficient such as liquids or condensing vapours flows in the tubular member. The fluid of smaller heat transfer coefficient such as gases or air flows between the turns - the fins - of the helical member at right angles to the longitudinal or principal axis of the tubular member and, thus, to the finned tube itself.
Helicoidally finned tubes having solid helical surfaces the plane of the turns of which is at right angle to the axis of the tubular member are already known. Such geometry permits the adaption of simple manufacturing methods which consist either in winding and fixing a band of rectangular or L-shaped cross sectional area onto the tubular member or in die-rolling helical ribs from the body thereof. In the latter case the turns of the helical member have outwardly diminishing cross sectional areas which means outwardly increasing gaps between the fins. In either case heat transfer is uneven along the radial extension of the fins, which is undesirable for thermodynamic reasons because it results in relatively low mean temperature changes in the external fluids as will immediately be explained:
~Z~53S2 If, for instance, the tubular member has a fluid flowing in it which is warmer than that air, the temperature of the fins decreases with increasing distance from the tubular member. At the same time the flow rate of air increases in the same direction because in the gaps between the fins less air will flow in the proximity of the tubular member than farther out. This is due to the increasing flow resistances met by the external fluid.
Namely, the flow path of the air is longer in central regions of the fins than at the periphery thereof. In addition, air flowing at the foot of the fins contacts the outer surface of the tubular member, in contrast to the air flowing at the periphery where it sweeps only the side surfaces of the fins. Such difference is even more prominent with tubes having die-rolled fins where besides a radial and outwards decrease of flow path lengths, also the gaps between ad~acent fins widen towards the periphery thereby augmenting the cross sectional flow area of air and diminishing the flow resistance thereagainst.
Thus, air flow in the gaps between adjacent fins is uneven which is responsible for the already mentioned low values of the mean temperature change in the air passed over the fluid.
It has been recognized that an economical increase in the performance of helicoidally finned tubes could be obtained if the bulk of the external fluid sweeping the tube would be forced to flow in the proximity of the hot tubular member rather than at the relatively cold periphery of the turns of the helical member.
Furthermore, it has been recognized that such inward shift of the flow area of air could simply be obtained by solid '.~
" ~ ~
~2~53~2 fins the shape of which is other than planar. More particularly, if the fins were provided with ripples the depth of which decreased in an inward direction, also the flow resistance to be met by the external fluid would vary in a similar manner which would mean that more fluid would flow in the proximity of the tubular member than at the outer periphery of the helical member.
Where the ripples were deeper, the fluid flow might even part from the fin surface. Then eddies would form behind the ripples. On the one hand, such eddies would increase the flow resistance and, thereby, the baffling effect. On the other hand, they would cause a detachment of the boundary layers sweeping the fin surfaces and, thereby, entail an increase of the heat transfer coefficient of the peripheral portions of the fins. The total effect would be an increase of the mean temperature change of the fluid along the whole radial length of the turns of the finned tube.
Such heat exchanger tubes with peripherally rippled fins have been disclosed in U.S. 2,667,337. A continuous helical fin is provided with gentle corrugations near the outer edge of the fin~ The corrugations extend radially inwardly up -to the approxi-mate midpoint between inner and outer edges. Thereby the zone ofthe fin adjoining the corrugated area is undistorted to provide for unobstructed flow of air adjacent the tube while the corru-gated area produces a turbulent scrubbing action of the air which accounts for an additional thermal transfer.
A similar heat exchanger tube is described in U.S.
2,731,245, where a copper tube or body has an aluminum fin spirally wound therearound. The latter consists in a ribbon which ~, lZlS352 has a flange on one of its marginal edges. This is encased or covered preferably on both sides by a copper jacket or facing strip. The aluminum ribbon, together with its copper facing strip, is spirally wrapped about the tubing and the ribbon or fin is secured thereto by bonding. The problem dealt with is fixing a spirally wound fin of a certain metal to a tubular member of a different metal.
As will be seen, both prior disclosures are concerned with finned tubes meant for heat exchangers with spirally wound fins which are continuously rippled at their outer edges at their whole length.
Also ~E-A-1,527,860 discloses a finned tube with which a band is wound onto a tubular member. Previously, both sides of the band are provided with undulations of inwardly decreasing depth. Such undulations represent material for peripheral portions of the wound up band and permit the use of extremely thin steel strips and materials of low tensile strength such as aluminum without the danger of breaking. Prior to winding, the sides of the band are bent up whereby a helicoid of asymmetric turns is obtained the plane of the turns of which is not perpen-dicular to the principal axis of the finned tube so that two kinds of gaps between fins will be present. In addition, undulations are practically straightened out in the course of winding. Thus, the prior device is obviously unsuitable for obtaining an even air flow because, on the one hand, practically there are no efficient ripples to baffle the external fluid towards the tubular member and, on the other hand, the presence of two kinds of gaps between ~, the fins causes from the beginning an asymmetry in the fluid flow since in one of two adjacent gaps heat transfer is necessarily better than in its fellow gap.
Finned tubes for heat exchangers with which the fins of the tube are provided with ripples, the depth of which decreases toward the center of the tube, are also described in Hungarian Patent Specification No. 136,634. However, the fins of the prior device are disks which have to be positioned on a tubular member individually rather than solid turns of a helical member because they are indented according to a given pattern so as to increase the heat transfer capacity by breaking the air flow. However, such indenting can be carried out in sheet form of the fin material only. Due to the indentations the air flow is not only broken but also let through the fins rather than being baffled towards the tubular member.
A similar device is disclosed in CH-A-414,705. Here, the fins are again disks or ribs arranged parallel to one another the surface of which is interrupted by surface discontinuities to break up border layers of flowing gases like in the previously mentioned case rather than provided with ripples to inwardly baffle an air flow. The discontinuities are indentations or holes or both. The prevailing idea is an interruption of the rib sur-face along its whole periphery whether by indentations or openings.
SUMMARY OF THE INVENTION
The present invention provides a helicoidally finned tube, consisting of an inner tubular member and an outer helical .~
lZ153SZ
member, the helical member having solid turns with generatrices perpendicular to the principal axis of the tubular member and with ripples which extend inwardly from the outer periphery of the turns and the depths of which decrease with the radial distance therefrom, characterised in that the helical member has rippled sections alternating with ripple-free sections, and both types of sections registering with one another, respectively, in the direc-tion of the principal axis of the tubular member, the spacing of the sections being substantially equal to a quarter of the circum-ference of the tubular member so that the rippled sections of thehelical member occupy diametrically opposite positions on the tubular member.
Preferably, ripples projecting in the same direction from a pair of adjacent turns of the helical member register with one another in the direction of the principal axis of the tubular member. On the one hand, with such arrangement ripples of greater depth at the periphery of the fins generate eddies and, thereby, increase both the flow resistance and the heat transfer co-efficient. On the other hand, such registering results in gaps of uniform width which, in turn, goes with uniform flow rates and, thus, with less probability of dust particles and other impurities being precipitated in the gaps between the fins.
However, a pair o adjacent turns may occupy mutual positions with which ripples projecting in opposite directions from a pair of adjacent turns of the helical member register with one another in the direction of the principal axis of the tubular member. Such registering is responsible for alternate accelera-121S35?
tions and decelerations in the fluid flow the cross sectional areaof which varies between increasingly distanced values towards the outer periphery of the fins. Such fluctuations in the fluid flow further increase the peripheral flow resistance and, thereby, the inwardly directed baffling effect and the efficiency of heat transfer. At the same time, tendency to dust precipitation is practically negligible since it is counteracted by the pulsating nature of fluid flow.
Within an axial portion e.g. one turn of the helical member, the ripples may have at least partly different spacings whereby one and the same helicoidally finned tube will be dis-tinguished by a simultaneous presence of the advantages of both previously described expedients.
The finned tubes are installed with the rippled sections lying in the flow direction of the external fluid, so that the in-12~352 let and outlet sections of the fin~ will be free fro~
ripples whereby re~oval of i~purities probably precipi-tated in the gaps between the fin~ will substan-tially by facilitated.
l'he ripples ~ay be a~y~etric with respect to the plane of the -turns of the helical ~e~ber. For instance, they 0ay protrude fro~ the fin~ on one side only. Such asy~etric arrange~ent ha~ it~ significance a~ regards manufacture as will be apparent to the skilled art worker.
The ripples ~ay have angular cross sectional areas with the advantage of enhancing a breaking and eddying of the external fluid flow and, thereby, increasing the heat tranafer coefricient.
BRIE~ DESCRIPTION 0~ TIIE ~R~WING
~he invention will hereinafter be described in closer detail~ by taking reference to the acco~panying drawing which shows various exe~plified e~bodi~ents of the invention and in which:
Fig. 1 i9 a longitudinal sectional view of a conventional helicoidally finned tube.
Fig. 2 show~ a sec~tional view taken along the line II-II
of ~ig. 1.
~ig. 3 represents a diagra~.
Fig. 4 illustrate~ a perspective view of an exe~plified detail.
Fig. 5 shows, by way of exa~ple, a side elevational view of ~n e~bodi~ent of the helicoidally finned tube 28 according to the inven~tion.
lS352 Fig. 6 i~ a sectional view taken along the line VI-VI
of I~'ig. 5.
~ig. 7 representæ u Jide elevational view of a further exe~pli~ied e~bodi~ent of the in~ention.
~ig~ 8 illustrates an unfolded side elevational view of a detail of a fin.
~ig. 9 shows a cross sectional view of another exe~pli-fied e~bodi~ent of the invention.
~ig. 10 is a side elevational view of a detail of still another exe~plified e0bodi~ent.
~ig. 11 represents a side elevational view of a detail of a further exe~plified e~bodi~ent.
~ig. 12 illustra-te~ a cross sectional view tRken along the line XII-XII of ~ig. 11.
Sa~e reference characters refer to si~ilar details throughout the figures of the drawing, D~SCRIPTION 0~ PRE~ERRED EMBODIMENTS
In principle, ~ conventional helicoidally finned tube is built up as shown in I~`igs. 1 and 2 of the drawing. An inner cylindrical and tubular ~e~ber 20 carries a solid helical ~e~ber or helicoid 22 which snugly surrounds the for~er and ~ay be integral therewith as in the case of die-rolled fins. The plane of the turns 22a of the helical ~e~ber enclose~ a right angle with the generatrice~ of the tubular ~e~ber 20 one of which has been repre~ented by a dash-and-do-t line and designated by re~erence character 20a in ~ig. 1. The fins of the helicoidally finned tube 28 are for~ed by the turns 22a of the helical ~e~ber 22.
~ S3S~
A~ is known, cooling ~ir or another gaseous fluid flows at right angle with respect to the generatrices 20a of the tubu-lar ~ember 20 as indicated by arrows 24 and 26 in ~ig. 2. 13ue to ~uch ~utual positions of t~be and fluid flow direction the 5 flow path of` air in the proximity OI the tubul.ar ~e~ber 20 is the longest and becoDle~ gradually shorter toward~ the outer ri~ or border 22b of the fin as de~on~trated by decrea~ing lengths 24a and 26a of the arrows 24 and 26, re~pectively. More-over, also the surface swep-t by air is greater in the neighbour-10 hood of -the tubular ~e~ber than at the periphe-:/ of -the fin be-cause at it~ inner side the cro~s ~ectional flow area of air contact~, in addition to the confining fin surfaces, the sur-face of the tubular ~nember a~3 well. This ~eans that con~iderably larger areas are swept by air at the foot of the fins than 15 farther out, Thus, in the proxi~ ty of the tubular ~e~ber 20 relatively les~ air will flow in the gaps ?8 be-tween the turns 22a than at a distance therefrom.
It i9 such uneven distribution of the air flow which considerably ia~pairs the cooling properbie~ o -the tube, and, 20 thereby the therDIodyna~nic balance of heat trunsfer.
~ his clearly appears frool the graph shown in ~ig. 3 in which the teDlpera-ture t and the air flow vel~city v are plotted against the distance 1 frosn the principal axis 30 of the helicoidally finned tube when the tubular ~e~ber 20 25 has a ~ediu~ o:~ higher hea-t tran~3fer coefficien-t flowin~
in it in the direction of arrow 32 while the fin~3 are swept by a ~ediu~ of lower heat transfer coefficient flowing 28 between the turns 22a in the direction o~ arrows lZlS35~
24 and 26.
~e~perature variation~ along the cros~ ~ec-tional area of the helicoid~lly finned tube are repre~ented by a temperature curve 34. Section 35 of the latter i9 characteri~tic of a heat tran~is~ion between the ~ediu~
flowing in the -tubular ~le~ber 20 and the ~etallic wall thereof. Its ~ection 37 ~hows the course of heat conduction in the wall of the tubular ~e~ber 20. The vertical section 39 of the temperature curve 34 represents a temperature drop due to fittin~ between tubular ~e~ber 20 and helical ~ember 22. Section 41 illu~trates a te~perature decrease cau~e by a finite hea-t tran3fer coefficient o r the ~in.
While the temperature of the fins decreases with the distance from the tubular ~e~ber 20, velocity and quantity of air flowing in the fin gaps 28 increa~e in the same direction a~ demonstrated in ~ig. 3 by curve 36 which illustrates variations in the velocity v of the air flow.
Causes of the incre~e of velocity v in outward radial direction have already been explained hereinbefore when radial variations of flow path of the air and ~urface areas ~wept by it were pointed out (arrows 24 and 26).
Variations in the te~perature of the air withdrawing from the fin gaps 28 are represented by the te~perature curve 38 o~ the diagram ~hown in ~ig. 3: the te~perature ~5 of air con-tinually decreases wQth the distance from the tubular member 20 and is ~ub~tantially lower at the outer ri~ of the fins than in the pro~imi-ty of the tubular 28 ~ember. Consequently, if a~ount~ of air flcwin~ in the fin gop~ 28 along -the ou-ter periphery of fins are baffled towards the tubular me~ber 20 where they can contact with surfaces o~ elevated ternpt?rature, -the -te~perature curve 38 beco~e~ ~ore horizontal which ~eans a higher ~nean temperature of -the withdrawing air and, thereby, a ~ore efficient heat transfer.
As ha~ been ~entioned, the air flowing in the fin gaps 28 will, in co~npli~nce with the ~ain feature of the invention, be baffled towards the tubular ~etnber 20 if the turns 22a oI` the hellca] ~e~nber 22 are provided with ripples which extend fro~ the ou-ter periphery 22b of the fins and the depth of which decreases towards the tubular Inel~ber 20. ~uch turn 22a is shown in ~ig. 4.
One o~ the ripples is desi~nated by reference character 22c, A9 will be apparent, -the technical term "ripple"
re~er~ to portions of -the -turn 22a which project fro~
the turn plane between a pair of radii in one axial direction. As illus-trated in ~ig. ~, ripples 22c ~ay project ~ro~ the plane of the turn 22a on both sides thereof and turn in~to one another in an undulatory ~anner with spacings s.
A helical ~e~ber 22 consi~ting of turns 22a and provided with ripples 22c is shown on a tubular ~e~ber 20 in ~ig~. 5 and 6 of which ~ig. 5 illus-trate~ an axial portion of a helicoidally ~inned tube, and I~ . G
represents a cross sec-tional area thereo~. `,'~ith the represen-ted e~bodi~ent ripples 22c projec-tin~ -fro~ the 28 turn plane of a pair of adjacen-t turns 22a of the helical :~ZlS35Z
member 22 in the direction of the principal or central axis 30 o~ the tubular member 20 register with one an-other becau~e the peripheral length of the fins i~ an inte~ral ~ultiple of the spacing s of the ripples 22c.
If, in operation, the flow of cooling air i~pinges on the finned tube from right to left as regards the drawing, the air flow will be ~haped a~ indicated by a host of arrow~ in Figs.5 and 6, More particularly:
Where the air flow reaches the fin gap~ 2~ in direction of arrow 40 opposite to the ripples 22c, it ~eets hardly any flow resistance ~o that it withdraws without essential direction change~ by ~weeping the surfflces of the tubular me~ber 20 and of the foot of the fins or turns 22a. ~his means a contact with the hotte~t part of the finned tube and, thereby, a suitable cooling.
In contra~t, where the air flow reache~ the ripple~
22c laterally as e.g. in case of arrow ~2, air is compelled to an undulatory flow that is to a repeated change of flow direction as ~hown in Fig. 5. 'rhis Per ~e mean~ an elevated flow resistance. In addition, where the ripples 22c are relatively deeper that is at the periphery of the fins, the air flow will part with the fin surface when leaving a wave crest and go over into a whirling ~otion as suggested by small arrows 4~ in Fig. 5. Flow resi~tance is further increased -thereby. At -the same ti~e by a breaking of the border layers of a laminar flow al~o the heat transfer coefficient is considerably increased.
28 Due to such locally increased flow resistance the flowing air will try to pa~ the finned tube at portion~
of lower flow re~i3tance of the fin gaps 2~ that i~ in the proxi~ity of the tubular ~ember 20 where ripples 22c already di~appear or are too ~hallow to cause any flow di~turbances. Con~equently, air flow is concentrated to region~ clo~e to the tubular member 20 that is to places of highest te~peratures a~ ~uggested by the density of the ho~t of arrows in ~ig. 6.
At the same ti~e - as has been hinted at - relatively low amount~ of air flowing at the rims of the fins improve the heat transfer coefficient by breaking the border layers of la~inal air flow 90 that also 9uch air a~ounts withdraw at relatively higher temperature~. ~ue to such flow conditions the temperature curve 38 of the with-drawing air beco~es - as it were - more horizontal which i~ equivalent to an increase of both the mean te~perature and, thereby, the intensity of heat e~change. This, how-ever, i9 the main purpose of the invention.
Since, in axial direction, ripples of adjacent fins occupy similar angular positions and, thus, register with one another, the cros~ sectional flow area~ are practi-cally the ~ame even in rippled portions of the fin gaps.
This ~eans a relatively uniform flow velocity which counteract~ a precipitation of impurities probably carried along with flowing air.
The exemplified embodiment according to l~ig. 7 is distingui~hed from the previou~ one just by that the 28 circu~ference of the fins i9 by half of the spacing greater than an integral ~ultiple of the spacing 9 and, thu~, in the direction of the axi9 30 of the tubular ~e~ber 20 ripples 22c projecting fro~ the turn plane of a pair of adjacent turn~ 22a in oppo~ite direction~
regi~ter with one another. Therefore, where ripple~ of a pair of adjacent turn~ project toward~ each other as at 28a in ~ig. 7, flow velocity increases. On the other hand, where regi~tering ripple~ 22c point away fro~ one another a~ e. 6- at 28b of the fin gap 28, the flow velocity be-co~e~ relatively lower. Such alternate acceleration and deceleration at the periphery of the fin~ further in-crease~ the flow re~istance and, thereby, the inwardly directed baffling action. Eventually, it ~ean~ an i~prove~en-t of heat tran~fer although probable precipi-tation of i~puritiea i8 ~o~ewhat enhanced as well which, however, a~ a rule, does not counterbalance the i~prove~ent obtained in heat tran~fer properties of the finned tube.
~he expedient~ shown in Figs, 5 and 6 a~ well as in Fig. 7, re~pectively, ~ay be e~ployed al~o ~i~ultaneously.
Such co~bination will be obtained if within an axial length or portion of the helical ~e~ber the ripple~ follow one another by different spacing~.
An exe~plified e~bodi~ent of a helical ~ember with differe~t ~pacings of the ripple~ i~ partly ~hown unfolded in ~ig. 8. It will be ~een that wil;'~in an a~ial portion or section S of a helical ~e~ber 22 there are four kind3 of ~pacings sl, s2, s3 and 9~ ~etween the ripples 22c which 28 gradunll~ increase fro~ sl to s4 while t-he ripple~ 22c ~215~SZ
lie alternately on opposite sides of a plane of sy~etry indicated by a da~h-and-do-t line 46 and coinciding with the plane of the turns of the helicoid. obviously, in case of such helical ~e~ber 22 ripples 22c of adjacent turns 22a ~lay occupy ~o~t varied ~utual angular positions and ~ay alternately overlap each other, register with one another and ~eet oppo~itely, respectively, ~s the case 0ay be. Thu~ effects of various flow re~istance~ will, as it were, comple~ent each other.
It will be understood -that not only spacing~ within a ~ection S ~ay be dif-ferent but the sections S the~selves may differ fro~ one another. Whut ~atters is that the ripples have ~t least partly different spacing~ and, -there-by, ensure a ~i~ultaneous presence of the effects of various flow resi~tances.
~ig. 9 shows, by way o~ exa~ple, an e~bodiment of the invention with which the e~ploy~ent of ripples 22c i9 re-stricted to dia~etrically opposite ~ections Sl and S2 of the turn~ 22a of a helical ~e~ber 22. Such finned tubes have to be built in 90 that the rippled sections Sl and S2lie in the flow direction of cooling air indicated by an arrow 48 in the drawing.
With the represen-ted e~bodi~ent the central angle of the sections Sl and S2 a~ounts to ~0 degrees. Preferably, no greater values for the central angles will be selected ~ince the significance of such expedient lies in that ripple-free sec-tions facilitate a re~oval of i~purities probably precipitated in the fin gaps. The absence of ripples i3S~
between the sections Sl and S2 ~oe~ no-t es~en-tially influ-ence the hea-t tran~fer propertie~ of the finned tubes according to the invention becau~e -the rippled ~ection~
occupy portions of the circumference o~ the fin~ where the velocity of air flowing between the fin~ i3 the highe~t and, thus, rippling is ~ost efficient as regards air flow and hest tran~fer.
Hereinbefore only embodi~ents have been described with which ripple~ project in both direction3 and to the sa~e extent fro~ the plane of the turns of the helical member, However, ripple~ on both ~ide~ of the turn plane may also have different heights. Moreover, for reasons of manu facturing facilitie~ the u~e of helical ~elnber~ may be preferable which have ripples projecting fro~ the plane of the turns in one direction only. In both ca~e3, the ripples are asym~etric with respect to the plane of the turns of the helicoid. One-sided ripples can obviou~ly be produced by ~eans of relatively siu~ple tooling even if the ripples have different heights~
A detail of a turn of a helicoidally finned tube provided with such a~y~etric ripple~ 22c is repre~ented in ~ig. 10. As will be appreciated, ripples 22c are provided but above the plane of the turn 22a~ the plane being indicated by its trace line 46.
The ripples 22c oL the exe~lplified embodi~ents shown in Fig~. 4 to 9 co~pose e~sentially 8 wavy form while with the embodiment shown in ~ig. 10 the~ are arcuate surfaces~
28 Both kinds of ripple form favour la~inar ~low. Detachment
As will be seen, both prior disclosures are concerned with finned tubes meant for heat exchangers with spirally wound fins which are continuously rippled at their outer edges at their whole length.
Also ~E-A-1,527,860 discloses a finned tube with which a band is wound onto a tubular member. Previously, both sides of the band are provided with undulations of inwardly decreasing depth. Such undulations represent material for peripheral portions of the wound up band and permit the use of extremely thin steel strips and materials of low tensile strength such as aluminum without the danger of breaking. Prior to winding, the sides of the band are bent up whereby a helicoid of asymmetric turns is obtained the plane of the turns of which is not perpen-dicular to the principal axis of the finned tube so that two kinds of gaps between fins will be present. In addition, undulations are practically straightened out in the course of winding. Thus, the prior device is obviously unsuitable for obtaining an even air flow because, on the one hand, practically there are no efficient ripples to baffle the external fluid towards the tubular member and, on the other hand, the presence of two kinds of gaps between ~, the fins causes from the beginning an asymmetry in the fluid flow since in one of two adjacent gaps heat transfer is necessarily better than in its fellow gap.
Finned tubes for heat exchangers with which the fins of the tube are provided with ripples, the depth of which decreases toward the center of the tube, are also described in Hungarian Patent Specification No. 136,634. However, the fins of the prior device are disks which have to be positioned on a tubular member individually rather than solid turns of a helical member because they are indented according to a given pattern so as to increase the heat transfer capacity by breaking the air flow. However, such indenting can be carried out in sheet form of the fin material only. Due to the indentations the air flow is not only broken but also let through the fins rather than being baffled towards the tubular member.
A similar device is disclosed in CH-A-414,705. Here, the fins are again disks or ribs arranged parallel to one another the surface of which is interrupted by surface discontinuities to break up border layers of flowing gases like in the previously mentioned case rather than provided with ripples to inwardly baffle an air flow. The discontinuities are indentations or holes or both. The prevailing idea is an interruption of the rib sur-face along its whole periphery whether by indentations or openings.
SUMMARY OF THE INVENTION
The present invention provides a helicoidally finned tube, consisting of an inner tubular member and an outer helical .~
lZ153SZ
member, the helical member having solid turns with generatrices perpendicular to the principal axis of the tubular member and with ripples which extend inwardly from the outer periphery of the turns and the depths of which decrease with the radial distance therefrom, characterised in that the helical member has rippled sections alternating with ripple-free sections, and both types of sections registering with one another, respectively, in the direc-tion of the principal axis of the tubular member, the spacing of the sections being substantially equal to a quarter of the circum-ference of the tubular member so that the rippled sections of thehelical member occupy diametrically opposite positions on the tubular member.
Preferably, ripples projecting in the same direction from a pair of adjacent turns of the helical member register with one another in the direction of the principal axis of the tubular member. On the one hand, with such arrangement ripples of greater depth at the periphery of the fins generate eddies and, thereby, increase both the flow resistance and the heat transfer co-efficient. On the other hand, such registering results in gaps of uniform width which, in turn, goes with uniform flow rates and, thus, with less probability of dust particles and other impurities being precipitated in the gaps between the fins.
However, a pair o adjacent turns may occupy mutual positions with which ripples projecting in opposite directions from a pair of adjacent turns of the helical member register with one another in the direction of the principal axis of the tubular member. Such registering is responsible for alternate accelera-121S35?
tions and decelerations in the fluid flow the cross sectional areaof which varies between increasingly distanced values towards the outer periphery of the fins. Such fluctuations in the fluid flow further increase the peripheral flow resistance and, thereby, the inwardly directed baffling effect and the efficiency of heat transfer. At the same time, tendency to dust precipitation is practically negligible since it is counteracted by the pulsating nature of fluid flow.
Within an axial portion e.g. one turn of the helical member, the ripples may have at least partly different spacings whereby one and the same helicoidally finned tube will be dis-tinguished by a simultaneous presence of the advantages of both previously described expedients.
The finned tubes are installed with the rippled sections lying in the flow direction of the external fluid, so that the in-12~352 let and outlet sections of the fin~ will be free fro~
ripples whereby re~oval of i~purities probably precipi-tated in the gaps between the fin~ will substan-tially by facilitated.
l'he ripples ~ay be a~y~etric with respect to the plane of the -turns of the helical ~e~ber. For instance, they 0ay protrude fro~ the fin~ on one side only. Such asy~etric arrange~ent ha~ it~ significance a~ regards manufacture as will be apparent to the skilled art worker.
The ripples ~ay have angular cross sectional areas with the advantage of enhancing a breaking and eddying of the external fluid flow and, thereby, increasing the heat tranafer coefricient.
BRIE~ DESCRIPTION 0~ TIIE ~R~WING
~he invention will hereinafter be described in closer detail~ by taking reference to the acco~panying drawing which shows various exe~plified e~bodi~ents of the invention and in which:
Fig. 1 i9 a longitudinal sectional view of a conventional helicoidally finned tube.
Fig. 2 show~ a sec~tional view taken along the line II-II
of ~ig. 1.
~ig. 3 represents a diagra~.
Fig. 4 illustrate~ a perspective view of an exe~plified detail.
Fig. 5 shows, by way of exa~ple, a side elevational view of ~n e~bodi~ent of the helicoidally finned tube 28 according to the inven~tion.
lS352 Fig. 6 i~ a sectional view taken along the line VI-VI
of I~'ig. 5.
~ig. 7 representæ u Jide elevational view of a further exe~pli~ied e~bodi~ent of the in~ention.
~ig~ 8 illustrates an unfolded side elevational view of a detail of a fin.
~ig. 9 shows a cross sectional view of another exe~pli-fied e~bodi~ent of the invention.
~ig. 10 is a side elevational view of a detail of still another exe~plified e0bodi~ent.
~ig. 11 represents a side elevational view of a detail of a further exe~plified e~bodi~ent.
~ig. 12 illustra-te~ a cross sectional view tRken along the line XII-XII of ~ig. 11.
Sa~e reference characters refer to si~ilar details throughout the figures of the drawing, D~SCRIPTION 0~ PRE~ERRED EMBODIMENTS
In principle, ~ conventional helicoidally finned tube is built up as shown in I~`igs. 1 and 2 of the drawing. An inner cylindrical and tubular ~e~ber 20 carries a solid helical ~e~ber or helicoid 22 which snugly surrounds the for~er and ~ay be integral therewith as in the case of die-rolled fins. The plane of the turns 22a of the helical ~e~ber enclose~ a right angle with the generatrice~ of the tubular ~e~ber 20 one of which has been repre~ented by a dash-and-do-t line and designated by re~erence character 20a in ~ig. 1. The fins of the helicoidally finned tube 28 are for~ed by the turns 22a of the helical ~e~ber 22.
~ S3S~
A~ is known, cooling ~ir or another gaseous fluid flows at right angle with respect to the generatrices 20a of the tubu-lar ~ember 20 as indicated by arrows 24 and 26 in ~ig. 2. 13ue to ~uch ~utual positions of t~be and fluid flow direction the 5 flow path of` air in the proximity OI the tubul.ar ~e~ber 20 is the longest and becoDle~ gradually shorter toward~ the outer ri~ or border 22b of the fin as de~on~trated by decrea~ing lengths 24a and 26a of the arrows 24 and 26, re~pectively. More-over, also the surface swep-t by air is greater in the neighbour-10 hood of -the tubular ~e~ber than at the periphe-:/ of -the fin be-cause at it~ inner side the cro~s ~ectional flow area of air contact~, in addition to the confining fin surfaces, the sur-face of the tubular ~nember a~3 well. This ~eans that con~iderably larger areas are swept by air at the foot of the fins than 15 farther out, Thus, in the proxi~ ty of the tubular ~e~ber 20 relatively les~ air will flow in the gaps ?8 be-tween the turns 22a than at a distance therefrom.
It i9 such uneven distribution of the air flow which considerably ia~pairs the cooling properbie~ o -the tube, and, 20 thereby the therDIodyna~nic balance of heat trunsfer.
~ his clearly appears frool the graph shown in ~ig. 3 in which the teDlpera-ture t and the air flow vel~city v are plotted against the distance 1 frosn the principal axis 30 of the helicoidally finned tube when the tubular ~e~ber 20 25 has a ~ediu~ o:~ higher hea-t tran~3fer coefficien-t flowin~
in it in the direction of arrow 32 while the fin~3 are swept by a ~ediu~ of lower heat transfer coefficient flowing 28 between the turns 22a in the direction o~ arrows lZlS35~
24 and 26.
~e~perature variation~ along the cros~ ~ec-tional area of the helicoid~lly finned tube are repre~ented by a temperature curve 34. Section 35 of the latter i9 characteri~tic of a heat tran~is~ion between the ~ediu~
flowing in the -tubular ~le~ber 20 and the ~etallic wall thereof. Its ~ection 37 ~hows the course of heat conduction in the wall of the tubular ~e~ber 20. The vertical section 39 of the temperature curve 34 represents a temperature drop due to fittin~ between tubular ~e~ber 20 and helical ~ember 22. Section 41 illu~trates a te~perature decrease cau~e by a finite hea-t tran3fer coefficient o r the ~in.
While the temperature of the fins decreases with the distance from the tubular ~e~ber 20, velocity and quantity of air flowing in the fin gaps 28 increa~e in the same direction a~ demonstrated in ~ig. 3 by curve 36 which illustrates variations in the velocity v of the air flow.
Causes of the incre~e of velocity v in outward radial direction have already been explained hereinbefore when radial variations of flow path of the air and ~urface areas ~wept by it were pointed out (arrows 24 and 26).
Variations in the te~perature of the air withdrawing from the fin gaps 28 are represented by the te~perature curve 38 o~ the diagram ~hown in ~ig. 3: the te~perature ~5 of air con-tinually decreases wQth the distance from the tubular member 20 and is ~ub~tantially lower at the outer ri~ of the fins than in the pro~imi-ty of the tubular 28 ~ember. Consequently, if a~ount~ of air flcwin~ in the fin gop~ 28 along -the ou-ter periphery of fins are baffled towards the tubular me~ber 20 where they can contact with surfaces o~ elevated ternpt?rature, -the -te~perature curve 38 beco~e~ ~ore horizontal which ~eans a higher ~nean temperature of -the withdrawing air and, thereby, a ~ore efficient heat transfer.
As ha~ been ~entioned, the air flowing in the fin gaps 28 will, in co~npli~nce with the ~ain feature of the invention, be baffled towards the tubular ~etnber 20 if the turns 22a oI` the hellca] ~e~nber 22 are provided with ripples which extend fro~ the ou-ter periphery 22b of the fins and the depth of which decreases towards the tubular Inel~ber 20. ~uch turn 22a is shown in ~ig. 4.
One o~ the ripples is desi~nated by reference character 22c, A9 will be apparent, -the technical term "ripple"
re~er~ to portions of -the -turn 22a which project fro~
the turn plane between a pair of radii in one axial direction. As illus-trated in ~ig. ~, ripples 22c ~ay project ~ro~ the plane of the turn 22a on both sides thereof and turn in~to one another in an undulatory ~anner with spacings s.
A helical ~e~ber 22 consi~ting of turns 22a and provided with ripples 22c is shown on a tubular ~e~ber 20 in ~ig~. 5 and 6 of which ~ig. 5 illus-trate~ an axial portion of a helicoidally ~inned tube, and I~ . G
represents a cross sec-tional area thereo~. `,'~ith the represen-ted e~bodi~ent ripples 22c projec-tin~ -fro~ the 28 turn plane of a pair of adjacen-t turns 22a of the helical :~ZlS35Z
member 22 in the direction of the principal or central axis 30 o~ the tubular member 20 register with one an-other becau~e the peripheral length of the fins i~ an inte~ral ~ultiple of the spacing s of the ripples 22c.
If, in operation, the flow of cooling air i~pinges on the finned tube from right to left as regards the drawing, the air flow will be ~haped a~ indicated by a host of arrow~ in Figs.5 and 6, More particularly:
Where the air flow reaches the fin gap~ 2~ in direction of arrow 40 opposite to the ripples 22c, it ~eets hardly any flow resistance ~o that it withdraws without essential direction change~ by ~weeping the surfflces of the tubular me~ber 20 and of the foot of the fins or turns 22a. ~his means a contact with the hotte~t part of the finned tube and, thereby, a suitable cooling.
In contra~t, where the air flow reache~ the ripple~
22c laterally as e.g. in case of arrow ~2, air is compelled to an undulatory flow that is to a repeated change of flow direction as ~hown in Fig. 5. 'rhis Per ~e mean~ an elevated flow resistance. In addition, where the ripples 22c are relatively deeper that is at the periphery of the fins, the air flow will part with the fin surface when leaving a wave crest and go over into a whirling ~otion as suggested by small arrows 4~ in Fig. 5. Flow resi~tance is further increased -thereby. At -the same ti~e by a breaking of the border layers of a laminar flow al~o the heat transfer coefficient is considerably increased.
28 Due to such locally increased flow resistance the flowing air will try to pa~ the finned tube at portion~
of lower flow re~i3tance of the fin gaps 2~ that i~ in the proxi~ity of the tubular ~ember 20 where ripples 22c already di~appear or are too ~hallow to cause any flow di~turbances. Con~equently, air flow is concentrated to region~ clo~e to the tubular member 20 that is to places of highest te~peratures a~ ~uggested by the density of the ho~t of arrows in ~ig. 6.
At the same ti~e - as has been hinted at - relatively low amount~ of air flowing at the rims of the fins improve the heat transfer coefficient by breaking the border layers of la~inal air flow 90 that also 9uch air a~ounts withdraw at relatively higher temperature~. ~ue to such flow conditions the temperature curve 38 of the with-drawing air beco~es - as it were - more horizontal which i~ equivalent to an increase of both the mean te~perature and, thereby, the intensity of heat e~change. This, how-ever, i9 the main purpose of the invention.
Since, in axial direction, ripples of adjacent fins occupy similar angular positions and, thus, register with one another, the cros~ sectional flow area~ are practi-cally the ~ame even in rippled portions of the fin gaps.
This ~eans a relatively uniform flow velocity which counteract~ a precipitation of impurities probably carried along with flowing air.
The exemplified embodiment according to l~ig. 7 is distingui~hed from the previou~ one just by that the 28 circu~ference of the fins i9 by half of the spacing greater than an integral ~ultiple of the spacing 9 and, thu~, in the direction of the axi9 30 of the tubular ~e~ber 20 ripples 22c projecting fro~ the turn plane of a pair of adjacent turn~ 22a in oppo~ite direction~
regi~ter with one another. Therefore, where ripple~ of a pair of adjacent turn~ project toward~ each other as at 28a in ~ig. 7, flow velocity increases. On the other hand, where regi~tering ripple~ 22c point away fro~ one another a~ e. 6- at 28b of the fin gap 28, the flow velocity be-co~e~ relatively lower. Such alternate acceleration and deceleration at the periphery of the fin~ further in-crease~ the flow re~istance and, thereby, the inwardly directed baffling action. Eventually, it ~ean~ an i~prove~en-t of heat tran~fer although probable precipi-tation of i~puritiea i8 ~o~ewhat enhanced as well which, however, a~ a rule, does not counterbalance the i~prove~ent obtained in heat tran~fer properties of the finned tube.
~he expedient~ shown in Figs, 5 and 6 a~ well as in Fig. 7, re~pectively, ~ay be e~ployed al~o ~i~ultaneously.
Such co~bination will be obtained if within an axial length or portion of the helical ~e~ber the ripple~ follow one another by different spacing~.
An exe~plified e~bodi~ent of a helical ~ember with differe~t ~pacings of the ripple~ i~ partly ~hown unfolded in ~ig. 8. It will be ~een that wil;'~in an a~ial portion or section S of a helical ~e~ber 22 there are four kind3 of ~pacings sl, s2, s3 and 9~ ~etween the ripples 22c which 28 gradunll~ increase fro~ sl to s4 while t-he ripple~ 22c ~215~SZ
lie alternately on opposite sides of a plane of sy~etry indicated by a da~h-and-do-t line 46 and coinciding with the plane of the turns of the helicoid. obviously, in case of such helical ~e~ber 22 ripples 22c of adjacent turns 22a ~lay occupy ~o~t varied ~utual angular positions and ~ay alternately overlap each other, register with one another and ~eet oppo~itely, respectively, ~s the case 0ay be. Thu~ effects of various flow re~istance~ will, as it were, comple~ent each other.
It will be understood -that not only spacing~ within a ~ection S ~ay be dif-ferent but the sections S the~selves may differ fro~ one another. Whut ~atters is that the ripples have ~t least partly different spacing~ and, -there-by, ensure a ~i~ultaneous presence of the effects of various flow resi~tances.
~ig. 9 shows, by way o~ exa~ple, an e~bodiment of the invention with which the e~ploy~ent of ripples 22c i9 re-stricted to dia~etrically opposite ~ections Sl and S2 of the turn~ 22a of a helical ~e~ber 22. Such finned tubes have to be built in 90 that the rippled sections Sl and S2lie in the flow direction of cooling air indicated by an arrow 48 in the drawing.
With the represen-ted e~bodi~ent the central angle of the sections Sl and S2 a~ounts to ~0 degrees. Preferably, no greater values for the central angles will be selected ~ince the significance of such expedient lies in that ripple-free sec-tions facilitate a re~oval of i~purities probably precipitated in the fin gaps. The absence of ripples i3S~
between the sections Sl and S2 ~oe~ no-t es~en-tially influ-ence the hea-t tran~fer propertie~ of the finned tubes according to the invention becau~e -the rippled ~ection~
occupy portions of the circumference o~ the fin~ where the velocity of air flowing between the fin~ i3 the highe~t and, thus, rippling is ~ost efficient as regards air flow and hest tran~fer.
Hereinbefore only embodi~ents have been described with which ripple~ project in both direction3 and to the sa~e extent fro~ the plane of the turns of the helical member, However, ripple~ on both ~ide~ of the turn plane may also have different heights. Moreover, for reasons of manu facturing facilitie~ the u~e of helical ~elnber~ may be preferable which have ripples projecting fro~ the plane of the turns in one direction only. In both ca~e3, the ripples are asym~etric with respect to the plane of the turns of the helicoid. One-sided ripples can obviou~ly be produced by ~eans of relatively siu~ple tooling even if the ripples have different heights~
A detail of a turn of a helicoidally finned tube provided with such a~y~etric ripple~ 22c is repre~ented in ~ig. 10. As will be appreciated, ripples 22c are provided but above the plane of the turn 22a~ the plane being indicated by its trace line 46.
The ripples 22c oL the exe~lplified embodi~ents shown in Fig~. 4 to 9 co~pose e~sentially 8 wavy form while with the embodiment shown in ~ig. 10 the~ are arcuate surfaces~
28 Both kinds of ripple form favour la~inar ~low. Detachment
3~ej2 o~ flowing air and, ~ore particularly, breaking of border layers and, thereby, increasing of flow re~i~tance ~ay be enhanced by e~ploying ripples of sharp angled cross 3ectional area~.
Such e~bodi~ent i~ ~hown by way of exa~ple in ~ig. 11 where ripples 22c have trapezoid shaped cros~ ~ectional area~. At the angles of the trapezoid the air flow parts with the ripple ~urface and turns into vortex ~otion where~
by la~inar flow i~ practically destroyed.
Obviously, cros~ sectional areas other than trapezoids ~ay be ~elected a~ well. ~or instance, the ripples ~ay have oro~ sectional areas in the for~ of acute-angled triangles. Other for~s of cro~s sectional areas ~ay suit in a like ~anner provided the depth of the ripples di~ini~hes toward the center of the finned tube as is required in co~pliance with the ~ain feature of the invention.
In case of both e~bodiments shown in l~ig~. 10 and 11, re~pectively, a radial cro~s ~ectional view of the turn 22a is illu~trated in ~ig. 12.
~urn~ 22a ~ay be fixed to a tubular ~e~lber 20 by ~eans of any o~ conventional ~ethod9 ~uch as welding, soldering, i~er~ing in ~etal baths and the like. ~ur-thermore, the turns ~ay be ~itted into groove~ on the cylindrical surface of the tubular ~e~ber, fixing being obtained by defor~ing the groove side~ and pres~ing the~ onto the foot of the turn~. Helical ~e~bers ~ay be produced by e~ploying b~nd~
of ~-shaped cro~s sectional area of unequal leg~. Upon 28 winding the band on-to the tubular ~e~ber -the ~horter leg of 1~53S2 the band will cover the tubular me~ber between sub~equent turn~ in the manner of a ~leeve. As has been ~entioned above, it is al~o po~ible -to die-roll the fin~ fro~ the body of the tubular ~e~ber in which case tubular ~ember and helical me~ber are integral with one another and the fin gap~ are broadening toward the peripherg of the ~ins.
Irre~pective of the way of manufacture it i~ importa~t that the plarle of the turns be perpendicular to the gener-atrice~ of the tubular ~e~ber or, what i~ the ~ame, to the principal a~is o~ the latter because such mutual positions of tubular ~e~ber and turn~ is of high significance with re~pect to both manufacturing technology and thermodynamic operational condition~. Namely, in ca~e of helical ~e~bers the plane of the turn~ of which i:3 perpendicular to the ge~neratrice~ of the tubular ~ember, ripple~ ~ay easily be provided prior a~ well as after winding up of a band. Even die-rolled fins ~ay be rippled during or a~ter die-rolling.
Aa regard~ thermodyna~ic~ f turn~ the plane of which i~
perpendicular to the generatrice~ of the tubular member ensure a maximum contact area be-tween a cooling ~edium and a finned tube.
Hereinbe~ore it ha~ ~ostly been assumed that the tubular ~e~ber ha~ a mediu~ of higher heat tran~fer co-efficient such ag wnter or conden~ing vapour or ~tea~l flowing in it wllile out3ide the tubular member be-tween the fin~ a ~edium of lower heat tran~fer coe~ficient ~uch a~
cooling air i~ flowing. ~Iowever, a finned tube according 28 to the invention i~, independent of the nature of the ~edia 5~SZ
participating in a heat exchange and of the direction of the latter, applicable everywhere where the heat of a mediu~ of higher heat transfer coe~ficient is to be transferred into a ~ediu~ of lower heat tran~fer coefficient.
Thus, e~g. conden~ing gase~ ture~ of vapours and liquid3 as well as ~a~es other than air ~ay be proces~ed by ~eans of finned tubes according to the invention.
~uch tubes are particularly suitable for being u~e~ in heat exchangers. However, it will be appreciated that they will ~uitably work in other ca~e9 or a~ individual pieces as well where a heat transfer i~ ai~ed at between ~edia of different heat transfer coefficient~.
~'~.153SZ
~IST 0~1 RE~T~'RENCE CHARAC~ERS AND ~SOCIATED TERMS
20 tubul~r ~e~ber 41 ~ection 20a generstrix 42 arrow 22 helical ~e~ber 44 arrow~
22a turn 46 dash-and-dot line 22b (outer) ri~ 48 arrow 22c ripple 24 arrow t te~perature 24a length v velocity 26 arrow 1 di.stance 26a length ~ ~pacing 28 fin gap S section 28a po~ition S1 ~ection 28b position S2 ~ection 3 axi~
32 arrow ~1 ~pacing 34 te~perature curve 92 ~pacing 35 ~ection ~3 ~pacing 36 velocity curve ~4 ~pacing 37 section 38 te~perature curYe 39 ~ection arrow ~`
Such e~bodi~ent i~ ~hown by way of exa~ple in ~ig. 11 where ripples 22c have trapezoid shaped cros~ ~ectional area~. At the angles of the trapezoid the air flow parts with the ripple ~urface and turns into vortex ~otion where~
by la~inar flow i~ practically destroyed.
Obviously, cros~ sectional areas other than trapezoids ~ay be ~elected a~ well. ~or instance, the ripples ~ay have oro~ sectional areas in the for~ of acute-angled triangles. Other for~s of cro~s sectional areas ~ay suit in a like ~anner provided the depth of the ripples di~ini~hes toward the center of the finned tube as is required in co~pliance with the ~ain feature of the invention.
In case of both e~bodiments shown in l~ig~. 10 and 11, re~pectively, a radial cro~s ~ectional view of the turn 22a is illu~trated in ~ig. 12.
~urn~ 22a ~ay be fixed to a tubular ~e~lber 20 by ~eans of any o~ conventional ~ethod9 ~uch as welding, soldering, i~er~ing in ~etal baths and the like. ~ur-thermore, the turns ~ay be ~itted into groove~ on the cylindrical surface of the tubular ~e~ber, fixing being obtained by defor~ing the groove side~ and pres~ing the~ onto the foot of the turn~. Helical ~e~bers ~ay be produced by e~ploying b~nd~
of ~-shaped cro~s sectional area of unequal leg~. Upon 28 winding the band on-to the tubular ~e~ber -the ~horter leg of 1~53S2 the band will cover the tubular me~ber between sub~equent turn~ in the manner of a ~leeve. As has been ~entioned above, it is al~o po~ible -to die-roll the fin~ fro~ the body of the tubular ~e~ber in which case tubular ~ember and helical me~ber are integral with one another and the fin gap~ are broadening toward the peripherg of the ~ins.
Irre~pective of the way of manufacture it i~ importa~t that the plarle of the turns be perpendicular to the gener-atrice~ of the tubular ~e~ber or, what i~ the ~ame, to the principal a~is o~ the latter because such mutual positions of tubular ~e~ber and turn~ is of high significance with re~pect to both manufacturing technology and thermodynamic operational condition~. Namely, in ca~e of helical ~e~bers the plane of the turn~ of which i:3 perpendicular to the ge~neratrice~ of the tubular ~ember, ripple~ ~ay easily be provided prior a~ well as after winding up of a band. Even die-rolled fins ~ay be rippled during or a~ter die-rolling.
Aa regard~ thermodyna~ic~ f turn~ the plane of which i~
perpendicular to the generatrice~ of the tubular member ensure a maximum contact area be-tween a cooling ~edium and a finned tube.
Hereinbe~ore it ha~ ~ostly been assumed that the tubular ~e~ber ha~ a mediu~ of higher heat tran~fer co-efficient such ag wnter or conden~ing vapour or ~tea~l flowing in it wllile out3ide the tubular member be-tween the fin~ a ~edium of lower heat tran~fer coe~ficient ~uch a~
cooling air i~ flowing. ~Iowever, a finned tube according 28 to the invention i~, independent of the nature of the ~edia 5~SZ
participating in a heat exchange and of the direction of the latter, applicable everywhere where the heat of a mediu~ of higher heat transfer coe~ficient is to be transferred into a ~ediu~ of lower heat tran~fer coefficient.
Thus, e~g. conden~ing gase~ ture~ of vapours and liquid3 as well as ~a~es other than air ~ay be proces~ed by ~eans of finned tubes according to the invention.
~uch tubes are particularly suitable for being u~e~ in heat exchangers. However, it will be appreciated that they will ~uitably work in other ca~e9 or a~ individual pieces as well where a heat transfer i~ ai~ed at between ~edia of different heat transfer coefficient~.
~'~.153SZ
~IST 0~1 RE~T~'RENCE CHARAC~ERS AND ~SOCIATED TERMS
20 tubul~r ~e~ber 41 ~ection 20a generstrix 42 arrow 22 helical ~e~ber 44 arrow~
22a turn 46 dash-and-dot line 22b (outer) ri~ 48 arrow 22c ripple 24 arrow t te~perature 24a length v velocity 26 arrow 1 di.stance 26a length ~ ~pacing 28 fin gap S section 28a po~ition S1 ~ection 28b position S2 ~ection 3 axi~
32 arrow ~1 ~pacing 34 te~perature curve 92 ~pacing 35 ~ection ~3 ~pacing 36 velocity curve ~4 ~pacing 37 section 38 te~perature curYe 39 ~ection arrow ~`
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Helicoidally finned tube, consisting of an inner tubular member and an outer helical member, the helical member having solid turns with generatrices perpendicular to the principal axis of the tubular member and with ripples which extend inwardly from the outer periphery of the turns and the depths of which decrease with the radial distance therefrom, characterised in that the helical member has rippled sections alternating with ripple-free sections, and both types of sections registering with one another, respectively, in the direction of the principal axis of the tubu-lar member, the spacing of the sections being substantially equal to a quarter of the circumference of the tubular member so that the rippled sections of the helical member occupy diametrically opposite positions on the tubular member.
2. Finned tube as claimed in claim 1 characterised in that ripples projecting in the same direction from a pair of adjacent turns of the helical member register with one another in the direction of the principal axis of the tubular member.
3. Finned tube as claimed in claim 2 characterised in that ripples projecting in opposite directions from a pair of adjacent turns of the helical member register with one another in the direction of the principal axis of the tubular member.
4. Finned tube as claimed in claim 1, 2 or 3 characterised in that within one turn of the helical member the ripples have at least partly different spacings.
5. Finned tube as claimed in claim 1, 2 or 3 characterised in that the ripples are asymmetric as regards the plane of the turns of the helical member.
6. Finned tube as claimed in claim 1, 2 or 3 characterised in that the ripples have angular cross-sectional areas.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000425391A CA1215352A (en) | 1983-04-07 | 1983-04-07 | Helicoidally finned tubes |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000425391A CA1215352A (en) | 1983-04-07 | 1983-04-07 | Helicoidally finned tubes |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1215352A true CA1215352A (en) | 1986-12-16 |
Family
ID=4124955
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000425391A Expired CA1215352A (en) | 1983-04-07 | 1983-04-07 | Helicoidally finned tubes |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1215352A (en) |
-
1983
- 1983-04-07 CA CA000425391A patent/CA1215352A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |