Note: Descriptions are shown in the official language in which they were submitted.
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
-- 3 --
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
-- 4 --
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
~,
5352
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
-- 6 --
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?
-- 7
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
35Z
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
-- 13 --
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
121535Z
-- 14 --
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
12153S2
- 15 -
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~
-- 1 7 --
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
- 18 -
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
-- 19 --
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
- 20 -
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
~`
