DE7422107U - Finned tube - Google Patents

Description

OIPL.-ING M. SC Dl «L> · '·» (

HÖGER - LEGAL RIGHT - GRIESS3ACH - HAECKER

PATENT LAWYERS IN STUTTGART

Λ 'tü7 5l b

1 - - 1 <'*. i ' _t J ■. ■>

June 27th 19

UNIVERSAL OIL PRODUCTS COMPANY TVn Uü? Pliiza — A l ^ oii- ^ ü ίίΐ &! ^v : t Pi'ospect. Roadc Deö Plair.es, Illinois, USA

Finned tube

"■ -" y * * *; * ' ί''eir-' ι, "j * y> T ~ * ΐ *
- ^ i ^ .. J WiIf--, ij _ l.- 1 j 1 1 t a finned tube with molded outer outward ; US SN inner: ribs, d ie from the pipe wall radially 997, March 1972), respectively . stick out inside. U.S. Patents 3,217,799, 3,463 37 as well as in some previous registrations is very 3 4 fal 39 ^ and 3 5t> 9 4 N 674 611 of October 11, 1967 the Anrr.oidorin (US-S 1972 and US SN 232 571 from 7 22-4 09p from February 2nd this is referred to,
- 2nd on their revelation 742210726.9. η

Λ ΊΟ781 b k - 163

June 27th 197'l - 2 -

described in detail that by special design of the inner and / or outer wall of pipes in terms of Wiirnipilbertra.punc; considerable improvements over smooth Pipes achieved can be grounded. As far as the outer pipe wall is concerned, so one has reached a state of the art in the formation of the ribs, according to which greatly enlarged surfaces and other favorable! properties can be achieved can show significant improvements in the coefficient of heat transfer for the liquid film flowing along the outside of the pipe. Based on these Connections it turned out that one for certain heat exchanger systems an additional improvement by changing the inner wall from the outside with ribs provided tubes sought to achieve. One of these attempts is to create helical or annular ribs on the inner pipe wall generate turbulence in the through the pipe to promote flowing liquid. Examples of such internal ribs and their use can be found in U.S. Patents

2 181 927, 2 220 726, 2 432 308, 2 913 009, 3 088 ^ 9 ^ and

3 612 175.

To make comparisons between the heat transfer performance of The following special form of the Sieder-Tata equation was used to enable pipes with differently designed inner walls set up:

h _i d _i / k = C ₁ Cd ₁ GZyU) ⁰ - ⁸ (C ^ u / l0 ^1/3 9u // i _w ) ° - ¹ ^ (1) In this equation:

H. = internal heat transfer coefficient, Btu / hr-sq ft- ⁰ P, d- = inside diameter of tube, ft;

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June 27, 1974 - 3 -

k = thermal conductivity of the liquid inside the pipe at a temperature at which there is still a closed Fl üPii gl-rfti sampling flow, btu / nr-sq 1 t- r / ft,

C. = internal heat transfer coefficient i ent (dimensionless constant),

G = mass velocity, lb / hr-sq ft, C = specific heat, Btu / lb ° P,

u · "- viscosity of the liquid inside the tube at the mean temperature at which a closed Liquid flow is present, lb / ft-hr,

u _w = viscosity of the liquid inside, of the pipe at the average WanQoe,;. temperature, lb / ft-hr.

The equation is applicable to a single-phase liquid, either with a smooth interior or one with internal ribs provided pipe forms a turbulent flow, provided that the correct value C- is used. The internal heat transfer coefficient C. can be determined experimentally for a specific pipe with the help of a modified one Wilson recording technology, as described in the magazine "Industrial Engineering Chemistry Process Design & Development" Vol. 10, No. 1, 1971, pages 19 to 30 in the Work "Steam condensation on vertical rows of horizontally corrugated and flat tubes" by J.G.Withers and E.H. Young is described. Although it is generally desirable to design a pipe so that C. is a maximum value,

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June 27, 197 ¹ y

there are many instances in which it might be desirable for C. to have a lower but predetermined value. This c: <. ,, "*. ^: ",, i"", nn (-o α!,. 1-1 hoi ^ riiplRWPiüP in K / i LJ en erpteoen, ir, who have very strict restrictions with regard to the pressure drop. In cases where the designer has regard to the choice of the design of the inner wall of the pipe is limited by limited options, metalworking or because of the need to save material, it may be important not _{to achieve the absolute highest value for C 1} , but the maximum possible value for C ₁ From the foregoing it is clear that it is very desirable to be able to predict the heat transfer performance as a function of the geometrical shape of the girders or ribs on the inner wall of the pipe.

Based on the stated prior art and the Prob lenat U- shown above: the invention is the Task based on a metallic finned tube as a heat exchanger tube suggest which one inside it like that is designed, ate a pre-improved heat transfer performance results.

This task is achieved by a finned tube of the type described at the outset Type solved, which is characterized according to the invention in that the inner ribs are multi-threaded Are ribs, the angle of which with a plane perpendicular to the longitudinal axis of the pipe is less than 60 °, that between adjacent inner ribs in the longitudinal direction of the pipe in section are flat inner wall areas that the inner ribs a Have a cross-sectional profile that includes two side lines,

-R-

'· - ■'. - ·. · -.:; _ ':. ο :. - nnev.w-ir.'lü-vrei jne "'.!' _ -ieri ^ Γ ¹ 1 t ζ ο \ ~. oer inner: -. :: γ ·· :; verb i :: · ϊο. \ ; .η.ΐ each consisting of a ko: kav and a '. ■::.'. ··: ·: ;; ■ '> · "".: -. ·;>: -. Curve η te: 1 : u? ar ^ orin; e3et "t are, and that the '. ·.' · .- :. : vT;:. l ·: "--r side line :: opposite the tip of the rib: · :: ■.! i'ii.:.:.: ·. offset on the outside ur.d is at a distance from the. 'ν ·! *. ·· - Ι' .- ϊ-π "which is', ·:! one than the height of the rib. In ei: · ->. ■ '• - ■ preferably ^ er-i embodiment of a finned tube according to the: ■': ■ · ":: vi \ inr, which is composed of I-ietali _s improved V. ' ^: i: -: ro ";be:" - i: ragur.g to or from the inside of the pipe f LI e ^ e. · -.:; ·?:; Liquid achieved by at least one ar .geformr.v? outer v; end-shaped rib with a predetermined rilrpe .'- i'-spacing and a predetermined pitch angle provided Lsv., because. ⁵ several molded helical inner ribs are vorgeso'neri, which from the inner wall of the tube stand inward in the radial direction so that the inner ribs have an angle of less than 60 (measured with respect to a perpendicular to the longitudinal axis of the pipe) and a distance between the individual ribs. each other, which is greater than the distance between the individual rib threads of the min lest.ens an outer rib, but the pitch angle of the at least one outer rib and the pitch angle of the inner ribs differ in size and / or direction from each other. In this finned tube, the inner w; i: ii of the tube is shaped so that a profile results in a longitudinal section in which a flat intermediate piece is present between adjacent inner ribs, the inner ribs having a cross-sectional profile which two: 'ei th! inien comprises, eg the flat intermediate corrugation or '.'. '' indbereich before the pipe connecting between adjacent ribs with the ... '■ points of the same, with the.'. lateral lines respectively

A .'10781 b U

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June 27, 1974 - 6 -

are composed of a concave and a convex section, which merge at a turning point, which is offset in the radial direction outward relative to the tip of the ribs and which at a distance of this point, which is less than the height of the rib.

The object on which the invention is based is solved by a metallic heat exchanger tube according to the invention, which multi-thread on its cylindrical inner surface or several individual helical, molded-on ribs besiezt, which has other advantages. The function of the ribs is to swirl the liquid flowing in the tube, so that along the The pipe wall cannot form boundary layers that could reduce the heat exchange between the liquid and the pipe wall would hinder. Although some important considerations regarding the geometrical shapes have already been made earlier which influence the heat transfer performance, it has not yet been possible to establish a connection between the geometric shapes and the heat transfer capacity that would enable the internal heat transfer coefficient predicting changes in geometric shapes. U.S. Patent 3,217,799 deals, for example, solely with the ratio of the axial distance between adjacent hips to the height of the Ribs as the crucial parameter. While this relationship is indeed essential, its knowledge is not sufficient to approximate the most favorable pipe design in a way that predicts internal heat transfer efficiency or could be optimized.

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June 27, 197 ^ - 7 -

An earlier registration (official file number P 23 10 315.3) the applicant discloses a relationship between C. and a geometric parameter, which is called severity-factor is designated. This parameter 0 is a dimensionless quantity which defines the rib height e, the slope ρ and the Inside diameter d. linked according to the following equation:

0 = e ^£ Vpd _i (2)

In the earlier application mentioned above, it appears that for tubes having a single helical inner

Rib a maximum value for C. is possible and that this value is reached at a certain value of 0 and not in a range of V / erten for 0. After it has been determined that the maximum value for C. for pipes with a single helical inner rib is obtained when 0 = 0.365 x 10, it is possible to construct such pipes in such a way that between the achievable maximum value and any desired value for C. can be obtained from the value for the smooth tube.

Although the link between C. and 0 for pipes with a single helical inner rib was developed, this relationship is also of interest for pipes, on the inner wall of which several perforated ribs are formed. It has been shown that it is possible to use multiple helical ribs for a given value of "severity" or the pressure drop has a higher heat transfer coefficient than with pipes with a single turn 1-

Λ. ', 07Sl b ■' - ■

June 27, 107- ^{| J} - ■ · -

i'Oi'mi gen inner rib rr.'J fl 11 cn i :: '... i'.e; the vr-i '] ier; en1or. . "'. rf charge plays nor sever ity-f actor ¹ Z ¹ a roller blind .- ·. 1 s Rrihrner.e le-ent the present Krf i tr! ung st ··.:! * I' · -! · ·. ··! · ·: ■ ::. "■ '; ■ r ·;:. ': herunp? : e 3 state-of-the-art technology, as it is the ■■ roI ie of the hipster. Torrn and the role of the dimensions of the rib :. and de: ·: Rohrs in improving the heat transfer performance in pipes rr: with several helical inner: \ ippeii V. J arct.:-1 it. The present E r ί 'i η u UiTg bcfa ß tsic hi η sbe r. rod ere τη i t. i ;: η e: er: pipe \> i a η ei u η gen, which are designed in such a way that e: n cross-section prcfi 1 in the longitudinal direction shows flat intermediate pieces "between inner ribs, where: -v>; Isclien the rib splinter zev \ and the intermediate pieces from convex and concave sections i'.uöamnengeset '/. te intersectioninit: η "1 i egen.

The mentioned iJJ-PS "';': 81 39'l oiTenbai't different embodiments of pipes, in each of which several outer ribs and a single inner rib or edge are provided . Although the distance between the individual rib passages of the single inner rib In the case of a tube according to US Pat. No. 3,331,39, is of course greater than the distance between successive rib threads of the outer ribs, the pitch of the inner rib is the same as the pitch of the outer ribs, since the inner rib is simultaneously with the embossing of the Courage is created which delimits two adjacent outer ribs. The reduction in the outer diameter of the tube, adjacent to the inner rib, results in the known tube being less stiff and thus more sensitive to vibrations than tubes according to the invention. in which the pitch angle of the helical inner ribs is greater than the pitch angle of the outer ribs

Λ ΊΟ781 b

k - \ * 'j'j

June 27, 197 ') - 9 -

'! er 'ιΐΛ'ϊ j ntiurin i'ühi'l also to titier grüir> ei -'- 'ii Vurial lüiiabi'-eiU iir ·! .! or · construction j because the beet, the shape, the number and the angle of inclination of the inner ribs can be selected according to the influence of Moser parameters on the heat transfer and the pressure drop and is not already largely predetermined by the shape of the outer ribs. The finned tube according to the invention also has a uniform wall thickness below the ribs, with the exception of those parts that are reinforced by inner ribs. In contrast, in the case of the finned tube according to US Pat. No. 3,381,394, if this is produced, for example, by a method described in US Pat. No. 3,559,437, thinner wall areas can occur in the vicinity of the inner ribs. In order to achieve a given strength, less material is therefore required in the finned tube according to the invention.

After manufacturing and testing a number of finned tubes, each with a plurality of internal ribs of different profiles and dimensions, it has been possible to develop a nrither.at isches model or equation which gives a fairly accurate prediction of the internal heat transfer coefficient 'f i ~ i enter; C. enables. It is the other way round, ν. ··: · :: Γ. ·: -.: '.' ::: bos ■ iir.nter value of f ärmeübertragungskcef izienten C is desired, it is possible, certain parameters of the finned tube as zH the base width of the ribs, which lead to the desired value of C. predict . · Within the range of applicability of the equation, the heat transfer performance seems to increase when the rib height is increased IIPA when the ridge width is decreased. There are, however

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Λ no78l b'I

k - 163 p

27-June 197 '"- 10 - i

many factors that shape the geometric shape of the inner Within be ^ i π Π u Ren = - °> ο, for example, the machinability dey metals limit the extent to which the metal of the tube can be preformed radially inward, so that the maximum rib height is limited. When narrow internal ribs If desired, it can prove to be a problem to find suitable metalworking tools to produce the to manufacture inner ribs. On the other hand, ribs of greater width can be produced more easily than narrow ones Ribs and also prove to be more resilient when brought into contact with an erosive liquid will. However, these advantages may come at the expense of an inordinate amount of material for the pipe or pipe bought at the cost of having a surface on the outside of the pipe that contributes to the heat transfer.

The above equation 1, which was developed to predict C., can be written as follows:

C ₁ = 0.0264 + (22.1) (0) (1-b / p) (e / y) ^1/3 (3) In this equation:
0 = severity factor (equation 2)

b = foot or base width of the inner ribs (in the axial direction)

ρ = distance between the inner ribs, measured between corresponding points on adjacent ribs in axial direction

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A IIO78I b

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June 27, 1974 - 11 -

e = height of the inner ribs

y = Π rib cap height, measured in radial Π ί ent un ^ - /. wi sohen the top of the rib and the turning point on the flank of the rib.

The equation is applicable to finned tubes which have helical inner fins in their interior, with between adjacent inner rib passages are cylindrical inner wall areas. To achieve excellent finned tubes According to the invention, the following limits must be observed when applying the above equation: k; p should be between 0.10 and 0.20, 0 should be less than 0.25 x 10 ~ and p: v should be between 1.50 and 5.00.

Further details and Vo: · "':.' Ile of the invention are given below Explained in more detail with reference to a drawing and / or are the subject of the claims for protection. In the drawing show:

Fig. 1 is a partial representation of a finned tube according to the invention, the larger part in axial Direction is cut;

Figure 2 is a graph of the internal heat transfer factor C. as a function of the severity factor 0 for certain finned tubes with several helical inner fins and flat wall areas between the ribs;

3 shows a graphic representation of the relationship between the values of the determined in experiments

- 12 -

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June 27, 1974 - 12 -

Heat transfer factor C ^ and the precalculated Values for various ripper tubes with several spiral-shaped inner ribs and intervening flat wall areas;

Fig. Ί

b i l; 7 different preferred rib profiles as shown in A finned tube of predetermined severity can be used, the profiles in cross-sections are a plane perpendicular to the rib;

Fig. 8 is a view like FIG ^r> corresponding illustration for a widened rib, wherein the cross section is taken in the axial Kichtung.

Fig.?

to 11 are graphs showing the calculated b from the equation 3 Influence of changes in the severity factors (d and the ratio of Kippenabir.essungen: p and s: y ^ n d on the inner V / AER üioübertragungsfaktoi · 'Z. illustrate and

Fig. 12 is a graphic representation of the dependency of the internal transmission factor from the pressure drop for two different finned tubes with helical inner ribs.

Tm shows the axial section through the inventive Finned tube 10 in Fig. 1 that the finned tube 10 has several outer fins 12.1 * 1 and several inner ribs 16.18

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ν.;: '·. ·: ·'.: ξι. ΓΊ-i "• u / .ei'en ribs 12,1 ¹ I and the inner ribs 1 ■, - ^: ·. ·; -: ·! · It: -.- ·. Νorzugz-v .--. ?; se at the same time on the wall area 20: ·. · - ■: ·.!:: - ·. ·.: · ':: r_: 1.'vr-'f".r.-rr _s vr'ihrond sich ir. Inside the: -. : yy ·· "':.: ·' :: rr a rr't:. ^: ute :: provided thorn (not shown) ': ■ ·:" ::.: · _ · "..!'! e Ir.r.er.war.d 22 of the finned tube lCj is cylindrical: ■. "".. · ". .: ·:. ■ ":! ·.:". ·? 1 ^ r interruptions through the inner ribs 1 ', 1 :. The width of the inner ribs is denoted by b, 'iir Ab. «'..:"! Rd ::; ■ :: see adjacent inner ribs is denoted by ρ V.-.- ze icn :: e "and d.er The helix angle of inclination is θ be: ". · - ■ - ■! :: ir. ■ - ··., V.-jbei © against a plane perpendicular to the pipe axis r -.>-; - s.; E: . v; ird.

! '■: · - e i nr.rilnen parameters were actually herger.teliteo Finned tube according to the invention as it is in section ::. i-'ig. .1 g ^ show * "is selected as follows:

- ■ = \: '' 7 ^J , "; ρ = Ο, 3 '· 3"; d, = 0.820 "; 0 = 0.116 Χ 10 ~ ² ; • = -Λ, ->·" - ■ »"; y = 0.0089 "; b / p = 0.2; e / y = 2.00; C. (previously

z-ir / r < = "i, 052; C. (measured) = 0.0 ₅ 2; β = yf; number of Ι ';;':.;: ·.-on ribs = 3; number of inner Ribs = 6; material = ':'. Up for.

Fig. 2 shows a graph of the severity factor 7 < ,: related to the internal heat transfer factor C. for a number of tubes. The lower curve 2b represents the line for finned tubes which have a single rib in the form of a rib and which have a curved inner v / it is disclosed in the earlier application (. · <::. ': .iohes file number P 23 10 315-3). The upper line 28 represents the performance line for a finned tube la: ¹ , which has several helical inner ribs and

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June 27, 1974

which has flat inner wall areas between the ribs. The curves 26 and 28 intersect at the point C- - 0.0264, ie at the value for tubes with a smooth inner wall, where 0 = 0. In general, the lines 26 and 28 show the heat transfer characteristics of the tubes and the M ε H, the improvement that can be achieved compared to a tube with a smooth inner wall. The relationship between heat transfer and pressure drop is clear from FIG. 12, where the relationship between the heat transfer factor C. and the friction factor f is shown. The pressure drop is directly proportional to the friction factor when comparing pipes of a given diameter with the same Reynolds number. The improvement in the heat transfer factor C. for a given pressure drop and for tubes according to the invention (for which line 29 applies) compared to the previously known tubes (for which line 30 applies) is given in Pig. 12 clearly. The previously proposed tubes to which line 30 applies are described in the aforementioned earlier application and have a single helical inner rib and a curved inner wall profile.

FIG. 1 shows a graphical representation of the experimentally determined internal heat transfer factor C. compared to the internal heat transfer factor C. determined in accordance with equation 3 for several finned tubes according to the invention, each with more rigid helical internal ribs and flat! No. ti wall areas between the rib passages and for different rib shapes. The graphical representation shows *? L11 very precise relationship between the advance

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Λ ^J l073l b k - 163

June 27, 197 ^ - 15 -

</ ΰ

said and the experimentally determined values, since the various points corresponding to the experiments, especially in the area for C.-0.0'Ib very close to the line 32, so that one can speak of a practically perfect connection through equation 3. As from the Equations 2 and 3 clearly play the height, the width, the shape and the spacing of the ribs of the inner Ribs I6, 18 all play an essential role in determining the heat transfer factor and pressure drop of a particular finned tube.

Figs. 1) to 7 show four different rib profiles, which were determined in a plane perpendicular to the rib axis, with all ribs having the same width b (cos θ) and the same rib height e, which in the profiles shown - ■ b (cos θ) / 2. Each of the rib profiles according to FIGS. 4 to 7 has a side line which is composed of a concave curve part 36 and a convex curve part 38. The curve parts 36, 38 abut one another in the area of a turning point 'JO. The ribs ΊΊ shown in profile, which are delimited by the curve parts 36 and 38, have a rib cap 46, the height y of which is equal to the radial distance between a rib tip Ί8 and the turning point IO. The ribs ΊΊ also have a rib base 50 which has a width b (cos θ) and a height ey. The various rib profiles in FIGS. Ί to 7 differ in the different heights y of the rib caps 46, the ratio of e: y = 1.50, 2.00, 3.00 and 4.00 in the four figures . The rib profile shown in FIG. 8 is identical to that according to FIG. 5

- 16 -

Λ - ¹ JOTB ι b - -J

k - Ιο;

2'ϊ. June IQ? '''- 1 ·' -

icieri Li sc-h with the exception of ά'ι'λ die ':'. '. pier-i-tar pe and the
Rib base by length i "._ (c '<c ^) broader.:. I :: d, where the noise f / ·: \ _ d · r lire" ·. · ■ · -: e; -. f'.a ■ :: ·· :. R i: r · ·:. · - :. \ - δ ■ · ί -: · γΛ. · rricht. Since the FLc. % ei: - "- ::.".;·; ». · rs ch :: Lt" · r ;: ¹ · :: die iiippe ", Vi ^:, as he cioh in axirtlei-: ii cht'i :: ^ "r- ^ ib ·, W'-ivieri di- · ir; Fir. 5 vorhrtridenep r'.rt. · i sb" -f * eM!:; Fir. ^{l <} :: u> · i 1 i] Ί ': .-. ? h <~ -r. : -. "ζοη, polygamy - ini * i \ (cos ei) - u in d» .-: i F. ·; ', ·· ": ·! / ·. · ~ ν er 1. ^: !:. £ * are.
With a rib re'nr tp.j ·, ce ^ -djener! '.-.-.- rte :. rilr; er: severity factor lüiii den Abstarid :: yjs; - ;. '.'! i d '"- ^v i R i pperir \'! r ::? e: · leads the broader basis M ^ r ri Ippo: inr "fi is j'er. ^: ir ·. ? ip *. R "u a lower Vläi'meiiberf.i'a.runnsi - '. Oe-f f iz i'Mi' - 'ü than d ^ n profile
according to FIG. For example, it's easier to use a mandrel
Making wide grooves than buckling a mandrel
Grooves. Furthermore, it is easier ·, · the ΐ '·· 1, α11 of the gla'. 'Eri tube in the manufacture ... it Ri ppenr obres so vu vei'dringt ^ n that wide ribs arise, and no narrow ribs. If there is an erosive or corrosive one through the finned tube
PJüßigkeit is to be directed, also results from
wider ribs less wear. It is quite difficult to grind grooves in a dome which lead to the curved profiles according to Fig. > \ To 8. It has been shown, however, that satisfactory results can also be obtained if the curve parts 36, 38 are approximated by straight lines, as is shown, for example, by the dashed lines 36 ¹ , 36 ″ and 38 ′, 38 in FIG '' is indicated. The advantage of the approximation of the curves by straight line parts is that the very thin grinding wheels which are used to produce the flutes in the mandrel are provided with straight grinding edges

- 17 -

Λ '107 31 b

k - IG ',

June 27, 197Ί - 17 -

which can be easier to manufacture and easier to erect '.M'hri i'-en aim]., As a curved profile ».

Pig. 9 shows a graph of the relationship; ^t .w laugh ötin severity factor 0 and the heat transfer coefficient 1 were used by C. according to equation 3> v: if 1 for b: p the value 0.15 is assumed, while e: y forms the parameter, the graph shows that for a given value of the severity factor 0, the value of C. increases when the ratio e: y is increased from 1.5 to 5.0. The lines 51, 5?, 5'i and 55 correspond to aen values 1,5-, 2 .; 3 and 5 for the ratio e: y. With the aid of graphical representations, as shown in FIG. 1, one can easily determine the shape of the ribs which must be dug in order to obtain a given worm transfer factor C for a given severity factor and for a given ratio of b: p eir. From Fig. 9 results: z \ z \\ example: eise, with a st? Verity factor of 0 j 15: ■: 10 '"for'?. A fourth of 0.067 can be obtained Rib shape with a ratio e: y = ·,, 0 v / fihlt, v / ie di is shown in Fig. 7. The rib, which is easier to manufacture, has a wider rib cap, according to Fig. K, with v.'elcher e / y = 1 , 5 is v; ürde for a severity factor of C, 1-} χ 10 "i: u a heat transfer factor C. = 0.059

Fig. Vj shows a similar to FIG. 9 graphical representation of the relationships according to equation 3, where C. over various Ratios of b: p is plotted. The representation shown in Fig. 10, which is for a constant value of the severity

-2
factors of 0 = 0.1 χ 10, indicates that the value of

- 18 -

b - 18 τ f ³ Γ V Fl Y> Π Ί JTiTTj f ^ _ V / θ Π Π riss 22nd Λ '107 ^ 1 k - 163 197I June 27 Γ Hr- i

ratio b: p increases. Lines 62 and 63 counted for a Ratio e: y = 2 or 5. The graph thus makes it clear that the heat transfer performance improves if one reduces the width b of the ribs compared to the distance ρ of the same.

Fig. 11 shows the graphs of FIG 9 and in which unte _r based on the equation 0) C .. various values of e 10 graph similar to Fig. Y is applied. The illustration according to FIG. 11 applies

-ρ for a fixed value of the severity factor 0 of 0.1 χ 10 It can be seen that for a given precaution b: p the value of C. increases as the ratio e: y increases. Lines 71 and 72 correspond to the ratio b: p = 0.1 and 0.2.

From equation 3 and FIGS. 9 to 11 it is clear that it is possible to use a finned tube provided with outer fins, which has several inner helical ribs, with flat inner wall areas between the individual rib passages are to be designed in such a way that there is an improvement over the prior art and also so, iaß for the heat transfer coefficient C ^ a certain Value results. For example, if it is assumed that a pipe has an inside diameter of 0.8 "and that the coefficient of heat transfer C. due to the given ratios = 0.056, then the following procedure can be used in order to to determine the width b of the rib:

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June 27, 1971 - 19 -

a) It should be assumed that the maximum possible rib height e = O_, O17 ^r >"* and zw« "\ r due to d <= r known restrictions in metalworking.

b) Furthermore, it should be assumed that the smallest rib spacing ρ which can be achieved with six helical ribs ist = 0.3 ". The angle of inclination of the ribs results automatically when the pipe diameter, the rib height, the number of helical ribs and the rib spacing are known.

c) The value 0 is calculated from equation 2. The result is: 0 = e ² /? A _i = 0.128 χ ίο " ² .

d) The rib shape is selected so that e: y - 2, as shown in FIG. 5, since tilting of this type is easy to manufacture on the one hand and on the other hand are sufficiently resistant.

e) Equation 3 is solved:

C _± = 0.026 ') + 22.1 (0) (1-b / p) fe / y] ^1/3

0.056 = 0.0264 + (22.1) (0.0128) (lb / p) (2) ^1/3 1-b / p = 0.833
b / p = 0.167-da ρ = 0.3
it follows that b = 0.167 (0.3) = 0.050 "

- 20 -

Claims (5)

A 4O78l b k -103 June 27, 1974 - 20 - Proverbs 1) finned tube with indicated outer and inner fins, which protrude radially outward or inward from the pipe wall, characterized in that the inner Ribs (44) are multiple helical ribs, the angle of which with a plane perpendicular to the longitudinal axis of the pipe is less than 60 that between adjacent inner ribs (44) in the longitudinal direction of the tube in section are flat inner wall areas (22) that the inner ribs have a cross-sectional profile that includes two side lines that form the flat ones Inner wall areas (22) connect with the tips (48) of the inner ribs (44) and each consist of a concave and a convexly curved curve part (36,38) are composed, and that the point of inflection (40) of the side lines opposite the tip (48) of the ribs (44) is offset radially outward and at a distancefyj from the tip (48), which is smaller than the height ie) of the rib, 2) finned tube according to claim 1 with at least one outer molded helical rib with a · * ¹ . predetermined distance between the rib threads and a predetermined inclination angle, characterized in that the helical inner ribs have a distance between the rib threads, which - 21 - .Jui _: L 1'Ί7 Ί - 21 - is greater than the distance :: wi :: chen the rib edges egg at least one outer :: rib ΠΓ ', Ι'ί) and d ^ f; die i-'t-MPLincsYiinkel dor ri ndea tons one; ^: U ⁿ VJR:! I rib (12, ^I:! ') And the inner ?: · ^"1 :: rib ■.' 1 ', 1 ^ο,:. · · ■' in nrößo and / or direction νer3chi edο :: sir: d. 3) finned tube according to claim 1 mil ringförni re: i outer. Ribs, let have a predetermined distance from one another in the longitudinal direction, a? .- characterized by the fact that the distance between the length of the EIppeng.änge the inner hi pr.er. (- '^) greater η Ig is the distance -between the: .outer-n ribs (12,1 ¹ I). Ό Ribbed tube according to claim 1 to ^T », characterized in that the ratio of the Ri p * -, enbrei te (b) in the axial direction to the spacing (p) of the rib threads is between 0.10 and 0.20, that the ratio the rib height (e) to the distance (y) of the inflection point (Ί0) from the tip of the rib ('4 * 0 between 1, SO and' 3.0 and that the value of the severity factor (0) is less than 0 , 0025, where ΐ - e ^ / pd. And where d is the maximum inside diameter of the rib tube. 5) finned tube according to claim 'ί, characterized in that for the internal heat transfer coefficient C. die the following equation applies: C = O, O26'I + (22.1) (0) (1-b / p) (e / y) ^1/5 , where 0 ranges between 0.00057 and 0.0025; where e ranges between 0.0125 and 0.075; where ρ ranges between 0.25 and 0.70; wocei d ^ ranges between 0.20 and 3.00; wherein b ir. the range between 0.02 and 0.15 and wherein y is in the range from 0.0065 to 0 _sec 05th