Grooved tubes for heat exchangers for single-phased typically aqueous fluids

[0001] The invention relates to the field of pipes for heat exchangers, in particular the field of pipes for heat exchangers using a medium called "single phase", i.e. a medium for which the heat exchange does not include an evaporation and condensation cycle, the media called "two phase" are those which bring heat hidden in evaporation and condensation.

Background Art [0002] A large number of documents are known describing the geometry of grooved pipes used in heat exchangers.

[0003] By way of example, patent application EP-A2-0 148 609 may be mentioned, which describes tubes with triangular or trapezoidal grooves having the following characteristics:

- the H / Di ratio between 0.02 and 0.03, where H is the depth of the grooves (or the height of the fins) and Di is the inside diameter of the grooved pipe,

- helix angle β in relation to the pipe axis between 7 and 30 °,

- the S / H ratio between 0,15 and 0,40, where S is the cross-section of the groove,

- apex angle α of the ribs between 30 and

60^about.

These pipe characteristics are adapted to phase change factors, and the pipe parameters are analyzed separately during refrigerant evaporation and refrigerant condensation.

[0004] Japanese Patent Application No. 57-58088 describes pipes with V-shaped grooves, with H comprised between 0.02 mm and 0.2 mm, and with an angle β comprised between and^about.

Similar tubes are described in Japanese Patent Application No. 57-58094.

[0005] Japanese Patent Application No. 52-38663 describes tubes with V or U-shaped grooves, with H comprised between 0.02 and 0.2 mm, pitch P comprised between 0.1 and 0.5 mm and angle β comprised between 4 and

15o.

US Patent No. 4,044,797 describes tubes with V or U-shaped grooves similar to previous tubes.

[0006] Japanese Utility Model No. 55-180186 describes tubes with trapezoidal grooves and triangular fins, with a height H from 0.15 to 0.25mm, pitch P from 0.56mm, apex angle α (the angle called in this document θ) typically equal to 73o, angle 30o and average thickness

0^,44mm.

[⁰⁰⁰7] ^Patenty ^US No. ^{4,545,428 and} No. ^4,480,684 about^piSUJ^and pipes with V-shaped grooves and triangular ribs, with a height H between 0.1 and 0.6 mm, pitch P between 0.2 and 0.6 mm, apex angle α between 50 and 100 °, line slope helical β comprised between 16 and 35% [0008] Japanese Patent No. 62-25959 describes grooved pipes and trapezoidal ribs with a groove depth

H between 0.2 and 0.5 mm, pitch P between 0.3 and 1.5 mm, with the average width of the grooves being at least equal to the average width

<td>ribs. IN</td><td>example</td><td colspan="2">pitch P is</td><td>0.70 mm and angle</td>

<td>tilt</td><td>helix</td><td>β</td><td>thi^{t 10}^</td><td></td>

<td>[0009] Na.</td><td colspan="2">end, patent</td><td>European</td><td>EP-B1-701 680,</td>

<td>granted</td><td>the applicant,</td><td></td><td>describes the pipes</td><td>grooved, with</td>

grooves with a flat bottom and ribs of varying heights

H, the helix angle β between 5 and 50o, the apex angle α between 30 and 60 °, in such a way as to obtain better parameters after pressing the pipe and mounting in the exchangers.

[0010] In a general way, the technical and economic parameters of the pipes, which result from the choice of a combination of pipe defining elements (H, P, α, β, the shape of grooves and ribs, etc ...) generally refer to four types of considerations:

- on the one hand, the characteristics relating to heat transfer (heat transfer coefficient), the field in which grooved pipes are much more favorable than non-grooved pipes, so that with equivalent heat exchange, the necessary length of the grooved pipe will be less than the length of the non-grooved pipe .

- on the other hand, the characteristics relating to pressure losses, small pressure losses allow the use of pumps or compressors of lower power, size and cost,

- in addition, the possibility of industrial manufacture of pipes and the speed of production, which determines the price of pipe production at the pipe manufacturer

- finally, characteristics relating to mechanical properties typically in connection with the type of alloys used or the average thickness of the pipe, the thickness that determines the weight of the pipe per unit length, and thus affects its production price.

Problems raised [0011] On the one hand, as is apparent from the prior art, there is a large number and very large variety of grooved pipe tips that generally aim to optimize heat transfer and reduce pressure loss.

On the other hand, each of these tips themselves usually offers a wide range of options, and the parameters are generally defined by relatively wide ranges of values.

Finally, these guidelines apply, when specified, exchanges with two-phase media, i.e. where a medium is used that evaporates in a part of the medium circuit in the exchanger and which condenses in another part of the circuit, and the same grooved pipe is not equally efficient at evaporation and condensation.

Ultimately, the skilled person has a lot of difficulty getting the most relevant prior art data from such a large amount of data, sometimes conflicting. However, the skilled person knows that a typical commercial pipe with triangular ribs as shown in figure 1 has typically the following characteristics: outer diameter De = 12 mm, rib height H = 0.25 mm, wall thickness Tf =

0.35 mm, number of ribs N = 65, helix angle β = 18 °, apex angle α = 55 °.

The invention relates to pipes or exchangers in the field of single-phase media and for reversible applications, i.e. pipes or exchangers which can be used with water or water with glycol as cooling or heating agents, i.e., or typically for cooling air in exchangers of air conditioners , or typically for heating air in said exchangers.

[0013] The Applicant has therefore researched and developed pipes and exchangers at the same time economical, with relatively low weight per meter, increased heat exchange parameters, and low pressure loss, for applications or fields that use single-phase factors.

Description of the invention [0014] According to the invention, metal grooved pipes, Tf thickness at the bottom of the groove, with an outer diameter De, typically intended for the production of heat exchangers using a single-phase type cooling or heating medium, internally grooved by N helical fins, with an angle α, with height H, base width Ln and helix angle β, with two successive ribs separated by a groove with a typically flat bottom width Lr, with a pitch P equal to Lr + Ln, they are characterized by:

a) the thickness Tf of said pipe is such that Tf / De is equal to 0.023 ± 0.005, where Tf and De are expressed in mm, with De having 4 mm to 14.5 mm,

b) said ribs are of height H such that H / De is equal to 0.028 ± 0.005, where H and De are expressed in mm,

c) the number of ribs N is such that N / De is equal to 2.1 ± 0.4, the corresponding pitch P is equal to n.Di / N, with Di equal to De-2. Tf and De are expressed in mm,

d) said base widths Ln and Lr are such that Ln / Lr is between 0.20 and 0.80,

d) said apex α is from 10 ° to 50^about,

e) said helix angle β is from 20 ° d^about 50 °, so that it is possible to use a typically single-phase medium typically containing water or water with glycol as the cooling or heating medium, so as to achieve an increased heat transfer coefficient for heating and cooling and low pressure loss, and so as to have a low weight / meter.

[0015] Indeed, by studying single-phase medium heat exchanger systems, unlike two-phase medium systems, in which part of the system with respect to the heat source is the place of evaporation, while part of the system with regard to the cold source is the place of condensation, the applicant could observe that grooved pipes that had higher parameters with a two-phase medium could not be adapted to single-phase media.

The applicant has managed to obtain pipes simultaneously adapted to single-phase media, with low pressure loss and low weight per meter, thanks to the combination of the above-mentioned means a) to e).

Especially since, contrary to the state of the art, these pipes have at the same time a small number of fins and a relatively small thickness.

Description of the figures [0016] Various parameters used to define the pipe according to the invention are shown in figures 1a and 1c to illustrate their meaning.

Figure 1a shows a partial view of a grooved pipe (1) in partial cross section along the pipe axis so as to illustrate the helix angle β.

Figure 1b shows a partial view of a grooved pipe (1), in a partial cross-section perpendicular to the pipe axis, so as to illustrate the case of a pipe containing a string of fins (2) with a height H, fins approximately triangular in shape

L_n at the base and the apex angle a, separated by grooves (3) of approximately trapezoidal shape and width Lr, where Lr is the distance between the two grooves of the rib. This pipe has a thickness Tf, an outer diameter De, an inner diameter Di and a pitch P equal to Lr + Ln.

Figure 1c is a partial view of a grooved pipe in which trapezoidal ribs H1 height and H2 &lt;H1 height are arranged alternately.

Figure 2a, analogous to figures 1b or 1c, shows the rib (2) of the pipe according to test A.

Figure 2b, analogous to Figure 2a, shows the rib (2) of the pipe according to test C.

<td>Figure</td><td>2c,</td><td>analogical</td><td>to the figure</td><td>2a, presents</td>

<td>rib</td><td> (2)</td><td>compatible pipe</td><td>with trial F.</td><td></td>

<td>Figure</td><td>3a^,</td><td>analogical</td><td>to the figure</td><td>2a, presents</td>

<td>rib</td><td> (2)</td><td>compatible pipe</td><td>with test A '</td><td>close to A.</td>

<td>Figure</td><td> 3^</td><td>analogical</td><td>to the figure</td><td>2a, presents</td>

<td>rib</td><td> (2)</td><td>compatible pipe</td><td>with test B.</td><td></td>

<td>Figure</td><td> 30,</td><td>analogical</td><td colspan="2">to figure 2b, there is her</td>

variety.

<td>Figure 4a</td><td>is a view</td><td>parts</td><td>surface</td>

<td>internal</td><td>grooved pipe</td><td>according</td><td>invention</td>

<td>provided with</td><td>in the counter nursery</td><td>axial</td><td>(30) of,</td>

below, a simplified presentation.

Figure 4b is a simplified perspective view of a battery (4) of pipes (1) with wings (5) that were used for testing.

Figures 5a and 5b are graphs showing the exchange factor Hi (in W / m²K) on the ordinate as a function of pressure loss dP in Pa / m on the abscissa, when the cooling medium is the aqueous solution of K formate, at +5 ° C (figure 4a) and -5 ° C (figure 4b) respectively.

Figures 6a and 6b are analogous to figures 4a and 4b, but in the case where the cooling medium is an aqueous solution of propylene glycol.

Figure 7 is a graph showing the exchange factor Hi (in W / m²K) on the ordinate as a function of the Reynolds number on the abscissa when the cooling medium is an aqueous solution of propylene glycol.

Detailed description of the invention [0017] According to the invention, said helix angle β can preferably be from 25 ° to 35 °. Indeed, it is the range that allows for an increased Hi exchange factor and which enables the pipe to be grooved, whereby the Hi exchange factor decreases significantly for smaller helix angle β values, and the production speed decreases for larger helix angle β .

[0018] According to the invention, said apex angle α may typically be less than 45 ° and may preferably be between 15 and 30t

Indeed, for larger values ​​of the apex angle α, the coefficient of exchange Hi tends to decrease, and for smaller values, there are manufacturing difficulties, especially due to the wear of tools or forming holders, and in addition acute angles are easily destroyed when forming batteries with flaps, during pipe expansion.

[0019] It has been found to be advantageous especially in relation to the exchange factor Hi, that the ratio S / H, where S is the surface contained between two successive grooves, is between 0.8 mm and 1.5 mm, where S and H are expressed in mm respectively² and in mm.

[0020] Preferably, the H / De ratio can be 0.028 ± 0.3. Indeed, as mentioned previously, it is preferred that the ribs are high enough for the Hi exchange ratio to be increased, however, the height cannot be too large so that the ribs are both easy to make and relatively insensitive to pipe expansion during the production of pipe batteries with wings.

[0021] As it turns out especially when evaluating the tests carried out, the P / H ratio can be from 3.5 to 7, but better results were obtained when this ratio was preferably from 4 to 6 (see for example test A), and especially for relatively high H value, at least equal to 0.30 mm.

[0022] According to the invention, said ribs may have a triangular, trapezoidal or quadrangular cross-section, and the apex angles may optionally be rounded.

[0023] As shown in figure 2a, said ribs may have a trapezoidal profile with base and apex, said apex comprising a central portion approximately flat and possibly inclined with respect to said base as shown in figure 2c.

Especially when the rib profile forms a trapezoid, the top of said rib forming the small side of the trapezoid can have rounded edges, which is often the case when the rib profile forms a triangle.

[0024] Thus, said rounded apex and / or said rounded edges may have curvature radii less than 100 pm, the rib connections of said typically flat bottoms have curvature radii less than 100 pm, preferably from 20 to 50 pm.

[0025] Said rounded apex or said rounded edges may have a radius of curvature preferably smaller than 80 pm, said radius of curvature may typically be from 40 pm to 80 pm.

[0026] In a preferred embodiment of the invention, and as shown for example in Figures 2a, 3a or 3b, said ribs can be symmetrical and join with said bottoms typically flat with right and left connection angles Θ1 and Θ2 such that Θ1-Θ2 typically equal to 0 or at most equal to 10 °, so as to form symmetrical or nearly symmetrical ribs.

However, as shown in Figures 2b and 2c, said ribs may attach to said bottoms typically flat with right and left junction angles Θ1 and Θ2 such that Θ1- Θ2 is at least equal to 10, so as to form asymmetrical or inclined ribs.

As shown in figure 3c, said ribs can form an alternating string of ribs having right and left connection angles Θ1 and Θ2 for one and Θ2 and Θ1 for the other.

[0027] As shown in figure 3b, said ribs may have a triangular base at height hp and a trapezoidal tip at height h_s, with H equal to hp + h_s, and hp / hg typically between 1 and 2. As shown in figure 1c, said ribs can form a string of fins with height H1 = H and height H2 =

a.H1, between 0.1 and 0.9, with the H1 rib being the primary rib and the H2 rib being the secondary rib. Typically, said string may be an alternating string of H1 fins and H2 fins separated by a flat bottom groove. See test E with H1 = 0.25 mm and H2 =^0,22 mm.

As shown in figures 3a and 3b, said pipes may comprise additional ribs with a height H '&lt;0.5.H and typically positioned halfway between two ribs with a height H or height H1 and H2.

[0028] According to the invention, and as shown in figure 4a, said pipes may further comprise axial grooving forming in said ribs cutouts with a typically triangular profile with a rounded apex, said apex having an angle γ from 25 to 65 °, and said bottom part or the vertex is at a distance h from the bottom of said grooves having from 0 to

0.2 mm.

[0029] Grooved pipes according to the invention may be made of Cu and Cu, Al alloys and Al, Fe alloys and Fe alloys. These pipes, typically not grooved, can be obtained typically by grooving pipes, or alternatively by grooving flat metal strip and then making a welded pipe.

These pipes may have a typically circular, oval or rectangular cross-section. They may have an oval or rectangular cross section, especially for welded pipes.

[0030] Another object of the invention is heat exchangers using the pipes of the invention.

As shown in Figure 4b, these exchangers may include heat exchange fins in contact with said tubes on parts of said tubes in which the maximum distance between said wings and said tubes on the non-contacting portion is less than 0.01 mm, and preferably less than 0.005 mm.

[0031] Another object of the invention is the use of the pipes according to the invention, and the use of the exchangers according to the invention, pipes and exchangers in which the cooling or heating medium is used as a single phase medium typically selected from: water, aqueous solutions and glycols typically with 30% glycol solutions K formate and / or acetate, coolants, organic fluids, liquid CO2.

According to the invention, the cooling or heating medium can be used as a single phase medium typically selected with dynamic viscosity coefficients comprised between

0.5 and 30 m.Pa and Prandtl number between 5 and

160.

Examples of implementation

A) Manufacture of pipes [0032] Grooved copper pipes according to the invention with an outer diameter of De 12.0 mm, pipes marked A, B, C, D and G, as well as control pipes marked E, F and G, the pipe marked L corresponds to the smooth control tube.

In addition, other tests were carried out with other De diameters, tests which showed that the grooving according to the invention allows the thickness Tf to be selected at the bottom of the groove so that Tf / De is 0.023 ± 0.005, which leads to a thickness Tf clearly less than the standard thickness, i.e. for a significant gain on the weight of the pipe, while maintaining satisfactory mechanical performance.

<td>Mark.</td><td>H mm</td><td>Angle α °</td><td>Angle β °</td><td>N</td><td>^Typ *</td><td>Tfmm</td><td>^LN^{/ L}R</td><td>P / H</td><td>P mm</td><td>S / H</td>

<td>AND</td><td> 0,337</td><td> 29</td><td> 24</td><td> 22</td><td>T1</td><td> 0,30</td><td> 0,28</td><td> 4,84</td><td> 1,63</td><td> 1,36</td>

<td>B</td><td> 0,280</td><td> 33</td><td> 25</td><td> 20</td><td>T1-2</td><td> 0,30</td><td> 0,29</td><td> 6,89</td><td> 1,93</td><td> 1,47</td>

<td>C</td><td> 0,227</td><td> 70</td><td> 30</td><td> 40</td><td>T2</td><td> 0,30</td><td> 0,77</td><td> 4</td><td> 0,91</td><td> 0,61</td>

<td>D</td><td> 0,304</td><td> 41</td><td> 25</td><td> 29</td><td>T1</td><td> 0,32</td><td> 0,51</td><td> 4,12</td><td> 1,25</td><td> 0,85</td>

<td>E</td><td> 0,25 0,22</td><td> 40</td><td> 18</td><td> 70</td><td>T2</td><td> 0,35</td><td> 1,15</td><td> 2,56</td><td> 0,64</td><td> 0,35</td>

<td>F</td><td> 0,23</td><td> 53</td><td> 28</td><td> 65</td><td>T1</td><td> 0,35</td><td> 1,8</td><td> 2,39</td><td> 0,55</td><td> 0,26</td>

<td>G</td><td> 0,280</td><td> 70</td><td> 10</td><td> 22</td><td>T1</td><td> 0,30</td><td> 0,28</td><td> 5,80</td><td> 1,62</td><td> 1,36</td>

<td>L</td><td> -</td><td> -</td><td> -</td><td> -</td><td></td><td> 0,40</td><td> -</td><td> -</td><td></td><td> -</td>

<td colspan="11">* Rib type: T1 trapezoidal, T2 triangular, T1-2 shaped mixed</td>

[0033] It should be noted that pipes C and G have asymmetrical grooves, while pipes grooves A, B, D, E and F are symmetrical.

B) Results obtained:

[0034] The pipes were tested with two types of single-phase agents: on the one hand a 30% (by volume) aqueous solution of monopropylene glycol, and on the other a K formate solution capable of operating up to -30 ° C, the latter having a freezing point of -55 ° C while the aqueous solution of monopropylene glycol -40 ° C.

The tests were performed at +5

C.

The dynamic viscosity (m.Pa.s) of the solutions used was measured at two temperatures:

<td>T</td><td>Monopropylene glycol (m.Pa.s)</td><td>K formate solution</td>

<td>+ 5 ° C</td><td> 20</td><td> 4,5</td>

<td>+ 5 ° C</td><td> 10</td><td>2, S</td>

[0035] In addition, a Prandtl number for monocrocneene glycol was measured: 142 at -5 ° C, and 80 at +5 ° C. For the K formate solution, the Prandtl number is 20 at + 5 ° C.

B1) Weight per meter [0036] Pipes A, B, C, D and G have a weight per meter of 125 g / m, while control pipes E and F, which correspond to grooved pipes of the technical state oO, have a weight per meter of 140 g / m, the L pipe has a weight per meter of 130 g / m. As a result, with the pipes of the invention, the weight gain is 10% relative to the prior art grooved pipes and 4% relative to the plain pipe generally used in this application.

B2) Tests with a 30% vol. Monopropylene glycol solution

1) Tests at - 5o C:

[0037] For pipes A, C and L, the exchange factor Hi (W / m) was measured².K) as a function of Re, Reynolds number, for laminar flow, which corresponds to the range 2000 &lt;Re &lt;3200.

The following table gives the Hi value for three values

Re: 2400, 2600 and 2800.

<td>Re</td><td>Hi pipes A = HiA</td><td>Hi pipe C = HiC</td><td>Hi pipe L = HiL</td><td>HIA / HiL</td><td>HIC / HiL</td>

<td> 2400</td><td> 3250</td><td> 2300</td><td> 2125</td><td> 1,53</td><td> 1,08</td>

<td> 2600</td><td> 3500</td><td> 2550</td><td>232S</td><td> 1,50</td><td> 1,10</td>

<td> 2800</td><td> 3750</td><td> 2750</td><td> 2500</td><td> 1,50</td><td> 1,10</td>

[0038] For pipes A, C, E, F, G and L, the exchange coefficient Hi as a function of pressure loss dP (Pa / m) was measured. The following table gives the Hi values ​​for pressure losses of 14 KPa / m and 16 KPa / m:

<td>DP KPa / m</td><td>Hia</td><td>Hic</td><td>HIG</td><td>HiF</td><td>HiE</td><td>HiL</td>

<td> 14</td><td> 3209</td><td> 2777</td><td> 2640</td><td> 2300</td><td> 2300</td><td> 2300</td>

<td> 16</td><td> 3664</td><td> 3300</td><td> 3050</td><td> 2936</td><td> 2709</td><td> 2709</td>

[0039] The following table gives the ratios of exchange coefficients, where the smooth pipe L is taken as reference:

<td>DP Kpa / m</td><td>HIA / HiL</td><td>HIC / HiL</td><td>HIG / HiL</td><td>HiF / HiL</td><td>HiEHiL</td><td>HiL / HiL</td>

<td> 14</td><td> 1,395</td><td> 1,21</td><td> 1,15</td><td> 1</td><td> 1</td><td> 1</td>

<td> 16</td><td> 1,35</td><td> 1,22</td><td> 1,13</td><td> 1,08</td><td></td><td> 1</td>

[0040] Thus, for a pressure loss of 14KPa / m, pipe A has, compared to smooth pipe L, and also relative to grooved pipes F and E in the state of the art, a gain of 39%, i.e. significant.

[0041] For the pipes according to the invention marked A and G, the influence of the helix angle is examined, with the other grooving parameters being the same.

The following table gives the exchange factors and their ratio for identical pressure losses of 14 KPa / mi

18KP^and/ M.

<td>DP KPa / m</td><td>Hia</td><td>HIG</td><td>HIA / hig</td>

<td> 14</td><td> 3239</td><td> 2630</td><td> 1,23</td>

<td> 18</td><td> 3674</td><td> 3090</td><td> 1,19</td>

2) Tests at + 5 ° C:

[0042] Tests at + 5 ° C were carried out on pipes A, B, C, E, F and L. The exchange factor Hi was measured as a function of pressure loss dP (Pa / m). The following table gives the Hi values ​​for pressure losses of 4 KPa / m, 8 KPa / m and 12^KPAAM:

<td>Dp KPa / m</td><td>Hia</td><td>HiB</td><td>Hic</td><td>HiE</td><td>HiF</td><td>HiL</td>

<td> 4</td><td> 2545</td><td> 2273</td><td> 1591</td><td> 1591</td><td> 1591</td><td> 1591</td>

<td> 8</td><td> 4000</td><td> 3545</td><td> 2455</td><td> 2273</td><td> 2273</td><td> 2273</td>

<td> 12</td><td> 4545</td><td> 4409</td><td> 3409</td><td> 3045</td><td> 2909</td><td> 2773</td>

[0043] The table below gives the exchange coefficient ratios, where the smooth pipe L is taken as reference:

<td>Dp KPa / m</td><td>HIA / HiL</td><td>HiB / HiL</td><td>HIC / HiL</td><td>HiE / HiL</td><td>HiF / HiL</td><td>HiL / HiL</td>

<td> 4</td><td> 1,60</td><td> 1.43</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 8</td><td> 1,76</td><td> 1,47</td><td> 1,08</td><td> 1</td><td> 1</td><td> 1</td>

<td> 12</td><td> 1,64</td><td> 1,59</td><td> 1,23</td><td> 1,10</td><td> 1,05</td><td> 1</td>

B3) Tests with an aqueous solution of potassium formate

1) Tests at -5 ° C [0044] For pipes A, B, C, E, F, and L, the exchange coefficient Hi as a function of pressure loss dP (Pa / m) was measured. The following table gives the Hi values ​​for pressure losses of 4, 8 and 12 KPa / m:

<td>Dp KPa / m</td><td>Hia</td><td>HiB</td><td>Hic</td><td>HiE</td><td>HiF</td><td>HiL</td>

<td> 4</td><td> 2423</td><td> 1769</td><td> 1769</td><td> 1769</td><td> 1769</td><td> 1769</td>

<td> 8</td><td> 3615</td><td> 2615</td><td> 3000</td><td> 2615</td><td> 2615</td><td> 2615</td>

<td> 12</td><td> 4231</td><td> 3539</td><td> 4000</td><td> 3269</td><td> 3385</td><td> 3077</td>

[0045] The following table gives the exchange coefficient ratios, where the smooth pipe L is taken as reference:

<td>Dp KPa / m</td><td>HIA / HiL</td><td>HiB / HiL</td><td>HIC / HiL</td><td>HiE / HiL</td><td>HiF / HiL</td><td>HiL / HiL</td>

<td> 4</td><td> 1,37</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 8</td><td> 1,38</td><td> 1</td><td> 1,15</td><td> 1</td><td> 1</td><td> 1</td>

<td> 12</td><td> 1,38</td><td> 1,15</td><td> 1,30</td><td> 1,06</td><td> 1,10</td><td> 1</td>

2) Tests at +5 ° C [0046] For pipes A, B, C, E, F, and L, the exchange coefficient Hi as a function of pressure loss dP (Pa / m) was measured. The following table gives the Hi values ​​for pressure losses of 4, 8 and 12 KPa / m:

<td>Dp KPa / m</td><td>Hia</td><td>HiB</td><td>Hic</td><td>HiE</td><td>HiF</td><td>HiL</td>

<td> 4</td><td> 3256</td><td> 2325</td><td> 2791</td><td> 2325</td><td> 2325</td><td> 2325</td>

<td> 8</td><td> 4000</td><td> 3674</td><td> 4280</td><td> 3442</td><td> 3674</td><td> 3116</td>

<td> 12</td><td> 4744</td><td> 4465</td><td> 5000</td><td> 4465</td><td> 4465</td><td> 3581</td>

[0047] The table below gives the exchange coefficient ratios, where the smooth pipe L is taken as reference:

<td>Dp KPa / m</td><td>HIA / HiL</td><td>HiB / HiL</td><td>HIC / HiL</td><td>HiE / HiL</td><td>HiF / HiL</td><td>HiL / HiL</td>

<td> 4</td><td> 1,40</td><td> 1</td><td> 1,2</td><td> 1</td><td> 1</td><td> 1</td>

<td> 8</td><td> 1,28</td><td> 1,18</td><td> 1,37</td><td> 1,10</td><td> 1,18</td><td> 1</td>

<td> 12</td><td> 1,32</td><td> 1,25</td><td> 1,40</td><td> 1,25</td><td> 1,25</td><td> 1</td>

C) Conclusions [0048] In all cases of single-phase factors tested and at all temperatures tested, pipe A has particularly good parameters and advantages.

However, in special cases, pipes B and C may be preferred. Thus, pipe B may be advantageous in the event of heat exchange at +5 ° C with an aqueous solution of monopropylene glycol as a circulating medium in the exchanger. Also, pipe C may be advantageous for heat exchange at +5 ° C with an aqueous solution of K formate as a circulating medium in the exchanger.

Advantages of the invention [0049] The invention has great advantages.

[0050] Indeed, it allows, on the one hand, to obtain heat exchanger tubes with high efficiency in heat exchange due to the significantly increased coefficient Hi.

On the other hand, it makes it possible to obtain pipes with a low weight per meter, because the invention allows to obtain simultaneously pipes with a small diameter and a small thickness at the bottom of the groove and pipes with very good parameters, especially in terms of the heat exchange coefficient, which can replace pipes with a larger diameter and greater thickness at the bottom of the groove. In addition, the relatively small number of fins also reduces the weight of the pipe.

Finally, the pipes according to the invention are particularly suited to all single-phase medium heat transfer systems, especially those which use aqueous solutions, which is very advantageous in practice

List of reference symbols in the figures [0051]

<td>Grooved pipe</td><td> 1</td>

<td>Rib</td><td> 2</td>

<td>Groove</td><td> 3</td>

<td>Axial groove</td><td> 30</td>

<td>Battery</td><td> 4</td>

<td>The Wing</td><td> 5</td>

<td>Tube axis</td><td> 6</td>

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