IMPROVED TUBE FOR A HEAT EXCHANGER

A heat exchanger element includes a tubular body with a wall at least partly delimited by an inner surface and an outer surface. The wall has a twisted shape on a segment of the body. The inner surface has a groove with a shape corresponding to the wall. The groove extends helically over the segment. On the segment, the outer surface has a diameter between 18 and 30 millimeters, the groove has a pitch of less than 3.5 millimeters and a depth such that the ratio of the pitch at a real power between 1.5 and 2.5 to the depth is less than a threshold value close to 24. A heat exchanger, for example of condenser type, can include such an element.

Skip to: Description  ·  Claims  · Patent History  ·  Patent History
Description

The invention relates to an element for a heat exchanger of industrial type, in particular a condenser, of the type comprising a generally tubular body.

Condensers comprising such elements, also known as “tube condensers” are widely used in industry, in particular for electricity production. A first fluid, typically water in the liquid state, is circulated inside a plurality of tubes, while a second fluid in the gaseous state, generally steam, is brought into proximity with the tubes, outside them. Heat is then exchanged between the first and second fluids, through the wall of the tubes, which exchange causes the fluid in the gaseous state to condense.

Condensers of the industrial type must be able to condense large quantities of steam in as short a time as possible. The volume of steam that they are capable of condensing per unit of time at least partly characterises their performance. To this end, condensers of the industrial type are generally fitted with hundreds, or even thousands, of great-length tubes, typically up to around twenty metres long.

Originally, condensers of the industrial type were fitted with smooth tubes. To improve their performance, in particular regarding the flow rate of condensed steam, tubes of a new type started to be used, the body of which still retains its generally tubular shape, but the wall of which has a twisted shape extending over at least one segment of said body. This twisted shape of the wall results in an outer surface with a domed relief extending helically along the segment in question, and a corresponding groove on the inner surface of the body.

This particular configuration significantly improves the heat exchanges at the tubes: on the one hand, the twisted shape gives the wall a larger contact area between the fluids, both on the inside and the outside of the tubes; on the other hand, it causes turbulence in the fluid flowing inside the tubes, which is beneficial overall for the heat exchanges at the tubes. The twisted shape also improves the drainage of the drops that form on the outer surface of the tubes.

In the art, tubes with this type of configuration are known as “corrugated” or, more correctly, “equipped with corrugations”. The pitch of the twist, also known as the corrugation pitch, is generally greater than 20 millimetres.

The applicant has noted that, in general, the actual performance of the corrugated tubes, in particular regarding their ability to condense a fluid on their outer surface, is quite significantly lower than the expected performance.

The invention aims to improve the existing situation.

The proposed heat exchanger element comprises a tubular body the wall of which is at least partly delimited by an inner surface and an outer surface. The wall has a twisted shape on at least one segment of said body. The inner surface has at least one groove with a shape corresponding to said wall that extends helically over said segment. On said segment, the outer surface has a diameter comprised between 18 and 30 millimetres, while the groove has a pitch of less than 3.5 millimetres and a depth such that the ratio of the pitch at a real power comprised between 1.5 and 2.5 to the depth is less than a threshold value close to 24.

The invention will be better understood on reading the following detailed description, with reference to the attached drawings, in which:

FIG. 1 shows a diagram of a generic heat exchanger;

FIG. 2 is a top view of a tube element for the exchanger in FIG. 1;

FIG. 3 is a longitudinal cross-sectional view of a wall portion of a tube element for the exchanger in FIG. 1;

FIG. 4 shows a partially cut away perspective view of a twisted portion of a tube element for a heat exchanger.

The attached drawings contain elements of certain character. They may therefore be used not only to supplement the description of the invention, but also contribute to the definition thereof, as applicable.

Reference is made to FIG. 1. It shows, generically, a heat exchanger of industrial type in the form of a condenser 1.

The condenser 1 comprises a plurality of individual tubes 3 held in relation to each other in one or more bundles 5 by plates 7 distributed along the tubes 3. Each plate 7 is thus passed through by each of the tubes 3 in the bundle 5.

The condenser 1 also comprises a pair of header tanks 9 into which the opposite ends of each of the tubes 3 respectively open out.

One of the tanks 9 is in fluid communication with a fluid inlet 11, while the other tank 9 is in fluid communication with a fluid outlet 13.

The inlet 11 and outlet 13 can be connected to the rest of a circuit in which a first fluid circulates. Typically, the first fluid enters the condenser 1 through the inlet 11 in liquid form. It circulates from the corresponding header tank 9 to the other header tank inside the tubes 3 in one or more passes. From there, the first fluid leaves the condenser 1 for the rest of the circuit through the outlet 13.

The bundle 5 of tubes 3 is housed in an enclosure 15 provided inside what is known in the art as a shell 17. The shell 17 is equipped with a fluid inlet 19 and a fluid outlet 21 that open out into the enclosure 15.

The inlet 19 and outlet 21 allow the condenser 1 to be connected to a circuit in which a second fluid circulates.

The second fluid enters the enclosure 15 through the inlet 19 in gaseous form. On contact with the tubes 3, the second fluid exchanges heat with the first fluid circulating inside these tubes. As the first fluid is generally introduced at a lower temperature than that of the second fluid, the latter condenses on the outer surface of the tubes 3. The second fluid in liquid form leaves the enclosure 15 through the outlet 21.

Condensers of the type of the condenser 1 are widely used in industrial electricity production. In particular, steam is condensed by means of cold water circulating inside the tubes. To this end, great-length tubes each up to around twenty metres long are used.

Reference is made to FIG. 2. It shows a tube element TE that can be used in a condenser of the type of the condenser 1.

The tube element TE comprises a hollow elongated generally cylindrical, or tubular, body BDY with a length TL. The body BDY has two longitudinal end sections ES1 and ES2 connected to each other by a central section CS with a length CL. The length TL corresponds to the total length of the tubular element TE, including the central section CS and the end sections ES1 and ES2.

The end sections ES1 and ES2 are generally cylindrical, with an outside diameter TOD. The diameter TOD, as it is usually known in the art, corresponds to the nominal outside diameter of the element TE. The end sections ES1 and ES2 each have a smooth outer and inner surface.

The central section CS has a wall that extends along the body in a twist, or helically, or in a helix, forming spirals LP around the longitudinal axis LA of the tube element TE. Here, the spirals LP are contiguous.

This twisted configuration of the wall of the element TE results in an outer surface that, over the length of the central section CS, has a helical relief, made of hollows and bosses. This relief is likely to improve the heat exchange capabilities of the element TE, because the outer surface thereof is then more extensive than that of a smooth tube with the same outside diameter. Furthermore, it improves the drainage of the drops that form on the outer surface of the element TE. The central section CS retains the general appearance of a hollow cylinder, having an outside diameter COD.

Reference is made to FIGS. 3 and 4. These show, generically, a twisted portion CW of the wall and a configuration of said twisted shape. The twisted shape of the wall CW results in an inner surface IS with a relief made of peaks and hollows, with a shape corresponding respectively to the hollows and bosses on the outer surface OS. In other words, the inner surface IS has a groove that extends along a helix with contiguous spirals along the central section CS. In yet other words, the inner surface IS has a helical shape.

This relief is likely to improve the heat exchange capabilities of the element TE, due to the generation of eddies in the fluid flowing inside the element TE.

The twisted wall CW has a thickness TT. The thickness TT corresponds to the nominal thickness of the element TE, i.e. the thickness of the wall of the smooth tube on which the element TE is based. The central section CS has an inside diameter CID. The diameter CID corresponds to the diameter of a gauge just capable of passing through the inside of the element TE.

The twisted section CS has an outside diameter COD that corresponds to the nominal outside diameter of the element TE on the twisted section CS, i.e. the diameter of a cylindrical envelope surface of said section.

The twisted shape has a pitch CP, if applicable considered inside the tubular element. The depth CD of the inner groove resulting from the twisted shape is considered in relation to an inner envelope surface of the tubular element or, in other words, as the radial distance between the bottom of the hollows in the inner surface IS and the summit of the peaks.

Although it is not shown in the Figures, the dimension corresponding to the nominal inside diameter of the tube can be denoted TED, as it is usually known in the art, i.e. here, the nominal inside diameter of the smooth end sections ES1 and ES2.

According to a general aspect of the invention, the tube element TE has, on the twisted section CS, a nominal outside diameter COD comprised between 18 and 30 millimetres. The pitch CP of the twist is less than 3.5 millimetres. The depth CD is such that the ratio of the pitch CP raised to a real power R comprised between 1.5 and 2.5 to the depth CD, which is known as the form ratio FR, remains less than a threshold value TV. In particular, the threshold value TV is close to 24. In particular, the power R is close to 1.7. In other words, the depth CD verifies the conditions COND1, COND2 and COND3 set out below:


FR=CP̂R/CD  (COND1)


FR<24  (COND2)


1.5<R<2.5, and in particular R=1.7  (COND3)

Tables 1A and 1B below show data characteristic of the twisted section CS for tube elements TE according to three variants of the invention (Table 1A), and two embodiments (Table 1B). The dimensions are here expressed in millimetres. In each case, the tube elements according to these variants are such that they verify the conditions COND1, COND2 and COND3, in particular where R=1.7.

TABLE 1A Variant 1 Variant 2 Variant 3 TOD 19.05 22.22 25.40 COD 18.90 22.07 25.25 TT 0.5 0.5 0.5 CP between 2 and 3.5 between 2 and 3.5 between 2 and 3.5 CD between 0.15 and between 0.15 and between 0.2 and 0.3 0.3 0.3

TABLE 1B Embodiment 1 Embodiment 2 TOD 19.05 22.22 COD 18.90 22.07 TT 0.5 0.5 CP 2 2.5 CD 0.16 0.25

Tables 1A and 1B show that the twisted part of the tubes according to the invention has a very small pitch, less than 3.5 millimetres, and preferably less than 3 millimetres, compared with the pitch values conventionally used in corrugated tubes, which are typically greater than 20 millimetres. The tubes according to the invention therefore differ from conventional tubes in that the twisted section has a shape that resembles a spiral.

Table 2 below shows dimensional characteristics relating to a set of tube elements (marked I, . . . , XII) each with a twisted central section. The tube elements differ from each other in the profile of the respective twisted section thereof, characterised by pitch CP and depth CD values that differ from each other. Dimensions absent from Table 2 are common to the tubes I to XIV. In particular, the tube elements all have an outside diameter of 22.22 millimetres and a wall thickness of 0.5 millimetre. The tubes are made from grade 2 titanium.

The pitch CP and depth CD values are expressed in millimetres.

Table 2 also shows the corresponding values of the form ratio FR, calculated for a power R value of 1.7.

TABLE 2 CP CD FR I 2.0 0.14 23.21 II 2.3 0.19 21.92 III 2.5 0.25 18.84 IV 3.1 0.17 39.44 V 3.2 0.39 18.06 VI 3.3 0.24 31.83 VII 3.3 0.32 24.16 VIII 3.3 0.44 17.57 IX 4.2 0.47 24.42 X 4.3 0.49 23.96 XI 4.8 0.40 36.47 XII 4.9 0.64 23.24 XIII 1.3 0.04 39 XIV 1.5 0.06 33

In Table 2, tube elements II and III are according to variant 2. Tube element III is also according to embodiment 2. In addition, elements I, II, III, V and VIII are according to the invention in that they have pitch values CP of less than 3.5 millimetres and also verify conditions COND1, COND2 and COND3.

Tube elements IV and VI have dimensions according to variant 2, with the exception that they do not verify conditions COND1 to COND3.

Tube element X verifies conditions COND1, COND2 and COND3 where R=1.7.

Table 3 below shows the results of heat exchange capacity measurements taken on the elements in Table 2.

In Table 3, the coefficient K represents a heat exchange capacity measured for the tube element in question. The coefficient K is expressed in Watt per square metre Kelvin (W·m−2·K−1). The HER value, expressed as a percentage, corresponds to the improvement in the value of K for the element in question compared with a smooth element with otherwise similar dimensions.

TABLE 3 K HER I 7,901 50% II 7,646 45% III 8,098 54% IV 6,669 26% V 8,599 63% VI 6,771 28% VII 6,778 29% VIII 7,912 50% IX 6,659 26% X 8,081 53% XI 6,553 24% XII 7,698 46% XIII 6473 23% XIV 6007 13%

Table 3 shows that compliance with conditions COND1, COND2 and COND3 is generally associated with a significant increase in heat exchange performance. The rows corresponding to tube elements I, II, III, V, VIII, X and XII have coefficient K values at least 45% greater than the reference value for a smooth tube (5,272 W·m−2·K−1). A comparison in Table 2 of rows VII and X on one hand, and rows I, XIII and XIV on the other hand also shows a slight increase in heat exchange performance when the ratio FR exceeds the threshold value of 24. When the ratio FR is greater than the threshold value, the increase in heat exchange performance compared with a smooth tube is generally less than 30%.

Table 3 proves that the tube elements according to the invention have greatly improved heat transfer capabilities compared with smooth elements on the one hand, and elements the twisted section of which departs from the profile provided for by the invention.

Table 4 below shows the results of measurements taken on the tube elements in Table 2.

Table 4 also shows the values of the coefficient known as the Darcy or Darcy-Weisbach coefficient, for the tubes in question, as well as the increase DCR in the value of this coefficient compared with a smooth reference tube. The Darcy coefficient corresponds to a head loss coefficient. This dimensionless quantity represents the influence of the type of flow (laminar or turbulent) and the finish of a pipe (smooth or rough) on the head loss. Here, the Darcy coefficient is calculated for a flow rate of 2.5 cubic metres per hour.

An increase in the Darcy value is overall unfavourable to the performance of a tube element within a condenser. In particular, an increase in the Darcy value implies an increase in the energy consumption required for the circulation of the fluid inside the tubes. In other words, the increase in the Darcy value is detrimental to the condensation of the steam on the outside of the tube element for the same energy consumption.

TABLE 4 DARCY DCR I 0.032487593 48% II 0.032098063 46% III 0.032823286 49% IV 0.052203857 129% V 0.054736888 140% VI 0.043978584 95% VII 0.038960463 74% VIII 0.050991452 124% IX 0.071932623 211% X 0.068924461 199% XI 0.052814985 132% XII 0.073328679 217% XIII 0.029523637 41% XIV 0.03016296 44%

Table 4 shows in general terms that the tubes according to the invention have a significant increase in Darcy value. However, this increase remains limited (less than 140 and lower than for certain tubes not according to the invention, as shown by a comparison with rows X and XII). Furthermore, the relative increase in the Darcy coefficient is very small (close to, or even less than 100%) for the elements according to the second variant (tubes II and III) and for tube I, compared with the other tubes tested. The tubes of the second variant and tube I have an increase in the Darcy value that is markedly less than for the others.

As a result of the foregoing, the tubes with a twisted section according to the invention are capable of greatly improved performance regarding their capacity to condense a gas circulating outside the tube. This improved performance results from a twisted shape that greatly improves the heat exchange capabilities and substantially limits the head loss effects.

The comparison between examples I and II with examples XIII and XIV shows that the lowering of the pitch allows to lower the Darcy coefficient, but fulfilling the conditions COND1, COND2, COND3 allows to improve the heat exchange performance.

Furthermore, the tubes according to variants 1 to 3 and embodiments 1 and 2 are capable of showing condensation performance that is further improved due to heat exchange capabilities comparable to the other tubes according to the invention and substantially lower head losses compared with these tubes.

On the basis of the general embodiment of the invention and based on tests the results of which are at least partly given in Tables 2 to 3, it is considered that the features below, which are optional, additional or alternative, are capable of further improving the condensation performance of a tube:

The outside diameter of the tube TOD is between 19 and 26 millimetres, preferably between 20 and 26 millimetres, and even more preferentially between 20 and 23 millimetres. In particular, the outside diameter TOD is close to 19.05 millimetres, 22.22 millimetres or 25.4 millimetres.

The outside diameter COD of the twisted part is between 18 and 26 millimetres, preferably between 20 and 26 millimetres, and even more preferentially between 20 and 23 millimetres. In particular, the outside diameter COD is close to 18.90 millimetres, 22.07 millimetres or 25.25 millimetres.

The pitch CP is strictly greater than 2 millimetres. It is less than 3 millimetres.

The depth CD is comprised between 0.05 and 0.6 millimetres, in particular greater than 0.15 millimetres.

The thickness TT of the wall CW of the tube is between 0.4 and 1 millimetre, for example of the order of 0.5 millimetre.

The invention is not limited to the embodiments described above, but encompasses all of the variants that a person skilled in the art might imagine.

Claims

1-9. (canceled)

10. A heat exchanger element comprising:

a tubular body with a wall at least partly delimited by an inner surface and an outer surface, the wall having a twisted shape on at least one segment of the body, and the inner surface including at least one groove with a shape corresponding to the wall and extending helically over the segment,
wherein on the segment, the outer surface has a diameter between 18 and 30 millimeters, while the groove has a pitch of less than 3.5 millimeters and a depth such that the ratio of the pitch at a real power between 1.5 and 2.5 to the depth is less than a threshold value close to 24.

11. An element according to claim 10, wherein the real power is close to 1.7.

12. An element according to claim 10, wherein the body has, on at least the segment, an outside diameter between 18 and 26 millimeters.

13. An element according to claim 10, wherein the body has, on at least the segment, an outside diameter between 20 and 26 millimeters.

14. An element according to claim 10, wherein the body has, on at least the segment, an outside diameter between 20 and 23 millimeters.

15. An element according to claim 12, wherein the body has, on at least the segment, an outside diameter close to 18.90, 22.07, or 25.25 millimeters.

16. An element according to claim 10, wherein the pitch is strictly greater than 2 millimeters.

17. An element according to claim 10, wherein the pitch is less than 3 millimeters.

18. An element according to claim 10, wherein the depth is between 0.05 millimeter and 0.6 millimeter.

19. An element according to claim 10, wherein the depth is greater than 0.15 millimeter.

20. An element according to claim 10, wherein the wall has a thickness between 0.4 and 1 millimeter on at least part of the segment.

21. An element according to claim 10, wherein the wall has a thickness close to 0.5 millimeter on at least part of the segment.

22. A heat exchanger comprising at least one element according to claim 10.

Patent History
Publication number: 20160341491
Type: Application
Filed: Jan 19, 2015
Publication Date: Nov 24, 2016
Applicant: NEOTISS SAS (Venarey-les-Laumes)
Inventors: Joël DUPRAT (Dijon), Pascal SAUSSIER (Menetreux le Pitois)
Application Number: 15/109,239
Classifications
International Classification: F28F 1/08 (20060101); F28F 1/42 (20060101); F28D 7/10 (20060101);