FR2789166A1 - METHOD, SYSTEM AND COMPONENT FOR INCREASING THERMAL TRANSFERS IN A HEAT EXCHANGER DEVICE - Google Patents

Abstract

The invention relates to methods for increasing heat transfers in a heat exchanging device. The heat exchanger comprises at least one pipe (fig 1) containing a circulating liquid, presenting a difference in temperature in comparison with the outer environment surrounding said pipe. According to the invention, contractions (5) and successive elongations (4) of the liquid are produced in directions that are perpendicular to the direction (1) in which the liquid flows. The mixture properties of the pipe are improved and the temperature gradients of the wall of the pipe are also increased, resulting in increased heat transfers.

Description

Method, system and component for increasing transfers

  thermal in a heat exchanger device.

  The present invention relates to methods, systems and components for increasing heat transfer in a heat exchanger device. The increase in heat exchange performance is at the heart of improving the efficiency of an exchanger, and therefore at the center of the energy optimization of industrial processes. Numerous studies have been and are devoted to the increase of transfer in tubes. Several technological options have been studied. Two of these options consist of positioning inserts inside the tubes or creating section reductions. These solutions have the drawback of generating significant additional pressure drops and, in particular for the second, of causing recirculation pockets giving rise to hot zones where the heat transfer is very low. An alternative is proposed by the use of micro streaks (single or crossed) on the inner surface of the tubes. This technique is very well suited to turbulent flows and leads, under these conditions, to an efficiency of the order of 1.2 {E = (h, / / t Ih) / (f / fr.), F being the coefficient

  pressure drop. and hn the inner tube transfer coefficient}.

  However, it turns out that this technique is less effective for

low Reynolds numbers.

  The present invention provides another solution to the problem of

  improving the efficiency of an exchanger.

  To increase the heat transfers in a heat exchanger device comprising at least one tube traversed by a fluid having a temperature difference with respect to the external environment surrounding said tube, the method according to the invention comprises the step of producing contractions and successive stretches of the fluid flowing in said tubing, in directions perpendicular to the direction of flow of the fluid in said tubing. Thus, the mixing properties of said tubing are improved and the temperature gradients in the vicinity of the wall of said tubing are increased, which has the effect of increasing heat transfers. Preferably, the method according to the invention further comprises the step of avoiding the formation of recirculation pockets in said tubing. We

  thus avoids the formation of zones where the heat transfer is very low.

  Advantageously, in order to produce a succession of stretches and contractions perpendicular to the direction of flow of the fluid in said tubing, while avoiding the formation of recirculation pockets in said tubing, the profile of said tubing is periodically modified.

  without appreciably modifying its section.

  The present invention also relates to a system for increasing heat transfers in a heat exchanger device comprising at least one tube traversed by a fluid having a temperature difference with respect to the external environment surrounding said tube. The system according to the invention is such that said tubing has a profile suitable for producing successive contractions and stretchings of the fluid, in directions perpendicular to the direction of flow of the fluid in said tubing. Thanks to this structure of the tubing, the mixing properties are improved and the temperature gradients are increased in the vicinity of the wall of said tubing. Thus, heat transfers are increased. Preferably further, said tubing has a suitable section to avoid the formation of recirculation pockets. So, we

  avoids the formation of zones where the heat transfer is very low.

  Advantageously, to produce a succession of stretches and contractions perpendicular to the direction of flow of the fluid, without causing the formation of a recirculation pocket, a tube is used whose profile varies periodically and whose section remains

substantially constant.

  The present invention also relates to a heat exchanger device comprising at least one tube traversed by a fluid having a temperature difference with respect to the external medium surrounding said tube. The exchanger according to the invention is such that the pipes have a profile suitable for producing successive contractions and stretching in directions perpendicular to the direction of flow of the fluid. The mixing properties of the pipes are thus improved and the temperature gradients in the vicinity of the wall of the pipes are increased, which has the effect of increasing the transfers.

  in the heat exchanger.

  In addition, preferably, the heat exchanger device is such that the pipes have an appropriate section to avoid the formation of recirculation pockets. So that we avoid the formation of areas where the

  heat transfer is very low.

  Advantageously, to produce a succession of stretches and contractions perpendicular to the direction of flow of the fluid, without causing the formation of recirculation pockets, pipes are used, the profile of which varies periodically and the section of which remains

substantially constant.

  The present invention also relates to a tubing component intended

  the production of a heat exchanger device. The component-

  tubing is intended to be traversed by a fluid having a gap of

  temperature in relation to the surrounding external environment. The component-

  tubing has a profile suitable for producing successive contractions and stretches of said fluid in directions perpendicular to the direction of flow of the fluid. So that the mixing properties of the tubing component are improved and that the temperature gradients in the vicinity of the wall of the tubing component are increased, which has

  the effect of increasing heat transfers.

  Preferably, moreover, the tubing component has an appropriate section to avoid the formation of recirculation pockets. Thus, the formation of zones where the heat transfer is very low is avoided. Advantageously, to produce a succession of stretches and contractions perpendicular to the direction of flow of the fluid, without causing the formation of recirculation pockets, the tubing component is such that its profile varies periodically and that its section remains

substantially constant.

  Other characteristics and advantages of the invention will become apparent on

  reading of the description of variant embodiments of the invention, given

  by way of an indicative and nonlimiting example, and of: - Figure 1 which schematically represents a perspective view of an example of a profile of the sections of a tubular element according to the invention, - Figure 2 which represents a perspective view of a heat exchanger

tubular heat.

  We will now describe FIG. 1. The tube, initially cylindrical, of axis 1, is deformed so as to produce, with substantially constant passage cross section, substantially elliptical shapes 2a, 2b and circular 3a, 3b, 3c successive alternating. The deformation parameters are the amplitude of the ripples A and the spatial wavelength L. The tube passes the fluid successively from a substantially elliptical vertical section to a substantially elliptical horizontal section, while maintaining a constant passage section. As shown schematically in Figure 1, a fluid element is then alternately stretched 4 in one direction and compressed 5 in the perpendicular direction during its flow in the tube. Air flow visualizations were carried out on a PVC tube with a diameter equal to 40 mm deformed according to this principle and compared with the case of a smooth tube. The visualization method used consists of injecting smoke locally into the center of the tube in isokinetic condition and observing, with the aid of a laser slice, the trace of smoke in the outlet section. In the case of a smooth tube, the film net is not mixed and remains approximately in the center of the tube, which is characteristic of a laminar flow. On the other hand, in the case of a deformed tube (like that described with reference to Figure 1), the smoke is this time largely mixed and very quickly reaches the wall. This phenomenon, directly linked to the stretches and compressions described above, has the corollary of an increase in heat transfer, since the temperature gradient close to the wall will, in this case, be increased

significantly.

  A similarly shaped copper tube with an internal diameter equal to 10 nm was tested on a hydraulic loop allowing simultaneous measurements of thermal performance and pressure drop. The amplitude of the deformations was fixed at 1.5 mrm, or 25% of the inside radius of the tube. The wavelength L of the deformations in the direction of flow is equal to 60 mm, or twelve times the inside radius of the tube. The efficiency factor E defined above is 1.2 for a laminar flow regime. Measurements were made for different values of the Reynolds number, for a smooth tube and for a deformed tube according to the invention. We

  notes that the efficiency E is increased in laminar regime.

  We will now describe FIG. 2 which represents a perspective view of an example of a heat exchanger using pipes according to the invention. The hot fluid is distributed by collectors 19a and 19b to the pipes 20a, 20b, 20c, etc. The cold fluid circulates between the

  pipes 20a, 20b, 20c in the direction of arrow 21.

Claims (12)

Claims.   1. Method for increasing heat transfers in a heat exchanger device (fig 2) comprising at least one tube (fig 1) traversed by a fluid having a temperature difference with respect to the external environment surrounding said tube, said method comprising step of producing successive contractions (5) and stretches (4) of the fluid flowing in said tubing, in directions perpendicular to the direction (1) of flow of the fluid in said tubing, so that the mixing properties of said tubing are improved and that the temperature gradients in the vicinity of the wall of said tubing   are increased, which has the effect of increasing heat transfers.   2. The method of claim 1 as further comprising the step of avoiding the formation of recirculation pockets in said tubing, so that the formation of zones o thermal transfer is avoided. is very weak.   3. Method according to claim 2 such that to produce a succession of stretching and contractions perpendicular to the direction of flow of the fluid in said tubing, avoiding the formation of recirculation pockets in said tubing, it is periodically modified ( L, 3a, 2a, 3b, 2b, 3c) the profile of   said tubing without substantially modifying its section.   4. System for increasing heat transfers in a heat exchanger device (fig 2) comprising at least one tube (fig 1) traversed by a fluid having a temperature difference with respect to the external environment surrounding said tube, said system being such that said tubing has a suitable profile (2a, 2b, 3a, 3b) for producing contractions (5) and successive stretches (4) of the fluid flowing in said tubing, said stretches (4) and contractions (5) effecting in directions perpendicular to the direction (1) of fluid flow in said tubing, so that the mixing properties of said tubing are improved and that the temperature gradients in the vicinity of the wall of said tubing   are increased, which has the effect of increasing heat transfers.   5. The system of claim 4 such that said tubing has a suitable section to avoid the formation of recirculation pockets in said tubing, so that it avoids the formation of zones o thermal transfer is very weak.   6. The system as claimed in claim 5, such as to produce a succession of stretches and contractions perpendicular to the direction of flow of the fluid in said tube, without causing the formation of recirculation pockets,   a tube is used, the profile of which varies periodically (L ,.   3a, 2a, 3b, 2b, 3c) and whose section remains substantially constant.   7. Heat exchanger device (fig 2) comprising at least one tube (20a, 20b, 20e)) traversed by a fluid having a temperature difference with respect to the external environment surrounding said tube, said tube having a profile suitable for producing contractions (5) and successive stretches (4) of said fluid, said stretches and contractions taking place in directions perpendicular to the direction (1) of fluid flow in said tubing, so that the mixing properties of said tubing are improved and that the temperature gradients in the vicinity of the wall of said tube   are increased, which has the effect of increasing heat transfers.   8. A heat exchanger device according to claim 7 such that said tubing has a section suitable for preventing the formation of recirculation pockets in said tubing, so that the formation of zones o thermal transfer is thus avoided. is very weak.   9. A heat exchanger device according to claim 8 such as to produce a succession of stretches (4) and contractions (5) perpendicular to the direction (1) of fluid flow in said tubing, without causing the formation of pockets recirculation, a tube is used whose profile varies periodically (L,   3a, 2a, 3b, 2b, 3c) and whose section remains substantially constant.   10. Tubing component (fig 1) intended for producing a heat exchanger device (fig 2), said tubing component being intended to be traversed by a fluid having a temperature difference with respect to the external environment surrounding said tubing (Fig 1), said tubing having a profile suitable for producing contractions (5) and stretching (4) successive of said fluid, said stretching and contractions taking place in directions perpendicular to the direction (1) of fluid flow in said tubing, so that the mixing properties of said tubing are improved and the temperature gradients in the vicinity of the wall of said tubing   are increased, which has the effect of increasing heat transfers.   11. Tubing component according to claim 10 such that said tubing has a section suitable for preventing the formation of recirculation pockets in said tubing, so that the formation of zones o thermal transfer is thus avoided. is very weak.   12. Tubing component according to claim 11, for producing a succession of stretches (4) and contractions (5) perpendicular to the direction (1) of fluid flow in said tubing, without causing the formation of recirculation pockets. , said tubing component being such that its profile varies periodically   (L, 3a, 2a, 3b, 2b, 3c) and that its section remains substantially constant.