Heat exchange element and heat exchanger produced therewith
A heat exchange element is described having adjacent, heat-transferring, smooth walls (1) which, between each other, delimit flow channels (4) with preselected channel widths (B) for at least one fluid and are provided with undulations (6) which protrude on both sides and transversely relative to imaginary central planes (7), said undulations having preselected wavelengths (λ) as well as apexes (9a, 9b) with radii of curvature (R) and apex spacings (W) measured transversely relative to the central planes (7). According to the invention inequalities 0.1≦B/W≦0.55 and R≧1.2 B apply at least partially to ratios of channel width (B)/apex spacing (W) and channel width (B)/radius of curvature (R) (FIG. 2).
The invention relates to a heat exchange element having adjacent, heat-transferring, smooth walls which, between each other, delimit flow channels with preselected channel widths for at least one fluid and are provided with undulations which protrude on both sides and transversely relative to imaginary central planes, said undulations having preselected wavelengths and apexes with radii of curvature and apex spacings measured transversely relative to the central planes. The invention also relates to a heat exchanger provided with such a heat exchange element.
BACKGROUND OF THE INVENTIONHeat exchange elements having adjacent, smooth walls which delimit, between each other, flow channels are, according to the purpose of use, components of pipe, plate or ribbed heat exchangers and/or are configured as fin arrangements or lamellae (corrugated ribs). They are used e.g. in automotive vehicles, compressors, washer-dryers, air-conditioning and refrigeration plants or refrigeration dryers for compressed air plants and also used for cooling electronic components and in numerous machines, such as e.g. building, agricultural and forestry machines. The flow channels of heat exchange elements of this type are generally delimited by smooth, flat walls through which, according to the purpose of use, a fluid, such as e.g. air, water or oil flows, and serve for the purpose of transferring heat to the respective fluid or respectively absorbing heat therefrom. In the flow channels, laminar or turbulent flows are thereby formed which, in the zones abutting on the walls, lead to characteristic boundary layers in which the throughflowing fluids are located in the ideal case of a laminar flow substantially in a stationary manner. In comparison thereto the fluids are moved forwards within the central core zones of the flow channels at the greatest speed.
The formation of the boundary layers has the result that the wall surfaces which are present are only incompletely usable for heat transfer and that the achievable heat exchange outputs are small. It has therefore already been known for a long time (DE-PS 596 871) to provide the walls of the flow channels with embossings which emerge from the wall surface and generate turbulence, said embossings being parallel or at acute angles to the flow axis. As a result, the parts of the fluid flows close to the walls are divided repeatedly with formation of local turbulences and the otherwise forming boundary layers are disrupted and destroyed. As a consequence thereof, a noticeable improvement in the heat exchange output occurs.
The described embossings which form turbulence can however lead to two disadvantages. On the one hand they are able not only to deflect the parts of the flow close to the walls in the direction of the core zones and consequently to increase the heat exchange output but also to reduce the flow cross-sections and consequently to lead to an undesired increase in the pressure losses occurring along the flow channels. As a result, the volume flows passing along the flow channels are correspondingly reduced with natural convection, whereas, with forced convection, more powerful fans, pumps or the like are required in order to maintain a preselected volume flow. On the other hand, embossings of the described type can have a tendency to become soiled because of their cross-sectional forms, in particular if they are used e.g. in coolers for agricultural, forestry and building machines or vehicles or in household washer-dryers and if the fluid is process air and/or cooling air.
Heat exchange elements of the initially described type have therefore also already become known (e.g. U.S. Pat. No. 3,907,032) in which the walls delimiting the flow channels are provided with undulations which extend transversely relative to the flow direction or are configured in a continuous undulating shape. Even with such heat exchange elements, no optimum results have been achieved to date since either an unfavourable output/pressure loss ratio is obtained or, in the attempt to optimise this, an increased tendency to become soiled. This applies even when the undulations are provided with predetermined dimensions or comparatively complicated forms (e.g. DE 195 03 766 A1, EP 1 357 345 A2). Likewise known heat exchange elements, in which adjacent walls are provided with differently structured undulations (e.g. DE 102 18 274 A1), have the disadvantage above all that their flow channels have greatly varying cross-sections which is not useful for reducing pressure losses.
SUMMARY OF THE INVENTIONIt is an object of the present invention to design the heat exchange element described above such that the heat exchange output (power) is enhanced and the pressure losses are reduced.
It is another object of the present invention to increase the ratio of heat exchange output to pressure loss of the heat exchange element mentioned above.
Another object of the present invention is to design the heat exchange element such that a reduction in the tendency to become soiled is achieved, particularly in case of heat exchange with gaseous fluids.
Yet another object of the present invention is to provide a heat exchanger with an increased ratio of heat exchange output to pressure loss and at the same time with a reduced tendency to become soiled.
These and other objects of the present invention are obtained by means of a heat exchange element of the type mentioned above and being characterized in that inequalities 0.1≦B/W≦0.55 and R≧1.2 B apply at least partially to ratios of channel width/apex spacing and channel width/radius of curvature. The invention further provides a heat exchanger having such a heat exchange element.
By means of the invention, increased heat exchange outputs are achieved, in particular in conjunction with gaseous fluids such as e.g. air without correspondingly increased pressure losses requiring to be taken into account. In addition, the undulations are configured such that the tendency to become soiled is low. The heat exchange elements according to the invention and heat exchangers equipped therewith are therefore very suitable in particular for applications in coolers for agricultural, forestry and building machines and also in washer-dryers, charge coolers of vehicles or devices for cooling electronic components.
Further advantageous features of the invention are revealed in the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The flow channels 4 are open at their front and rear ends in the longitudinal direction. The regions of the flow channels 4 which are open at the top or bottom in
The walls 1 comprise materials which are normal in heat exchangers (e.g. a metal such as aluminium or copper, graphite, a plastic material or the like). They are in addition preferably smooth, i.e. are provided at their broad sides 5a, 5b which are orientated towards the flow channels 4 and disposed between the upper and lower edges, neither with knobs, flakes, scales or other embossings nor with openings in the form of cuts, holes or the like. Consequently, disruptive dirt-collecting corners or the like are extensively or entirely avoided in the flow channels 4.
In order to improve the heat transfer between the walls 1 and the fluid which is reduced by slowly-moving or entirely immobile boundary layers, the walls 1 are provided in a manner known per se with undulations or sinusoidal undulations 6, these undulations 6 being obtained by deformation of the plates forming the walls 1 about lines which extend according to
In the embodiment, the undulations 6 in all the walls 1 of the heat exchange element according to
According to the invention, the heat exchange element is configured such that, on the one hand, an increase in output is achieved by increasing the heat-exchanging surfaces per unit of volume, and on the other hand, due to great radii of curvature within the flow channels 4, both the pressure loss and the tendency to become soiled is kept within limits.
In order to increase the output, it is provided to choose the channel width B of the heat exchange element according to the invention corresponding to the inequality B≦0.55 W significantly less than the apex spacing W. A ratio of B/W has proved to be advantageous which fulfils the inequality 0.1≦B/W≦0.55, the inequality 0.35≦B/W≦0.50 being maintained particularly preferably. It is consequently achieved that the fluid flow, as indicated in
In order to obtain despite the undulations 6 and the condition B≦0.55 W percentage pressure losses which are—as compared with flat walls—at best smaller than the percentage increases in output obtained by the undulations 6, it is proposed to choose the radii of curvature R in the region of the apexes 9a, 9b to be comparatively large. According to the invention, values of R have proved to be favourable for which the inequality R≦1.3 B applies. It is particularly advantageous if the ratio B/R of the inequality 0≦B/R≦0.75 and even more preferred the inequality 0.2≦B/R≦0.55 is fulfilled. The advantage is consequently achieved that the deflection of the fluid in the flow channels 4 is effected in fact noticeably but comparatively gently, in comparison to configurations in which the radii of curvature are at most 3 mm or even substantially lower, which results in substantially smaller pressure losses.
The configuration according to the invention of the undulations 6 and the channel widths B makes it possible in addition to use larger angles α and β (
Furthermore, the heat exchange elements are provided with dimensions λ≧15 mm or ≧4 W, preferably e.g. 18 mm, 2.4 mm≦R≦6.5 mm, α=β=approx. 30°, 0.08 mm≦S≦5 mm and B<2 mm, these dimensions of course representing merely examples from which a deviation can be made in the individual case according to requirement.
Finally,
According to a further embodiment, not shown, it is possible to replace the curved portions 18, shown in broken lines in
Furthermore, it can be expedient within the scope of the invention to let the wave lengths λ and/or the apex spacings W, in the flow direction 3, become gradually larger or—as is shown in the embodiment according to
The described heat exchange elements can be applied in different ways. For example,
The described embodiments offer in addition to a significant increase of the output (power) an only small percentage increase in pressure losses. This is a consequence of the fact that, on the one hand, there is a substantially greater, heat-exchanging surface and that the flow path for the fluid is correspondingly longer, whilst, on the other hand, the flow can follow the rounded flow channels easily. In addition, the advantage in particular is produced that the tendency to become soiled in the flow channels is low despite the undulations because the broad sides delimiting the flow channels are continuously flat or slightly rounded and smooth and no disruptive corners and angles are formed. This applies even if the dimension of the overlapping of the undulations 6, described with reference to
The invention is not restricted to the described embodiments which can be modified in many ways. This applies above all to the indicated shapes and/or sizes of the different undulations and also to the density of the arrangement thereof. The choice of different parameters is extensively dependent upon the individual case and the desired heat exchange or heat transfer output. In addition, it is possible to dispose the undulations of adjacent walls in the flow direction at a preselected offset if, as a result, the pressure losses are not increased in an undesired manner. Furthermore, the curved portions provided in the apexes of the undulations can have both a circular and an elliptical configuration or follow other curves. It is clear furthermore that the invention can be applied also to heat exchange elements other than those illustrated in the drawings, configured e.g. as fins, and heat exchangers equipped with these. Apart thereof, the given dimensions and/or inequalities should be used at least partly, with particular advantage however in a continuous manner throughout the heat exchange elements produced therewith. Deviations of these dimensions and/or inequalities are, however, also possible within one and the same heat exchange element or heat exchanger. Finally it goes without saying that the different features can be combined with each other in a manner other than that described and illustrated in the drawing.
It will be understood, that each of the elements described above or two or more together, may also find a useful application in other types of construction differing from the types described above.
While the invention has been illustrated and described as embodied in a heat exchange element and a heat exchanger, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
Without further analysis, the forgoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.
Claims
1. Heat exchange element having adjacent, heat-transferring, smooth walls (1, 11, 12, 20, 33, 46, 48) which, between each other, delimit flow channels (4, 41, 42, 51) with preselected channel widths (B) for at least one fluid and are provided with undulations (6, 14) which protrude on both sides and transversely relative to imaginary central planes (7), said undulations having preselected wavelengths (λ) and apexes (9a, 9b) with radii of curvature (R) and apex spacings (W) measured transversely relative to said central planes (7), wherein an inequality 0.1≦B/W≦0.55 applies at least partially to a ratio of said channel width (B) to said apex spacing (W) and wherein an inequality R≧1.2 B applies at least partially to a ratio of said channel widths (B) to said radius of curvature (R).
2. Heat exchange element according to claim 1, wherein an inequality 0≦B/R≦0.75 applies to said ratio of channel width (B)/radius of curvature (R).
3. Heat exchange element according to claim 2, wherein an inequality 0.2≦B/R≦0.55 applies to said ratio of channel width (B)/radius of curvature (R).
4. Heat exchange element according to claim 1, wherein an inequality 0.35≦B/W≦0.50 applies to said ratio of channel width (B)/apex spacing (W).
5. Heat exchange element according to claim 1, wherein an inequality 16 mm≦λ≦30 mm applies at least partially to said wavelength (λ).
6. Heat exchange element according to claim 1, wherein an inequality 2.4 mm≦R≦∞ applies at least partially to said radii of curvature (R), R=∞ corresponding to a wall portion (17) being disposed in a straight plane in the relevant apex and preferably parallel to an associated central plane (7).
7. Heat exchange element according to claim 1, wherein said undulations (6, 14) have first flat portions (15, 16) which rise and fall in straight planes and at the apexes second wall portions which connect the first portions (15, 16) and are continuously curved or are modelled as a polygon.
8. Heat exchange element according to claim 1, wherein said undulations (14) have first flat portions (15, 16) which rise and fall in straight planes and at the apexes second flat, straight wall portions (17) which connect said first portions (15, 16).
9. Heat exchange element according to claim 8, wherein said second flat wall portions (17) which are provided at the apexes are disposed parallel to said central planes (7).
10. Heat exchange element according to claim 1, wherein said undulations have respectively two half-waves (6a, 6b; 14a, 14b; 21a, 21b) which are disposed on opposite sides of said central planes (7).
11. Heat exchange element according to claim 10, wherein said half-waves (21a, 21b) are connected by flat portions (22) which are disposed essentially in said central planes (7).
12. Heat exchange element according to claim 1, wherein said undulations (6, 14) have an identical configuration.
13. Heat exchange element according to claim 1, wherein said flow channels (4) have inlet and/or outlet ends (27, 28) for said fluid extending essentially parallel to said central planes (7).
14. Heat exchange element according to claim 1, wherein said undulations are provided with wavelengths (λ1 to λ3) and/or apex spacings (W3 to W5) which are of different sizes in a direction of said flow channels.
15. Heat exchange element according to claim 1, wherein said walls (1, 11, 12, 20, 33, 46, 48) have a thickness (S) of 0.08 m to 5 mm.
16. Heat exchange element according to claim 1, wherein said undulations (6, 14) are provided with wavelengths (λ) which are at least four times as great as said apex spacing (W).
17. Heat exchange element according to claim 1, wherein said undulations (6, 14) of adjacent walls (1, 11, 12, 20, 33, 46, 48) are disposed without an offset relative to each other in a flow direction.
18. Heat exchange element according to claim 1, and being a part of a ribbed cooling body.
19. Heat exchange element according to claim 1, and being a part of a flat pipe heat exchanger.
20. Heat exchange element according to claim 1, and being configured as a fin.
21. Heat exchange element according to claim 1, and being configured as a lamella (corrugated rib) (32, 43, 44).
22. Heat exchanger having at least one heat exchange element according to claim 1.
Type: Application
Filed: Jun 19, 2006
Publication Date: Dec 28, 2006
Inventors: Joerg Leuschner (Liebenau), Michael Kozica (Immenhausen)
Application Number: 11/455,369
International Classification: F28D 1/02 (20060101);