Patent Application
20080148568
The invention relates to a process for making a heat exchanger.
Heat exchangers are generally known in the art and one common type consists of a number of parallel tubes, fin-like elements being provided between each part of neighbouring tubes. An example of such a heat exchanger has been described in U.S. Pat. No. 5,780,825. Such heat exchangers can be either a so-called parallel flow heat exchanger, or a single flow heat exchanger such as a serpentine like heat exchanger.
Normally such heat exchangers are produced by extruding a number of tubes, making a set of fins to be placed between each pair of neighbouring tubes, and providing end connectors or collectors to the end portion of the tubes, where upon the whole assembly is brased together.
It is an object of the invention to provide a process for making a heat exchanger, which is less complicated to make, and in which less components need to be handled in order to obtain the final assembly of the heat exchanger.
This and other objects are achieved in that a profile is extruded which is composed of a number of parallel tubes and web-like portions interconnecting said tubes, in that part of the connection made by the web-like portions is removed and the extruded product is expanded in a direction perpendicular to the longitudinal direction of the tubes, and in that connecting means are provided allowing a fluid to flow through the tubes.
In this way it is obtained that based upon a single extrusion a heat exchanger can be obtained which is as efficient as the standard heat exchanger, and which can be obtained with less efforts.
It must be remarked that it is well known that extruded aluminium profiles can be shaped and manipulated in order to produce mesh-shaped products. Such products have been described in GB-A-2 101176, AU-A 84 27 721 and GB-A-1 588 197. In all these examples the ribs forming the mesh have been considered as being solid and the product is only envisaged in a mesh functionality.
In this type the products, the aluminium extrusions comprising solid ribs lined by the webs in converted by cutting slots a specific length in the webs and thereafter stretching the profile laterally.
By using tubular elements in stead of solid elements and fin like protrusions it is possible to modify the heat transfer characteristics. By varying the length of the slots cut into the web part of the extruded profiles before stretching in a lateral manner, it is possible to affect the air flow patterns and induce turbulence which will further improve heat transfers.
Other advantages and characteristics of the invention will become clear from the following description reference being made to the annexed drawings, in which:
In
After extrusion of the profile, each web 3 is provided with a number of slots 4, extending parallel to the tubes 2. In the embodiment shown the slots 4 have a length which is substantially longer than the remaining web portion between two adjacent slots in the same web. Moreover the slots 4 in the different webs are all positioned in the same way with respect to the end face of the extruded profile.
After expansion of the profile in a direction perpendicular to the longitudinal direction of the tubes 2 a product as shown in
By providing suitable connecting means to the end portions of the tubes, so as to form an input and an output for a fluid and interconnecting the different tubes a fluid heat exchanger can be obtained.
In
In the
Each web 13 is provided with a number of protruding portions extending from both faces of the web 13. In the embodiment shown there are four protruding portions 14, 15, 16, 17 having a planar shape, and the extrusions 14 and 15 are located in the same plane as the extrusions 16 and 17 respectively.
It will be obvious that other types or shapes of protruding portions and different numbers than four are possible.
After extrusions of the profiles 11, a number of slots is made in each web, as shown in
Their position however is such that as seen along the longitudinal direction of the tubes 12 each slot 19 is extending halfway between two successive slots 18 in the neighbouring part of the same web 13.
In this way each web 13 is provided with a number of slots 18, 19 whereby the slots 19 are offset with respect to the slots 18.
After expansion of the extruded profile in the direction perpendicular to the axis of the tubes 12, a product as shown in
In order to test the performance of a heat exchanger obtained by means of the extruded and expanded products a test made with a heat exchanger of the type shown in
A profile consisting of 8 tubular members 8 mm outside diameter with a 1.0 mm wall thickness and an interconnecting web of 2 mm width similar to the profile shown in
Individual expanded profiles were assembled to make a panel with overall width of 360 mm and a height of 300 mm. Tubes were interconnected by means of ‘U’ bends so that flow paths within each set of panels could be controlled. The size of the panels was matched to the available opening on a wind tunnel that was used to assess the heat transfer efficiency of the system.
A conventional tube and fin brazed radiator, designed for automotive use, was used in the trials to provide comparative data to existing state of art heat exchangers.
Oil, preheated to 100° C., was passed through the tubular profiles at rates of either 150 or 300 litres per hour and the wind speed was varied from 4 metres per second up to 11 metres per second. The temperature of the out-going oil was measured after an operating time of 5 minutes.
Efficiency was calculated using the formula
(Toil inlet−Toil outlet)/(Toil inlet−TAir.)
Where oil inlet is 100° C. and the air temperature is 20° C.
Thus, for a panel consisting of 3 layer with each layer being a separate oil circuit and where oil flow rate is 150 litres/hr and the wind speed is 11 m/sec, the temperature drop for oil is (100-49.6)° C. and the difference between oil inlet and ambient air temperature is 80° C., an efficiency of 0.64 is calculated.
The results from the testing are detailed in table 1-6.
Best heat transfer results were obtained with oil flow of 150 litres per hour in the test panels as well as in the conventional radiator. Surprisingly, the extruded panel heat exchanger performed up to over 70% of the efficiency of the state of art heat exchanger. This is despite the fact that the air-side flow path had not been optimised and the shape of the tubular elements was not optimised. Ideally the tube profile would preferably be oval or tear-drop shaped and could incorporate internal fin to enhance heat transfer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04078496.9 | Dec 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2005/013711 | 12/20/2005 | WO | 00 | 10/10/2007 |
