US 3339627 A
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Description (OCR text may contain errors)
Sept. 5, 1967 J, VAN GEU ET AL 3,339,627
REGENERAT OR Filed March 22, 1965 INVENTORS. JOHANNES R. VAN GEL NS JAN MULDER AGENT United States Patent corporation of Delaware Filed Mar. 22, 1965, Ser. No. 444,099
5 Claims. (Cl. 165-4) The invention relates to a regenerator comprising a filling mass consisting of a plurality of stacked metal gauzes.
This kind of regenerators is known and is employed for example in coldgas refrigerators and other 'devices for producing cold. The regenerator is traversed altenately in one direction by a compressed medium, which gives off heat to the filling mass and in the other direction by an expanded medium which absorbs heat from the filling mass.
A problem involved in this kind of regenerators resides in that the material of the gauze, for example copper, Phosphor bronze etc. does not have an adequately high specific heat at very low temperatures. This means that at these low temperatures the filling mass cannot store an adequate quantity of heat, neither can it give off an adequate quantity of heat. When these known regenerators are employed, it is therefore not possible to attain extremely low temperatures.
It is known that other materials still have a satisfactory specific heat at said low temperatures, but these materials have the disadvantage that they are all so weak and have such a small tensile strength that no gauze can be made from them.
The use of gauzes as a filling mass has the advantage that owing to their structure such gauzes have point contacts only locally. This means that the thermal resistance between two adjacent gauzes is fairly high without the need for using additional insulating means. Therefore, the thermal conductivity in the direction in which the medium passes through the filling mass will be small. A further advantage of gauze regenerators is that the medium is not compelled to follow fixed channels of flow so that behind each gauze the medium can mix to some extent in a transverse direction.
The invention has for its object to provide a regenerator which operates satisfactorily at extremely low temperatures, while the favourable properties of the gauze are maintained.
The regenerator according to the invention is characterized in that the wires of the metal gauze are provided after the manufacture of the gauze at their surface with a metal layer of a metal which has a comparatively high specific heat below 100 K.
In a further advantageous embodiment of the regenerator according to the invention the metal gauze is made of wire material having a diameter of not more than 100 microns while the meshes of the gauze have a width at least equal to the wire diameter, the metal gauze being provided with a metal layer having a thickness smaller than half the size of mesh, preferably smaller than 90% of half the size of mesh. Thus a regenerator is obtained which has a very satisfactory degree of efficiency at very low temperatures, While the thermal conductivity in the direction of flow is small without additional precautions. The specific dimensions of the gauzes have been chosen for a good filling factor; a good heat transfer surface, and a sufficient mass of material for storing heat.
It has been found by surprise that the metal layers according to the invention can be electrolytically deposited on the gauze. The gauze structure (hills and valleys) is maintained very satisfactorily, whilst the meshes are not closed. Of course, it is also possible to apply the metal layer to the gauze by chemical agency or by vapour-deposition.
' In 'a further embodiment the applied metal layer may consist of a metal of the group comprising lead, mercury, cadmium, thallium, rare earth metals, caseium, indium, bismuth or alloys thereof.
There is a possibility that at the contact areas of adjacent gauzes the soft surface layer should be flattened or even be pressed away, so that the thermal conductivity in the direction of flow might increase.
In order to overcome said risk an advantageous embodiment of the regenerator according to the invention has the feature that the surface layer consisting of a metal having a comparatively high specific heat at very low temperatures below K. is coated with a further layer consisting of a metal having a greater hardness than the first-mentioned layer.
The gauzes engage each other in this case with their hard surfaces, so that the contact surface and hence the thermal conductivity are smaller.
In a further advantageous embodiment the metal of the further surface layer is not only harder but also has, below 100 K., a smaller thermal conductivity than the material of the first surface layer.
The thickness of the further surface layer in a further advantageous embodiment is at the most 10 microns.
The material of the further surface layer my be chromium, nickel, iron or alloys hereof.
In a further advantageous embodiment of the regenerator according to the invention the wires of the gauze are provided with a number of surface layers, which consist alternately of a metal having a comparatively high specific heat below 100 K. and a metal having a greater hardness and a comparatively low thermal conductivity.
In the manner described above a very simple regenerator can be manufactured at low cost, which operates still satisfactorily at very low temperatures.
FIG. 1 is a cross-sectional view of the regenerator housing 1 having a stack 2 of Wire gauzes 3 therein.
FIG. 2 is a cross-sectional view of the wire gauges 3 having a nucleus 4 for example of copper or phosphorus bronze and an outer layer 5 of a material having a high heat capacity at low temperature, for example, lead.
FIG. 3 is a cross-sectional view of the wire gauze 3 in which a copper or phosphorus bronze nucleus 6 is provided with a layer 7 of a material having a high heat capacity at low temperatures, such as lead and an outer layer 8 is supplied provided with a metal having a greater hardness than the layer 7, such as chromium.
It should be noted that from British patent specification 931,260 there is known a regenerator, the filling mass of which consists of a number of stacked perforated metal plates provided With a surface layer of a metal having a satisfactory thermal capacity at a low temperture. A disadvantage of this regenerator is that additional expedients (spacers) are required for restricting the thermal conductivity in the direction of flow. The regenerator is therefore expensive. The invention obviates this disadvantage completely since gauzes, owing to the maintenance of their natural gauze structure, have only point contacts with each other, so that a satisfactory thermal resistance in the direction of flow is obtained.
What is claimed is:
1. A regenerator comprising a housing, a filling mass constituted of a plurality of stacked metal gauzes, said meal gauzes being provided with a coating constituted of a first metal layer having a comparatively high specific heat below 100 K. and a second layer of a metal having a greater hardness than said first layer.
2. A regenerator as claimed in claim 1 wherein the r 3 material of said second layer has a comparatively low thermal conductivity below 100 K.
3. A regenerator as claimed in claim 1 wherein said second layer has a thickness of not more than 10 microns.
4. A regenerator as claimed in claim 1 wherein said second layer is selected from the group consisting of chromium, nickel, iron and alloys thereof.
5. A regenerator as claimed in claim 2 wherein said coating is constructed alternately of said metal having a comparatively high specific heat below 100 K. and said metal having a greater hardness and a comparatively low thermal conductivity below 100 K.
4 References Cited UNITED STATES PATENTS 3,216,484 11/1965 Gifiord 1654 FOREIGN PATENTS 157,334 6/ 1954 Australia. 609,232 1 1 1960 Canada.
65,498 4/ 1950 Netherlands.
10 ROBERT A. OLEARY, Primary Examiner.
A. W. DAVIS, Assistant Examiner.