EP0289915A1

EP0289915A1 - Channeled plate evaporator for refrigerating apparatus

Info

Publication number: EP0289915A1
Application number: EP88106676A
Authority: EP
Inventors: Dino Bacci; Alessandor Ros; Edi Zorzit
Original assignee: Industrie Zanussi SpA
Current assignee: Industrie Zanussi SpA
Priority date: 1987-05-05
Filing date: 1988-04-26
Publication date: 1988-11-09
Also published as: IT1210380B; IT8745718A0

Abstract

Evaporator for refrigeration apparatus comprising steel plates (6,7) which are laser-welded together, so as to form suitable internal channel (20) for the refrigerant fluid, and then spot welded to ensure dimensional stability of the assembly.
Said channel (20) takes up a whole volume of the evaporator and has a substantially rectangular, large-sized cross-section.

Description

The present invention relates to an evaporator for refrigeration appliances, which is made up by two suitably shaped steel plates that are bonded together to form a single plate assembly containing the flow channels ensuring the passage of the refrigerant fluid.
Current channeled-plate evaporators are in most cases formed by two aluminium plates that are bonded together by pressure rolling with the interposition of an anti-bonding or bond-resist material therebetween along the path followed by the flow channels to be obtained.
The resulting evaporator plate assembly is then fed into a press, blown-in and inflated through a hydraulic pump so as to obtain said flow channels.
This process, which is known as "Roll-Bond" technique (a trade mark registered by Olin Mathieson Chemical Corp.), appears to be quite complex owing to the need of using special equipment.
Furthermore, it does not ensure the requi red constancy and repetitivity of the characteristics of the plate assemblies produced in this way, particularly as far as the volume of the flow channels is concerned.
It ensues, therefore, that these plate assemblies are very expensive to produce, not only due to the peculiarity of the materials and the processing techniques required, but also to the need of performing extensive testing and checking operations.
Evaporators are also known, which are made up by two iron plates that are bonded together by braze welding with the interposition of welding material or filler - usually a metal rod - therebetween (Italian patent no. 999.042). However, even this technique appears to be rather complex in that it requires the use of welding material, while the plates have to undergo a heat treatment in order to promote their bonding.
In any case, all known evaporators of the plate type exhibit an internal flow channeling of considerable overall lenght (approx. 3.50m) to compensate for a reduced-size cross-section (approx. 40 to 50 sq.mm) in order to ensure an adequate thermodynamic efficiency.
The main purpose of the present invention is to provide a channeled-plate evaporator which proves simple to produce in a reliable and repetitive way, based on the use of suitably shaped steel plates.
Welding of said plates for sealing purpose is preferably done by laser beam and, therefore, a further aim of the present invention is to reduce the number and the length of the welding paths or seams for a most suitable and economic construction of the evaporator, while preventing it from possibly warping or buckling due to internal pressure of the refrigerant fluid.
Furthermore, the evaporator according to the present invention shall be such as to ensure a better utilization of heat-exchange surfaces, so as to at least match current "roll-bond" evaporators in efficiency.
According to the present invention, therefore, it is provided a channeled plate evaporator, in particular for refrigeration appliances, formed by two suitably shaped steel plates that are welded together with a plurality of seams to form a single plate assembly containing at least a flow channel for the circulation of the refrigerant fluid, the evaporator being characterized in that the channel substantially takes the whole volume of the plate assembly, said plurality of seams including laser weldings, which ensure sealing of the said channel, and spot weldings giving the evaporator the required strength and dimensional stability.
The characteristics and advantages of the present invention will become apparent from the following description, given by way of a non-limiting example with reference to the enclosed drawings, wherein:

- Figs. 1 and 2 show respective schematic views of two different evaporators made according to the invention, and
- Figs. 3 and 4 show respective cross-sectional views of the evaporator as in fig. 1.

The evaporator according to the invention appears in the form of a plate assembly 5 (Figs. 1 and 2) involving two single plates 6,7 (Figs. 3, 4) of carbon steel, ie. a material with good forming properties.
One of said plates is preferably flat, while the second one has a substantially rectangular drawn portion, with rounded corners to facilitate the drawing operation. This solution has the advantage of ensuring a better, tighter contact of the flat evaporator side against the wall of the refrigerator liner.
It is of course possible to implement a solution where both plates are drawn into a suitable shape according to a suitable pattern. In the case of plates with a symmetrical pattern, a single forming equipment would be required to draw both of them.
This embodiment appears quite advantageous whenever the evaporator is attached freely, ie. not in a tight contact with the inner wall of the refrigerator.
After drawing, the plates 6 and 7 must be bonded together in order to ensure the tight separation of the channels. This is most suitably done by means of laser welding so that no filler or heat-treatment is required any longer, such as in the case of the known steel evaporator designs with braze-welded plates.
In order to make the process economically advantageous and accurate, it is important that both the length and the number of the welding paths or seams be minimized so as to reduce the intervals between successive weldings.
According to the main characteristic of the present invention, the proposed solution lies in the construction of an evaporator 5 having at least an inner channel 20 which substantially involves the whole volume of the plate assembly (Figs. 1 and 2).
Furthermore, unlike the solution used in evaporators of the known types which have a high number of parallelly running channels with a small sized circular cross-section, the channeling of the evaporator according to the invention has a quite limited length and a substantially rectangular, wide-sized cross-section (Figs. 3 and 4).
By way of example, it can be said that - for a rectangular plate evaporator having side dimensions of 41 x 31 cm - the traditional solution would imply channels with a cross-section size of 40-50 sq.mm for a total length of approx. 3.5 m, while a solution according to the present invention involves channels with a cross-section size of 110-120 sq.mm for a total length of just approx. 1.8 m.
The new solution enables laser weldings to be reduced to a minimum, ie. to just six seams, as indicated by the reference numerals 8,9,10,11,12,13 in Fig. 1, in the case of a dry expansion evaporator, or even to just three seams, as indicated by the reference numerals 14,15,16 in Fig. 2, in the case of a flooded-type evaporator.
Dry-expansion evaporators are fed with refrigerant fluid at a flow rate which ensures full vaporization of the same fluid on the outlet side of the evaporator; in Fig 1 the inlet or feeding side is indicated by the arrow A, while the outlet side is indicated by the arrow B.
Flooded evaporators (Fig. 2) do not vaporize the total volume of refrigerant in them, a part of which remains therefore in liquid state. This enables a high heat-exchange uniformity to be obtained and the evaporator to be given a more compact size for a same refrigeration load.
With both solutions, considering the feature of the invention according to which the channeling 20 has a very large cross-section size, the need arises to make a plurality of strengthening seams in order to prevent warping or buckling of the evaporator plate assembly as may be caused by internal pressure of the refrigerant fluid.
Fluid strengthening seams 21 are most advantageously made by resistance spot welding, having care to have the plate 7 (or both plates) provided with suitable indentations 22 (Fig. 3) as these can be directly obtained in the sheet metal during drawing of the same.
Such a construction also enables the thickness of the sheet metal to be reduced to a minimum, while ensuring best dimensional stability of the evaporator under operational conditions.
In case the evaporator is of the flooded type, channel 20 is preferably symmetrical to a centre line of the plate assembly 5 and also the laser welding seams 14,15,16, being in the number of three, are symmetrical to the same centre line.
Altogether, an evaporator is in this way obtained, which is cheaper than and at least as efficient as traditional designs, as it exploits a larger heat-exchange surface, ie. almost the whole plate surface.
As a matter of fact, the low number of welding seams and the very close contiguity of the flow channels are such as to minimize that part of the evaporator surface which is not directly involved by the circulating refrigerant fluid.

Claims

1. Channeled plate evaporator, in particular for refrigeration appliances, formed by two suitably shaped steel plates (6,7) that are welded together with a plurality of seams to form a single plate assembly (5) containing at least a flow channel (20) for the circulation of the refrigerant fluid, the evaporator being characterized in that the channel (20) substantially takes the whole volume of the plate assembly (5), said plurality of seams including laser weldings (8-13,14-16), which ensure sealing of the said channel (20), and spot weldings (21) giving the evaporator the required strength and dimensional stability.

2. Channeled plate evaporator according to claim 1, characterized in that at least one of the plates (7) is provided with a drawn portion forming said channel (20) and with indentations (22) for said spot weldings.

3. Channeled plate evaporators according to claim 1, characterized in that said channel (20) has a substantially rectangular cross-section and extends along closely contiguos paths.

4. Channeled plate evaporator according to claim 1, of the flooded evaporator type, characterized in that said channel (20) is symmetrical to a centre line of the plate assembly (5) and also said laser welding seams (14-16), being in the number of three,are symmetrical to the same centre line.