[0001] The present invention refers to a heat exchanger, in particular to a heat exchanger produced according to a Roll-Bond method, comprising at least one plate made of thermally conductive material which comprises channels to enable flowing of heat-transfer medium.

[0002] Known heat exchangers produced according to a Roll-Bond method comprise a channel system provided between two plates where normally heat-transfer medium conveys, which during flow through the heat exchanger transmits or receives the heat. Relatively small surface for transfer of heat represents a significant drawback of known heat exchangers, particularly in cases when the required heat is to be conveyed from the first medium to the second medium and vice versa and when said medium is in a gas state and flows over the outer surface of the heat exchanger. Therefore, balancing of heat resistances is required, that can be obtained by increasing the surface of transfer to the medium in the gas state which transfers the heat.

[0003] Thus, for example, the document DE 19751768 discloses a solution for increasing the surface of the Roll-Bond heat exchangers by flexing a plate in the sense of the letter U or similar, obtaining therewith two or more parallel planes a winding section can be placed between said planes being in a thermally conductive contact with the plates. A drawback of such a solution is a relatively low efficiency of the ribs and, respectively, the winding sections since the height of the winding sections depends on the spacing between the neighbouring plates.

[0004] Furthermore, the document EP 2 438 380 discloses a solution which provides folding the plates in the shape of a flattened spiral and cutting-off parts of the plate between the parallel channels in order to increase the surface for heat transfer. A drawback of said provision lies in an unsatisfied increase of the surface for heat transfer when compared to plate fin heat exchangers or similar.

[0005] It is the object of the present invention to create a heat exchanger, particularly a heat exchanger produced according to a Roll-Bond method which remedies drawbacks of the know solutions. [0006] According to the present invention the object as set above is solved by features set forth in a characterizing clause of the Claim 1. Details of the invention are disclosed in respective sub-claims.

[0007] The invention is further described in detail by way of non-limiting embodiment, and with a reference to the accompanying drawings, where

Fig. 1 shows a heat exchanger according to the invention in a three-dimensional view,

Fig. 2 shows a heat exchanger of Fig. 1 viewed in direction of the arrow II,

Fig. 3 shows a heat exchanger of Fig. 1 viewed in direction of the arrow III,

Fig. 4 shows a heat exchanger of Fig. 1 viewed in direction of the arrow IV,

Fig. 5 shows a heat exchanger of Fig. 1 showing no means for improving heat transfer,

Fig. 6 shows means for improving heat transfer in a partial three-dimensional view.

[0008] Throughout the following description, the expression„heat transfer" refers to each thermal conduction, thermal convection or thermal radiation from one medium and/or matter to the other. Moreover, a heat exchanger is further described on the basis of an embodiment selected in the particular case as an evaporator for a cooling and/or freezing apparatus. It is understood that the heat exchanger according to the invention can be used in other areas such as with devices exploiting magnetocaloric or elastocaloric effect, heat pumps, air conditioning devices and similar. The heat exchanger according to the invention is formed of plurality of plates arranged in approximately parallel planes and mutually interconnected by means of webs, so that the heat exchanger in general resembles a form of a spiral or a meander. In the present embodiment the heat exchanger comprises two mutually parallel plates 1, 2 preferably integrally connected by means of a web 3, wherein the heat exchanger resembles an approximate form of the letter U. Said heat exchanger is preferably made by a so called Roll-Bond process or similar process by means of which and in a manner known per se at least one channel 4 is created in the plates 1, 2 through which medium for heat transfer flows. Obviously, an embodiment of the heat exchanger comprising only one plate is possible, without departing form the spirit of the invention.

[0009] Preferably, said channel 4 is formed and implemented in each plate 1, 2 in a manner of a meander, and via a web 3 fluidly connects the plates 1, 2. An embodiment of the heat exchanger is possible, where said channel 4 branches off at the first free end of the plate 1, 2 into at least two further channels 4', which join at the other end of the plate 1, 2 to form the original channel 4, which in turn again branches off into at least two further channels 4'. Said branching and joining the channel 4 runs alternately over the entire width of the plate 1, 2, whereby both the branching and the joining of the channel 4 is provided in the area of the worst efficiency. Furthermore, according to the present invention an embodiment is provided where each of the one upon the other lying channel 4 of the first plate 1 and the channel 4 of the second plate 2 are mutually transversally offset with regard to the extension of the channel 4.

[00010] It is provided for according to the present invention that at least one of the flat sides of the plates 1, 2 is, preferably at least two of the flat sides of the plates 1, 2 are, and more preferably all of the flat sides of the plates 1, 2 of the heat exchanger are provided with at least one means 5, 6 for improving heat transfer. Said means 5, 6 for improving heat transfer can be selected in the sense of at least one longitudinal thin-layer wave like structure, a plurality of ribs or fins and similar. The height of each means 5, 6 i.e. the measurement thereof in direction perpendicularly with regard to each plate 1, 2, and, respectively, in direction perpendicularly off each flat side of each plate 1, 2 is preferably equal over the entire length and/or width of the heat exchanger. An inlet pipe 7 for delivering cooling agent is associated with the entering end of said channel 4, whereas an outlet pipe 8 for discharging cooling agent is associated with the exiting end of said channel 4.

[00011] Each said means 5, 6 is formed at the side averted form the plate 1, 2 and, optionally, at the side facing the plate 1, 2 (in Fig. 6 shown with a dashed line) with at least one groove 9 to accommodate a heating pipe 10, which is preferably formed and implemented in grooves 9 in a manner of a meander. The formation of the means 5, 6 with the groove 9 on both said sides of the plate 1, 2 enables installation of the means 5, 6 without taking care about the orientation thereof at the assembly. In the present embodiment said means 5, 6 is formed as a wave like structure comprising crests 11 and troughs 12. According to the invention it is preferably provided for that the wavelength t between each crest 11 and each trough 12 of the first means 5 differs from the wavelength t with the second means 6. In the present embodiment said wavelength t of the first means 5 is longer than the wavelength t of the second means 6. As a result, the efficiency of the heat exchanger increases significantly, and simultaneously accumulation of frost is prevented in the area of the first means 5. Particularly advantageous solution represents a possibility that the means 5 having longer wavelength t is arranged on the heat exchanger at the side where the air enters the heat exchanger. Moreover, it is provided for that also the wavelengths t of the first means 5 and/or the second means 6 mutually differs. Said at least one groove 9 is formed in the direction transversally with regard to the extension of said waves and in the area of the extreme of each crest 11 and, respectively, the trough 12.

[0010] Furthermore, it is provided according to the present invention that said wave like structure of the means 5, 6 is configured in a manner that it cooperates with the flat sections of the plates 1, 2 between each neighbouring channels 4. To this end the wave like structure of the means 5, 6 is formed at the place of the cooperation with the plate 1, 2 with a respective offset for passing the channel 4 through. In this manner plates 1, 2 and means 5, 6 can be connected in various ways.

[0011] An embodiment of the means 5, 6 is also possible where said offset cooperates with the channel 4 and, respectively, with the top thereof, whereby the heat transfer and, thus, the efficiency of the heat exchanger is significantly improved. In this case the sections with said offsets are preferably formed as tongues cooperating with the channel 4. Due to contact bond in this places heat transfer is also achieved between the tops of the channel 4 and the means 5, 6, thus improving the efficiency of the heat exchanger.

[0012] Moreover, an embodiment of the means 5, 6 is possible that cooperate both with the flat sections of the plates 1, 2 between each neighbouring channels 4 and with the channel 4 and, respectively, the top thereof.

[0013] Said wave like structure of the means 5, 6 is preferably made by punching out, or cutting, or by means of plastic deformation such as a deep-draw, for instance, and is configured in a manner that it can be placed on either side of the plate 1, 2. Thus, the production costs of the means 5, 6 and, as a result, the production costs of the heat exchanger are substantially lowered.

[0014] According to the invention is further provided that a partial air-stop is inserted into the area 13 of the web 3 connecting each plates 1, 2, said air-stop being intended to homogenize the velocity of the circulating air in all sections of the heat exchanger. Uncontrolled escape of the air through the sections having the lowest air resistance is thus prevented, and, simultaneously, the surfaces are used to transfer heat. Said air-stop can be selected as a fin, net, foam or a section being in contact with the plate 1, 2, whereby along with the preventing increase of the air velocity in said area the surface for heat transfer and, thus, efficiency of the heat exchanger is increased.

[0015] With the second embodiment of the heat exchanger according to the invention it is provided for that the heating pipe 10 is placed directly onto the plate 1, 2, whereby the latter is pre-formed in a manner that after the assembly the heating pipe 10 is sunken into the surface of the plate 1, 2 and attached in a manner know per se, not shown in detail. Such direct contact of the heating pipe 10 with the plate 1, 2 enables larger contact surface between the heating pipe and the plate, and as a result thawing of the heat exchanger is improved due to the better heat transfer between the heating pipe 10 and the plate 1, 2. With said second embodiment the means 5, 6 for improving heat transfer can be particularly simply arranged onto the plate 1, 2 and, respectively, over the heating pipe 10, since the groove 9 on the means 5, 6 is formed on both sides thereof. Said two-sided formation of the groove 9 on the means 5, 6 enables also two heating pipes 10 to be installed easily, the first one at the side averted from the plate 1, 2, and the second one at the side facing the plate 1, 2.