Generally, plate-tube type heat exchangers are comprised by a plurality of tubes and plates, which are bonded to each other by mechanical fastening or tack welded in order to shape the exchanger structure.
Particularly, such heat exchangers are used as condenser and evaporator in domestic and commercial refrigeration systems, they can also be found on water heaters by means of solar energy, air heaters including inside the tubes, an electric resistance, natural convection static condensers, forced air condensers, natural convection static evaporators and forced air evaporators.
In spite of the widely spread use of these equipments, they have been observed as presenting some drawbacks. In first instance, it may be said that manufacturing process of these equipments is quite complex, since upon being comprised of multiple components, steps to assemble them are burdensome, such as the bonding step between tubes and plates via tack welding, in which it is necessary to bond the tubes one by one to the plates.
Likewise, such a traditional method of binding tubes and plates is not that suitable for the equipments previously mentioned to achieve a efficient heat transfer between the environment and the heating or refrigeration fluid which is inside the tubes, particularly, because the contact surface between tubes and plates is significantly reduced, as may be seen in FIG. 1, showing a cross sectional cut of a “half coverage” type assembly used in plate-tube type heat exchangers of the prior art. In such an assembly, a tube is housed in a plate channel, remaining fixed and contacting directly therewith only through a welding point.
A variant of this traditional method of assembly by welding can be appreciated in FIG. 2, (total coverage), wherein a pair of plates similar to those in FIG. 1 are welded to each other by welding tacks, enclosing the tube between the channel thereof. This variant is neither efficient, since most of times the tube does not fit correctly the space formed by the plate channels, thus having a little direct contact between plates and tube for heat conduction.
On the other hand, there is an additional problem related to maintenance and cleaning of these equipments, specially forced air condensers which include fins, such as those used in domestic or commercial refrigeration systems. In said condensers, spacing between fins is significantly reduced, generally between 2 to 3 mm, which favors adhesion and accumulation of dust, grime and crap therebetween. Said accumulation becomes so important that in many cases, the air passage through fins may be obstructed, thereby causing reduction in condenser's heat exchange ability with the environment and consequently, the refrigeration system stops functioning and cooling properly, affecting other elements of the refrigeration system. Additionally, cleaning said dust or grime adhered to the fins is made difficult due to the space quite reduced existing between fins.
Thus, in the state of the art, it may be found systems which intent to reduce on one hand, the assembly steps of these heat exchangers, such is the case of evaporator described in U.S. Pat. No. 2,212,912, which is formed from an extruded sheet integrally including tubes and fins. However, in order to give the evaporator a final shape, the tubes included in said plates need to be welded to a header or headers using several accessories. Similarly, when it is desired to form condensers with a higher capacity, it is necessary to weld bonding two extruded sheets or to change the size of extrusion die used to manufacture said sheets, thus increasing manufacturing costs.
On the other hand, the European Patent No. 0157370, is directed to a panel for an evaporator or condenser heat exchange, said panel is also formed from an extruded sheet which includes a plurality of oval-shape grooves in cross section; inserting a tube in each of said grooves, said tube undergoes a plastic deformation at its circular wall to refill and to fit the oval contour of the groove walls, thus remaining fixed inside, reason why it is not necessary to use welding in order to bind tubes to the extruded sheet. However, when it is desired to bind two panels to form a larger condenser, this document only provides the use of a piping to connect both panels, without mentioning the existence of a direct and firm bonding therebetween; this lack does not allow to manipulate such panels together so as to form different condenser or evaporator configurations and arrangements.
Finally, both documents from the prior art, do not consider among its objects to form a heat exchanger, on which said problems regarding adhesion, accumulation, and dust and grime cleaning between its components are minimized, which as mentioned above, decrease the capacity of equipment performance.
An additional prior art document is U.S. Pat. No. 2,732,615, related to a method for securing a tube to a metal plate, whereby the plate is deformed to form a channel, and further to the placement of a tube in said channel, pressing the plate against the tube in order to deform it and secure it. This document does not show how to join two or more plates in order to form a tridimensional heat exchanger, neither it indicates the employment of alternative extruded plates.
Accordingly, it has been sought to suppress the drawbacks of the tube-plate-type heat exchangers from the current art, and to provide a tube-plate-type heat exchanger not requiring maintenance, of a very simple and convenient construction, which allows to reduce the number of components and work used during its manufactures, thus eliminating the use of welding to join the tubes and plates, or to join two or more plates to each other, in which cleaning of dust and grime that may be adhered and accumulated between its components is easy.