WO2000022366A1

WO2000022366A1 - High efficiency heat exchanger with oval tubes

Info

Publication number: WO2000022366A1
Application number: PCT/RO1998/000018
Authority: WO
Inventors: Panait Niculescu; Gheorghe Sora; Cristinel Crisan
Original assignee: S.C. Romradiatoare S.A.
Priority date: 1998-10-09
Filing date: 1998-10-09
Publication date: 2000-04-20

Abstract

The invention covers a high efficiency heat exchanger with oval tubes (9A) intended for use as main cooling radiator within the cooling systems of vehicles equipped with internal combustion engines. As per the invention, the high efficiency heat exchanger with oval tubes (9A) is characterized by the fact that it features a special constructive design of the core (9) based on one or two rows of coolant circulating tubes (9A) having an oval section, and on special design dissipating fins (9B). The tight fixing of the tubes (9A) in the header plates (3 and 7) is performed either by means of a special adhesive, or by local brazing of the mounting zone. The heat exchanger also features side component parts (4A, 4B, 8A, and 8B) of a special configuration designed to ensure the mechanical protection of the core. The high efficiency heat exchanger with oval tubes offers a substantial increase of the heat dissipating performance level as compared to other heat exchangers with oval tubes featuring a compact design of the core.

Description

HIGH EFFICIENCY HEAT EXCHANGER WITH OVAL TUBES

The invention covers a highly efficient heat exchanger with oval tubes intended for use as main cooling unit in the cooling system on motor vehicles powered by internal combustion engines.

The heat exchanger is described as a global example for the constructive principle used in the design and manufacturing of heat exchangers typically used on car, small and medium capacity trucks, vans and utility vehicles. By taking some special, constructive measures, intended to improve the mechanical resistance to the complex strains induced in running, the constructive principle can be extended to other applications of cooling units on heavy duty trucks, busses, industrial or agricultural tractors or on any other transportation means equipped with water or monoethylenglycol/poliethylenglycol solution cooled internal combustion engines needing a heat exchanger in the system.

From the numerous types of heat exchangers designed and manufactured so far, all of which being equivalent to a heat dissipating device or instrument, better known and referred to, hereinafter, as "radiator", a special place is taken by the constructive system based on aluminum radiant element, assembled either by integral brazing or by expanding the fluid circulating tubes and having plastic tanks.

Very important in the case of a radiator is the specification of a certain fluid, heat carrying agent, which is going to be used, referred to hereinafter as "coolant", and of a certain fluid or cooling agent, referred to hereinafter as "cooling agent" which has to absorb the quantity of heat released by the coolant. The most important functional characteristics, monitored as specific performance level of the radiator are as follows: mechanical strength of the unit, sealing capacity, endurance to a certain working pressure (internal and external), differential pressure (pressure drop) of the coolant and cooling agent between radiator inlet and outlet and, more so, the heat exchanging capacity. All these general technical requirements are referred to under the generic designation of "functional performance".

For description and reference purposes it is necessary to present the definitions, basic functions and the generally accepted designations, abridged forms, of the main component parts - simple parts and subassemblies -of some heat exchangers in the range of automotive radiators. The main component parts of an aluminum core radiator with plastic tanks are:

• tanks, manifolds or basins are the component parts ensuring the intake, distribution, guiding, collection and exhaust of the whole coolant flow which enters, passes through and exits the radiator; these component parts are referred to hereinafter as "tanks";

• header plates, end plates, or grids are the component parts that connectthe tubes for the internal circulation of the fluid inside the dissipating element, to the tanks of the radiator, acting as an intermediate, shock resisting and perfectly sealed component part, ensuring the continuity of the inner hydraulic circuit of the radiator by connecting the tanks to the core. These component parts are referred to hereinafter as "header plates"; the connecting ports in the base plates corresponding to the tubes for the internal circulation of the fluid are referred to as "cavities"; the metallic header plates are assembled to the tanks by "set mounting, which is the equivalent of folding the edges of the header plates over a number of specially designed projections of the tanks to eliminate any possible relative displacement between these two component parts;

• the side supporting sections, the stiffening sections, the side brackets are the component parts (parts or subassemblies) which secure the core against any potential mechanical strain both generally, through an optimum rigidity, and locally (on the extremities of the element), this local protection being mainly against the direct mechanical contacts that can occur during usage; these components are complete with mechanical constructive elements (such as supports, sections, rods, clamps, collars, etc.) which are designed for assembling purposes of the radiator to the frame of the engine the radiator is intended for, and/or to fit the fan funnel, the intake and outlet tubing of the cooling agent, or generally referred to as "the forced cooling group", thus ensuring a perfectly tight proof circuit for the cooling agent (usually the atmospheric air) through the core, namely the radiator; these components are referred to hereinafter as Jside brackets";

• the protective side sections, fin protection guards, side guards or fake side brackets are the component parts that exclusively secure the extremities of the core against mechanical strains (especially the dissipating fins), this type of protection referring to the possible mechanical impacts which may occur during manufacturing, mounting or use of the radiator; these optional component parts are designed to complete the side brackets of the radiator in case the stiffening and mounting functions of the side brackets permit shortening; these component parts are referred to hereinafter as "side guards";

• the gaskets represent those parts which ensure a perfectly sealed mechanical assembling of the tanks to the header plates of the radiators ensuring the continuity of the internal hydraulic circuit of the radiator (there are models where this particular assembling is made through soldering or binding with adhesives, all these methods implying a technological material); these component parts are referred to hereinafter as "gaskets".

• the core is the subassembly which must ensure the main heat transfer (total thermal flux) for which the radiator was designed and sized; this subassembly consists of tubes permitting the internal circulation of the coolant, referred to hereinafter as "tubes", and of the dissipating fins which are designed to increase the total heat exchange surface, hereinafter called "fins"; for lack of a more succinct denomination, the subassembly shall be called "core".

In the range of radiators there are some types of heat exchangers which aluminum core with oval tubes and plastic tanks in order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines.

The core with oval tubes is part of the category of "cores featuring a mechanical contact between tubes and fins" which, sometimes, is also referred to as "expanded core" a denomination which expresses the procedure through which the contact between tubes and fins is obtained ("expanding", i.e. mechanical increase of the outer dimensions of the tubes, from the inside towards the outside, over the equivalent internal dimensions of the corresponding ports in the fins, which, from material strength point of view is defined as hooping; the procedure is well known in radiator manufacturing for it needs no material addition, as in the case of radiators assembled through binding, or as in the case of radiators assembled through brazing).

In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines there are some types of heat exchangers which use plastic tanks and aluminum core with oval tubes arranged in one row and plastic tanks (French Patents No. 2602582, 2690229 and 2690230); this solution has the following shortcomings: limited functional performance level and, implicitly, substantial limits in application.

In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines there are some types of heat exchangers which use plastic tanks and aluminum core with oval tubes, with a monoblock design of the tanks and header plates (British Patent No. 2180634) or with two symmetrical halves (French Patent No. 2602581); these types have the following shortcomings: the block component parts can be manufactured of plastic materials only and the shape of the respective parts complicates a lot the plastic injection technique and the dies.

In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines there are some types of heat exchangers which use the aluminum core with oval tubes, the sealing between the tubes and the header plates being made by means of gaskets; this method has the following shortcomings: the gaskets used to ensure perfectly sealed radiators may require extremely complex shapes or sophisticated tightening devices (British Patent No. 2049151 A, American Patent No. 4917182 and French Patents Nos. 2690230, 2690230); some gasket types do not offer sufficient sealing surface (American Patent No. 4997035).

Today, the manufacturers of radiators with oval or elliptic tubes use another method to assemble the tubes to the header plates by means of a gasket (the perfect shape of the gasket being of a lesser importance, the only problem with this method is the geometrical match between the cross section of the tubes and the shape of the cavities in the base plate). The method consists of shaping the end of the tubes over a length at least equal to the length of the contact zone with the cavities in the base plate. The shaping of the ends of the tubes is still performed in three ways:

1. by changing the oval or elliptical contour of the tube into a round (cylindrical) contour;

2. by keeping the oval or elliptical shape but increasing the cross section by contour expansion (procedure known as local "expanding", the expanding procedure being dealt with under the section "General Definition of the Expanded Core"); 3. by changing the oval or elliptic contour into a sufficiently regular one (for instance square with round corners, rectangular with small semicircular sides, etc.) to permit an easy shaping of the tools used to pierce through and chamfer the cavities in the header plates, or to make the gasket, respectively; from this point of view it can be seen why the shaping of the tube ends by the first method is the simplest and most advantageous from the point of view of costs. In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines there are some types of heat exchangers which use the aluminum core with oval tubes at which the sealing between the tubes and the header plates is obtained without the use of any gasket; this technique has the following disadvantages: the tubes are fitted into the header plates by sophisticated means implying a high accuracy of the shape of the cavities in the header plates (British Patent No. 2171192A); there are radiator models needing header plates of complex constructive shapes which can be obtained only through plastic injection (German Patent No. 4028233) or metallic header plates with thickness values exceeding certain limits (American Patent No. 5046555) implying large mass component parts and machining difficulties even if made of aluminum or aluminum alloys; other radiators require a high accuracy mounting of the tanks to the core (British Patent No. 2138335A).

In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines there are some types of heat exchangers which use the aluminum core with oval tubes with integrated internal turbulence promoting elements (French Patent No. 2690233); this solution presents the following disadvantages: to overcome the technical difficulties encountered when shaping and tight sealing oval tubes there is only one industrial procedure known so far which is good in theory but less used in the industrial practice.

In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines there are some types of heat exchangers which use the aluminum core with the tubes having an oval shape only at the assembling ends to the header plates, the big axis of the oval shape being parallel to the longitudinal axis of the base plate, the rest of the tube being cylindrical (French Patent No. 2605726); this solution presents the disadvantage of a lesser heat exchange, from this respect the cylindrical tubes being reputed to be less efficient than the oval ones.

In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines there are some types of heat exchangers which use the aluminum core at which the assembling of the tubes to the header plates is performed by means of adhesives; this solution has known several variants so far, all requiring plastic header plates of unusual shapes: either with grooves (French Patent No. 2642155) presenting the disadvantage of a special mechanical shaping of the tube ends, either with an adhesive retaining ring chamber and side port for the injection of the adhesive at each tube fitting cavity in the base plate (French Patents Nos. 2602582 and 2214875), or with adhesive injection groove network (French Patent No. 2499234), with all the disadvantages implied by complex component parts: very costly, high complexity injection dies and techniques, which, together with the adhesive, push way high the production costs of radiators.

In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines there are some types of heat exchangers which use the aluminum core using mixed solutions for the assembling of the core, i.e. brazing after expanding (British Patent No. 2194469); this solution presents the disadvantage that it has been used so far only in the case of some constructive systems of the core for which the shapes of fins and tubes have not been sufficiently matched (to reach high functional performance levels), for such a rather expensive mixed solution.

In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines there are some types of heat exchangers which use the aluminum core with oval tubes with two unkeyed rows or arranged in a "chequered pattern" (French Patent No. 2605726, Japanese Patent No. 61-211693, "Standardisierung von Motorkuhlern, MTZ magazine, 56- 1995-6); this solution presents the following disadvantages: it implies large gaps between two consecutive tubes in the same row, low efficiency of the heat exchange and two header plates of different geometry due to the rules of the "symmetry in the mirror" which lead to increased costs of the tools required to machine the header plates; in case the sealing is obtained by means of gaskets the manufacturing costs are even higher because of the expensive tools required to manufacture the gaskets which, according to the principle of the symmetry in the mirror must have different shapes for the two header plates.

In order to dissipate the heat generated during the combustion process taking place inside the internal combustion engines, there are some types of heat exchangers which use the aluminum core with oval or cylindrical tubes, the fins of which have no deflecting ports of optimum shape, number and arrangement to ensure a turbulent flow and to efficiently absorb the heat dissipated by the coolant as it passes through the tubes, from the fins to the cooling agent (usually atmospheric air) driven either by natural suction or forced suction by means of a fan; in the case of this model the fin elements which ensure a constant distance between two consecutive fins and/or a turbulent flow of the cooling agent, also known as spacers, are not arranged according to optimum dynamic flow principles and have shape limitations due to fin execution techniques, the simplifying tendency generally imposing the trapeze shape with the smaller base downwards (British Patent No. 2071304A); in most cases the simple trapeze spacers have the disadvantage of playing exclusively the role of spacers between fins and which, when assembling the core, require special devices for guiding, positioning and centering the pack of fins to permit the fitting of the tubes. The present invention solves the problem of a small size heat exchanger (upper dimensions strictly limited) with as little mass as possible, able to ensure a maximum heat exchange. Theoretically, the heat exchanger is characterized by a global heat exchanging coefficient as high as possible, and practically by as large a quantity of dissipated heat as possible per time unit, through a special design of the core based on oval tubes and fins with an optimum geometrical arrangement. The thermal-hydraulic and dynamic optimization of the unit has implicitly influenced the geometrical shaping of the tubes, fins and header plates, respectively:

- for tubes, considering the cross section and knowing that all the dimensions of the tubes are given for the exterior of the section and represent the value measured before expanding or before any other processing technique:

- the length of the oval section: between 8 and 14 mm (12 mm as per the invention);

- width of the oval section: between 1.8 and 6 mm (3.2 mm as per the invention);

- thickness of tube wall: between 0.2 and 0.5 mm ( 0.35 mm as per the invention);

- the ratio between the length and width of the oval section: between 2 and 6.5 (3.75 , before expanding and 3.365 after expanding, as per the invention);

- the tube width / tube wall thickness ratio: between 5 and 15 (9J4, as per the invention).

- for fins and, respectively for base plate cavities arrangement, (from the point of view of cavities the geometry of the base plate depends on the geometry of the core while from the point of view of tubes and fin cavities arrangement it depends on the applied constructive system; taking into account that the core, the importance of which in the system is to ensure a major functional performance, i.e. the heat exchange - is the basic subassembly (the leading component part) of the radiator, it is obvious that the sizing up shall be done according to the algorithm "the base plate shall be adapted to the arrangement of the tubes and not the other way round):

- maximum width: 20 mm for the constructive solution of one single row of tubes (17 mm as per the invention) and 38 mm for the constructive solution with two rows of tubes (32 mm, as per the invention);

- pitch between tubes (the distance between the longitudinal axes of two consecutive tubes (in the same row): the optimum interval is between 10 and 15 mm (11 mm , as per the invention);

- the distance between the rows of tubes, for two rows system only (the distance between the cross axes of two neighboring tubes in two consecutive rows) shall be between 12 and 20 mm (16 mm, as per the invention);

- fin thickness: 0.06 ^ 0J2 mm (0.08 mm as per the invention for cost efficiency) - the pitch between the fins (the distance between two position corresponding points on the fin surface, measured between two consecutive fins) shall be between 1.00 and 1.50 mm; the invention provides for this pitch to be altered (depending on each individual application on a certain type of radiator) and it is obtained through special technological measurements within the range 1.25...1.50 mm. The pitch between fins is usually constant for the core of a certain type of radiator but the constructive solution proposed herein, together with the intended manufacturing procedure (the fin is stamped out, the blade type spacers are calibrated at different heights depending on the calibration post of the die) permits practically to obtain various cores, though almost identical, with the only difference in the pitch between the fins and, implicitly in the total number of fins used to make the respective variants of dissipating elements. According to the invention, the high efficiency heat exchanger with oval tubes eliminates all the aforementioned shortcomings by using a core made of oval tubes with a sufficiently high number of flat fins ensuring an optimum coolant passage section - in the case of the tubes - and also a cooling agent passage section through the core to avoid substantial pressure drops of the coolant - in the case of the fins. According to the invention, the fins are designed to eliminate the shortcomings mentioned above by an optimum location of the tube cavities, a special geometry of the spacers, deflecting ports for a turbulent flow of the cooling agent, bilateral side recesses for an easy mounting of the side guards and of the side brackets, and folds at tube longitudinal ends, reinforced with corner cross ribs ensuring a high rigidity of the respective fin ends. According to the invention, the high efficiency heat exchanger with oval tubes eliminates the shortcomings above by being fitted with a special cross section design side guards, with an optimum geometry, to drastically reduce the total weight of the heat exchanger wherever the application field permits the use of these component parts. The tanks and the gaskets ensure an increased sealing capacity.

The solution offered by the invention features the following advantages:

- an enlarged passage section for the coolant through an increased number of tubes as compared with other designs featuring oval tubes, thus ensuring a relatively low pressure drop between the inlet and outlet of the coolant in the radiator and high flow rates of the coolant in the cooling system; both these advantages correspond to the present requirements and tendencies encountered in the field of cooling systems and radiators intended for use with internal combustion engines;

- plastic material tanks made with the classic plastic injection techniques without needing special technologies, tools or equipment other than those used or applied today;

- the header plates of the radiator can be made according to well known cold plastic deformation procedures (technologies and tools for cold pressing); from the point of view of cavities arrangement, a sinqle constructive type of base plate is used;

- there is no need for shaping tube ends either before assembling and fitting onto the header plates of the radiator, or afterwards; thus a series of costs specific to this operation are eliminated with a substantial increase of productivity in radiator manufacturing;

- two different procedures may be used to mechanically fit and seal the core onto the header plates of the radiator: adhesive gluing or local brazing; the adhesive gluing procedure permits an easy disassembling of the component parts of the respective radiators, for material reuse, later on when they are put out of work; .

- a much simpler shape and function of the sealing gaskets, the sealing function being covered through the assembling of the tanks and base plates; the gaskets are identical, of one and the same constructive type for a certain type of radiator;

- different constructive systems may be used both with one row of tubes and with two rows of tubes, the final result being a very wide range of radiators for various applications;

- the fins ensure a maximum total surface of the core for heat exchange, an important contribution to this advantage being brought by the spacers which are specially shaped for this purpose as well as to facilitate the assembling of the fins to the tubes;

- according to each separate application, the radiators are fitted with plastic, side guards which reduce the weight of the radiator, improve the mechanical protection characteristics of the core and give a better general aesthetics of the radiator;

Further on, several examples of radiator execution are given in relation with Figures 1 ,2,3,4,5,6,7,8,9,10 and 11 , which represent:

- Figurel : perspective view of the radiator (isometric - axonometric projection), with details of the main components made of parts and subassemblies ready for the final assembling;

- Figure 2: side and front orthogonal view of the assembled radiator showing partial section routes, detailed in figures 3,4 and 9.

- Figure 3: partial section through the assembling area between the core, header plates and tanks, by means of gaskets, with three detailing variants (marked (a), (b) and (c)) for assembling the base plates to the tubes, plus two detailing variants for the assembling of base plates, gaskets and tanks, resulting from the two constructive variants with sealing gaskets;

- Figure 4: partial section through the assembling area between the core and header plates, in two variants (marked A and B) with the respective details for each variant;

- Figure 5: partial view of the core, isometric-axonometric projection with a detailed presentation of the geometrical shape of the fins for a construction solution with symmetrical geometry of the fin;

- Figure 6: Orthogonal view of the fins, both for the constructive variant with only one row of tubes and for the constructive variant with two rows of tubes, with a detailed presentation of the geometrical shape (for both variants);

- Figure 7: partial view of the core, in isometric-axonometric projection, the constructive variant with two rows of tubes, with a detailed presentation of the geometrical shape of the fins for the constructive variant with asymmetrical geometrical shape of the fins;

- Figure 8: partial view of the core, in isometric-axonometric projection the constructive variant with one row of tubes with detailed presentation of the geometrical shape of the fins, the constructive variant with a simplified geometry of the fin;

- Figure 9: partial cross section through the core , both in the area of the side brackets and in the zone of the side guards, the basic variant for this component, and presentation of some distinct constructive variants of the side guards (marked (a), (b), (c), (d), (e) and (f));

- Figure 10: partial cross section through the assembling area between header plates and tanks; representation of two of the most frequent application constructive principles for setting the header plates over the respective zones in tank structure specially designed for this purpose, representations marked A and B;

- Figure 11 : partial cross section through a portion of the dissipating element, fin, respectively, relevant for the relative positioning of one spacer versus two neighboring spacers; the detailed geometry of the spacer is also presented in cross section plus a magnified detail, to which the phases of the spacer execution technology are added marked (a), (b) and (c).

According to the invention and to Figures 1 and 2, the high efficiency heat exchanger with oval tubes consists of an inlet tank (1), a sealing gasket (2) for the assembling of the inlet tank (1) to the respective base plate (3), a number of lower side guards (4A) and (4B), an assembled lower side plate (4), an outlet tank (5), a sealing gasket (6) for the assembling of the outlet tank (5) to the respective base plate (7), a number of upper side guards (8A) and (8B), an assembled upper side plate (8) and a core (9). The core (9) consists of a number of oval tubes (9A) and flat fins (9B) with both ends of the tubes in tight proof assembling with the header plates (3) and (7). The assembling is performed either by gluing with a special adhesive or by local brazing.

According to the invention, to figure 3 and to the execution examples in details S, both tanks of the high efficiency heat exchanger with oval tubes unit, inlet tank (1) and outlet tank (2), respectively, benefit from a triangular or semicircular section rib on the whole perimeter of the contact zone with the sealing gaskets (2) and (6) penetrating in a recess in the gaskets having the same shape, which determines an increased safety and sealing surface when assembling the tanks (1) and (5) to the header plates (3) and (7). The tanks of the radiator are made of a special plastic material, with high mechanical strength, which preserves its geometrical shape in time and the properties of which are not influenced by environmental changes, coolant temperature fluctuations or chemical agents encountered in actual working-conditions. According to the invention and to Figure 3 with the two execution examples given in details S, the gaskets of the high efficiency heat exchanger with oval tubes (2) and (6), can cover either the bottom of the groove in the base plate specially designed for gasket mounting, or both the bottom and one of the sides of the respective groove (the side conventionally located towards the interior of the tank is to be preferred); the second execution example is more advantageous since it ensures an wider sealing surface and an increased safety level when assembling the tanks (1) and (5) to the header plates (3) and (7), respectively. The gaskets are made of a heat resistant rubber not affected by the chemical action of the coolant used in the cooling system of the internal combustion engine, and they are identical in shape and, therefor, interchangeable.

As per the invention and figure 4, the header plates (3) and (7) of the high efficiency heat exchanger unit with oval tubes have oval shape cavities (chamfered holes for tube ends) either on the tank cavity side (in the tube mounting direction when assembling to the core) - variant A in Figure 4 -, or on the core side (in a direction opposite the mounting direction, when assembling to the core) - variant B in Figure 4. For technological reasons, according to the invention and as per Figure 1 and Figure 3 - front view of the base plate, the basic execution example has, after the final assembling, the cavities of the base plate located on the side facing the tank cavities - variant A in Figure 4. Other execution examples, as per Figure 10, show header plates having either straight or knurled longitudinal edges which influence the execution technology and setting tools used to assemble the header plates to the tanks; according to the invention and as shown in Figure 1 , the basic execution example given is based on a base plate with knurled edges (variant A in Figure 10); these component parts which are made of aluminum or aluminum alloy plate, are identical in shape and therefor, interchangeable.

According to the invention and as per detail shown in Figure 2, the assembling of tubes (9A) of the core (9) to the header plates (3) and (7) is performed by means of a special adhesive intended for use exclusively with aluminum and/or aluminum alloy component parts ensuring an outstanding and durable mechanical and chemical resistance of the bound to the temperature, pressure and chemical action of the coolant as well as to environment agents during vehicle engine operation. In the general presentation of the execution examples in detail X, Figure 3, three basic variants are given in the detailed models marked (a), (b) and (c) , within the frame of the same figure.

The execution example (a) is the simplest and it does not lead to deformation neither of the tube nor of the cavity after mounting but it is less reliable since both ends where the adhesive is applied are open constructions which means that, irrespective of the assembling position, the adhesive paste may flow out through one of them before it starts to cure. The example (b) -implies only tube deformation by local, contour expanding, while example (c) i ptfes only the deformation of the cavity chamfered edge. The execution examples (b) and (c) offer the advantage of a closed end for the adhesive layer which permits a gravimetrical positioning (downwards) of this end at assembling and throughout the whole curing period required by the adhesive. As per the section detail in Figure 2 and variants A and B in Figure 4, the basic execution example is based on model (c); the technological procedure used by which the edges of a chamfered hole are folded towards the interior is known under the name of "bordering" or "pointing".

As per the invention and figures 5 and 6 , the core (9) of the high efficiency heat exchanger unit with oval tubes consists of oval tubes (9A) and of a number of fins (9B). The oval tubes (9A) are made of aluminum or aluminum alloy (the most frequently encountered is AIMnl and ENAW-3103, respectively, in compliance with SR EN 573-3 or DIN 1795) and do not alter the shape of the cross section both during assembling of the core and after the ulterior assembling operations; with the exception of the expanding operation when only the dimensions of the cross section suffer some changes, the tubes are not altered on their whole length. According to the invention, the fins (9B) of the core of the high efficiency heat exchanger unit with oval tubes are presented both within the assembly of the core as per figure 5, and in separate detail, as per figure 6. According to the invention, and in both constructive models, with one row of oval tubes and with two rows of oval tubes, respectively, the fins consist of the following distinct constructive elements: edge folding (91) reinforced by means of some corner cross ribs (92) designed for set mounting the upper side part (8) and the lower side part (4) and for lengthwise slide mounting or forced opening mounting followed by resilient recovery inside the respective recesses in the core (9), of the lower side guards (4A) and (4B) and upper side guards (8A) and (8B), respectively, a number of cavities (94) for the passage, mounting and fixing of the tubes (9B) by expanding inside the core assembly, a number of deflecting ports (95) symmetrically open and arranged ("in the mirror") as to the longitudinal axis of fin surface intended to ensure a turbulent flow of the cooling agent through the core (with the same dynamic-flow parameters, irrespective of its flowing direction through the core), a number of spacers (96) which also ensure the relative centering of one fin as to the neighboring one(s), as well as longitudinal stiffening folds (97) intended to increase fin resistance and to avoid lengthwise local deformation when mounting the core. The fins are made of thin strips of aluminum or aluminum alloys.

According to the invention, the spacers (97), as presented in detail in Figure 6 and as per Figure 11 , are designed to be executed through the technological phases in Figure 11 permitting to obtain two simple spacers with the same puncher frustum of a cone shaping by pre-stamping (a), cut-out and bilateral trapeze shape chamfering (b) of the bottom of the frustum of a cone, and calibration (c), optionally either with straight or arched widening at extremities, of the two simple spacers common to a single pre-stamping. As per the invention and geometrical analysis detail in Figure 11, the optional, straight or arched widening technological phase depends on the final value of the height of the spacer (h) which is equivalent with "fin pitch" parameter, specific to the core. In order to obtain a different value of this parameter permitting to obtain spacers ensuring different pitches from one application to an other and observing the geometrical analysis detail in Figure 11 , a special alαorithm has been devised to calculate certain geometrical parameters of the spacers, namely, of the tools used to execute the spacers. This calculation algorithm consists of the following equation system (with R, r, α, β, γ unknown data):

h = (s + R) x sinγ + (R-r) x sinβ + r + s e = (r+s) x sinα + (R+s) x (1 - cosβ) R x sin (α + β + γ) = (R - r) x sinα , where D_e x 180/π = α x (r + s/2) + (β + γ) x (R + s/2) α + β = 90 h = height of the spacer (fin pitch), between 1.25 and 1.50 mm;

R = inner radius for spacer curvature; r = inner radius for bending the foot of the spacer; s = thickness of the spacer material, 0.08 mm; e = the projection of the spacer within the plane of the fin (to be adopted);

De = the perimeter of the spacer (to be adopted); α = the bending angle of the base of the spacer according to radius r; β = the complementary angle of angle α; γ = the angle of curvature of the spacer according to radius R - < (β).

According to the invention, the spacers have a double function: the part having the shape of a frustum of a cone from which protrude the two spacers ensure an increase of the heat exchanging surface of the fin (equivalent to an increase of the parameter also called "surface rib coefficient"), and a self- centering of the two spacers located accordingly on the surface of the neighboring fin which come into contact with the cone shaped zone from the open side of the pre-stamping, thus substantially facilitating the mounting of the fins (9B) and avoiding the scattering of the pack of fins when assembling to the tubes (9A) of the core (9).

According to the invention, and as per the example presented in Figure 7, the core (9) of the high efficiency heat exchanger unit with two rows of oval tubes consists of oval tubes (9A) and fins (9B) featuring a simplified configuration, the fins having the following distinct constructive elements: edge bends (91) reinforced with comer cross ribs (92), bilateral side recesses (93) intended for use to set mount the upper side brackets (8) and lower side brackets (4), respectively, and to mount the lower side guards (4A and 4B) and upper side guards (8A and 8B) either by longitudinal sliding or by forced opening followed by resilient recovery inside the recesses of the core, a number of cavities (94) for ulterior passage, mounting and fixing of the tubes (9B) through expanding inside the core assembly, a number of deflecting ports (95), constantly open but different in number and arranged asymmetrically versus the longitudinal axis of the surface of the fins aiming at ensuring a turbulent flow of the cooling agent through the core, having different dynamic flow parameters (depending on the direction of flow of the cooling agent through the core) and a number of spacers (96) the only role of which being to ensure the pitch of the fins. As far as fin execution technology is concerned, this execution example is simpler as compared to the previously described basic execution example, but, still, the final assembling of the heat exchanger must be performed cautiously in order to mount the core with the front surface correctly oriented according to the direction of flow of the cooling agent because the dynamic flow parameters ensure functional levels which turn the unit into an irreversible heat exchanger with increased efficiency at cooling agent level too. This phenomenon makes it possible to use the unit under special practical requirements.

As per the invention, another example of execution of the high efficiency heat exchanger with a single row of oval tubes is given in Figure 8, the unit consisting of oval tubes (9A) and fins (9B) with a simplified configuration. The fins have the following distinct constructive elements: edge bends (91) reinforced with corner cross ribs (92), bilateral side recesses (93) intended for use to set mount the upper side brackets (8) and lower side brackets (4), respectively, and to mount the lower side guards (4A and 4B) and upper side guards (8A and 8B) either by longitudinal sliding or by forced opening and resilient recovery inside the recesses of the core (9), a number of cavities (94) for the passage, mounting and fixing of the tubes (9B) through expanding inside the core assembly, a number of deflecting ports (95), constantly open and equal in number and arranged symmetrically versus the longitudinal axis of the surface of the fins, aiming at ensuring a turbulent flow of the cooling agent through the core, having constant dynamic flow parameters independent from the direction of flow of the cooling agent through the core and a number of spacers (96) the only role of which being to ensure the pitch of the fins. As far as fin execution technology is concerned, this execution is simpler and, from the point of view of cooling agent floe, it gives the core a perfectly reversible character in strict compliance with the basic execution of the model with one single row of oval tubes.

As per the examples a, b, c, d, e, f in Figure 9, the lower side guards (4A and 4b) and upper guards (8A and 8b) of the high efficiency heat exchanger with oval tubes are component parts mounted onto the edges of the core, either before the assembling of the header plates (execution variants a,b,c and d), or during any of the technological phases following the assembling of the core (execution variants e and f) intended to ensure the mechanical protection of fin extremities - edge bend zone (91) and of the bilateral marginal recesses (93) when assembling or handling the heat exchanger unit and throughout the working life and maintenance/repair of the unit ; the side guards may have other cross section shapes, many more than those given here as examples. The limitations in the design of the heat exchangers are imposed only by the constructive requirements, namely: cross section resilience, optimum mechanical contact with the bilateral marginal recesses (93) in the fins, but not along the whole- cάtltOUr of the recesses tb facilitate mounting onto the core either by sliding the section in the bilateral marginal recesses (93) or by forced opening of the section arms with application of the guards over the zone of the edge bends (91) of the fins followed by elastic recovery of the initial shape with the two open arms of the guards penetrating the bilateral marginal recesses (93). The limitations in the design of new shapes of the section of the side guards are also imposed by the execution technique used and the need for a reduced weight. The side guards can be made of plastic materials having lesser characteristics than the one used to make the tanks because the side guards do not come into contact with the fluid circulating through the tubes (9A) of the core and through the tanks provided these materials have the right resistance to the working temperature of the core (9).

According to the invention, to assemble the high efficiency heat exchanger with oval tubes the following assembling order must be observed: preliminary assembling of the core 99) by introducing the tubes (9A) in the respective cavities in the fins (9B), the final assembling of the core by expanding the tubes, the mounting of the side guards (4A, 4B, 8A, 8B) on the core (optionally, depending on the necessity of use or on the shape of their section), gluing the two base plate (3) and (7) onto the oval tube ends by means of special adhesive (10), complete curing of the adhesive, mounting the two gaskets (2) and (6) in the gasket groove in the header plates, mounting of the two tanks (1) and (5) over the gaskets and set mounting of the header plates and set mounting of the side brackets (4) and (8) on the edges of the core.

As per Figure 2, the functioning of the high efficiency heat exchanger with oval tubes is identical and already well known in the field of automotive radiators, namely: from the inlet duct the coolant enters the radiator at inlet level into the inlet tank (1), assembled to the respective base plate (3) be means of sealing gasket (2), penetrates and passes through the oval tubes (9A) of the core (9) thus dissipating a certain quantity of heat - both through the tubes and through the flat fins (9B) the role of which is to increase the dissipating surface for heat exchange, then the coolant is released into an outlet tank (5) which is mounted to the respective base plate (7) by means of sealing gasket (6). From the outlet tank the coolant leaves the radiator and enters the outlet duct of the cooling circuit.

Simultaneously with the circulation of the coolant through the internal circuit of the radiator in one direction only (the circulation direction of the coolant can be reversed but, in such a case, and from a hydraulic point of view, the passage through the circuit will be less efficient, hence the irreversibility of the radiator) and with the heat dissipation through the core a cooling agent (usually atmospheric air) sweeps the front surface of the core in an orthogonal direction thus intensifying the heat exchange and turning the heat exchange thermal- dynamic model from dissipation to convection. The core (9), consisting of a number of oval tubes (9A), arranged in one or two parallel rows, and of a number of flat fins (9B), is assembled at both ends of the tubes (9A) to the header plates (3) and (7) by means of a special adhesive (10) or through local brazing. This assembling technique seals off the internal circuit of the radiator and determines the final working pressure resistance performance level of the heat exchanger.

Claims

1. The high efficiency heat exchanger with oval tubes features an inlet tank (1) a sealing gasket (2) for the assembling of inlet tank (1) to the respective base plate (3) a number of lower side guards (4A and 4B), an assembled lower side plate (4), a relief tank (5), a sealing gasket (6) for the assembling of the relief tank (5) to the respective base plate (7), a couple of upper side guards (8A) and (8B), an assembled upper plate (8) and a core (9). The core (9) consists of a number of oval tubes (9A), arranged in one or two parallel rows and a pack of flat fins (9B), in a sealed off assembly with the header plates (3) and (7) the assembling being made at both ends of the oval tubes by means of a special adhesive (10) or through local brazing.

2. As per claim 1 , the inlet tank (1) and outlet tank (5) of the high efficiency heat exchanger with oval tubes, characterized by the fact that they are made of proper plastic materials and have a triangular or semicircular rib along the whole perimeter of contact with gaskets (2) and (6), the rib penetrating into a recess of similar shape in the gasket thus increasing the sealing surface of the tanks when assembling to header plates (3) and (7) and a safer assembling of tanks (1) and (5) to header plates (3) and (7).

3. As per claims 1 and 2, gaskets (2) and (6) of the high efficiency heat exchanger with oval tubes, characterized by their identical shape and interchangeability, cover both the bottom of the gasket groove and the side of the groove conventionally placed towards the interior of the tanks; the gaskets feature a triangular or semicircular section recess, of identical shape, taking the rib of the tanks, along their entire perimeter of the contact zone with tanks (1) and (5) thus ensuring an increased sealing surface and a safer assembling of tanks (91) and (5) to the respective header plates (3) and (7). The gaskets are made of a heat and chemical agent resisting rubber.

4. As per claim 1 , the header plates (3) and (7) of the high efficiency heat exchanger with oval tubes, are characterized by the fact that they are designed with oval cavities (chamfered holes for tubes) on the side of the header plates facing the tank cavities, oriented in the direction in which the tubes (9A) are introduced when assembling the core (9). The final shape of the cavities is obtained by shaping the chamfered edges of the cavities towards the interior . The header plates are made of aluminum and aluminum alloy. They have the same shape, knurled longitudinal and cross edges and are interchangeable.

5. As per claim 1 , and to ensure optimum heat exchanging performances and the best efficiency, the oval tubes of the high efficiency heat exchanger unit are characterized by the fact that they are manufactured by observing the following geometrical parameters of the cross section: 12 mm long oval contour, 3.2 mm wide oval contour, 0.35 mm thick oval tube wall, oval contour length to width ratio : 3.75 before expanding and 3,365 after expanding, the tube width to tube wall thickness: 9J4. The tubes are made of aluminum or aluminum alloys (AIMnl type alloy, and, respectively, EN AW-3103 as per SR EN 573-3 or DIN 1795) and they maintain the shape of their cross section and are not altered in any way throughout their whole length both when assembling the core and during the ulterior assembling operations, the only exception being the expanding operation when only the dimensions of the cross section change.

6. As per claim 1 , the fins (9B) of the core of the high efficiency heat exchanger unit with oval tubes are characterized by the fact that in both constructive models, with one row of oval tubes and with two rows of oval tubes, the fins consist of the following distinct constructive elements: edge folds (91) reinforced by means of some corner cross ribs (92), bilateral side recesses (93) designed for set mounting the upper side part (8) and the lower side part (4) and for lengthwise slide mounting or forced opening mounting followed by resilient recovery in the respective recesses in the core (9), of the lower side guards (4A and 4B) and upper side guards (8A and 8B), respectively, a number of cavities (94) for the passage, mounting and fixing of the tubes (9B) by expanding inside the core assembly, a number of deflecting ports (95) symmetrically open and arranged ("mirror image") as to the longitudinal axis of fin surface intended to ensure a turbulent flow of the cooling agent through the core (with the same dynamic-flow parameters irrespective of its flowing direction through the core), a number of spacers (96) which also ensure the relative centering of one fin as to the neighboring one(s), as well as longitudinal stiffening folds (97) intended to increase fin resistance and to avoid lengthwise local deformation when mounting the core. The fins (9B) are made of thins strips of aluminum or aluminum alloys so that the core should feature superior heat exchange performances which, automatically, increase the overall efficiency of the heat exchanger. The fins have the following geometrical parameters: fin width: 17 mm for the one row model and 32 mm for the two row model; pitch between tubes: 11 mm distance between tubes, 16 mm distance between tube rows only in the case of the two row model, fin thickness: 0.08 mm; pitch between fins constant for the same core but it can be different in the case of other core models with values in the range between 1.25...1.50 mm, depending on the special technological procedures used to execute the fins.

7. As per claims 1 and 6 the spacers (97) of the high efficiency heat exchanger with oval tubes are characterized by the fact that they are designed in a way permitting to obtain two simple spacers with the same puncher through the following technological phases: frustum of a cone shaping by pre-stamping , cut-out and bilateral trapeze shape chamfering of the bottom of the frustum of a cone, and calibration, optionally either with straight or arched widening of the two simple spacers common to a single pre-stamping. The optional, straight or arched widening technological phase depends on the final value of the height of the spacer (h) which is equivalent to "fin pitch" parameter specific to the core. In order to obtain a different value of this parameter permitting to obtain spacers ensuring different pitches from one application to an other, a special algorithm has been devised to calculate certain geometrical parameters of the spacers, namely, of the tools used to execute the spacers. This calculation algorithm consists of the following equation system (with R, r, α, β, γ unknown data): h = (s + R) x sinγ + (R-r) x sinβ + r + s e = (r+s) x sinα + (R+s) x (1 - cosβ)

R x sin (α + β + γ) = (R - r) x sinα , where

D_e x 180/π = α x (r + s/2) + (β + γ) x (R + s/2) α + β = 90 h = height of the spacer (fin pitch), between 1.25 and 1.50 mm;

According to the invention the spacers have a double function: the part having the shape of a frustum of a cone from which protrude the two spacers ensure an increase of the heat exchanging surface of the fin (equivalent to an increase of the parameter also called "surface rib coefficient"), and a self-centering of the two spacers located accordingly on the surface of the neighboring fin which come into contact with the cone shaped zone from the open side of the pre-stamping, thus substantially facilitating the mounting of the fins (9B) and avoiding the scattering of the pack of fins when assembling to the tubes (9A) of the core (9).

8. As per claims 1 and 4, the assembling of the tubes (9A) of the dissipating element (9) to the header plates (3) and (7) of the high efficiency heat exchanger with oval tubes is characterized by the fact that it is performed either by means of a special adhesive (10) intended for use with aluminum or aluminum alloy components only, or through local brazing of tubes (9A) with the cavities in the header plates (3) and (7). The pointed shape of the cavity borders offers the advantage of a closed end for the adhesive layer which permits a gravimetrical technological positioning of this end for the curing of the adhesive.

9. As per claims 1 , 5 and 6, the core of the high efficiency heat exchanger with oval tubes, is characterized by the fact that it consists of oval tubes (9A) arranged on two rows and of fins (9B) with a simplified shape and consisting of the following distinct constructive elements: oval tubes (9A) and fins (9B) featuring a simplified configuration, the fins having the following distinct constructive elements: edge bends (91) reinforced with corner cross ribs (92), bilateral side recesses (93) intended for use to set mount the upper side plate (8) and lower side brackets (4), respectively, and to mount the lower side guards (4A and 4B) and upper side_αuards (8A and 8B) either by longitudinal sliding or by forced opening followed by resilient recovery inside the respective recesses of the core (9), a number of cavities (94) for ulterior passage, mounting and fixing of the tubes (9B) through expanding inside the core assembly, a number of deflecting ports (95), constantly open but different in number and arranged asymmetrically as to the longitudinal axis of the surface of the fins, aiming at ensuring a turbulent flow of the cooling agent through the core, having different dynamic flow parameters (depending on the direction of flow of the cooling agent through the core) and a number of spacers (96) the only role of which being to ensure the pitch of the fins. The final assembling of the heat exchanger must be performed in a way to ensure the mounting of the core with the front surface correctly oriented according to the direction of flow of the cooling agent because the dynamic flow parameters ensure functional levels which turn the unit into an irreversible heat exchanger with increased efficiency at cooling agent level too.

10. As per claims 1 ,5,6 and 9, the core of the high efficiency heat exchanger with oval tubes, is characterized by the fact that it consists of oval tubes (9A) arranged in a single row and fins (9B) with a simplified configuration and having the following distinct constructive elements: edge bends (91) reinforced with corner cross ribs (92), bilateral side recesses (93) intended for use to set mount the upper side plate (8) and lower side plate (4), respectively, and to mount the lower side guards (4A and 4B) and upper side guards (8A and 8B) either by longitudinal sliding or by forced opening and resilient recovery inside the recesses of the core (9), a number of cavities (94) for the passage, mounting and fixing of the tubes (9B) through expanding inside the core assembly, a number of deflecting ports (95), constantly open and equal in number and arranged symmetrically versus the longitudinal axis of the surface of the fins, aiming at ensuring a turbulent flow of the cooling agent through the core, having constant dynamic flow parameters independent from the direction of flow of the cooling agent through the core and a number of spacers (96) the only role of which being to ensure the pitch of the fins.

11. As per claims 1 ,6,9 and 10, the lower side guards (4A) and (4B) and the upper side guards (8A) and (8B) of the high efficiency heat exchanger with oval tubes are characterized by the fact that they are executed in six constructive variants having different cross section shapes which permit the mounting onto the core (9) either before assembling the header plates or during any of the technological phases ulterior to the assembling of the core, by strictly observing the following requirements: high resilience of the cross section, good mechanical contact with the bilateral side recesses (93) in the fins, but not on their whole perimeter, to facilitate the assembling of the onto the core either by longitudinal sliding of the arms of the cross section of the guards, or by forced opening of the arms of the section, over the side bends (91) of the fins followed by elastic recovery of the initial shape with the penetration of the two open arms of the guards into the bilateral side recesses (93) in the fins; the side guards shall be made of plastic materials less pretentious but with a good resistance to the operating temperatures of the core (9).