DE69031047T2 - Evaporators for coolers in motor vehicles - Google Patents

Abstract

An evaporator comprising a plurality of unit heat exchangers (A, B) each of which has a circuit formed therethrough for a heat exchanging medium and a connecting means (220, 230) for connecting the circuits in fluid communication with each other, each of the unit heat exchangers comprising a plurality of tubes (1) arranged in parallel with each other, a plurality of fins (2) each interposed between the two adjacent tubes (1) and a pair of hollow headers (3, 23 and 4, 24) to which both ends of each tube (1) are connected in fluid communication. The unit heat exchangers (A, B) are arranged fore and aft in a direction of air flow so that one of them faces windward, with the other lying leeward and unit air flow paths are defined between the adjacent tubes (1) and separated by the fins (2), such that a cross-sectional area of each unit air flow path in the leeward unit heat exchanger is larger than that in the windward one, whereby an amount of condensed water on the leeward unit heat exchanger is prevented from being scattered therefrom. <IMAGE>

Description

The present invention relates to an evaporator having a plurality of heat exchanger units for use in radiators in motor vehicles.

EP 0 401 752 describes a condenser for a coolant of an air conditioning system for motor vehicles with adjacent assemblies that are mechanically connected to one another via their ribbed area, but the average thermal conductivity λm is 20% lower than the thermal conductivity λ of the material of the ribbed area of the two adjacent assemblies in a connection zone between two adjacent assemblies.

US-A-3 229 760 comprises a heat exchange device, in particular a radiator structure provided with cooling fins which are mounted in a main housing provided with a plurality of spaced-apart fluid conduits, and a protective structure is provided for protecting the fins.

US-A-4 531 574 provides such an installation for attaching an oil cooler to a radiator so that it is thus located in a series arrangement in the path followed by the cooling air.

A multiple flow type heat exchanger is described in Japanese Patent Publication Kokai 63-34466 and has such a structure that a plurality of parallel flat tubes are connected to a pair of hollow headers at their opposite ends, with a corrugated fin being arranged between one such flat tube and the next. In operation, heat exchange takes place between the coolant and the ambient air flowing through the spaces defined between the tubes as the coolant flows through a coolant circuit composed of the flat tubes. The known multiple flow type heat exchanger can be made thinner in dimension in a direction of air flow than the other known heat exchangers without affecting the heat exchange efficiency. The multi-flow type heat exchanger has therefore proven to perform better than the other known heat exchangers of various types, such as the coil tube type.

An object of the present invention is to provide an evaporator adapted to increase its heat transfer capacity without requiring an excessively wide space.

According to the present invention, an evaporator consists of a plurality of heat exchange units, each of the heat exchange units having a circuit for a heat exchange medium formed therethrough, and a connecting device for connecting the circuits in a mutual fluid connection, each of the heat exchanger units comprising a plurality of tubes arranged in parallel to each other, a plurality of fins each arranged between two adjacent tubes, and a pair of hollow headers to which the two ends of each tube are connected in fluid connection, characterized in that the heat exchanger units are arranged front and rear in a direction of air flow such that one of them is oriented windward while the other is leeward, and air flow path units are defined between the adjacent tubes and separated from each other by the fins such that a cross-sectional area of each air flow path unit in the leeward side heat exchanger unit is larger than that in the windward side unit, thereby preventing an amount of water condensed on the leeward side heat exchanger unit from being scattered therefrom.

Each heat exchanger unit may be designed such that a pitch of the fins in the leeward heat exchanger unit is larger than the pitch in the windward unit, so that the cross-sectional area of each air flow path unit in the former heat exchanger is larger than that in the latter.

Advantageously, the heat exchanger units are arranged in such a way that the head pieces of each heat exchanger unit are arranged horizontally on its upper and lower sides.

Preferably, the heat exchanger units are connected to each other in parallel so that the heat exchange medium flows through the heat exchanger units simultaneously.

The invention will now be further described using an embodiment with reference to the accompanying drawings, in which

Fig. 1 is a perspective view showing a duplex heat exchanger in a separated state of a front and a rear heat exchanger unit;

Fig. 2 is a front view of the entirety of the duplex heat exchanger shown in Fig. 1;

Fig. 3 is a plan view of the whole;

Fig. 4 is a similar side view of the whole;

Fig. 5 is a perspective view showing a separated state of a header, tubes and corrugated fins of the front or rear heat exchanger unit;

Fig. 6 is a cross-section along line 6-6 of Fig. 2;

Fig. 7 is an enlarged cross-sectional view of the front or rear heat exchanger unit in a view in the same direction as in Fig. 6;

Fig. 8 is an enlarged front view showing the tubes and the corrugated fins;

Fig. 9 illustrates a coolant circuit in the duplex heat exchanger shown in Fig. 1;

Fig. 10 is a perspective view of a duplex heat exchanger;

Fig. 11 is a perspective view showing an essential part of the duplex heat exchanger shown in Fig. 1; and

Fig. 12 is a schematic plan view illustrating another embodiment of a duplex heat exchanger.

Figs. 1 to 9 show an embodiment in which the invention is applied to a condenser made of an aluminum-based alloy and used as an automobile radiator. Reference symbol "H" indicates a duplex heat exchanger consisting of a front heat exchanger unit "A" arranged on an upstream side and a rear heat exchanger unit "B" arranged on a downstream side with respect to a direction "W" of air flow.

The front heat exchanger unit "A" consists of a plurality of horizontally arranged tubes 1 stacked in a vertical direction, corrugated fins 2, which are arranged between two adjacent tubes, and a left head piece 3 and a right head piece 4. The tubes 1 consist of an extruded tube profile made of the aluminum-based alloy. Alternatively, the tubes 1 may be porous or perforated tubes, such as "harmonica tubes", or they may be made of a "butt welded" tube. The corrugated fins 2 have substantially the same width as the tubes 1 and are brazed thereto. The corrugated fins 2 are made of the same or a different aluminum-based alloy and are preferably formed with cooling slots cut into and raised from the main bodies of the fins. A cylindrical tube made of an aluminum-based alloy and having inner and/or outer surfaces coated with a solder is used to make the headers 3 and 4. Tube receiving openings 5 are formed at regular intervals in a longitudinal direction of each header so that the respective ends of each tube 1 are inserted into the tube receiving openings and securely brazed thereto. Cover plates 6 are attached to an upper end and a lower end of the left header 3, and other cover plates 7 are similarly attached to an upper end and a lower end of the right head piece 4. Side plates 8 are arranged outside the outermost corrugated ribs 2.

The rear heat exchanger unit "B" consists of tubes 21, corrugated fins 22, a left header 23 and a right header 24, in which tube receiving openings 25, cover plates 26 and 27 and side plates 28 in in the same way as in the front heat exchanger unit "A". However, a gap "LB" between the left and right headers is larger in the rear heat exchanger unit "B" than an equal gap "LA" in the front heat exchanger unit "A". As a result of such a difference between the gaps "LA" and "LB", the front and rear headers overlap, which are arranged between two adjacent tubes, and a left header 3 and a right header 4. The tubes 1 consist of an extruded tube profile made of an aluminum-based alloy. Alternatively, the tubes 1 may be porous or perforated tubes, such as "harmonica tubes", or they may consist of a "butt-welded tube". The corrugated fins 2 are not alternate in the rear headers and the depth of the duplex heat exchanger as a whole is reduced by a considerable amount. This increases the compactness of the heat exchanger, so that the space occupied by it in motor vehicles or the like is advantageously reduced.

The coolant paths of the front heat exchanger unit "A" are connected in series with those of the rear unit "B". In detail, a coolant inlet pipe 40 is connected to an upper portion of the left header 23 of the rear heat exchanger unit "B". A coolant outlet pipe 50 is connected to an upper portion of the left header 3 of the front heat exchanger unit "A". The left headers 3 and 23 of the front and rear heat exchanger units "A" and "B" are connected to each other by a connecting pipe 60. The reference numerals 71 and 72 in Fig. 2 and 3 designate supports for mutual fastening of the heat exchanger units.

A partition plate 29 in the left header 23 is arranged in the middle part thereof so that this header 23 of the rear heat exchanger unit "B" is divided into an upper and a lower chamber. On the other hand, further partition plates 9 are arranged in the left header 3 above and below its middle part so that this header 3 of the front heat exchanger unit "A" is divided into three chambers. Still another partition plate 10 at a middle part of the right header 4 divides it into two chambers for the front heat exchanger unit "A". As a result of the partitions 29, 9 and 10, a coolant flows in the manner shown in Fig. 9, the coolant entering the left header 23 of the rear heat exchanger "B" via the coolant inlet pipe 40 so that it undergoes a U-turn within this heat exchanger before flowing into the lower chamber of this header 23. The coolant then passes through the connecting pipe 60 into the lower chamber of the left header 3 of the front heat exchanger "A". Thereafter, the coolant undergoes a three-fold turn from one group of pipes to the next group of pipes within the front heat exchanger "A" to rise from the bottom thereof. Upon arrival in the upper chamber of the left header 3, the coolant leaves it through the coolant outlet pipe 50. Between an air flow indicated by an arrow "W"* and the coolant flowing through the pipes of the heat exchanger units "A" and "B", a Heat transfer takes place. A sufficient difference is ensured between the temperature of the coolant and the temperature of the air flow in this embodiment because the coolant is flown from the rear heat exchanger located leeward to the front one located windward. It is also an important feature that the number of turns of the coolant between the groups of tubes in the front heat exchanger "A" is greater than that in the rear heat exchanger "B". Such a structure results in a smaller total cross-sectional area of the coolant paths in the front heat exchanger "A" than that in the rear heat exchanger "B" in accordance with a change in the volume of the coolant flowing through the duplex heat exchanger used as a condenser. In this connection, it is to be noted that the coolant flowing into the rear heat exchanger "B" is still in its gas state with a larger volume, but it is gradually cooled therein to its liquid state with a smaller volume. The larger cross-sectional area of the coolant paths in the rear heat exchanger "B" is therefore useful in this heat exchanger for sufficient heat transfer of the coolant in its gaseous state. At the same time, although the cross-sectional area in the front heat exchanger "A" decreases in accordance with the shrinkage of the coolant therein, an undesirable pressure loss is reduced to a minimum, thereby improving the heat transfer efficiency of the duplex heat exchanger as a whole. The cross-sectional area in the front heat exchanger "A" is reduced to 30 to 60% of that in the rear heat exchanger "B". In the case where the area in the front heat exchanger "A" adapted for supercooling the coolant is less than 30%, this excessively reduced area will, on the one hand, result in an undesirably large pressure loss in this heat exchanger "A", while an excessively large area of the coolant paths in the rear heat exchanger "B" adapted for condensing the coolant will, on the other hand, result in an undesirable reduction in the flow rate of the coolant, thereby lowering the efficiency of heat transfer. In the case where the area of the coolant path in the front heat exchanger "A" is more than 60% of that of the rear heat exchanger "B", such a small area in "B" will increase the pressure loss of the coolant therein and will lower the capacity of heat transfer as a result of an insufficient area of the heat transfer surfaces. It is therefore desirable to set the cross-sectional area of the coolant paths in the front heat exchanger "A" to 30 to 60%, and more preferably to 35 to 50%, of that in the rear heat exchanger "B" in order for the duplex heat exchanger to perform effective heat transfer at a low pressure loss.

Further parameters for better performance of the front and rear heat exchangers "A" and "B" are as follows.

The aforementioned tubes 1 and 21 may preferably have a width "Wt" of 6 to 20 mm, a height "Ht" of 1.5 to 7 mm and an inner height "Hp" of the coolant path of 1.0 mm or more. The corrugated fins 2 and 22 may preferably have a height "Hf" (i.e., a distance between two adjacent tubes 1 or 21) from 6 to 16 mm and a fin pitch "Fp" from 1.6 to 4.0 mm. The reasons for these dimensions are given below.

A tube width "Wt" of less than 6 mm will result in too narrow a width of the corrugated fins 2 and 22 arranged between two adjacent tubes 1 or 21. A larger tube width of more than 20 mm will result in an excessively large width of these fins 2 and 22, which in turn will result in an increased resistance to the air flow in addition to an excess weight of the condenser. The range of 6 to 20 mm is therefore desirable, and a range of 10 to 20 mm is even more desirable.

A tube height "Ht" of more than 7 mm will increase the resistance of the tubes to the air flow, and a height of less than 1.5 mm will make it difficult to obtain the internal height "Hp" of the coolant path of more than 1.0 mm with a sufficient wall thickness of the tubes. The range of 1.5 to 5 mm and especially a range of 2 to 4 mm is preferred.

If this internal height "Hp" of the coolant path were less than 1.0 mm, then the loss of coolant pressure would undesirably increase a lowering of the heat transfer efficiency. A range of 1.0 to 3.0 is preferred.

A fin height "Hf" of less than 6 mm results in an increased pressure loss of the air flow passing through the fins, although a fin height of 16 mm or more will reduce the number of fins installed, reduce the "fin effect" and deteriorate the heat transfer performance. The fin height is therefore selected from the mentioned range of 6 to 16 mm, or is more preferably selected from a range of 8 to 12 mm.

As for the fin pitch "Fp", the air flow pressure loss increases if the value is less than 1.6 mm, while the heat transfer performance deteriorates if the value is more than 4.0 mm. The most preferred range is 2.0 to 3.6 mm.

As described above, the most appropriate dimensions are selected with respect to the shapes of the tubes 1 and 21 and the corrugated fins 2 and 22, which have important influences on the performance of the condenser. The selection of the dimensions of the tube width, tube height, internal height of the coolant path, fin height and fin pitch from the ranges given above results in a condenser that can be efficiently operated in an optimum manner, realizing a good balance between the pressure loss of the coolant or air flow and the heat transfer characteristics, without being accompanied by a considerable increase in the weight of the condenser.

Fig. 10 and 11 show an embodiment applied to an evaporator for radiators of motor vehicles. In this embodiment, which is suitable for reducing the pressure loss of the coolant in evaporators, the tubes 1 of a front heat exchanger "A" as well as the tubes 1 of a rear heat exchanger "B" are arranged vertically and in parallel in a right-to-left direction. Corrugated fins 2 are arranged between adjacent tubes 1. Upper headers 3 and 23 and lower headers 4 and 24 are arranged horizontally. A branched inlet pipe 220 for a coolant is connected to the left ends of the upper headers 3 and 23. Similarly, a branched outlet pipe 230 is connected to the right ends of the lower headers 4 and 24, whereby coolant paths of the two heat exchangers "A" and "B" run parallel to each other. The coolant flows into the heat exchangers "A" and "B" via the inlet pipe 220, falls down into the lower headers 4 and 24, and then flows out of the heat exchangers via the outlet pipe 230. As shown in Fig. 11, the fin pitch "FpB" of the corrugated fins 22 in the rear heat exchanger "B" is made larger than the pitch "FpA" in the front heat exchanger "A". Such larger fin pitch "FpB" in the rear heat exchanger prevents the so-called flying of water drops which would otherwise be caused by the air flow and would press such condensed water retained between the fins in the rear heat exchanger as a result of the capillary phenomenon against the passenger compartment of an automobile. Some partition plates may be attached inside the upper and lower headers to meander the coolant along zigzag paths.

Three heat exchanger units "A", "B" and "C" may be combined as shown in Fig. 12, although two heat exchanger units are arranged at the front and rear. Furthermore, four or more heat exchanger units may be combined according to the invention.

As is apparent from the above description, the duplex heat exchanger is designed such that the fins are each arranged between two adjacent tubes, the ends of which are each connected to hollow headers in fluid communication therewith. A plurality of heat exchanger units are mutually aligned in the direction of air flow, and the coolant paths of the heat exchangers are connected to each other in series or parallel. The capacity of heat transfer can therefore be increased for the entirety of the duplex heat exchanger since each heat exchanger unit therein contributes to the heat transfer. Such a combination of two or more heat exchanger units provides a higher degree of freedom in selecting the number and/or arrangement of the partition plates to form a desired flow circuit of the coolant. An optimal design of the duplex heat exchanger can thus be used for a higher efficiency of heat transfer and for a lower pressure loss, which is essential for a good heat exchanger.

Claims (4)

1. An evaporator comprising a plurality of heat exchanger units (A, B), each of the heat exchanger units having a circuit for a heat exchange medium formed therethrough, and a connecting device (220, 230) for connecting the circuits in fluid communication with one another, each of the heat exchanger units having a plurality of tubes (1) arranged parallel to one another, a plurality of fins (2) arranged between two adjacent tubes (1), and a pair of hollow headers (3, 23 and 4, 24) to which the two ends of each tube (1) are connected in fluid communication, characterized in that the heat exchanger units (A, B) are arranged in front and rear in a direction of air flow such that one of them is oriented windward while the other is leeward, and air flow path units are defined between the adjacent tubes (1) and are formed by the fins (2) are separated from each other such that a cross-sectional area of each air flow path unit in the leeward heat exchanger unit is larger than that in the windward unit, thereby preventing an amount of water condensed on the leeward heat exchanger unit from being scattered therefrom. 2. Evaporator according to claim 1, characterized in that each heat exchanger unit (A, B) is designed such that a fin pitch (FpB) in the leeward heat exchanger unit is larger than the pitch (FpA) in the windward unit, so that the cross-sectional area of each air flow path unit in the former heat exchanger is larger than that in the latter. 3. Evaporator according to claim 1 or 2, characterized in that the heat exchanger units (A, B) are arranged in such a way that the head pieces (3, 23 and 4, 24) of each heat exchanger unit are arranged horizontally on the upper side and lower side thereof. 4. Evaporator according to claim 1, 2 or 3, characterized in that the heat exchanger units (A, B) are arranged parallel to one another so that the heat exchange medium flows simultaneously through the heat exchanger units.