FAN AND HEAT EXCHANGER FOR A COOLING SYSTEM

Abstract: A centrifugal fan (20) for use with a heat exchange system has a plurality of scrolls (23) for supplying air to respective air outlets (21); for example the scrolls extend around the axis of the fan on opposite sides and the outlets are diametrically opposed. The heat exchanger (50) has respective passages (51) for a working fluid and passages for cooling air (52) and a centrifugal fan (20) providing high pressure air to the cooling air passages which are dimensioned in relation to the fan such that turbulent air flow through the cooling air passages is achieved.

Description: FAN AND HEAT EXCHANGER FOR A COOLING SYSTEM This invention relates to heat exchangers and to fans for use therewith. This invention has particular application to a cooling system for vehicles especially trucks and the like, and it is in the context of trucks that this invention will be described, although the invention is also applicable to other installations such as in cars and in building air conditioners. The present invention, in one aspect thereof, provides a centrifugal fan for use with a heat exchanger. The fan has a plurality of scrolls supplying air to respective air outlets. In the preferred embodiment, there are two scolls and two outlets with the scrolls extending around the axis of the fan on opposite sides thereof and the outlets being diammetrically opposed. The outlets may be connected directly to ducts for directing air to one heat exchanger or to separate heat exchangers. The ducts may incorporate controlling .means for maintaining the flow through each duct in a desired proportion of total flow. The controlling means may be in the form of butterfly valves, orifice plates, flow restrictors or the like. Certain embodiments of the above described centrifugal fan have the advantage that they may be used on automobiles, trucks and the like in place of the axial flow fan currently used. This allows the heat exchanger for the vehicle to be placed at a more convenient location. Also, two or more heat exchangers may be located at different locations with each heat exchanger having its own duct from the fan. Thus, there is no need for the cooling air to pass through more than one heat exchanger thereby allowing maximum cooling efficiency from the cooling air. The centrifugal fan also allows the heat exchangers to be cooled by forced flow created by a positive pressure difference rather than from a vacuum difference. The centrifugal fan is able to create a greater pressure SUBSTITUTE Si:£ET ' difference than the standard axial flow fan used on vehicles. By relocating the heat exchanger away from the front of the truck, the si∑se of the engine compartment may be reduced. Generally, the cooling system occupies a space above the top of the engine. If this space can be reduced, the frontal dimension of the truck can be reduced or modified according to aerodynamic requirements to reduce the losses due to air resistance. In a second aspect, the present invention provides a heat exchange apparatus comprising: a heat exchanger having passages therethrough for a working fluid and cooling air, allowing the interchange of heat therebetween; and a centrifugal fan coupled to the heat exchanger for providing high pressure air to the cooling passages of the heat exchanger, wherein the cooling air passages and the characteristics of the fan are selected to create turbulent air flow through the cooling air passages. Preferably, the heat exchanger is a plate-type heat exchanger which is arranged in a single pass counterflow configuration. Ideally, the length of the passages through the heat exchanger is relatively long compared to standard radiator cores, i.e. in the order of 300 to 800 millimetres. Preferably, the cooling air is caused to become turbulent within the cooling air passages due to the increase in temperature of the cooling air as it passes through the heat exchanger. The use of turbulent flow for the cooling air allows maximum heat exchange to take place between the cooling air and the heat exchanger. In a further aspect, the present invention provides a heat exchanger comprising a plurality of passages for cooling air and for a working fluid, wherein forced air flow is provided to some of the cooling passages and air flow is induced to flow in at least some of the remaining air passages by the air leaving the forced air flow passages cooperating with diverter elements located at the exhaust end of the cooling air passages. Preferably, the diverter elements are aerofoil shaped devices placed at the outlet of the forced air passages. However, where the heat exchanger is a plate-type heat exchanger, air flow may be induced in the passages adjacent to the forced air flow passages by shaping or bending the plates at the exhaust end of the air passages. The air passages may be grouped in three's in which forced air flow is provided in the middle passage of the three and flow is induced in the other two passages. Preferably, the forced air flow through the heat exchanger is substantially turbulent flow. Certain embodiments according to this aspect of the invention is particularly advantageous in the area of vehicle technology in that forced air flow may be provided through-some of the air passages from a cooling fan, such as the centrifugal fan previously described, with air being induced to flow in the remaining air passages. The induced air flow passages may be connected to a skiff or duct for providing ram air through the induced air passages when the vehicle is travelling. It is possible, especially at highway speeds, that the ram air may be sufficient to provide these entire cooling requirements of the vehicle, in which case the forced air flow may be suspended by particular arrangement of the diverter elements. The ram air through the induced flow passages may induce flow in the forced flow passages when the fan providing the forced flow is not operating as it may, for example, be fitted to a thermostatic fan as to only provide cooling as required. In a further aspect, the present invention provides a plate-type heat exchanger for parallel flow heat exchange comprising: a plurality of plate members; a plurality of passages for circulating the hot fluid; and a plurality of passages for cooling air, wherein the heat exchanger is formed from the plate members cooperating to provide said passages which are elongate and parallel, each cooling air passage has a wall provided by a portion of a plate member which also provides a portion of the wall of an adjacent hot fluid passage, whereby the hot fluid passages and the cooling air passages are in primary heat exchange relationship. Preferably, the hot fluid passages are separated by webs defining the cooling air passages, the webs being formed by a portion of respective plate members thereby being primary heat exchange surfaces. Preferably, the passages through the heat exchanger are provided by voids in between pairs of plate members in the form of corrugated sheets. Secondary heat exchange may be provided by incorporating a flat plate located between the adjacent pairs of the plate members. Alternatively, each plate member may comprise a flat plate and a plurality of single corrugated strips spaced across one or each side of the flat plate and forming channels along the flat plate, wherein the flat plates are secured together such that the channels form the hot fluid passages and the voids between the channels form the-cooling air passages. Secondary heat exchange surfaces may be provided in the form of an additional flat plate installed between adjacent flat plates in heat exchange contact with the channels. A particularly advantageous cooling system for a vehicle can be created by combining the centrifugal fan previously described with the heat exchanger or heat exchange apparatus previously described. Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates in schematic representation a centrifugal fan having dual outlets; Figure 2 is a schematic representation of the fan of figure 1 coupled to dual heat exchangers superimposed over a conventional truck cooling system; Figure 3 is a side view of the arrangement of figure 2. Figure 4 depicts in schematic sectional view a truck radiator core using a prior art method of- inducing turbulent flow through the radiator; Figure 5 is a schematic representation of a plate-type heat exchanger having forced turbulent flow cooling air passages shown in sectional view; Figure 6 illustrates a long sectional view through a plate-type heat exchanger for inducing air flow in non-forced flow cooling air passages showing six cooling air passages in sectional view; Figure 7 is a similar view to figure 6 illustrating an alternative form of inducing the flow; Figure 8 is a cross sectional view of a heat exchanger for maximising primary heat exchange surface; Figure 9 is an exploded view showing the construction of the heat exchanger of figure 8; Figure 10 is an exploded cross sectional view of an alternative method of forming a heat exchanger similar to figure 8; Figure 11 is an exploded schematic cross sectional view of an alternative form of heat exchanger for maximising primary heat exchange surface wherein the cooling and working passages are of similar size; and Figure 12 is a similar view to figure 11 showing the addition of a secondary heat exchange surface. As can be seen from figure 1, the centrifugal fan 20 of the preferred embodiment has two outlets 21 and a single inlet 21. The two outlets are formed by creating the casing for the impeller with two scoll sections 23 thereby dividing the output of the fan into the two outlets. The two scrolls may be created equal or one may be larger than the other to create proportional flows through the outlets 21. The fan is coupled to two ducts (not shown) to direct the air from the fan to the required heat exchangers. In figure 2, the size of the fan 20 and heat exchangers 30 are compared with a comparable conventional truck cooling system. As can be seen from figures 2 and 3, the frontal area and height of the fan and in the heat exchangers of the preferred embodiment are significantly smaller than that of the conventional cooling system. Also, the inlet 22 to the centrifugal fan 20 is substantially unblocked by obstructions at the front of the truck and the heat exchangers 30 as the air from the fan is ducted directly to them do not develop areas in which cooling air does not pass. This must be compared with the conventional cooling system (shown in ghost) in which the lower portion of the radiator 25 is blocked by the harmonic balancer 26 and bumper bar 27, and other portions of the radiator are usually blocked by other obstructions such as bull bars. The axial flow fan of the conventional cooling system is also limited in size by the presence of the harmonic balancer 26 and generally only causes air to be drawn through the radiator 25 in a .localised area. Also, the radiator is usually associated with other heat exchangers such as an oil cooler 28 and combustion air cooler 29 which heat the cooling air before the cooling air reaches the radiator. The preferred embodiment, which utilises a centrifugal fa forced feeding the cooling air to the heat exchangers, can produce greater pressure differences thereby creating a greater velocity of air flow through the heat exchangers than is possible with the suction produced by the axial flow fans of the conventional cooling system. Also, as the air from the centrifugal fan is ducted, the heat exchangers may be located at any convenient location and not necessarily in the front of the engine compartment. . Conventional cooling systems use a radiator in which the core is narrow so that the cooling air passing through the radiator does not rise significantly during its path through the radiator cor in an effort to maintain cooling efficiency substantially constant along the cooling path. It has been recognised however that turbulent air has a greater cooling efficiency than laminar flow air and i figure 4, a prior art method of inducing turbulent flo in the radiator core is illustrated. Only four radiator fins 40 are illustrated for clarity. The air flow 41 is directed to the upstream end of the radiato fins. This particular end is turned downwardly as illustrated by referenced numeral 42 to direct air upwardly between the fins 40. At the bend in each fin is located a series of holes 43 through which a portio 44 of the air flow 41 between the fins passes. This air flow 44 confronts the air flow 45 passing through the immediately above air passage. This confrontation produces an interruption to the air flow 45 creating a turbulent flow 46 between the radiator fins 40, at least in the immediate vicinity of the interruption. In practice, however, the turbulent flow quickly settles down to laminar flow and the holes 43 which ar very small are quickly filled with dust entrained in the air flow 41, thereby blocking the holes resulting in laminar flow only through the radiator core. If the air flow through the heat exchanger cooling air passages can be maintained at a sufficiently high velocity so that the Reynold's number approaches 1 x 10 then the flow through the air passages will be turbulent, resulting in greater heat transfer efficiency. The Reynold's number is a factor dependent upon the velocity of the air, the temperature of the air, and the dimensions of the air passage. Also, true turbulent flow creates a mild scrubbing effect, keeping the passages of the heat exchange clean. The source of pressurised air for supplying the cooling air to the heat exchanger may be any convenient source although preferably, a centrifugal fan, as previously described, is used. Referring to figure 5, a plate-type heat exchanger 50 is shown. The heat exchanger comprises a plurality of passages 51 for the passage of the working fluid and a plurality of passages 52 for the passage of cooling air. The cooling air is introduced into the passages by a manifold 53 under sufficient pressure to create turbulent flow in the air passages 52. The air passages 52 are allowed to exhaust to the atmosphere while the working fluid is forced circular through the heat exchanger by way of a pump and manifolds not shown for clarity. It should be realised that the forced air supplied to the heat exchanger may not be turbulent when it enters the cooling air passages but due to the heat exchange taking place between the heat exchanger and the air, the temperature of the air may increase sufficiently to create turbulent flow part way along the cooling air passage. In this manner, the pressure of the forced air supplied may be lower than otherwise required allowing a smaller fan or a fan operating at lower speeds than otherwise required to be utilised. For a standard radiator of the prior art cooling system, the induced flow on the suction side of the axial flow fan is typically 11 metres per second of flow rate velocity whereas at highway speed, the air flow rate velocity is typically 24 metres per second. For genuine turbulent flow to exist in the standard radiator, the flow rate velocity must be increased to approximately 180 metres per second which is not a practical proposition for current radiators and fan units. In the heat exchanger of the present embodiment, turbulators in the form of fins, bumps etc., may be utilised to create genuine turbulent flow 5 at Reynold numbers below 1 x 10 . However, care must be taken to ensure that the cooling air flow is, indeed, genuinely turbulent. If forced cooling air is only directed to some of the cooling air passages, it is possible to create induced flow in the remaining air passages thereby reducing the volume of air required for the forced air flow passages. In figure 6, six air flow passages are illustrated in longitudinal cross section. The six air passages may be divided into two groups of three. The middle air passage 61 is connected to a manifold 62 for supplying forced flow cooling air. The walls of the cooling air passages 63 are extended at the exhaust end of the cooling air passages thereby defining the groups of three. Located between the extended walls and directly in line with the forced air passages 62 is located diverter elements 64. These diverter elements cooperated with the air exhausting from the forced air passages to induce air flow in the other two air passages 65. As the forced air exhaust from the forced air passage 61, it strikes the diverter element 64 and is deflected. The deflection of the air flow creates an area of low pressure at the exhaust end of the induced flow passages 65 and as the inlet to the induced flow passages 65 are unrestricted, air flows naturally along the induced air passages 65 absorbing heat from the heat exchanger.. Figure 7 illustrates an alternate form of inducing cooling air flow in a plate-type heat exchanger. Again, six air passages of the heat exchanger are illustrated in longitudinal section for clarity. In this embodiment, the air passages are again grouped in three's with the middle air passage 71 being connected to a source of pressurised air for supplying forced flow cooling air. The other two air passages 73 and 74 of the group of three are unobstructed. The wall between the forced air flow passage 71 and air passage 74 is reduced in length at the exhaust end and the remaining wall of air passage 71 is bent towards air passage 74 thereby causing a restriction in the outlet of the forced air flow passage 71 and induced air flow passage 74. As the air exhausts from air passage 71, an area of low pressure is created at the outlet of air passage 74 thereby inducing air flow along air passage 74 which absorbs heat from the heat exchanger. Air passage 73 may be arranged to receive ram air cooling or simply left open. In many heat exchangers, the majority of heat is transferred by secondary heat exchange surfaces. This is especially so in the radiators of vehicle cooling systems in which the majority of cooling is accomplished by the radiator fins. However, maximal heat transfer occurs across primary heat transfer surfaces, i.e. surfaces which are in contact with both the working fluid and cooling air. In standard plate-type heat exchangers, the working fluid passes between two plates and the cooling air is passed between two adjacent plates. The only way of providing for greater heat rejection is to increase the size of the cooling air passages by separating the plates or by reducing the working fluid passages by placing the plates closer together. While this may allow for a variation in the amount of heat rejection able to be conducted by the heat exchanger, the actual surface area in contact with the cooling air or the working fluid is not varied. In the heat exchangers depicted in figures 8 to 12, the size of the cooling air passages or the working fluid passages may be varied according to the particular application of which the heat exchanger is to be used. In this embodiment, the heat exchanger is formed by securing together a plurality of three plates 81, 82 and 83; plates 81 and 82 are corrugated or folded or are plates with a series of channels formed therein; plate 82 being a mirror image of the plate 81. When the plates 81 and 82 are joined together, a passage 84 is formed by the two channels. The plates and channels are more clearly shown in figure 9. Each passage 84 is interconnected by a web 86 formed where the two plates are contiguous. Adjacent pairs of plates 81/82 are joined together so that their passages 84 are aligned. In this manner, the webs 86 of adjacent pairs of plates form a further passage 85 for the cooling air. Plate 83 may be inserted between adjacent pairs of plates 81/82 and divides the air passages 85. By this manner, the webs 86 are primary heat exchange surfaces as they are in contact with both the cooling air and the hot working fluid in passage 84. The plate 83 is a secondary heat exchange surface as it is only in contact with the cooling air in the passage 85 although because the channels are square bottomed, the surfaces of the working fluid passage 84 are flat, providing a large surface contact with the secondary heat exchange surface plate 83 resulting in excellent heat exchange between the plates 81, 82 and the plate 83. The secondary heat exchange surface 83 may be omitted if not required, in which case, the entire heat exchange surface is in primary heat exchange configuration. Figure 10 illustrates an alternative method of forming the heat exchanger of figure 8. In this case, plates 81 and 82 are replaced by a single flat plate 87. To plate 87 is attached a series of small channels extending the length of the plate 87, the small channels forming the working fluid passage 84. Again, the channels are arranged so that when the plates are joined together, the passages 84 are aligned. The cooling air passages 85 are formed between the adjacent channels although figure 10 illustrates channels being placed on both sides of plate 87, satisfactory results may be achieved by placing the channels on only one side of plate 87. Also, plate 83 may be omitted, in which case, only primary heat exchange surfaces are used. The webs 86 are only one plate thick. Figures 11 and 12 illustrate a further alternate method of forming a heat exchanger utilising primarily primary heat exchange surfaces in which the heat rejection requirements of the heat exchanger can be determined to suit the particular application. In figure 11, plates 111 and 112 are deformed such that plate 112 is a mirror image of plate 111. The plates, when joined together, form voids where the plates are corrugated or folded and these voids are interconnected by webs 86. Again, adjacent pairs of plates are joined together so that the voids are aligned. The voids 113 form the working fluid passages. Between adjacent pairs, voids 114 are formed which are used as the cooling air passages. The sizes of these voids are easily varied by varying the size of the deformation or the length of the web 86. Figure 12 illustrates how a secondary heat exchange surface may be inserted between pairs of deformed plates thus dividing the cooling air passages. The shapes of the deformations formed in the plates 111 and 112 are flat bottomed V shapes. The heat exchange contact surface between the secondary heat exchange plate 83 and the primary heat exchange plates 111 and 112 can be sufficient to allow efficient heat transfer to the secondary heat exchange surface rather than the usual knife edge contact normally available in prior art radiator cores across which the flow of heat is greatly restricted. The V-shaped deformations create a honeycomb-shaped pattern in the heat exchanger when reviewed in cross section. By knowing the temperature of the working fluid, the temperature difference required to be created by the heat exchanger, the volume of the flow of the working fluid, the heat conduction efficiency of the material from which the plates of the heat exchanger are made, the required volume of cooling air and the cooling air temperature, the required proportional sizing of the working fluid and cooling air passages may be determined to ensure the required heat rejection capacity from the heat exchanger is achieved. As the sizes of the passages are varied, the proportion of primary heat exchange surface in contact with the working fluid or cooling air is also changed so that maximum efficiency can be gained from the heat exchange characteristics of the cooling air and working fluid. As an example of the fan and heat exchanger hereinbefore described, it is envisaged that the dual outlet centrifugal gan would replace the axial flow fan of the cooling system used on a heavy haulage truck engine. The cooling water flow through the duct water jacket heat exchangers is approximately 800 1/min. Each heat exchanger would be approximately 450 mm high and between 100 mm and 200 mm wide with the length of the flow path being in the range of 300 to 600 mm long. The size of the cooling air passages may be 4 mm high by between 15 to 20 mm wide with the hot fluid passages ranging from 2 x 2mm to 4 x 5 mm. Of course, other configurations are possible without departing from the spirit of the invention. Cooling systems for automobiles which require a water circulation rate as low as 20 1/min are comparably proportioned.

Claims: CLAIMS : 1. A centrifugal fan for use with a heat exchanger, having a plurality of scrolls supplying air to respective air outlets. 2. A fan as claimed in claim 1, wherein there are two scrolls and two outlets, the scrolls extending around the axis of the fan on opposite sides thereof and the outlets being diammetrically opposed. 3. A fan as claimed in claim 1 or claim 2, wherein the fan outlets are connected to ducts for directing cooling air to the or each heat exchanger. 4. A fan as claimed in claim 3, wherein the ducts incorporate controlling means for maintaining the flow through each duct in a desired proportion of total flow. 5. A fan as claimed in claim 4, wherein the controlling means is a butterfly valve. 6. Heat exchange apparatus comprising: a heat exchanger having passages therethrough for a working fluid and cooling air, allowing the interchange of heat therebetween; and a centrifugal fan coupled to the heat exchanger for providing high pressure air to the cooling air passages of the heat exchanger, wherein the dimensions of the cooling air passages and the characteristics of the fan are selected to create turbulent air flow through the cooling air passages. 7. A heat exchange apparatus as claimed in claim 6, wherein the heat exchange is a plate-type heat exchanger. 8. Heat exchange apparatus as claimed in claim 6 or claim 7, wherein the heat exchanger is a single pass counter flow heat exchanger. 9. Heat exchange apparatus as claimed in claim 8, wherein the length of the passages through the heat exchanger is approximately 300 to 800 mm long. 10. Heat exchange apparatus as claimed in any one of claims 6 to 9, wherein the cooling air is caused to become turbulent within the cooling air passages due to the increase in temperature of the cooling air as it passes through the heat exchanger. 11. A heat exchanger comprising a plurality of passages for cooling air and for a working fluid, wherein forced air flow is provided to some of the cooling air passages and air is induced to flow in at least some of the remaining air passages by the air leaving the forced air flow passages cooperating with diverter means located at the exhaust end of the cooling air passages. 12. A heat exchanger as claimed in claim 11, wherein the diverter means comprises aerofoil shaped diverter elements placed in the outlet of the forced air passages. 13. A heat exchanger as claimed in claim 11 or 12, wherein the air passages are grouped in three's and forced air flow is provided in the middle passage of each group of three and flow is induced in the other two passages of each group. 14. A heat exchanger as claimed in claim 11, wherein the heat exchanger is a plate-type heat exchanger and air flow is induced in passages adjacent to the forced air flow passages by arrangement of the plates at the exhaust end of the passages. 15. A heat exchanger as claimed in any one of claims 11 to 14, wherein the forced air flow through the heat exchanger is substantially turbulent flow. 16. A plate-type heat exchanger for parallel flow heat exchange comprising: a plurality of plate members; a plurality of passages for circulating the hot fluid; and a plurality of passages for cooling air, wherein the heat exchanger is formed from the plate members cooperating to provide said passages which are elongate and parallel, each cooling air passage has a wall provided by a portion of a plate member which also provides a portion of the wall of an adjacent hot fluid passage, whereby the hot fluid passages and the cooling air passages are in primary heat exchange relationship. 17. A heat exchanger as claimed in claim 16, wherein the hot fluid passages are separated by webs defining the cooling air passages, said webs being formed by a portion of respective plate members. 18. A heat exchanger as claimed in claim 16 or 17, wherein the plate members are corrugated sheets and the the passages are formed by voids in between adjacent sheets. 19. A heat exchanger as claimed in claim 18, wherein a flat plate is located between adjacent pairs of corrugated plates to provide a secondary heat exchange surface. 20. A heat exchanger as claimed in claim 16 or 17, wherein each plate member comprises a flat plate with a plurality of single corrugated strips spaced across one or each side of the flat plate and forming channels along the flat plate, wherein the flat plates are secured together such that the channels form the hot fluid passages and the voids between the channels form the cooling air passages. 21. A heat exchanger as claimed in claim 20, further comprising secondary heat exchange surfaces in the form of additional plates inserted between adjacent flat plates and being in heat exchange relationship with the channels. 22. A cooling system for a vehicle comprising a centrifugal fan as claimed in any one of claims 1 to 5 and a heat exchanger as claimed in any one of claims 11 to 21. 23. A vehicle incorporating a heat exchange apparatus as claimed in any one of claims 6 to 10.

Inventors: FRITZ PETER, FRITZ, PETER
Applicants: FRITZ PETER, FRITZ, PETER
Application year: 1989
Main classification: F04D29
IPC codes: B60H1, F04D29