Abstract:
A guiding device for use with a fan-radiator cooling system wherein the fan is upstream from the radiator. The guiding device comprises a series of guide vanes in combination with at least one guide ring. When placed between the fan and the radiator, the device improves the heat transfer capacity of the cooling system by directing air flow through the radiator center, a region that typically suffers from reduced flow due to the air flow pattern in and around the fan hub. Furthermore, the guide vanes align the air flow from the fan so that it is generally parallel with the axis of the fan. The guiding device permits greater heat removal with a given fan and radiator without increasing the speed of the fan.

Description:
TECHNICAL FIELD 
     This invention relates generally to cooling systems and, more particularly, to a guiding device for use with a fan-radiator cooling system wherein the radiator is positioned downstream from the fan. 
     BACKGROUND OF THE INVENTION 
     Cooling systems capable of removing a heat load from a heat-producing source are well known. For modest loads, a forced air system is often adequate. Forced air systems typically utilize an axial or centrifugal fan to pull or push air across the heat-producing source. For more substantial heat loads such as internal combustion engines, a liquid coolant heat exchanger or “radiator” may be used in conjunction with the fan. 
     The fan typically comprises a series of fan blades coupled to a spinning hub and positioned to direct ambient air flow over the radiator. The radiator comprises a plurality of tubes which are oriented generally normal to the fan axis. Each tube includes a series of fins to increase its surface area (and thus its heat transfer capacity). A liquid coolant is circulated through the heat-producing source wherein it absorbs heat energy. The coolant then passes through the radiator tubes, transferring heat energy through the tubes and fins to the ambient air flowing through the radiator. The cooled liquid is then routed back through the heat-producing source where it is once again heated. Accordingly, heat energy is continuously removed by the liquid coolant and transferred to the moving air. 
     Generally speaking, fan-radiator cooling systems can be classified based on the direction of air flow. In “pull” systems, the fan is positioned downstream from the radiator wherein it draws or pulls air therethrough. Pull systems are commonly found on motor vehicles such as automobiles and on some industrial cooling systems. Fan-radiator cooling systems may also be configured as “push” systems. As the name implies, push systems position the fan upstream from the radiator where the fan exhausts or pushes air through the radiator. Push-type systems are often selected based on packaging or installation limitations or where it is desirable to have cooler air passing over the fan. The present invention is directed to push-type systems and the remainder of the discussion will focus accordingly. 
     While push-type fan-radiator systems are effective heat exchangers, problems nevertheless remain. One problem is related to the flow characteristics of the axial fan. In particular, the output of an axial fan is not entirely axial but rather helical. The resulting flow thus has both an axial and a circumferential component. Since the circumferential flow component is not aligned with the tubes and fins of the radiator (i.e., it is not normal to the radiator surface), it contributes little to cooling. Rather, this circumferential flow increases entrance loss into the radiator, degrading overall efficiency. 
     Yet another problem with these systems is caused by the fan hub. Specifically, since the fan blades do not extend inwardly past the hub, the fan is unable to efficiently generate air flow into the region of the radiator that is aligned with the hub. Accordingly, a lower volumetric flow rate exists in and around the radiator center region. Stated alternatively, an inactive zone is produced in the radiator center wherein coolant flowing therethrough is unable to transfer the same amount of heat energy as coolant flowing elsewhere through the radiator. Thus, the overall heat removal capacity of the radiator is reduced. Depending on such factors as hub size, fan/radiator spacing and fan speed, the effect of the inactive zone on heat removal may be substantial. 
     While not known for use with fan-radiator systems, downstream guide vanes are often used with axial compressors and the like to address the problem of flow alignment. Downstream guide vanes collect air discharged by the compressor and redirect it in a generally axial direction. Unfortunately, these guide vanes do nothing to address the reduced flow through the inactive zone as discussed above. 
     Another means to increase volumetric flow is to increase the size of the radiator and fan or, alternatively, increase the fan speed. While these solutions improve overall heat transfer, they are disadvantageous in terms of cost, size and power requirements. In addition, they too do not address the issue of flow in the inactive zone. 
     Thus, there are unresolved issues with current fan-radiator cooling systems. What is needed is a push-type fan-radiator system that provides uniform, axial air flow through the radiator and, in particular, provides improved flow to the portion of the radiator located directly downstream from the fan hub. What is further needed is a system that can provide this uniform flow while minimizing pressure loss. 
     SUMMARY OF THE INVENTION 
     A device to control air flow between a fan and a radiator in a fan-radiator cooling system is provided comprising a plurality of guide vanes that radiate outwardly about a first axis from a first, inner diameter to a second, outer diameter. The device further includes a generally annular guide ring coupled to the guide vanes, wherein the guide ring is adapted to direct a portion of the air flowing through the device toward an inactive region of the radiator. 
     A method for using an axial fan to push air through a radiator is also provided. The method comprises providing a cooling system having an axial fan. The fan has a plurality of blades coupled to a rotating hub wherein the hub is adapted to selectively receive power from a power source. The system further includes a radiator positioned generally perpendicular to an axis of the axial fan and located downstream therefrom, and a guiding device intermediate the fan and radiator. The method also includes generating air flow by selectively engaging the power source to rotate the fan blades and directing the air flow with the guiding device so that a portion of the flow is directed to a center region of the radiator. 
     In another embodiment, a fan-radiator cooling system is provided including an axial fan having a plurality of fan blades emanating from a central hub wherein the central hub has a hub diameter and the fan blades define a blade diameter. The system further includes a radiator downstream and spaced apart from the axial fan and a guiding device between the axial fan and the radiator. The device includes a plurality of stationary guide vanes that radiate outwardly about a first axis from a first, inner diameter to a second, outer diameter; and a generally annular guide ring coupled to the guide vanes. The guide ring is adapted to direct a portion of the air flowing through the device toward a center region of the radiator, the guide ring defining a second axis substantially coaxial with the first axis. 
     In yet another embodiment, a generator set is provided which includes a heat-producing prime mover; a converting apparatus that converts work output of the prime mover into electrical energy; and a cooling system for removing heat generated by the prime mover. The cooling system includes an axial fan having a plurality of fan blades emanating from a central hub. Also included is a radiator downstream and spaced apart from the axial fan and a guiding device between the axial fan and the radiator. The guiding device is comprised of a plurality of stationary guide vanes that radiate outwardly about a first axis from a first, inner diameter to a second, outer diameter; and a generally annular guide ring coupled to the guide vanes, wherein the guide ring is adapted to direct a portion of the air flowing through the device toward a center region of the radiator, the guide ring defining a second axis substantially coaxial with the first axis. 
     Advantageously, the present invention provides an improved fan-radiator cooling system. By sitting between the fan and radiator, the guiding device of the present invention allows more uniform flow through the radiator by redirecting a portion of the flow to the radiator center. Accordingly, inefficiencies attributable to reduced flow through the radiator center are minimized or eliminated. Thus, a given heat load can be removed with a smaller fan and radiator than would otherwise be required. In addition, the guiding device redirects non-axial flow so that it is generally parallel with the fan axis, thus providing smoother flow through the radiator. Smoother flow equates with reduced entrance loss, which in turn, permits higher volumetric flow. The redirection of flow also results in a conversion of kinetic (i.e., velocity) energy into static pressure, which also contributes to increased air flow through the radiator. Thus, the overall efficiency of the cooling system is increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention described herein will be further characterized with reference to the drawings, wherein: 
     FIG. 1 is a diagrammatic perspective view of a generic generator set having a cooling system in accordance with one embodiment of the invention; 
     FIG. 2 is an diagrammatic, exploded perspective view of a fan-radiator cooling system in accordance with one embodiment of the present invention; 
     FIG. 3 is an enlarged view of a portion of the radiator of FIG. 2; 
     FIG. 4 is a perspective view of a guiding device for use with a fan-radiator cooling system in accordance with one embodiment of the invention; 
     FIG. 5 is a front elevation view of the guiding device of FIG. 4; 
     FIG. 6 is a section view of the guiding device of FIG. 5 taken along lines  6 — 6  of FIG. 5; 
     FIG. 7 is a diagrammatic perspective view of a fan-radiator cooling system in accordance with another embodiment of the present invention; 
     FIG. 8 is a diagrammatic side elevation view of a fan-radiator cooling system in accordance with another embodiment of the present invention; and 
     FIG. 9 is a front elevation view of a guiding device in accordance with another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description of the embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     Generally speaking, the instant invention is directed to a push-type fan-radiator cooling system. In particular, the invention is directed to a guiding device for guiding the flow of air from the fan and uniformly distributing it over the entire radiator face including the radiator center region. The radiator center typically experiences reduced air flow in push-type systems. This is primarily due to the fact that the flow-producing blades do not extend into the hub region. As such, a region of reduced flow exists directly downstream (i.e., axially aligned) from the fan hub near the radiator center. Because the air flow is reduced, the ability of the radiator to transfer heat from this region is also diminished. The area affected by this reduced flow will hereinafter be referred to, for lack of a better term, as the inactive region or zone. Since the inactive zone has diminished capacity to transfer heat, overall heat transfer capacity of the cooling system is likewise decreased. To counteract this problem, fan engineers have generally had to provide larger fans and/or larger radiators to remove a given heat load. 
     The present invention permits diversion of a portion of the fan-generated air flow to the center of the radiator, increasing the volumetric flow rate in the inactive zone and thus improving the heat transfer capacity of the radiator through that region. While the invention may be utilized in most any system requiring a push-type cooling system, the inventors perceive one particularly advantageous application is with generator sets and the remainder of this discussion will address the same. 
     With this brief introduction, attention will now be focused on exemplary embodiments of the invention. While the embodiments that follow are described in sufficient detail to enable one skilled in the art to make and use the invention, the reader is reminded that they are nonetheless exemplary and, as such, are not intended to limit the scope of the invention in any way. 
     Referring first to FIG. 1, a generator set  50  is illustrated having a cooling system  10  therein. The generator set includes a converting apparatus  51  which converts mechanical work done by a prime mover—such as a internal combustion engine  54 —into electrical energy. Generators sets are used for various purposes such as emergency backups and as remote power supplies to name a few. 
     Referring now to FIG. 2, the cooling system  10  is shown in an exploded perspective view. The system, in one embodiment, comprises a guiding device  100 , a fan assembly  200  and a radiator or radiator assembly  300 . Although not central to the invention, the operation of the fan and radiator assemblies will be briefly described. The fan assembly  200  includes an axial fan  201  having a plurality of blades  202  coupled to a central, rotating hub  204 . The fan blades  202  are airfoil shaped or alternatively, generally planar. Each blade has a distal tip  203  which defines the blade diameter. The blades, in one embodiment, are surrounded along their distal tip  203  by a circumferential shroud  206 . A power source such as an electric motor  208  (see FIG.  8 ), supported by a series of radial supports (not shown) connected to the shroud  206 , is operatively coupled to an axis of the hub  204  to selectively rotate the fan  201 . 
     Mounted downstream of the fan assembly  200  generally perpendicular to the fan axis is the radiator assembly  300 . The radiator assembly is a heat exchanging device used to remove heat from a heat-producing source which, for purposes of this discussion, will hereinafter be referred to as the internal combustion engine  54 . In operation, fluid circulated through the engine absorbs heat therefrom. The fluid then passes through a plurality of tubes  302  (see FIG. 3) located within the body of the radiator assembly  300 . Each tube  302  has a plurality of fins  304  attached thereto. As the fluid moves through the tubes, air is continually passed through the radiator assembly by the fan assembly  200 . By continually moving air across the tubes and fins, beat energy is transferred through the tube walls to the ambient air flow stream where it is carried away and dispersed to the atmosphere. 
     The fins  304  are used to increase the surface area of the tubes  302  exposed to the passing air, thus further improving the heat transfer capacity of the radiator assembly. After passing through the radiator assembly, the now-cooled fluid is once again recirculated through the engine  54 . By repeatedly circulating the fluid through the engine  54  and the radiator assembly  300 , heat energy is effectively removed from the generator set  50  (see FIG.  1 ). To prevent the air flow produced by the fan from exiting circumferentially or radially, a duct  400  (removed for clarity in FIG. 2 but shown in FIG. 8) is provided, in one embodiment, between the downstream side of the fan and the upstream side of the radiator. The duct generally prevents fan-generated air from escaping to atmosphere until it has entered the radiator assembly  300 . 
     Having described the cooling system  10  generally, attention will now be focused on the air flow guiding device  100 . When used in conjunction with the fan assembly  200  and radiator assembly  300  described above, the guiding device  100  provides improved air flow through the radiator assembly and more effective heat transfer from the cooling system  10 . 
     Referring briefly to FIGS. 2 and 4, the device  100 , in one embodiment, is a stationary component that sits between the fan assembly  200  and radiator assembly  300 . The device  100  comprises a first plurality of outer guide vanes  102  and a second plurality of inner guide vanes  104 . The guide vanes  102 ,  104  extend outwardly about a common axis to form guide surfaces. The vanes  102  and  104  are each secured to an annular guide ring  106 . The device  100  is further defined by a first side  108  located proximal the fan assembly  200  and a second side  110  adjacent the radiator assembly  300 . On the first side  108 , each vane  102 ,  104  is defined by a leading edge  112  while, on the second side  110 , the vanes are each defined by a trailing edge  114 . 
     Unlike pull-type fan-radiators such as those frequently found in automobiles, the cooling system  10  (see FIG. 2) of the present invention positions the fan assembly  200  upstream from the radiator assembly  300  so that air is pushed through the latter rather than pulled. Pull-type fan systems are not prone to the problems inherent in push-type systems as fans develop generally uniform, axial flow (i.e., flow generally parallel to an axis of rotation of the fan) on their upstream side. Unfortunately, the flow developed on the downstream side of the fan is not nearly as uniform. This problem is partially due to the orientation of the fan blades  202  relative to the axis of the fan. Since the blades are angled (or airfoil shaped) they impart motion to the air not strictly in the axial direction but rather in a direction normal to the blade surface. As such, the downstream flow, while having a predominantly axial component, also has a circumferential or rotational component. Since only axial flow passes smoothly through the radiator, this circumferential flow component is, undesirable. 
     Accordingly, one object of the guiding device  100  is to capture the flow and redirect it in the axial direction. As such, the leading edges  112  are generally aligned with the direction of air flow exiting the fan while the trailing edges are generally aligned to direct the air flow parallel to the axis of the fan ( i.e., normal to the radiator assembly  300 ). In the embodiment shown in the figures, this results in a curvilinear guide vane shape. While not required, the inner guide vanes are shaped similar to the outer guide vanes. The shape of the guide vanes  102 ,  104  permits efficient collection and “straightening” of the air flow discharged by the fan so that it flows generally in the axial direction. The result is that air is passed more smoothly through the radiator. In addition, the redirection of air flow by the vanes  102 ,  104  results in a conversion of air velocity (kinetic energy) into static pressure, which further increases the flow of air through the radiator assembly  300 . 
     While the guide vanes  102 ,  104  straighten the air flow, it is the guide ring  106  in conjunction with the vanes that directs the air flow to the inactive zone of the radiator assembly  300 . Referring particularly to FIGS. 5-6, the inner vanes  104  extend toward the center to define an inner diameter  116 . The particular size of the inner diameter  116  is adapted to ensure adequate flow toward the radiator center. The actual size depends on many factors including the fan size, angle/shape of the fan blades and guide vanes, and the relative location and shape of the guide ring, among others. In a typical configuration, the fan motor  208  (see FIG. 8) is located on the side of the fan opposite the device  100 . In an alternative embodiment where the fan motor  208  is located between the fan and the device  100  (not shown), the inner diameter  116  is sized to accommodate the fan hub  204  and motor  208  therein (i.e., the fan and hub fit within the inner diameter). 
     In the embodiment shown in FIGS. 7 and 8, the device  100  is placed in close proximity to the fan assembly  200  to better capture the circumferential flow generated by the fan. Accordingly, the output of the fan assembly  200  is more efficiently utilized. To further increase efficiency, the device  100 , in one embodiment, has an outer diameter  128  (see FIG. 6) larger than the fan blade diameter (i.e., the distance across the distal tips  203  of the fan  201 —see FIG. 2) to more effectively collect the air discharged proximal the distal tip  203  of the fan  201 . 
     Referring once again to FIG. 6, the ring  106 —like the vanes  102  and  104 —also includes a leading edge  118  on the first side  108  and a trailing edge  120  on the second side  110 . At the leading edge  118 , the ring  106  forms an entrance diameter  122  while at the trailing edge  120  it forms an exit diameter  124 . The entrance and exit diameters have a common axis which is generally coaxial with the axis about which the guide vanes  102 ,  104  extend (and thus, also generally coaxial with axis of the fan). In the embodiment shown, the ring is bowed outwardly towards its center to form a diverging region  125  having an expansion diameter  126 . Accordingly, air drawn into the entrance diameter  122  diverges or expands momentarily into the expansion region and then converges toward the exit diameter  124 . The convergence of the ring forces air toward the radiator center, effectively eliminating the inactive zone experienced with conventional push-type systems. By controlling the radial location and geometry of the ring  106 , the volumetric flow that is redirected towards the center can be controlled. In one embodiment, the ring is located and configured such that the average volumetric flow rate per unit area through the ring is generally equal to the average volumetric flow rate per unit area outside the ring. By controlling the ring size and configuration, uniform flow over the entire radiator surface is achieved. While the bowed ring profile minimizes pressure drop across the ring, other ring configurations (e.g., straight taper from entrance to exit) are also possible without departing from the scope of the invention. 
     In one embodiment, the leading and trailing edges  118 ,  120  are generally coplanar with the leading and trailing edges  112 ,  114  respectively of the vanes  102 . That is, the depth of the ring  106  is approximately identical to the vane depth  129  (see FIG.  6 ). However, embodiments where the ring  106  extends beyond the vanes (in either the upstream or downstream directions) are also possible without departing from the scope of the invention. Similarly, embodiments where the vanes  102 ,  104  extend beyond the ring  106  are also possible. 
     Referring now to FIG. 7, the device  100  is shown as positioned between a diagrammatically represented fan assembly  200  and radiator assembly  300 . The general direction of air flow through the cooling system is represented by arrows  123 . FIG. 8 shows a partial cross section of the assembled system  10 . Although the embodiment shown illustrates the motor  208  on the upstream side of the fan, embodiments wherein the motor is located on the downstream side are also possible within the scope of the invention. 
     In one embodiment, a tubular duct or shroud  400  as shown in FIG. 8 is provided. The duct  400  effectively contains air flowing between the fan assembly  200  and the radiator assembly  300 . The duct  400  spans from the downstream side of the fan assembly  200  to the upstream side of the radiator assembly  300 . By utilizing the duct  400 , air entering the cooling system  10  can then generally exit the system only after passing through the device  100  and the radiator assembly  300 . The duct includes mounting provisions for securing the device  100  therein. 
     In one embodiment, the guiding device  100  comprises fifteen outer guide vanes  102  and eight inner guide vanes  104 . However, this configuration is specific to one particular application and embodiments utilizing differing numbers and differing configurations of guide vanes are possible without departing from the scope of the invention. 
     In addition to varying the guide vanes  102 ,  104 , other embodiments such as that shown in FIG. 9 are also possible. FIG. 9 shows the device  100  with supplemental rings  130  and  132  located on the outer diameter  128  and the inner diameter  116  respectively. These rings are used not only to assist with flow containment and direction, but also to provide structural support when the vanes are unusually long or flexible. Like the ring  106 , the rings  130 ,  132 , in one embodiment, extend beyond the first or second side  108 ,  110 . Nevertheless, in order to prevent interference with flow into the inactive zone, the leading edge of the ring  132  does not extend substantially beyond the device  100 . In one embodiment, the ring  132  has a leading edge which extends beyond the first side  108  of the device  100  a distance of no more than one third the depth  129  (see FIG.  6 ). 
     Advantageously, the present invention provides an improved fan-radiator cooling system. By sitting between the fan and radiator, the guiding device of the present invention allows more uniform flow through the radiator by redirecting a portion of the flow to the radiator center. Accordingly, inefficiencies attributable to reduced flow through the radiator center are minimized or eliminated. Thus, a given heat load can be removed with a smaller fan and radiator than would otherwise be required. In addition, the guiding device redirects non-axial flow so that it is generally parallel with the fan axis (and thereby perpendicular to the radiator), thus providing smoother flow through the radiator. Smoother flow equates with reduced entrance loss, which in turn, permits higher volumetric flow. The redirection of flow also results in a conversion of kinetic (i.e., velocity) energy into static pressure, which also contributes to increased air flow through the radiator. Thus, the overall efficiency of the cooling system is improved. 
     Preferred embodiments of the present invention are described above. Those skilled in the art will recognize that many embodiments are possible within the scope of the invention. Variations, modifications, and combinations of the various parts and assemblies can certainly be made and still fall within the scope of the invention. Thus, the invention is limited only by the following claims, and equivalents thereto.