HEAT EXCHANGER HAVING INCLINED TUBES

Abstract: A heat exchanger (10) has first and second cores (12, 14) arranged in a "V" configuration with the inner, directly adjacent ends being spaced apart a preselected distance for purging debris. The first core (12) has an axis "A" and a plurality of fins (40) defining an inlet surface (18) and an outlet end (44). An elongated tube (46) extends through the fins (40) and has a transverse axis "T" oriented with respect to axis "A" at a preselected angle to increase air flow and reduce pressure drop across the core. The second core (14) has a plurality of fins (40) defining an inlet surface (22) and an outlet end (44). The first and second core fins (40) are truncated at the corner defined by the respective inlet surface (18, 22) and outlet end (44) to expose more core surface area for a given frontal area.

Description: Description . Heat Exchanger Having Inclined Tubes -Technical Field This invention relates to a heat exchanger and, more particularly, to core construction for in¬ creasing heat rejection and improving air flow. Background Art Heat exchangers of the type used in earth- moving vehicles must have sufficient capacity to cool the engine by the passage of air through and around the heat exchange- element. In the past, it has been necessary sometimes to use large fans operating at high speeds to provide sufficient air flow through the heat exchange element. Unfortunately, large fans use excessive power, cause vibration and noise which is undesirable. Because of current noise regulations, the use of large fans is now restricted and other means must be found to provide effective cooling without excessive noise. One way to increase cooling capacity is taught by Roelf J. Meijer and Jan Mulder in U.S. Patent No. 4,034,804 which issued July 12, 1977. Meijer and Mulder disclose a radiator operable with a flow of air for cooling a quantity of water and formed as zigzag or folded walls, each of which contains air ducts. Cooling water pipes are arranged in a number of flat cores, the upper and lower sides of which are located in the front and rear planes, respectively, of the radiator. The cores are connected together alternately on their front and rear sides in an airtight manner. The zigzag pattern increases the cooling capacity by increasing the surface area exposed to the flow of air without increasing the size of the radiator. There is, however, a problem with debris plugging the cores and reducing cooling capacity. Under some field conditions where large quantities of airborne fuzz and debris are present, the debris and fuzz may be readily caught by the front edges of the water tubes which are flush with the front of the core and also become embedde between the cooling fins. At the junction of the cores at the rear of the radiator, air flows downward which increases the opportunity for airborne debris to collect on the fins thereby reducing cooling. Furthermore, at low vehicle speeds there may not be any air flow at the junction— hence no cooling. Meijer and Mulder recognize that plugging may be a problem and provide a fine gauge to be placed around the outside of each core.- This in effect is a mere screen which itself can become plugged. Since the air flow changes direction abruptly inside the radiator from a horizontal flow to a down¬ ward vertical flow, areas exist where there is little or no flow and plugging occurs. Because of the change in direction of the air flow, even the fine gauze will clog. Recognizing that clogging is a problem with zigzag or folded core radiators, Erwin Bentz devised a novel way to easily unclog a radiator core as described in U.S. Patent No. 4,076,072 granted February 28, 1978. Bentz uses reversible cores which can be rotated 180° to expose a clean core surface to incoming air while the reverse, clogged core surface is cleaned by the exit flow of air through the core. While this rever¬ sibility allows the clogged cores to be cleaned easily, . reversing the cores takes time and is done when the radiator is visibly clogged. Apparatus is provided for rotating all the cores at one time, but again this is done in response to a visual observation. /., Charles Miller and Raymond Stratton devised a heat exchanger similar to the heat exchanger of Bentz which uses recessed tubes, closely spaced fins, and a space or gap at the junction so that the inner directly adjacent legs are spaced apart. Unfortunately, the extremely close fin spacing, 0.79 to 1.57 fins per mm, restricts air flow through the core; yet, this close spacing is necessary to prevent plugging. It is therefore desirable to have a heat ex- changer with closely spaced fins which does not unduly restrict air flow through the cores. It is also desir¬ able to increase the heat rejection of the. core for a given frontal area thereby increasing the cooling effectiveness of the heat exchanger. Disclosure of Invention In one aspect of the invention, a heat ex¬ changer comprises first and second cores each having an inlet surface and an outlet end. The cores are- posi¬ tioned with the inlet surfaces facing toward one another and are angularly oriented one relative to the other forming a general "V" configuration with the inner adjacent ends being spaced apart. Each of the cores is truncated at the corner defined by the respec¬ tive inlet surface and outlet end. In another aspect of the invention, a heat exchanger comprises a plurality of closely spaced fins defining a first core having an axis "A" and an inlet surface and at least one tube extending through the fins of the first core and spaced from the inlet surface. The tube has a transverse, axis "T" oriented with respect to the axis "A" at a preselected angle. By truncating the corners of the cores they can be fitted more closely together to increase cooling capacity for a given overall heat exchanger dimension. Angularly orienting the tube relative to the core axis OMPI Λ. WIPO also orients the tube relative to the incoming air- stream to increase the heat rejection. Thus, the heat exchanger has closely spaced truncated fins and angu¬ larly oriented tubes to decrease the pressure drop across the cores thereby increasing cooling effective¬ ness. Brief Description of Drawings FIG. 1 is a sectional view of a heat ex¬ changer having a number of cores arranged in a zigzag pattern; FIG. 2 is a somewhat " enlarged partial section¬ al view of the cores showing the tubes angularly oriente relative to the axis of each core; FIG. 3 is a sectional view similar to FIG. 2 • but showing a different embodiment; and FIG. 4 is a partial sectional view taken along line IV-IV of FIG. 1. Best Mode for Carrying out the Invention Referring to FIG. 1, a self-purging heat ex- changer 10 has a number of cores, such as first, second and third cores 12,14, and 16 for example, arranged in a zigzag pattern as viewed from the top or along a horizontal cross section. The first core 12 has an inlet surface 18 and an outlet surface 20. The second core 14 has an inlet surface 22 and an outlet surface 24 and is positioned with the inlet surface 22 facing toward the inlet surface 18 of the first core 12. The cores 12,14 are angularly oriented one relative, to the other in a general "V" configuration with the inner, directly adjacent ends being spaced apart a distance in the range of about 2 to 10 mm. If the space or gap 26 is less than about 2 mm wide, air flow therethrough is extremely limited and debris will accumulate in the gap 26. Conversely, if the gap 26 is more than about 10 mm wide, there is too much airflow therethrough which reduces the airflow through the cores 12,14 and parti¬ cularly along the inlet surfaces 18,22. 5 Where there is only one core or an end core, such as the third core 16, a gap 26* is provided be¬ tween the core 16 and the surface 28 of a supporting frame 30. The gap 26' has a width in the range of about 3 to 10 mm. If the gap, 26' is less than about 10 3 mm, there, is insufficient width for debris to escape. If the gap 26' is larger than about 10 mm, airflow through the core 16 and particularly along its inlet surface 34 is reduced. The cores 12,14 define an included angle in 15 the range of about 20 to 70 degrees while core 16 and frame 30 define an angle in the range of about 10 to 35 degrees. The core 16 and frame 30 also have a general "V" configuration. Cores 16 and 12,14 may be used together with advantage, particularly where two or more •20 liquids require cooling. The third core 16 has an outlet surface 36 and is positioned with the outlet surface 36 facing toward the outlet surface 24 of the second core 14 in a general inverted "V" configuration. The inner 25 directly adjacent ends of: the inverted "V" are arranged to be substantially airtight so that no air flows therethrough but is diverted through the inlet surfaces 22,34. The third. core 16 may be substantially parallel to the first core 12 or may be nonparallel thereto. 30 Additionally, each "V" may be symmetrical or nonsymmetri- . cal with.other "V's". Referring to FIGS. 1 and 4, each core, core 12 for example, is comprised of a plurality of closely spaced. £ins 40 defining.the inlet and outlet surfaces 35 18,20 and defining inlet and outlet end surfaces 42,44. The number of fins per mm is in the range of about 0.79 OMPI to 1.57. The fins preferably have a straight longitudi¬ nal profile but can have a wavy, serpentine profile. Straight fins are preferred from the standpoint of purging while wavy- fins dissipate more heat for given core dimensions. Referring to FIGS. 1-4, each core has at least one tube 46 extending through the fins 40 and spaced from the inlet surface 18 a distance in the range of about 2 to 4 mm. The tube 46 is preferably spaced from the outlet surface 20 a similar distance. At distances less than about 2 mm the tube 46 is exposed to debris which is snagged and held by the tube 46 thereby contributing to core plugging. At distances greater than about 4 mm, heat transfer from the front of the tube 46 adjacent the inlet surface 18 is affected . and the fins 40 are subject to mechanical stress and bending. Each core has a thickness-in the range of abou 15 to 40 mm as measured between the inlet and outlet sur faces 18,20. Where there are a plurality of tubes, whic is preferred, they are spaced apart about 10 mm or so and have a thickness in the range of about 2 to 3 mm. By this construction a heat exchanger 10 is formed which has a core thickness to hydraulic diameter of about 10 to 50. The hydraulic diameter is defined as four times the flow area divided by the perimeter of the opening for the flow and refers to the space between the fins 40, not within the tubes 46. It is this con¬ struction which, while providing adequate cooling and not plugging, creates a pressure drop across the cores and therefore does not offer maximum heat rejection. The heat rejection is improved by the construction as set forth below. Referring to FIG. 2, the first core 12 has an axis "A" and the second core 14 has an axis "B". The tube- 46 has a transverse axis "T" oriented with ' respect to the axis "A" at an angle a in the range of about 100 to 120 degrees. Similarly, tube 46' has its axis • "T" oriented with respect to the axis "B" at an angle. b in the range of about 100 to 120 degrees. The first . and second cores 12,14 are angularly oriented one relative to the other at angle c in the range of 20 to 70 degrees as previously mentioned. By this construction, the axes "A","B" of the first and second cores 12,14 are each angularly oriented in a range of about 10 to 35 degrees from the direction in a range of about 120 to 140 relative to the direction "D" of the fluid stream. At angles less than about 120 degrees, the fluid stream is reflected by the tubes 46 in a direction opposite to direction "D" thereby impeding the fluid stream and creating a greater pressure drop across the core. At angles greater than about 140 degrees, the air flows generally over the tubes but the flow path length is increased which increases the pressure loss. By inclining the tubes 46 at an angle of about 120 to 140 degrees, instead of at 110 or 180 degrees, heat rejection is improved by about 3 to 6 percent which is a significant gain. This construction produces incidence angles X' , V in the range of about 40 to 60 degrees. The incidence angle is typically defined as the supplement of angles X and Y so that an incidence angle of zero is derived where the air flow is aligned' with the tubes and flows over the inlet edge of tubes first. Referring to FIGS. 2 and 3, the first core 12 is truncated at the corner defined by its inlet surface 18 and outlet end 44. The second core 14 is truncated at the corner defined by its inlet surface 22 and outlet end 44" and is spaced from the first core 12 a OMPI /,, WIPO „ distance in the range of 2 to 10 mm at the truncated corners. Each of. the cores 12,14 is truncated at the corner defined by the respective outlet surface 20,24 and inlet end 42,42' with the truncated corners abuttin the immediately adjacent core. The truncated corners are preferably chamfered (FIG. 2) but can be of a rounded configuration (FIG. 3) . The chamfers preferably have a width in the range of about 1.5 to 8 mm. A chamfer about 1.5 mm wide at the two opposite corners of each core reduces the projected frontal area of each core by about 3 mm while reducing core width by about.31/2 percent. By tipping the tubes to an incidence angle of about 120 to 140 degrees and providing chamfers about 1.5 mm wide, heat rejection for a given total frontal area increases by about 4 to 6 percent. The square corners can be trun¬ cated because they are the part of the fins furthest from the tubes and thus transmit less heat. Tipping the tubes allows a larger chamfer to be made, hence only opposite corners need be chamfered rather than all four corners. Industrial Applicability During operation, air approaches the heat exchanger 10 from the front in direction "D". Because the tubes 46 are inclined with respect to the direction "D" of the air stream, the air is urged over the tube surfaces and between the tubes as indicated by arrow "E". The cores are fitted into a smaller space because the opposite corners are truncated. By having the gap 26 between the adjacent truncated corners, two results are achieved. First, debris entering between the cores has a place to exit and, second, air flowing through the gap 26 causes a tangential flow "F" parallel to the inlet surfaces of the cores. Thus, the flow is rm - D ORlG1 A!S ε] divided into a component "E" which flows over and be¬ tween the tubes 46 and a smaller component "F" which flows out through the gap ' 26. Other aspects, objects and advantages of t is • invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims: Claims . 1. A heat exchanger (.10), comprising: a plurality of closely spaced fins (40) defi a first core (12), having an axis "A", an inlet surfac (18) , and an outlet end (44) ; and at least one elongated tube (46) extending through the.fins (40) of the first core (12) and space from the inlet surface (18) , .said tube (46) having a transverse axis "T" oriented with respect to the axis at an angle in the range of about 100° to 120". 2. A heat exchanger (10), as set forth in claim 1, including: a second plurality of closely spaced fins (4 defining a second core (14) having an axis "B" , an inl surface (22), and an outlet end (44'); and at least one elongated tube (46') extending through the fins (40') of the second core (14) and spa from the- respective inlet surface (22) , said first and second cores (12,14) being angularly oriented in a gen "V" configuration with the inner adjacent ends being spaced a distance in the range of about 2 to 10 mm one from the other, each of said first and second pluralit fins (40,40') each being truncated at the corner defin by the respective inlet surface (18,22) and outlet end (44,44'). 3. A heat exchanger (10) , as set forth in claim 1, wherein the axis "A" of the first core (14) i oriented in a range about 10° to 35° from a direction "D" of a fluid stream relative to the first core (12) the tube axis "T" is oriented in a range of about 120° 140° relative to the direction-"D" of said fluid strea - fy 4. A heat exchanger (10) , as set forth in claim 1, wherein the fins (40) have a width in the range of about 15 to 40 mm. 5. A heat exchanger (10) , as set forth in claim 1, wherein the number of fins (40) per mm is in the range of about 0.79 to 1.57. 6. A heat exchanger (10), comprising: a first core (12) having an inlet surface (18) , an outlet surface ( . 20) t and an outlet end (44) ; a second core (14) having an inlet surface (22), an inlet end (42'), an outlet surface (22), and an outlet end (.44'), and being positioned with the inlet-surface (22). facing toward the inlet surface (18) of the first core (12) , said cores (12,14) being angularly oriented one relative to the other and forming a general "V" configuration with the inner adjacent ends being spaced a distance in the range of about 2-10 mm, each of said cores (12,14) being chamfered at the - corner defined by the inlet surface (18,22) and outlet end (44,44'), each of said chamfers having a width in the range of about 1.5 to 8 mm. 7. A heat exchanger (10) , as set forth in claim 7, including: a third core (16) having an inlet surface (34) , an inlet end (42") , and an outlet surface (36) and being positioned with the outlet surface (36) facing toward the outlet surface (24) of the second core (14) forming a general inverted "V" configuration, each of said- second and- third cores- (14,16) being chamfered at the corner defined by the outlet surface (24,36) and inlet end (42',42"), each of said chamfers having a width- in the range of about 1.5.to 8 mm and abutting one another. 8. A heat exchanger (10) , as set forth in claim 6, wherein the first and second cores (12,14) each include a plurality of closely spaced fins (40) defining the inlet (18,22) and outlet (20,24) surfaces of the core (.12) ; and at least one elongated tube (46) extending through the fins (40) of the core (12) and spaced from the inlet surface (18) . - /..

Inventors: HESTON D, MILLER C
Applicants: CATERPILLAR TRACTOR CO, HESTON D, MILLER C
Application year: 1978
Main classification: F28D1
IPC codes: F16J15, F28D1, F28F1