Heat exchanger

Abstract

A heat exchanger includes a plurality of tubes and a plurality of projection portions. Each of the plurality of tubes has a flat cross section that is taken along a plane perpendicular to a tube longitudinal direction. The plurality of projection portions is formed on an inner wall of each of the plurality of tubes and is arranged in the tube longitudinal direction. Each projection portion projects from the inner wall in a tube short-side direction that extends along a transverse axis of the cross section. The projection portion has a curved surface part on a surface thereof. The projection portion has an elongated shape when observed in the tube short-side direction. The projection portion is angled relative to a tube long-side direction, which extends along a longitudinal axis of the cross section, in a manner similar to each other.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2010-26834 filed on Feb. 9, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a heat exchanger that exchanges heat between internal fluid, which circulates inside a tube, and external fluid, which circulates outside the tube.

2. Description of Related Art

A conventional heat exchanger is known to have a tube provided with dimples (projections) that inwardly project from an inner wall of the tube (see, for example, JP-A-2001-311593). In the conventional heat exchanger, the dimples stir or agitate the cooling fluid in the tube, and thereby generating turbulent flow. The conventional technique described in JP-A-2001-311593 prevents the decrease in the heat transmission ratio between the cooling fluid and tube by forming the turbulent flow of the cooling fluid. Also, the conventional technique prevents the increase of the number of components of the heat exchanger, and still enhances a heat dissipation capability of the heat exchanger.

In the above conventional technique, the heat dissipation capability is enhanced by forming the turbulent flow within the tube caused by each dimple. However, the performance of the heat exchanger is recently required to be further improved, and thereby the further improvement of the heat transmission ratio is required by facilitating the formation of the turbulent flow. When a dead water region (stagnant flow region), where flow is stagnant, is generated at a position downstream of the dimple, where the turbulent flow is less likely to be formed, the dead water region may provide hydraulic resistance, and thereby the improvement of the heat transmission ratio is erroneously disturbed disadvantageously.

SUMMARY OF THE INVENTION

The present invention is made in view of the above disadvantages. Thus, it is an objective of the present invention to address at least one of the above disadvantages.

To achieve the objective of the present invention, there is provided a heat exchanger that exchanges heat between internal fluid and external fluid, the heat exchanger including a plurality of tubes and a plurality of projection portions. Each of the plurality of tubes has a flat cross section that is taken along a plane perpendicular to a tube longitudinal direction. The plurality of tubes allows the internal fluid to flow therethrough. The external fluid flows outside the plurality of tubes. The plurality of projection portions is formed on an inner wall of each of the plurality of tubes and is arranged in the tube longitudinal direction. Each of the plurality of projection portions projects from the inner wall in a tube short-side direction that extends along a transverse axis of the cross section. Each of the plurality of projection portions has a curved surface part on a surface thereof. Each of the plurality of projection portions has an elongated shape in a plan view observed in the tube short-side direction. Each of the plurality of projection portions is angled relative to a tube long-side direction, which extends along a longitudinal axis of the cross section, in a manner similar to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a perspective view illustrating a schematic structure of a radiator of a heat exchanger according to the first embodiment of the present invention;

FIG. 2 is a diagram illustrating a configuration of a tube according to the first embodiment;

FIG. 3 is a plan view illustrating a configuration of inclined projection portions located inside the tube according to the first embodiment;

FIG. 4 is a side cross-sectional view illustrating a configuration of the inclined projection portion inside the tube according to the first embodiment;

FIG. 5 is a diagram for explaining a mechanism of a flow of internal fluid that flows over the inclined projection portion inside the tube;

FIG. 6 is a plan view for explaining the mechanism of the flow of internal fluid that flows over the inclined projection portion inside the tube;

FIG. 7 is a chart illustrating a visualization test result of flow inside the tube according to the first embodiment;

FIG. 8 is a chart illustrating a performance evaluation result of a heat dissipation amount of an actually-used radiator having the tube according to the first embodiment;

FIG. 9 is a chart illustrating a performance evaluation result of a hydraulic resistance of the actually-used radiator having the tube according to the first embodiment;

FIG. 10 is a chart illustrating a performance evaluation result of a heat transmission ratio of the actually-used radiator having the tube according to the first embodiment;

FIG. 11 is a chart illustrating a performance evaluation result of a frictional resistance of the tube of the actually-used radiator according to the first embodiment;

FIG. 12 is a side cross-sectional view illustrating an inclined projection portion according to the first modification of the first embodiment;

FIG. 13 is, a side cross-sectional view illustrating inclined projection portions according to the second modification of the first embodiment;

FIG. 14 is a plan view illustrating inclined projection portions according to the third modification of the first embodiment;

FIG. 15 is a plan view illustrating inclined projection portions according to the fourth modification of the first embodiment;

FIG. 16 is a plan view illustrating inclined projection portions according to the fifth modification of the first embodiment;

FIG. 17 is a plan view illustrating inclined projection portions according to the sixth modification of the first embodiment; and

FIG. 18 is a plan view illustrating inclined projection portions according to the seventh modification of the first embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Multiple embodiments of the present invention will be described with reference to accompanying drawings. A component of one embodiment described in a preceding embodiment may be indicated by the reference numeral used in the preceding embodiment, and the explanation thereof may be omitted. When only a part of the configuration is described in a certain embodiment, the other part of the configuration employs any of the preceding embodiments. The combination of the embodiments is not limited to the combination specifically described in the present specification. For example, the embodiments may be partially combined with each other provided that the combination of the embodiment will not bring any difficulty even when the combination is not explicitly described.

First Embodiment

A heat exchanger according to the first embodiment of the present invention will be described below with reference to FIGS. 1 to 11. The heat exchanger of the first embodiment has multiple tubes, each of which has a flat cross section, and each tube has an inner wall surface formed with characteristic projection portions. An example of a radiator that employs the above heat exchanger will be described below. FIG. 1 is a perspective view illustrating a schematic structure of a radiator 1 according to the first embodiment.

As shown in FIG. 1, the radiator 1 is mounted in, for example, an engine compartment of a vehicle. Also, the radiator 1 is positioned adjacent a condenser (not shown) in a state, where a core part of the radiator 1 faces a core part of the condenser. The condenser serves as a heat exchanger for an air conditioning refrigeration cycle for a vehicle. The radiator 1 is positioned on a vehicle-rear side of the condenser. In other words, the radiator 1 is positioned downstream of the condenser in a flow direction of air.

The condenser and the radiator 1 are assembled integrally to an electric fan (not shown). For example, the electric fan serves as an air blower that forcibly blows air (external fluid) to both of the core parts for heat exchange between fluids flowing through the respective core parts. In the above state, the radiator 1 is mounted on the vehicle. As above, the condenser, the radiator 1, and the electric fan are integrally assembled to each other and constitute a cooling module. Air (external air) is delivered to both of the condenser and the radiator 1 by the electric fan in a direction (vehicle rearward direction) indicated by an arrow. As a result, the condenser and the radiator 1 are cooled by the delivered air. The radiator 1 is a heat exchanger that is connected with a coolant circuit of the engine of the vehicle, and cools a high-temperature coolant that has been heated by the engine.

The radiator 1 has a core part 2 and header tanks 5, 6. The core part 2 exchanges heat between (a) water (internal fluid), which flows inside the core part 2, and (b) air (external fluid), which flows outside the core part 2. Also, the header tanks 5, 6 are provided at both end portions of the core part 2 in an up-down direction. The core part 2 includes tubes 3 and fins 4, which are alternately arranged in a left-right direction (vehicle width direction), and which are integral with each other through blazing. Each of the tubes 3 has a flat cross section, and serves as a water passage. Each of the fins 4 is a corrugated fin that increases a heat transfer area.

Core plates (not shown) are provided at both respective ends of the core part 2 in the up-down direction, and the core plates joint and support the end portions of the multiple tubes 3. The core plates, the header tank 5, and the header tank 6 are integrally jointed with each other. Each of the header tanks 5, 6 defines therein an internal space that is communicated with the interior of all of the tubes 3. In other words, the header tank 5 is communicated with the header tank 6 through the tubes 3. Also, each of the header tanks 5, 6 has an elongated tubular shape that extends in a direction (vehicle width direction) orthogonal to a tube longitudinal direction Z of the tubes 3. For example, each of the header tanks 5, 6 is made of a resin, such as nylon, having a substantial heat resistance.

The outermost fins 4 are provided on both ends of the core part 2 in the vehicle width direction (left-right direction). In other words, the outermost fins 4 are positioned on the outermost ends of the core part 2 in the vehicle width direction. The side plates 7 are provided on the outer side of the outermost fins 4 in the vehicle width direction. Each side plate 7 is a reinforcement member that reinforces the core part 2, and has a cross section of a U shape. The side plate 7 extends in the tube longitudinal direction Z as shown in FIG. 1.

The upper header tank 5 is integrally formed with an inlet pipe 8 of an engine coolant, and with a hub portion for attachment to a body. The lower header tank 6 is integrally formed with an exit pipe 9 of the engine coolant, and with a hub portion for attachment to the body. Also, in the radiator 1, each component of the core part 2, such as the tubes 3, the fins 4, the core plates, and the side plates 7 are made of aluminum alloy, for example, and are integrally jointed to each other through blazing.

For example, the radiator 1 is provided with a shroud (not shown) that is made of a resin material, such as polypropylene. The shroud has an outer peripheral part adjacent the radiator 1. The outer peripheral part is formed to have a rectangular shape that extends along the outline of the radiator 1 and is gradually slanted in a direction (vehicle rearward direction) away from the radiator 1. Thus, the shroud forms an air duct for the fan. The shroud has a shallow cup shape that generally surrounds the electric fan, and is integrally fixed to the radiator 1 through bolts. The shroud is formed with a motor attachment part, to which a motor (not shown) of the electric fan is attached. The shroud, the radiator 1, and the condenser are integrated with each other to constitute the cooling module. Air supplied by the electric fan flows from the front side of the vehicle through the core part in the order of the condenser and then the radiator 1, to cool the internal fluid. Then, air flows through the air duct formed by the shroud, and flows out of the cooling module.

Next, a detailed configuration of each tube 3 will be described with reference to FIGS. 2 to 4. FIG. 2 is a diagram illustrating a configuration of the tube 3. FIG. 3 is a plan view illustrating a configuration of inclined projection portions 30 provided inside the tube 3. FIG. 4 is a side cross-sectional view illustrating a configuration of the inclined projection portion 30 inside the tube 3.

As shown in FIGS. 2 to 4, the multiple inclined projection portions 30 are formed and arranged in the tube longitudinal direction Z on the inner wall of each tube 3. The inclined projection portion 30 has a curved surface part 302 on the surface, and thereby has a smooth outer surface. The tube 3 has a transverse cross section having a flat shape. A tube long-side direction X is defined to correspond to a direction along the long side (longitudinal axis) of the flat transverse cross section. Also, a tube short-side direction Y is defined to correspond to a direction along the short side (transverse axis) of the flat transverse cross section. The tube longitudinal direction Z is defined to correspond to a direction, in which the tube 3 extends, and in which the internal fluid flows or travels. The inclined projection portion 30 projects from the inner wall of the tube 3 in the tube short-side direction Y, and has an elongated shape in a plan view observed in the tube short-side direction Y. Each inclined projection portion 30 is angled relative to the tube long-side direction X that is orthogonal to the tube longitudinal direction Z in a manner similar to each other.

The inclined projection portion 30 has an imaginary center axial line 301 that longitudinally extends through the elongated shape of the inclined projection portion 30. The center axial line 301 is angled relative to the tube long-side direction X by an inclination angle θ in the plan view observed in the tube short-side direction Y. The inclination angle θ defined by each inclined projection portion 30 forms the same acute angle with each other and is measured in the same direction with each other. In other words, the inclined projection portion 30 has an upstream end portion 305 and a downstream end portion 306 in the flow direction of the internal fluid. Thus, the end portions 305, 306 of the inclined projection portion 30 are displaced from each other in the tube long-side direction X. All the upstream end portions 305 of the multiple inclined projection portions 30 are positioned on one side of the tube 3 in the tube long-side direction X, and all the downstream end portions 306 of the multiple inclined projection portions 30 are positioned on the other side of the tube 3 opposite from the one side. It is not required that the same inclination angle θ be applied to all of the inclined projection portions 30 provided that the advantages of the present embodiment is achievable. Thus, the inclination angle θ of each inclined projection portion 30 may be different from each other. However, the inclined projection portions 30 are only required to be angled relative to the tube long-side direction X toward the same side.

As shown in FIG. 4, the inclined projection portion 30 has a top face 303 at an end remote from the inner wall. The inclined projection portion 30 has a height H measured between the tube inner wall surface 304 and the top face 303. The inclined projection portion 30 has a width W measured along the short side of the elongated shape of the inclined projection portion 30. In other words, the width W of the inclined projection portion 30 is measured in a direction orthogonal to a longitudinal direction (indicated by the center axial line 301) of the inclined projection portion 30 as shown in FIG. 3. The inclined projection portion 30 has a dimension L1 measured in the tube long-side direction X, and has a dimension L2 measured in the tube longitudinal direction Z. Also, a long-side dimension A is measured within the tube 3 between the opposing inner walls of the tube 3 in the long-side direction X. For example, the long-side dimension A corresponds to a longitudinal dimension of a cross section of the passage defined by the inner wall surface of the tube 3. A short-side dimension B is measured within the tube 3 between the opposing inner walls of the tube 3 in the short-side direction Y. For example, the short-side dimension B corresponds to a transverse dimension of the cross section of the passage defined by the inner wall surface of the tube 3. Also, for example, the two adjacent inclined projection portions 30 arranged in the tube longitudinal direction Z include a first inclined projection portion 30 and a second inclined projection portion 30 that is located downstream of the first inclined projection portion 30 in the flow direction of the internal fluid. The downstream end portion 306 of the first inclined projection portion 30 is spaced apart from the upstream end portion 305 of the second inclined projection portion 30 in the tube longitudinal direction Z. Also, the adjacent inclined projection portions 30 are arranged in the tube longitudinal direction Z at an interval of a pitch P as shown in FIG. 3. As above, the pitch P is greater than the dimension L2 of the inclined projection portion 30 in the tube longitudinal direction Z.

Each of the inclined projection portions 30 is formed through a press working of a flat plate material, which is to be bent to form the tube 3. Thus, the outer wall of the tube 3 has a recess at the position, at which the inclined projection portion 30 is formed. A process of manufacturing the tube 3 includes a blanking step, a forming step for forming the inclined projection portion 30, a bending step for forming a U shape, and a jointing step (for overlapping the end portions and for jointing the end portions) in this order.

Next, the effect of the inclined projection portion 30 given to the flow of internal fluid that flows through the tube 3 will be described with reference to FIGS. 5 and 6. FIG. 5 is a diagram for explaining a mechanism of flow of the internal fluid that flows over the inclined projection portion 30 within the tube 3. FIG. 6 is a plan view for explaining a mechanism of a flow of the internal fluid that flows over the inclined projection portion 30 within the tube 3.

In FIG. 5, a coordinate axis Xa corresponds to an imaginary coordinate axis that extends in the tube long-side direction X, a coordinate axis Ya corresponds to an imaginary coordinate axis that extends in the tube short-side direction Y, and a coordinate axis Za corresponds to an imaginary coordinate axis that extends in the tube longitudinal direction Z. For example, an upper side along the coordinate axis Ya in FIG. 5 is a positive side, and a lower side along the coordinate axis Ya in FIG. 5 is a negative side. Similarly, a right side along the coordinate axis Xa in FIG. 5 is a positive side, and a left side along the coordinate axis Xa is a negative side. In the above definition, a line Fc indicates a flow of internal fluid at a center section within the tube 3 in the tube short-side direction Y. A line Fw2 indicates a flow of internal fluid that flows in the vicinity of a tube inner wall surface located on the positive side of the tube 3 along the coordinate axis Ya. A line Fw1 indicates a flow of internal fluid that flows in the vicinity of another tube inner wall surface located on the negative side of the tube 3 along the coordinate axis Ya. Also, a chart Fdu indicates a flow rate distribution of the internal fluid at a position upstream of the inclined projection portion 30, and a chart Fddc indicates another flow rate distribution of the internal fluid of the center section at a position downstream of the inclined projection portion 30. Furthermore, a chart Fddw2 indicates a flow rate distribution of the internal fluid that flows in the vicinity of the tube inner wall surface on the positive side of the tube 3 along the coordinate axis Ya at a position downstream of the inclined projection portion 30. A chart Fddw1 indicates a flow rate distribution of the internal fluid that flows in the vicinity of the tube inner wall surface located on the negative side of the tube 3 along the coordinate axis Ya at the position downstream of the inclined projection portion 30.

The internal fluid in the tube 3 flows mainly in the tube longitudinal direction Z, and the internal fluid has a parabolic flow rate distribution of the flow along the coordinate axis Xa at a position upstream of the inclined projection portion 30 as shown in FIG. 5. More specifically, the flow along the coordinate axis Xa is directed toward the positive side. The flow rate distribution has the parabolic shape as shown in FIG. 5 because a flow rate of the flow Fc at the center section along the coordinate axis Ya is relatively large, and flow rates of the flow Fw1 and Fw2 in the vicinity of the tube inner wall surfaces are small due to the shear force caused by the wall surfaces.

A low-pressure region 307 is defined between (a) the top face 303 of the inclined projection portion 30 and (b) the opposing tube inner wall surface of the tube that faces the top face 303. The pressure in the low-pressure region 307 is lower than pressure around the low-pressure region 307, and the low-pressure region 307 has a shape that corresponds to the shape of the top face 303. There is formed a pressure difference in the tube 3 in the tube long-side direction X at a flow passage segment, at which the inclined projection portion 30 is formed. In other words, there is formed the pressure difference in the tube long-side direction X at the flow passage segment formed in the tube longitudinal direction Z by the length (dimension L2) of the inclined projection portion 30. Therefore, internal fluid around the low-pressure region 307 is caused to flow toward the low-pressure region 307. Thus, the flow rate distribution Fdu of the internal fluid along the coordinate axis Xa at the position upstream of the inclined projection portion 30 indicates the flow toward the low-pressure region 307, which is the positive side along the coordinate axis Xa.

As shown in FIG. 6, the magnitudes of the flow rates of the internal fluid at various positions are shown by Fuw1, Fuw2, Fdw1, Fdw2. The flow rate Fuw2 is the flow rate of the internal fluid that flows in the vicinity of the tube inner wall surface on the positive side along the coordinate axis Ya at the position upstream of the inclined projection portion 30. The flow rate Fuw1 is the flow rate of the internal fluid that flows in the vicinity of the tube inner wall surface on the negative side along the coordinate axis Ya at the position upstream of the inclined projection portion 30. Both of the flow rates Fuw1 and Fuw2 indicate the flow directed toward the positive side along the coordinate axis Xa. The internal fluid flows over the inclined projection portion 30 while having the flow rate distribution Fdu. Furthermore, when internal fluid flows to the position downstream of the inclined projection portion 30, the low-pressure region 307 is formed on the negative side along the coordinate axis Xa. As a result, after the internal fluid passes by the inclined projection portion 30 (or after the internal fluid flows to the position downstream of the inclined projection portion 30), the flow rate Fdw2 and the flow rate Fdw1 in the vicinity of the tube inner wall surfaces become directed toward the negative side along the coordinate axis Xa, in contrast to the direction (positive side along the coordinate axis Xa) at the position upstream of the inclined projection portion 30.

As above, when the internal fluid flows over the inclined projection portion 30, a vector direction along the coordinate axis Xa of the flow rate in the vicinity of the tube inner wall surface is reversed at the top face 303 of the inclined projection portion 30. For example, if the vector direction along the coordinate axis Xa of the flow rate is directed in one side at the position upstream of the inclined projection portion 30, the vector direction along the coordinate axis Xa of the flow rate is changed to the other side opposite from the one side along the coordinate axis Xa at the position downstream of the inclined projection portion 30. As a result, as shown in FIG. 5, the flow rate distributions Fddw2 and Fddw1 of the flow in the vicinity of tube inner wall surface at the position downstream of the inclined projection portion 30 indicate the opposite direction from the flow rate distribution Fddc of flow at the center section. Because the flow rate distribution of the flow in the vicinity of the tube inner wall surface is reversed as above, there is generated a change point, where the positive and negative of (or the vector direction of) the flow rate distribution on the XaYa-plane is reversed, near the tube inner wall surface in the flow passage downstream of the inclined projection portion 30. As a result, fine tumble vortex is generated adjacent the tube inner wall surfaces (see FIG. 6).

The generation of the tumble vortex stirs the flow within the tube 3 in the vicinity of both of (a) the inclined projection portion 30 and (b) the tube inner wall surface opposed to the inclined projection portion 30. As a result, turbulent flow of the internal fluid is effectively enhanced, and thereby heat transmission between the internal fluid and the tube 3 is enhanced. Therefore, the heat exchange performance is improved. Furthermore, the shape of the inclined projection portion 30, which has the curved surface part 302, and the generation of the tumble vortex are capable of causing the smooth flow and the activation of the flow around the inclined projection portion 30. As a result, it is possible to limit the generation of a stagnant flow region, where the internal fluid does not flow effectively, within the tube 3, and thereby it is possible to limit the increase of flow resistance. In the above, the stagnant flow region may be referred to as a “dead water region” if the internal fluid is water. It should be noted that the center section of the tube 3 in the tube short-side direction Y is not influenced by the low-pressure region 307 caused by the inclined projection portion 30. As a result, a parabolic flow rate distribution Fddc is formed on an XaYa-plane, and thereby the generation of the tumble vortex is effectively limited. Thus, the stir of the flow is less likely to occur.

Furthermore, the pitch P between the adjacent inclined projection portion 30, which are angled in the same direction, and which are arranged in the tube longitudinal direction Z, is greater than the dimension L2 of the inclined projection portion 30 measured in the tube longitudinal direction Z. As a result, the downstream end portion 306 of the first inclined projection portion 30 is spaced apart from the upstream end portion 305 of the second inclined projection portion 30 in the tube longitudinal direction Z. In the above, the second inclined projection portion 30 is positioned immediately downstream of the first inclined projection portion 30. Due to the above, the pressure difference across the inclined projection portion 30 in the tube long-side direction X is continuously generated in the tube longitudinal direction Z at predetermined cycles. Thus, it is possible to continuously generate the tumble vortex, and thereby continuously generating a turbulent flow region within the tube 3. Therefore, a heat transmission performance distribution in the tube longitudinal direction Z for each tube 3 is effectively improved, and thereby it is possible to improve the average heat transmission performance of each of the tubes 3 in the tube longitudinal direction Z.

Next, the result of a visualization test, in which a flow of the internal fluid that flows through the tube 3 having the inclined projection portion 30 is observed, will be described with reference to FIG. 7. More specifically, in the visualization test, dye (or color) is added to the internal fluid in the tube 3, and the flow of the internal fluid is observed based on the behavior of the dye. FIG. 7 is a chart made by plotting the visualization test result of the tube 3 of the present embodiment. The visualization test is executed under the following condition. The width W of the inclined projection portion 30 is 4 mm, the inclination angle θ is 45 degrees, Reynolds number that relates to the flow rate of the internal fluid is 1000, and the other conditions are fixed except that the height H (mm) of the inclined projection portion 30 and the short-side dimension B (mm) of the passage within the tube are changeable. In the chart illustrated in FIG. 7, a symbol “O” indicates that the tumble vortex is clearly identified, “Δ” indicates that the tumble vortex is less clearly identified compared with the case of “O”, and “X” indicates that the tumble vortex is not identified, or that the dead water region (stagnant flow region) is generated.

As is apparent from the chart illustrated in FIG. 7, the height H (mm) of the inclined projection portion 30 is set equal to or greater than 0.35 times of the short-side dimension B (mm) within the tube and also is set equal to or less than 0.63 times of the short-side dimension B (mm). In other words, when the ratio (H/B) of the height H of the inclined projection portion to the short-side dimension B within the tube is equal to or greater than 0.35 and is equal to or less than 0.63, it is possible to achieve the preferable heat exchange performance. As shown in the chart of FIG. 7, when the above condition is satisfied, the undesirable performance indicated by the symbol of “x” is effectively eliminated.

Also, in the chart of FIG. 7, in a first case, where the height H of the inclined projection portion 30 is 0.29 mm, and also in a second case, where the height H is 0.44 mm and the short-side dimension B is 1.38 mm, the tumble vortex is not identified. Also, in a third case, where the height H is 0.6 mm, the generation of the dead water region is not identified. In the above, because the width W of the inclined projection portion 30 is 4 mm under the visualization test condition, W/H is computed as follows: W/H=4/0.6=6.67. Thus, the width W of the inclined projection portion 30 is at least equal to or greater than 6.67 times of the height H of the inclined projection portion 30. Furthermore, the inclined projection portion 30 is designed to satisfy the following conditions:

W/H≧6.67; and

0.35≦H/B≦0.63.

Also, another visualization test is also executed while changing the value of the inclination angle θ of the inclined projection portion 30. In the visualization test, the conditions other than the inclination angle θ are fixed. Specifically, the inclination angle θ is set to 10 degrees, 20 degrees, 30 degrees, 40 degrees, 45 degrees, 50 degrees, 60 degrees, and 70 degrees. Due to the visualization test, when the inclination angle θ is 10 degrees or 70 degrees, the generation of the tumble vortex is not identified. However, when the inclination angle θ is 20 degrees, 30 degrees, 40 degrees, 45 degrees, 50 degrees, and 60 degrees, the generation of the tumble vortex is identified. Specifically, when the inclination angle θ is 40 degrees, 45 degrees, and 50 degrees, the generation of the clear tumble vortex is identified. However, when the inclination angle θ is 20 degrees, 30 degrees, and 60 degrees, the identified tumble vortex is less clear than the tumble vortex generated when the inclination angle θ is 40 degrees, 45 degrees, and 50 degrees. Due to the visualization test result, the preferable inclination angle θ, by which the center axial line 301 of the inclined projection portion is inclined relative to the tube long-side direction X, is equal to or greater than 20 degrees and equal to or less than 60 degrees. In a case, where the inclination angle θ is in a range equal to or greater than 40 degrees and equal to or less than 50 degrees, it is possible to effectively generate more suitable flow of the internal fluid.

Also, another visualization test is also executed while the ratio (L1/A) of the dimension L1 of the inclined projection portion 30 in the tube long-side direction X to the long-side dimension A within the tube is changed. In the visualization test, the conditions other than the ratio L1/A are fixed, and the ratio L1/A is changed to each of 0.3, 0.4, 0.5, 0.6, and 0.7. According to the visualization test, when the ratio L1/A is 0.3, the generation of the tumble vortex is not identified. However, when the ratio L1/A is 0.4, 0.5, 0.6, or 0.7, the generation of the tumble vortex is identified. According to the visualization test result, the dimension L1 of the inclined projection portion 30 in the tube long-side direction X is equal to or greater than 40% of the long-side dimension A within the tube.

FIG. 8 is a chart illustrating a performance evaluation result of a heat dissipation amount (kW) relative to a flow amount (L/min) when an actually-used radiator is used. FIG. 9 is a chart illustrating a performance evaluation result of a hydraulic resistance (kPa) relative to flow amount (L/min) when the actually-used radiator is used. In FIGS. 8 and 9, outlined diamond-shaped data markers indicate the performance of a conventional tube that has a flat inner wall surface without the inclined projection portions 30. Outlined square-shaped data markers indicate the performance of another conventional tube that has circular dimples (projections) formed on the inner wall surface. Filled-in square-shaped data markers indicate the performance of the tube 3 formed with the inclined projection portion 30 of the present embodiment.

As is apparent from FIGS. 8 and 9, although the tube 3 according to the present embodiment achieves the heat dissipation amount equivalent to the heat dissipation amount of the conventional tube having the dimples, a hydraulic resistance (flow resistance) of the tube 3 according to the present embodiment is smaller than that of the conventional tube having the dimples, and is equivalent to the other conventional tube having the flat inner wall surface. As above, because of the tube 3 of the present embodiment, it is possible to provide a heat exchanger that is capable of improving both of the flow resistance and the heat dissipation capability to be better than the above conventional arts. It should be noted that the performance test by using the actually-used radiator is executed under the following conditions. The short-side dimension B within the tube is 1.3 mm, the long-side dimension A within the tube is 13.5 mm, the height H of the inclined projection portion 30 is 0.45 mm, the dimension L1 of the inclined projection portion 30 in the tube long-side direction X is 9.5 mm, the width W of the inclined projection portion 30 is 4 mm, the inclination angle is 45 degrees, the pitch P between the inclined projection portions 30 is 75 mm.

FIG. 10 is a chart illustrating a performance evaluation result of a heat transmission ratio using the actually-used radiator. FIG. 11 is a chart illustrating a performance evaluation result of a frictional resistance of the tube 3 by using the actually-used radiator. It should be noted that NuPr^−0.4 in FIG. 10 indicates a heat transmission ratio of water, and Re shown in FIGS. 10 and 11 indicates Reynolds number of water. In the performance evaluation result of the hydraulic resistance shown in FIG. 11, a friction coefficient Γ is computed under a condition, where the resistance of the tube is neglected.

As is apparent from FIGS. 10 and 11, although the tube 3 of the present embodiment achieves the heat transmission ratio that is equivalent to that of the conventional tube having the dimples, the tube 3 of the present embodiment achieves the hydraulic resistance (flow resistance) that is effectively lower than that of the conventional tube having the dimples. As above, by using the tube 3 of the present embodiment, it is possible to provide a heat exchanger that is capable achieving both of the improved flow resistance and the improved heat transmission ratio compared with the conventional tube.

Furthermore, according to the performance test result related to the heat transmission ratio and the friction coefficient within the tube, the pitch P of the adjacent inclined projection portions 30 is desirably set equal to or greater than 25 times of the short-side dimension B within the tube.

The advantages achievable by the radiator 1 of the present embodiment will be described below. The radiator 1 exchanges heat between (a) coolant, which circulates inside the multiple tubes 3 each having a flat cross sectional shape, and (b) air, which circulates outside the multiple tubes 3. For example, the cross section of the tube 3 is taken along a plane perpendicular to the tube longitudinal direction Z. The multiple projection portions 30 are formed on an inner wall of each of the plurality of tubes 3 and are arranged in the tube longitudinal direction Z. Each of the multiple projection portions 30 projects from the inner wall in the tube short-side direction Y that extends along a transverse axis of the cross section. Each of the projection portions 30 has a curved surface part 302 on a surface thereof. Each of the projection portions 30 has an elongated shape when observed in the tube short-side direction Y. Each of the projection portions 30 is angled relative to a tube long-side direction X, which extends along a longitudinal axis of the cross section, in a manner similar to each other. Also, the multiple inclined projection portions 30 are required to be formed on at least one of the two opposing inner wall surfaces 304 that face with each other and that extend in the tube long-side direction X.

In the above configuration, each of the multiple inclined projection portions 30 has the elongated shape and is angled relative to the tube long-side direction X when observed in the tube short-side direction Y. Also, the multiple inclined projection portions 30 project from the tube inner wall surface 304. Thus, the low-pressure region 307, which has a relatively lower pressure in the tube 3, is formed at a position that corresponds to the top face 303 of the inclined projection portion 30. Also, a high-pressure region, which has a pressure higher than the low-pressure region 307, is formed on the other side of the tube 3 along the coordinate axis Xa opposite from the side, at which the low-pressure region 307 is formed. In other words, there is formed a pressure gradient within the flow passage in the tube 3 in the tube long-side direction X. As a result, the flow rate distribution at the position upstream of the top face 303 of the inclined projection portion 30 shows that the vector of the flow along the coordinate axis Xa, is directed toward the low-pressure region 307 (near the top face 303), in general. Also, the flow rate distribution at a position downstream of the inclined projection portion 30 shows that the flow at the center section that is separate from the tube inner wall surface 304 maintains the flow rate distribution at the upstream side of the inclined projection portion 30. However, because a flow directed toward the low-pressure region 307 is generated in the vicinity of the tube inner wall surface 304, the flow rate distribution of the flow in the vicinity of the tube inner wall surface 304 shows a reversed characteristic compared with that in the upstream side.

As a result, at a position downstream of the top face 303 of the inclined projection portion 30, the flow in the vicinity of the tube inner wall surface 304 is generated in the direction opposite from the direction of the flow at the center section. Thereby, the tumble vortex is generated in the vicinity of the tube inner wall surface 304. The tumble vortex may be generated in the vicinity of both of the opposing tube inner wall surfaces 304 that extends in parallel to a plane defined by an imaginary coordinate axis in the tube long-side direction X and another imaginary coordinate axis in the tube longitudinal direction Z. The generation of the tumble vortex causes the turbulent flow within the tube 3, and thereby facilitating the turbulent flow.

Because each inclined projection portion 30 has the curved surface part 302 formed on the surface thereof, and thereby having a smooth outline, the flow that flows over each inclined projection portion 30 has a smoothly formed. As a result, it is possible to limit the formation of the stagnant flow region (dead water region), in which the flow is stagnant, in the vicinity of the inclined projection portion 30. Accordingly, it is possible to reduce the flow resistance within the tube 3, and thereby it is possible to improve the heat exchange performance of the heat exchanger. As above, the formation of turbulent flow within the tube 3 and the reduction of the stagnant flow region are capable of providing a heat exchanger that improves the heat dissipation capability.

Also, the formation of all the multiple inclined projection portions 30 is not limited to only one of the opposing tube inner wall surfaces 304 that face with each other in the tube short-side direction Y. For example, a part of the multiple inclined projection portions 30 arranged in the tube longitudinal direction Z may be formed on one of the opposing inner wall surfaces, and the rest of the multiple inclined projection portions 30 may be formed the other one of the opposing inner wall surfaces alternatively. In the above alternative formation, similar to the above embodiment, the generation of the tumble vortex and the reduction of the flow resistance are both achievable. As a result, it is possible to improve the heat dissipation capability of the heat exchanger.

Other Embodiment

The present invention is not limited to the above embodiment. However, the present invention may be modified in various manners provided that the modification does not deviate from the gist of the present invention.

In the above embodiment, the inclined projection portion 30 has an elongated parallelogram in a plan view observed in the tube short-side direction Y. However, the inclined projection portion 30 is not limited to the above shape. The inclined projection portion 30 is required to have a certain length and shape such that the low-pressure region 307, which is formed correspondingly to the top face 303, is angled relative to the tube longitudinal direction Z, and thereby the low-pressure region 307 on the downstream side of the inclined projection portion 30 is displaced from the low-pressure region 307 on the upstream side of the inclined projection portion 30 in the tube long-side direction X (direction orthogonal to the tube longitudinal direction Z). As a result, the inclined projection portion 30 is required to have the elongated shape in the plan view observed in the short-side direction Y. For example, the inclined projection portion 30 may alternatively have a rectangular shape, an elongated oval shape, an ellipse shape, or a streamline shape.

The inclined projection portions 30 within each tube 3 of the above embodiment are arranged and spaced apart from each other in the tube longitudinal direction Z. However, the inclined projection portions 30 may be alternatively formed in a various manner provided that the alternative inclined projection portions are capable of generating the tumble vortex and of, reducing the formation of the dead water region. For example, a protrusion having a different shape from the inclined projection portion 30 may be formed between the inclined projection portions 30 that are angled in the same direction. Also, a reversely-angled inclined projection portion, which is angled toward one lateral side, may be formed between the inclined projection portions 30 that are angled toward the other lateral side.

The inclined projection portion 30 according to the above embodiment has a side cross section of a streamline shape. The side cross section is taken along a plane perpendicular to the long-side direction X, for example. However, an inclined projection portion 30A may have alternatively a semicircular cross section as shown in FIG. 12. Even if the side cross sectional shape of the inclined projection portion 30A has the semicircular shape, it is possible to achieve the advantages similar to those achieved by the inclined projection portion 30 as described above. FIG. 12 is a side cross-sectional view illustrating the inclined projection portion 30 of the first modification. Also, the side cross sectional shape of the inclined projection portion 30 may be an elliptical shape, a wing shape, or a shape having the different curved shape surface.

The inclined projection portion 30 of the above embodiment is integrally formed through the press work of the tube 3. However, the manufacturing method is not limited to the above method of the embodiment. For example, the inclined projection portion 30 may be made by fixing a separate member, which is formed separately from the tube 3, to the tube inner wall surface 304.

In the above embodiment, the inclined projection portions 30 are formed on only one of the opposing inner wall surfaces of the tube 3 that face with each other in the tube short-side direction Y. However, as shown in FIG. 13, the inclined projection portion 30 may be formed on both of the opposing inner wall surfaces. The above tube 3A is also capable of achieving the advantages similar to those achieved by the inclined projection portion 30 as described above. FIG. 13 is a side cross-sectional view illustrating the tube 3A according to the second modification having the inclined projection portion 30 on both of the opposing tube inner wall surfaces. In the second modification, the height H of the inclined projection portion 30 of the first embodiment corresponds to the sum of the height h1 and the height h2 of the inclined projection portions 30. Thereby, the sum (h1+h2) of the height of the inclined projection portions of both sides is desirably equal to or greater than 35% and equal to or less than 63% of the short-side dimension B within the tube.

As shown in FIG. 14, the multiple inclined projection portions 30 may be arranged in the tube long-side direction X within the tube 3. FIG. 14 is a plan view illustrating the third modification. A flat surface 31 is formed between the inclined projection portions 30. Even when foreign objects flows together with the internal fluid into the tube 3, it is possible to prevent the clogging of the foreign objects at the inclined projection portion 30 because the flow passage at the position that corresponds to the flat surface 31 is substantially wide. Thus, it is possible to prevent the stagnant flow caused by the clogging of the foreign objects. Also, the multiple inclined projection portions 30 of the fourth modification may be spaced apart from each other in the tube longitudinal direction Z by a predetermined distance by using a flat surface 32 as shown in FIG. 15. FIG. 15 is a plan view illustrating of the fourth modification of the first embodiment.

Also, as shown in FIG. 16, in the multiple inclined projection portions 30 of the fifth modification, the downstream end portion 306 of the upstream inclined projection portion 30 and the upstream end portion 305 of the downstream inclined projection portion 30 are overlapped with each other when observed in the tube longitudinal direction Z. FIG. 16 is a plan view illustrating the fifth modification of the first embodiment.

The tube 3 of the sixth modification of the above embodiment, as shown in FIG. 17, may have an inclined projection portion 30B that is tapered to be narrower toward the upstream end portion 305 from the downstream end portion 306 in a plan view observed in the short-side direction Y. The inclined projection portion 30B is capable of achieving the advantages similar to those achieved by the inclined projection portion 30 of the above embodiment. FIG. 17 is a side cross-sectional view illustrating the sixth modification.

Also, the tube 3 of the seventh modification of the above embodiment, as shown in FIG. 18, may have an inclined projection portion 30C that is tapered to be narrower toward the downstream end portion 306 from the upstream end portion 305 in a plan view observed in the short-side direction Y. The inclined projection portion 30C is capable of achieving advantages similar to those achieved by the inclined projection portion 30. FIG. 18 is a side cross-sectional view illustrating the seventh modification.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.

Claims

1. A heat exchanger that exchanges heat between internal fluid and external fluid, the heat exchanger comprising:

a plurality of tubes, each of which has a flat cross section that is taken along a plane perpendicular to a tube longitudinal direction, the plurality of tubes allowing the internal fluid to flow therethrough, the external fluid flowing outside the plurality of tubes; and

a plurality of projection portions formed on an inner wall of each of the plurality of tubes and arranged in the tube longitudinal direction, wherein:

each of the plurality of projection portions projects from the inner wall in a tube short-side direction that extends along a transverse axis of the cross section;

each of the plurality of projection portions has a curved surface part on a surface thereof;

each of the plurality of projection portions has an elongated shape in a plan view observed in the tube short-side direction; and

each of the plurality of projection portions is angled relative to a tube long-side direction, which extends along a longitudinal axis of the cross section, in a manner similar to each other.

2. The heat exchanger according to claim 1, wherein:

the inner wall has a tube inner wall surface;

each of the plurality of projection portions has a top face at an end remote from the inner wall;

each of the plurality of tubes has a short-side dimension measured thereinside in the tube short-side direction;

each of the plurality of projection portions has a height measured between the tube inner wall surface and the top face in the tube short-side direction; and

the height is equal to or greater than 35% of the short-side dimension and is equal to or less than 63% of the short-side dimension.

3. The heat exchanger according to claim 2, wherein:

each of the plurality of projection portions has a width measured in a transverse direction of the elongated shape; and

the width is equal to or greater than 6.67 times of the height.

4. The heat exchanger according to claim 1, wherein:

each of the plurality of projection portions has a dimension measured in the tube long-side direction;

each of the plurality of tubes has a long-side dimension measured thereinside in the tube long-side direction; and

the dimension is equal to or greater than 40% of the long-side dimension.

5. The heat exchanger according to claim 1, wherein:

each of the plurality of projection portions has an imaginary center axial line that is angled relative to the tube long-side direction by an inclination angle; and

the inclination angle is equal to or greater than 20 degrees and is equal to or less than 60 degrees.

6. The heat exchanger according to claim 1, wherein:

each of the plurality of projection portions has an imaginary center axial line that is angled relative to the tube long-side direction by an inclination angle; and

the inclination angle is equal to or greater than 40 degrees and is equal to or less than 50 degrees.

7. The heat exchanger according to claim 1, wherein:

the plurality of projection portions includes a first projection portion and a second projection portion that is located downstream of the first projection portion in a flow direction of the internal fluid;

the first projection portion has a downstream end portion in the flow direction;

the second projection portion has an upstream end portion in the flow direction; and

the downstream end portion of the first projection portion is spaced apart from the upstream end portion of the second projection portion in the tube longitudinal direction.