heat exchanger

Abstract

To provide a heat exchanger capable of achieving high cooling efficiency even though a pump with small power consumption and small output is used, and suppressing variation in a heat removal amount of an overall cooler.SOLUTION: A heat exchanger of the present invention includes a cooling liquid flow passage provided thermally connected to a heating element. A Reynolds number of cooling liquid flowing through the cooling liquid flow passage is less than a critical Reynolds number. The cooling liquid flow passage includes a plurality of weirs erected on an inner wall on the heating element side, and provided across a direction orthogonal to a direction of the cooling liquid flow passage. A shape of the weirs is a wave form rolling in the direction of the cooling liquid flow passage, and the weirs are arranged so that a heat transfer rate from the heating element to the cooling liquid on a downstream side of the cooling liquid flow passage is higher than on an upstream side, thereby providing a heat exchanger with high cooling efficiency capable of suppressing variation in a heat removal amount of an overall cooler.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat exchanger, and more particularly to a heat exchanger that can efficiently cool heat-generating elements such as battery modules and prevent localized temperature rises. [Background technology]

[0002] Electric vehicle battery modules require rapid charging capabilities, and the current that can be supplied during charging is limited by the temperature of the highest point in the battery module. Therefore, it is necessary to cool the battery module to ensure a uniform temperature.

[0003] Patent Document 1 discloses that by shortening the length of the plate-shaped fins that contact the individual cells of the battery module as they move downstream of the airflow channel, the thermal boundary layer on the fin surface relative to the airflow can be reduced, thereby enabling efficient heat transfer even in the downstream region where the air temperature rises. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5942765 [Overview of the project] [Problems that the invention aims to solve]

[0005] Generally, by using a liquid as a cooling medium and creating turbulent flow of the coolant using a high-output pump, the formation of a thermal boundary layer becomes less likely, thereby improving cooling efficiency.

[0006] However, heat exchangers for electric vehicle battery modules have a large cooling surface area and long coolant flow paths, but this also increases the power consumption of the pump that circulates the coolant. While this can improve cooling efficiency, the power consumed for cooling reduces the charging speed and shortens the driving range, thus limiting the pump output.

[0007] This invention has been made in view of the problems of the prior art, and its objective is to provide a heat exchanger that consumes little power, has high cooling efficiency even with a pump with low output, and can suppress variations in the amount of heat removed from the entire cooler. [Means for solving the problem]

[0008] The inventors of this invention have conducted extensive research to achieve the above objectives and have found that by providing a weir of a predetermined shape in a coolant flow path under conditions where the coolant flows in a laminar flow state, it is possible to generate a swirling flow while preventing an increase in pressure loss, thereby achieving the above objectives. This led to the completion of the present invention.

[0009] In other words, the heat exchanger of the present invention is equipped with a cooling liquid channel provided that is thermally connected to the heating element. Furthermore, the coolant flowing through the coolant channel has a Reynolds number less than the critical Reynolds number, the coolant channel has a plurality of weirs erected on its inner wall on the heat-generating element side and provided transversely in a direction perpendicular to the direction of the coolant channel, the shape of the weirs is a wave-like shape that undulates in the direction of the coolant channel, and the weirs are arranged such that the heat transfer coefficient from the heat-generating element to the coolant is higher on the downstream side of the coolant channel than on the upstream side. [Effects of the Invention]

[0010] According to the present invention, by providing a weir of a predetermined shape in the coolant flow path under conditions where the cooling water flows in a laminar flow, it is possible to generate a swirling flow while preventing an increase in pressure loss, thereby providing a heat exchanger that has high cooling efficiency and can suppress variations in the amount of heat removed from the entire cooler. [Brief explanation of the drawing]

[0011] [Figure 1] The top (plan view) and bottom (side view) of the heat exchanger of the present invention are shown. [Figure 2] This diagram shows the flow of coolant in the convex part of the weir (top) and the flow of coolant in the concave part of the weir (bottom). [Figure 3]This is a graph showing the relationship between the weir interval and the heat transfer coefficient. [Figure 4] This is a graph showing the relationship between the apex angle of the convex portion of the weir and the heat transfer coefficient. [Figure 5] This is a graph showing the relationship between the thickness of the weir and the heat transfer coefficient. [Figure 6] This is a graph showing the relationship between the offset period of the convex portion of the weir and the heat transfer coefficient. [Figure 7] This is a graph showing the relationship between the heat transfer coefficient and the heat removal amount of the heat exchanger. DESCRIPTION OF EMBODIMENTS

[0012] The heat exchanger of the present invention will be described in detail. The heat exchanger of the present invention includes a cooling liquid flow path provided in thermal connection with a heating element. The cooling liquid flowing through this cooling liquid flow path has a Reynolds number less than the critical Reynolds number, that is, forms a laminar flow that flows regularly in the flow direction.

[0013] Whether the cooling liquid flows regularly in the flow direction is determined by the flow velocity of the cooling liquid when the equivalent circular diameter of the cooling liquid flow path, the density and viscosity of the cooling liquid are constant.

[0014] Since the flow velocity of the cooling liquid flowing through the cooling liquid flow path of the present invention is a velocity that results in a laminar flow, heat exchange by a pump with low power consumption is possible.

[0015] Whether the cooling liquid flowing through the cooling liquid flow path forms a laminar flow can be known from the Reynolds number represented by the following formula (1).

[0016] Re=ρvD H / μ ···(1) Here, in formula (1), μ is the viscosity coefficient of the cooling liquid (Pa·s), and ρ is the density of the cooling liquid (kg / m 3 ), v is the average flow velocity of the cooling liquid (m / s), D His the hydraulic diameter (m) of the coolant flow path, expressed as 4B / Q, where B is the cross-sectional area (m²) of the coolant flow path. 2 Q is the circumference (m) of the portion of the coolant flow path cross-section that is in contact with the coolant (commonly also called the wetting edge length).

[0017] In the present invention, D of formula (1) H As a result, when the Reynolds number, calculated using the equivalent circular diameter of the coolant flow path in areas where a weir is not formed (as described later), is less than the critical Reynolds number (2300), the flow of the coolant through the coolant flow path was considered to be laminar.

[0018] As shown in Figure 1, the coolant flow path of the present invention has a weir of constant height erected on the inner wall on the heating element side. This weir extends in a direction perpendicular to the direction of the coolant flow path and is continuously provided from one end to the other in the width direction of the coolant flow path so as to traverse the coolant flow path.

[0019] As the coolant flows through the coolant channel, it forms a laminar flow, causing its temperature to rise on the side of the heat-generating element. However, the flow is obstructed by a weir erected on the inner wall on the side of the heat-generating element, resulting in a flow that overflows the weir.

[0020] Furthermore, because the weir of the present invention has a wave-like shape that undulates in the direction of the coolant flow path, the coolant that hits the convex portion (hereinafter sometimes simply referred to as the "convex portion") in the upstream direction does not flow straight over the weir, but also flows diagonally toward the concave portion (hereinafter sometimes simply referred to as the "concave portion") in the upstream direction.

[0021] Therefore, at the ridges of the weir according to the present invention, the flow of the coolant concentrates and becomes dense in the recesses, and becomes sparse in the convex portions, resulting in a pressure difference.

[0022] Therefore, as shown in the upper part of Figure 2, a swirling flow is generated in the coolant that has passed over the recess, while the coolant that has passed over the protrusion is drawn into the swirling flow and attracted to the inner wall on the heating element side, as shown in the lower part of Figure 2, and flows near the inner wall. Thus, even though the flow velocity of the coolant in the entire coolant flow path is such that it forms a laminar flow, the cooling efficiency can be improved.

[0023] The heat exchanger of the present invention has multiple weirs arranged in the coolant flow path, so that the heat transfer coefficient from the heat-generating element to the coolant is higher on the downstream side of the coolant flow path than on the upstream side. This prevents localized temperature increases in the heat-generating element, especially in the downstream region, and makes the temperature of the heat-generating element uniform.

[0024] Methods to increase the heat transfer coefficient from the heat source to the coolant on the downstream side of the coolant flow path compared to the upstream side include, for example, narrowing the spacing of weirs in the coolant flow path on the downstream side, installing weirs with small peak angles on the downstream side, installing weirs with thin thickness in the direction of the coolant flow path on the downstream side, and reducing the offset amount of the peak positions between adjacent weirs on the downstream side. These methods may be used individually or in combination.

[0025] This section explains the relationship between weirs and heat transfer coefficients. As described above, when the cooling water flows over the weir, a swirling flow is generated and it is agitated, which improves the heat transfer coefficient. Therefore, the heat transfer coefficient can be increased by narrowing the gap (P) between the weirs as you move downstream, where the temperature of the cooling liquid is higher.

[0026] Figure 3 shows the relationship between the spacing of the weirs and the heat transfer coefficient. Figure 3 shows a coolant flow path made of A6061 sheet metal, measuring 33 mm wide x 2.7 mm high and 100 mm long, with a weir measuring 1 mm thick and 0.5 mm high. The analysis conditions involved flowing a 50% LLC coolant at a flow rate of 0.5 L / min to 4 L / min, with an exothermic temperature of 50°C. An interval of 0 represents the heat transfer coefficient without the weir.

[0027] The spacing between weirs is preferably 10mm to 30mm, although this depends on the shape of the weirs and the viscosity of the coolant.

[0028] Furthermore, the heat transfer coefficient can be increased by reducing the peak angle (A) of the weir's waveform. Figure 4 shows the relationship between the peak angle of the weir waveform and the heat transfer coefficient. The analysis conditions are the same as in Figure 3. When the peak angle of the weir's waveform decreases, the coolant hitting the convex part of the weir flows more easily towards the concave part. This causes the coolant to concentrate in the concave part, creating a strong swirling flow and vigorously agitating the material, thus improving the heat transfer coefficient.

[0029] The peak angle of the weir's waveform is preferably 90° or more and less than 180°. If it is less than 90°, less coolant will collect in the recesses, and if it is 180°, no coolant will collect, so swirling flow will not occur. In this invention, the "peak angle of the waveform" can be defined not only for the sawtooth shape shown in Figure 1, but also for waveforms that include curved sections. For example, if the waveform is a sawtooth shape with rounded corners, where straight and curved sections are mixed, it refers to the angle between the tangents at the R-end points at both ends of the curved section, and if the waveform is composed of continuous curved sections, such as a sinusoidal wave, it refers to the angle between the tangents at the inflection point of the waveform.

[0030] Furthermore, the heat transfer coefficient can be increased by reducing the thickness (T) of the weir in the direction of the coolant flow path. The relationship between the weir thickness and the heat transfer coefficient is shown in Figure 5. The analysis conditions are the same as in Figure 3. Figure 5 shows that the heat transfer coefficient improves as the thickness of the weir decreases. Under the analysis conditions shown in Figure 5 (Figure 3), the weir thickness is preferably 1 to 2 mm. However, it is preferable to adjust the height and thickness of the weir according to the channel height and flow velocity (flow rate).

[0031] In addition, the heat transfer coefficient can be increased by reducing the offset period (θ) in the direction perpendicular to the coolant flow path direction at the apex positions of adjacent weirs.

[0032] Figure 6 shows the relationship between the offset period of adjacent weirs and the heat transfer coefficient. The analysis conditions are the same as in Figure 3. The offset period was defined as 0° when the convex portions of adjacent weirs coincided in the direction of the coolant flow path, and 180° when the convex portion and concave portion coincided.

[0033] Figure 6 shows that the heat transfer coefficient improves as the offset period between the apex positions of adjacent weirs decreases. The offset period is preferably between 0 and 90°.

[0034] The weir in the above-mentioned coolant flow path can be formed by forging, metal wire buildup, metal 3D printing, resin processing, etc.

[0035] The above-mentioned coolant flow path may have multiple branched sub-flow paths. In this case, it is preferable to provide weirs in each sub-flow path such that the heat transfer coefficient is equal in the region equidistant from the upstream end of the coolant flow path. By arranging the weirs in this way, the temperature of the coolant flowing through each sub-flow path is made uniform, and localized temperature increases can be prevented. [Examples]

[0036] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[0037] [Example 1] As a heat exchanger model for thermal circuit network calculation and analysis, a cooler measuring 512mm in length, 229mm in width, and 2.7mm in flow path height is placed on the bottom surface of 10 battery modules, each measuring 512mm in length, 229mm in width, and 102mm in height, which make up the battery pack. The heat transfer coefficient of the coolers is assumed to be 1000 W / m², with no weirs placed in the coolant flow paths of the five upstream coolers. 2 Assuming K is set and a weir is placed in the coolant flow path of the five downstream coolers, the heat transfer coefficient of the coolers is set to 1500 W / m 2was set to K. Further, cooling water with a temperature of 25°C at the upstream inlet of the coolant flow path and a long life coolant (LLC) concentration of 50% was caused to flow at 0.5 to 4 L / min, and a current value corresponding to 15 minutes of 150kW rapid charging was set. For the above heat exchanger model, thermal network calculation analysis was performed using thermal network calculation software Nodalnet, and the heat removal amount W of the cooler respectively corresponding to the most upstream battery module and the most downstream battery module of the coolant flow path was analyzed. The difference between the heat removal amount W of the outlet side (most downstream side) cooler and the heat removal amount W of the inlet side (most upstream side) cooler was calculated, and the result expressed as a ratio is shown in Fig. 7. The Reynolds number of the coolant flowing through these coolant flow paths was 400.

[0038] [Comparative Example 1] Without providing weirs in the cooling water flow path, the heat transfer coefficient of all 10 coolers was set to 1000W / m 2 A thermal network calculation analysis was performed on a heat exchanger model set in the same manner as in Example 1, except that the value was set to K.

[0039] [Comparative Example 2] Weirs were provided over the entire cooling water flow path, and the heat transfer coefficient of all 10 coolers was set to 1500W / m 2 A thermal network calculation analysis was performed on a heat exchanger model set in the same manner as in Example 1, except that the value was set to K.

[0040] Compared with the difference in heat removal amount of Comparative Examples 1 and 2, when a weir is arranged only on the downstream side and the heat transfer coefficient is set high in Example 1, the difference in heat exchange amount between the outlet and the inlet can be reduced, and the difference in heat exchange amount between the inlet and the outlet portion is smaller than in Comparative Examples 1 and 2. Accordingly, by providing a weir on the downstream side to increase the heat transfer coefficient, it is possible to make the heat removal amount of the entire cooler nearly uniform. [Description of Reference Signs]

[0041] Heat exchanger 2 Coolant flow path 3 Weir 31 Protrusion 32 Recess P Interval A Apex angle T Thickness θ Offset period F flow direction 4. Heating element (battery module)

Claims

1. It is equipped with a cooling liquid channel that is thermally connected to the heating element, The above-mentioned coolant flow path is a heat exchanger having a plurality of weirs erected on the inner wall on the heat-generating element side and provided to cross in a direction perpendicular to the direction of the coolant flow path, The Reynolds number obtained using the equivalent circular diameter of the coolant flow path for the coolant flowing in the area where the above-mentioned weir is not formed is less than the critical Reynolds number. The shape of the above weir is a wave-like shape that undulates in the direction of the coolant flow path. The weir is positioned such that the heat transfer coefficient from the heat-generating element to the coolant is higher on the downstream side of the coolant flow path than on the upstream side. The peak angle of the weir in the above waveform is 90° or more and less than 180°. A heat exchanger characterized by a smaller peak angle of the waveform in a weir located downstream than in a weir located upstream.

2. A cooling liquid channel provided which is thermally connected to the heating element, The above-mentioned coolant flow path is a heat exchanger having a plurality of weirs erected on the inner wall on the heat-generating element side and provided to cross in a direction perpendicular to the direction of the coolant flow path, The Reynolds number obtained using the equivalent circular diameter of the coolant flow path for the coolant flowing in the area where the above-mentioned weir is not formed is less than the critical Reynolds number. The shape of the above weir is a wave-like shape that undulates in the direction of the coolant flow path. The weir is positioned such that the heat transfer coefficient from the heat-generating element to the coolant is higher on the downstream side of the coolant flow path than on the upstream side. A heat exchanger characterized in that the thickness of the weir is in the range of 1 to 2 mm, and the weir located downstream is thinner in the direction of the coolant flow path than the weir located upstream.

3. A cooling liquid channel provided which is thermally connected to the heating element, The above-mentioned coolant flow path is a heat exchanger having a plurality of weirs erected on the inner wall on the heat-generating element side and provided to cross in a direction perpendicular to the direction of the coolant flow path, The Reynolds number obtained using the equivalent circular diameter of the coolant flow path for the coolant flowing in the area where the above-mentioned weir is not formed is less than the critical Reynolds number. The shape of the above weir is a wave-like shape that undulates in the direction of the coolant flow path. The weir is positioned such that the heat transfer coefficient from the heat-generating element to the coolant is higher on the downstream side of the coolant flow path than on the upstream side. The above-mentioned multiple weirs are a heat exchanger characterized in that the offset period in the direction perpendicular to the direction of the coolant flow path at the vertex positions of adjacent weirs is smaller on the downstream side than on the upstream side.

4. The coolant flow path has a plurality of branched side flow paths, The heat exchanger according to any one of claims 1 to 3, characterized in that each branch channel is provided with a weir such that the heat transfer coefficient is equal in the region equidistant from the upstream end of the coolant channel.

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