WO2021170541A1

WO2021170541A1 - Cooling arrangement for an electrical storage device allowing graded or variable local cooling

Info

Publication number: WO2021170541A1
Application number: PCT/EP2021/054357
Authority: WO
Inventors: Martin Alejandro DE LA VEGA LOPEZ
Original assignee: Abtery AB
Current assignee: Abtery AB
Priority date: 2020-02-27
Filing date: 2021-02-22
Publication date: 2021-09-02
Anticipated expiration: 2022-08-27
Also published as: SE544868C2; SE2030059A1

Abstract

A cooling arrangement (100) for cooling a heated surface of an electrical energy storage device. The cooling arrangement comprises a conduit (110) with a length, a wall (111), an inlet (121), and an outlet (122). The inlet is configured to receive a coolant and the outlet is configured to exhaust the coolant, thereby forming a coolant path (120) between the inlet (121) and the outlet (122). The conduit (110) is configured to transfer heat from the heated surface to the coolant along the coolant path (120) with an associated heat transfer rate, which is dependent on a heat conduction property of the wall (111) of the conduit (110). The wall of the conduit is arranged with variable heat conduction property, where the heat conduction property varies in dependence of a configuration of the electrical energy storage device.

Description

A COOLING ARRANGEMENT FOR AN ELECTRICAL STORAGE DEVICE

TECHNICAL FIELD

The present disclosure relates to cooling arrangements, particularly liquid coolant-based cooling arrangements and cooling arrangements for electrical storage devices.

BACKGROUND

Battery packs of electrical energy storage devices need cooling to operate in a preferred temperature span, which enables, i.a., the highest efficiency and the lowest wear. Liquid cooling is a common type of heat management system for electrical energy storage devices. Such systems generally operate by pumping a coolant along a coolant path in a conduit. Heat is transferred from the batteries to the coolant. At least one problem of liquid coolant-based cooling systems is that the coolant is heated up as it is pumped through the coolant path. The warmer the coolant is, the lower the heat transfer rate between the battery pack and the coolant is.

CN102881959B presents a water-cooled heat management system for an electric automobile battery pack which employs a cooling passage with a gradually increasing cross-sectional area, rather than a uniform cross- sectional area.

However, there is still a need for improved cooling arrangements.

SUMMARY It is an object of the present disclosure to provide an efficient cooling arrangement for an electrical energy storage device.

This object is obtained by a cooling arrangement for cooling a heated surface of an electrical energy storage device, the cooling arrangement comprising a conduit with a length, a wall, an inlet, and an outlet, wherein the inlet is configured to receive a coolant and the outlet is configured to exhaust the coolant, thereby forming a coolant path between the inlet and the outlet, wherein the conduit is configured to transfer heat from the heated surface to the coolant along the coolant path with an associated heat transfer rate, the heat transfer rate being dependent on a heat conduction property of the wall of the conduit, wherein the wall of the conduit is arranged with variable heat conduction property, where the heat conduction property varies in dependence of a configuration of the electrical energy storage device.

By varying the heat conduction property in dependence of the configuration of the electrical energy storage device, the rate of heat conduction through the conduit wall can be controlled and adapted for optimal cooling of the electrical energy storage device.

According to aspects, the heat conduction property of the conduit wall increases along the coolant path starting from the inlet. Due to the heat transfer from the electrical energy storage device to the coolant, the temperature of the coolant fluid increases along the coolant path, which can lead to a lower rate of heat conduction near the end of the coolant path. With the heat conduction property increasing along the coolant path this effect can be compensated for, promoting a substantially constant temperature of the electrical energy storage device along the coolant path.

According to other aspects, the heat conduction property of the conduit wall is piecewise constant. This has the advantage of making the conduit easier to design and manufacture.

According to aspects, the heat conduction property of the conduit wall is arranged to comprise one or more local maxima along the coolant path, configured in dependence of a configuration of the electrical energy storage device. For example, a local maximum of the heat conduction property can be arranged in proximity to a part of the electrical energy storage device that is anticipated to generate more heat than other parts of the electrical energy storage device. Advantageously, this enables efficient cooling of the part that generates more heat. According to some aspects, the wall of the conduit comprises a thermal insulator associated with a thickness and a thermal conductivity. The thickness can then be arranged to vary the heat conduction property of the conduit wall along the coolant path. The thermal conductivity of the thermal insulator can also be arranged to vary the heat conduction property of the conduit wall along the coolant path.

According to aspects, the conduit wall comprises fins, wherein the fins are arranged to vary the heat conduction property of the conduit wall along the coolant path. Advantageously, the fins increase the contact area between the conduit wall and the coolant, thereby increasing the heat conduction property with minimal effects on the cross-sectional area of the conduit.

According to aspects, the conduit wall comprises at least one section with high thermal conductivity, wherein the section with high thermal conductivity is arranged in dependence of local temperatures on the heated surface.

According to some aspects, the coolant path is arranged into branches, wherein the branches are arranged to vary the heat conduction property of the conduit wall along the coolant path. The branches can be arranged to be opened or closed off dynamically in dependence of local temperatures on the heated surface. An advantage of this arrangement is that the heat conduction property of the conduit wall can be changed during operation of the cooling system.

The object is also obtained through a method for dynamically controlling local cooling in a cooling arrangement for cooling a heated surface of an electrical energy storage device, the cooling arrangement comprising: a conduit with a length, a wall, an inlet and an outlet, wherein the inlet is configured to receive a coolant and the outlet is configured to exhaust the coolant, thereby forming a coolant path between the inlet and the outlet, wherein the conduit is configured to transfer heat from the heated surface to the coolant along the coolant path with an associated heat transfer rate, the heat transfer rate being dependent on a heat conduction property of the wall of the conduit, the method comprising arranging the conduit into branches to vary the heat conduction property of the conduit wall along the coolant path in dependence of a configuration of the electrical energy storage device, arranging the branches to be in either of an opened or a closed state, and controlling the states of the branches in dependence of local temperatures on the heated surface.

An advantage of this method is that the cooling system can be adapted to changes in the local temperature of the electrical energy storage device during operation.

The methods disclosed herein are associated with the same advantages as discussed above in connection to the different cooling arrangements.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure will now be described in more detail with reference to the appended drawings, where

Figure 1 schematically illustrates an example cooling arrangement.

Figure 2 schematically illustrates a conduit with smoothly varying wall thickness Figure 3 schematically illustrates a conduit with piecewise varying wall thickness

Figure 4 schematically illustrates a conduit with piecewise varying wall thickness Figure 5 schematically illustrates a conduit with piecewise varying wall material

Figure 6 schematically illustrates a conduit where the inner conduit wall is arranged with fins

Figure 7 schematically illustrates a conduit that is arranged into branches

Figure 8 schematically illustrates a conduit where one section of the conduit wall comprises a different material

Figure 9 is a block diagram showing a method for controlling a cooling arrangement

DETAILED DESCRIPTION Aspects of the present disclosure will now be described more fully with reference to the accompanying drawings. The different devices and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout. The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

A heat transfer rate Q between the walls of the coolant conduit and the coolant depends on, among other parameters, a temperature difference DG between the walls and the coolant, a flow velocity v of the coolant and a contact area A between the wall and the coolant. This can be expressed by the following equation:

Q = C A V^{0 8}AT, where a proportionality constant C is determined i.a. by the thermal and viscous properties of the coolant fluid. In the prior art, increasing the cross- sectional area of the conduit increases the contact area, which increases the heat transfer rate. However, the flow velocity is inversely proportional to the cross-sectional area and will therefore decrease as the cross-sectional area is increased, lowering the heat transfer rate. Other methods of increasing the contact area may be conceived which do not affect cross-sectional area, and thereby the flow velocity, in this manner.

Control over the heat transfer rate can also be achieved through control over the temperature difference between the inner conduit wall and the coolant fluid. The temperature of the inner conduit wall depends on a second heat transfer rate from the surroundings through the conduit wall, which in turn depends on several characteristics of the conduit wall. Such characteristics are for example a thermal conductivity of the wall material and a thickness of the wall material.

A combination of such characteristics, resulting in a heat transfer rate between the surroundings and the inner conduit wall, and characteristics which influence the contact area is referred to as a heat conduction property of the wall of the conduit. That is, the dimensions and geometry of the wall and the thermal conductivity and thickness of the wall material all contribute to the heat conduction property of the wall of the conduit.

Figure 1 shows a top view of cooling arrangement 100 for cooling a heated surface of an electrical energy storage device. The cooling arrangement comprises a conduit 110 with a length, a wall, an inlet 121 , and an outlet 122. The inlet is configured to receive a coolant and the outlet is configured to exhaust the coolant, thereby forming a coolant path 120 between the inlet 121 and the outlet 122. The conduit 110 is configured to transfer heat from the heated surface to the coolant along the coolant path 120 with an associated heat transfer rate.

The heat transfer rate from the heated surface to the coolant is dependent on, i.a., the heat conduction property of the wall of the conduit, the temperature difference between the heated surface and the coolant, the thermal conductivity of the coolant, the velocity of the coolant, and the kinematic viscosity of the coolant. The heat transfer rate may also be expressed in terms of the flow, e.g. the Reynolds numbers and/or the Prandtl number. The temperature of the coolant increases along the coolant path 120. The heat transfer rate, therefore, decreases along the coolant path, unless other factors affecting the heat transfer rate are modified along the coolant path. In an example electrical energy storage device comprising a plurality of equal battery packs equally distributed on a cooling arrangement, a decreasing heat transfer rate along the coolant path 120 results in higher operating temperatures of the battery packs closer to the outlet 122 compared to the battery packs further away from the outlet. The varying operating temperatures result in the battery packs operating under different efficiencies and different wear. Extra care must be taken such that the battery packs closest to the outlet do not become too hot, which can be very challenging indeed. Furthermore, if sufficient cooling is managed for the battery packs closest to the outlet, the battery packs closest to the inlet are exposed to excessive cooling, which can be seen as an unnecessarily costly and inefficient solution.

The disclosed cooling arrangement 100 is arranged with the wall of the conduit arranged with a variable heat conduction property, where the heat conduction property varies in dependence of a configuration of the electrical energy storage device. For example, the heat conduction property of the conduit wall may be arranged to increase along the coolant path 120 starting from the inlet 121. As such, the battery packs in an electrical energy storage device comprising a plurality of substantially equal battery packs distributed substantially equally on a cooling arrangement may be kept at a substantially similar temperature, despite the coolant heating up along the coolant path. In such example, the heat conduction property of the conduit wall may or may not be piecewise constant. In other words, the heat conduction property of the conduit wall may be arranged as an increasing step function along the whole coolant path or along sections of the coolant path.

The heat output from each battery pack in the electrical energy storage device is not necessarily equal. For example, the discharge rate of each battery pack may differ. Moreover, the external environment of the battery pack may affect the heat output. The isolation of the battery packs may differ, as in, e.g., isolation to the outside environment. Furthermore, the battery packs in the center of the electrical energy storage device may be affected by adjacent battery packs. Some battery packs may be arranged close to other heat sources, as in, e.g., a turbo. Therefore, the disclosed cooling arrangement 100 may be arranged with the heat conduction property of the conduit wall comprising one or more local maxima along the coolant path 120, configured in dependence of a configuration of the electrical energy storage device. This way, the cooling arrangement comprises one or more local sections along the coolant path where the heat transfer rate from the heated surface to the coolant is larger compared to the average heat transfer rate. A local maximum is a maximum value within an interval, e.g. a length interval along the coolant path. Herein, a length interval along the coolant path is in the order of the size of two to four battery packs.

Naturally, it is possible to arrange a combination of an increasing heat conduction property along the coolant path together with local maxima of the heat conduction property. This way, the degradation of the heat transfer rate due to increasing coolant temperature may be compensated for, while, at the same time, the heat transfer rate may be improved at sections where it is needed, i.e. at local hot spots.

The heat conduction property of the conduit wall is dependent on the dimensions, geometry, and thermal conductivity of the wall. For instance, the wall 111 of the conduit 110 may comprise a thermal insulator associated with a thickness and a thermal conductivity. This way, the thickness may be arranged to vary the heat conduction property of the conduit wall 111 along the coolant path 120. The larger the thickness, the lower the heat transfer rate between the heated surface and the coolant. By thermal insulator is meant a material with a low thermal conductivity, substantially a material with a thermal conductivity lower than 0.1 W/mK, preferably a material with a thermal conductivity below 0.05 W/mK. As an example, the material could be an aluminum oxide foam. As another example, the material could be calcium silicate. As a third example, the material could be foamed glass.

Figures 2, 3 and 4 show side views of different example conduits 110. Figure 2 shows a conduit comprising a wall with a gradually decreasing thickness along the coolant path 120 starting from the inlet 121 . If the wall comprises a thermal insulator, the heat transfer rate between the heated surface and the coolant increases along the coolant path starting from inlet 121 (if all other factors affecting the heat transfer rate remain constant). Thus, the heat transfer decrease resulting from the coolant heating up along the coolant path can be compensated for. Figure 3 shows a conduit comprising a wall with a step wise decreasing thickness along the coolant path 120. Figure 4 shows a conduit comprising a wall with a local minimum of the thickness along the coolant path 120. If the wall comprises a thermal insulator, the heat transfer rate between the heated surface and the coolant is increased at the local minimum of the thickness. This way, local hot spots may be cooled sufficiently.

The required variation in wall thickness along the conduit will depend on several factors, e.g. the length of the conduit and the distribution of local hot spots. As an example, the optimal thickness could be determined by mathematical calculation or numerical simulation of the heat flow in the cooling system. Methods for calculating or simulating heat flow are well known. As another example, the wall thickness could be decreased, gradually or stepwise, to between one half and one third of its starting value over the length of the conduit. As a third example, the wall thickness could be reduced to between one half and one third of its average thickness near local hot spots.

The thermal conductivity of the thermal insulator may be arranged to vary the heat conduction property of the conduit wall 111 along the coolant path 120. For example, different sections of the conduit wall may comprise different materials with different thermal conductivities. Figure 5 shows a conduit comprising a wall where the middle section 501 comprises a different material to other sections of the conduit, giving this section a different heat conduction property. According to an example, the section 501 can consist of a material with a higher thermal conductivity than other sections of the conduit wall. According to another example, the section 501 can consist of a material with a lower thermal conductivity than other sections of the conduit wall. A section of the wall is taken to mean a continuous part of the wall extending a finite length along the conduit.

The conduit wall 111 may comprise fins, as shown in figure 6, where the fins 601 are arranged to vary the heat conduction property of the conduit wall 111 along the coolant path 120. Thus, a varying geometry of the wall varies the heat conduction property of the conduit wall. The fins 601 increase the contact surface area between the coolant and the conduit wall without changing the cross-sectional area of the conduit.

The presence of fins may affect the type of flow of the coolant liquid. In fluid dynamics a distinction is made between laminar and turbulent flow of a fluid such as a liquid. During laminar flow the individual particles of the fluid generally follow smooth paths in the direction of the flow, essentially confined to narrow regions or layers in the fluid. In contrast, turbulent flow frequently involves particles moving in a direction other than the overall flow direction, for example as part of an eddy or swirl in the flow, leading to a higher degree of mixing in the fluid. Whether a fluid displays laminar or turbulent flow is dependent on i.a. the viscous properties of the fluid and the size and shape of the conduit.

In the context of liquid cooling, turbulent flow can lead to a higher degree of mixing between the fluid near the conduit wall and the fluid near the middle of the conduit, resulting in more efficient cooling. It may therefore be an advantage to arrange the fins 601 in a manner that promotes turbulent flow in the coolant liquid.

The optimal size and placement of the fins 601 along the conduit will depend on several factors, e.g. the length of the conduit and the necessary conditions for producing turbulent flow. As an example, the optimal size and placement could be determined by mathematical calculation or numerical simulation of the flow of liquid in the cooling system. Methods for calculating or simulating the flow of liquids are well known in the art.

The conduit wall 111 may comprise at least one section 801 with high thermal conductivity, as shown in figure 8, wherein the section 801 with high thermal conductivity is arranged in dependence of local temperatures on the heated surface. As an example, the section 801 with high thermal conductivity can be arranged in direct contact with a local hot spot, providing more efficient cooling of the hot spot. By high thermal conductivity is meant a thermal conductivity comparable to that of aluminum or copper, preferably a thermal conductivity above 100 W/mK.

The coolant path 120 may be arranged into branches, where the branches may be arranged to vary the heat conduction property of the conduit wall 111 along the coolant path 120. The branches may also be arranged to be opened or closed off dynamically in dependence of local temperatures on the heated surface.

An optimal design of the cooling arrangement, comprising features such as conduit length, width and shape as well as the heat conduction property of the conduit wall, will depend among other things on the requirements posed by the specific application and the properties of the electrical energy storage device. As an example, an application can be to cool a traction battery pack in a propulsion device for automotive applications, which may introduce limits on the coolant arrangement size or weight.

A design for the cooling arrangement could for example be found through numerical simulations. System properties to be simulated may include the estimated heat flow from different parts of the energy storage device, the heat flow thought the conduit walls, mechanical strain in the system, and the flow rate of the coolant liquid. Methods for numerical simulation of heat flow, mechanical strain and fluid dynamics are well known. According to another example, a design of the cooling arrangement could be found through experimentation. There is also disclosed herein a method for dynamically controlling local cooling in a cooling arrangement 100 for cooling a heated surface of an electrical energy storage device. The cooling arrangement comprises a conduit 110 with a length, a wall, an inlet 121 and an outlet 122, wherein the inlet is configured to receive a coolant and the outlet is configured to exhaust the coolant, thereby forming a coolant path 120 between the inlet 121 and the outlet 122. The conduit 110 is configured to transfer heat from the heated surface to the coolant along the coolant path 120 with an associated heat transfer rate, the heat transfer rate being dependent on a heat conduction property of the wall of the conduit.

The method, shown in Figure 9, comprises arranging S1 the conduit into branches to vary the heat conduction property of the conduit wall along the coolant path 120 in dependence of a configuration of the electrical energy storage device, arranging S2 the branches to be in either of an opened or a closed state and controlling S3 the states of the branches in dependence of local temperatures on the heated surface.

The cooling arrangements and methods disclosed here are applicable regardless of the coolant used. As an example, coolants based on ethylene glycol or propylene glycol can be used. As another example, water can be used as a coolant fluid.

Claims

1. A cooling arrangement (100) for cooling a heated surface of an electrical energy storage device, the cooling arrangement comprising a conduit (110) with a length, a wall (111), an inlet (121 ), and an outlet (122), wherein the inlet is configured to receive a coolant and the outlet is configured to exhaust the coolant, thereby forming a coolant path (120) between the inlet (121) and the outlet (122), wherein the conduit (110) is configured to transfer heat from the heated surface to the coolant along the coolant path (120) with an associated heat transfer rate, the heat transfer rate being dependent on a heat conduction property of the wall (111 ) of the conduit (110), wherein the wall of the conduit is arranged with variable heat conduction property, where the heat conduction property varies in dependence of a configuration of the electrical energy storage device.

2. The cooling arrangement (100) according to claim 1 , wherein the heat conduction property of the conduit wall (111) increases along the coolant path (120) starting from the inlet (121).

3. The cooling arrangement (100) according to claim 2, wherein the heat conduction property of the conduit wall (111 ) is piecewise constant.

4. The cooling arrangement (100) according to claim 1 , wherein the heat conduction property of the conduit wall (111) is arranged to comprise one or more local maxima along the coolant path (120) configured in dependence of a configuration of the electrical energy storage device.

5. The cooling arrangement (100) according to any previous claim, wherein the wall (111) of the conduit (110) comprises a thermal insulator associated with a thickness and a thermal conductivity.

6. The cooling arrangement (100) according to claim 5, wherein the thickness is arranged to vary the heat conduction property of the conduit wall (111) along the coolant path (120).

7. The cooling arrangement (100) according to claim 5, wherein the thermal conductivity of the thermal insulator is arranged to vary the heat conduction property of the conduit wall (111) along the coolant path (120).

8. The cooling arrangement (100) according to any previous claim, wherein the conduit wall (111) comprises fins (601), wherein the fins are arranged to vary the heat conduction property of the conduit wall (111) along the coolant path (120).

9. The cooling arrangement (100) according to any previous claim, wherein the conduit wall comprises at least one section (801) with high thermal conductivity, wherein the section with high thermal conductivity is arranged in dependence of local temperatures on the heated surface.

10. The cooling arrangement (100) according to any previous claim, wherein the coolant path (120) is arranged into branches (701), wherein the branches are arranged to vary the heat conduction property of the conduit wall (111) along the coolant path (120).

11. The cooling arrangement (100) according to claim 10, wherein the branches are arranged to be opened or closed off dynamically in dependence of local temperatures on the heated surface.

12. A method for dynamically controlling local cooling in a cooling arrangement (100) for cooling a heated surface of an electrical energy storage device, the cooling arrangement comprising: a conduit (110) with a length, a wall, an inlet (121 ) and an outlet (122), wherein the inlet is configured to receive a coolant and the outlet is configured to exhaust the coolant, thereby forming a coolant path (120) between the inlet (121 ) and the outlet (122), wherein the conduit (110) is configured to transfer heat from the heated surface to the coolant along the coolant path (120) with an associated heat transfer rate, the heat transfer rate being dependent on a heat conduction property of the wall of the conduit, the method comprising: arranging (S1) the conduit into branches (701) to vary heat conduction property of the conduit wall along the coolant path (120) in dependence of a configuration of the electrical energy storage device; arranging (S2) the branches (701) to be in either of an opened or a closed state; controlling (S3) the states of the branches (701) in dependence of local temperatures on the heated surface.