SE2030059A1

SE2030059A1 - A cooling arrangement for an electrical storage device

Info

Publication number: SE2030059A1
Application number: SE2030059A
Authority: SE
Inventors: La Vega Lopez Martin Alejandro De
Original assignee: Abtery Ab
Priority date: 2020-02-27
Filing date: 2020-02-27
Publication date: 2021-08-28
Also published as: SE544868C2; WO2021170541A1

Abstract

A cooling arrangement for cooling a heated surface of an electrical energy storage device. The cooling arrangement comprises a conduit with a length, a wall, an inlet, and an outlet. 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. The conduit is configured to transfer heat from the heated surface to the coolant along the coolant path with an associated heat transfer rate, which is dependent on a heat conduction property of the wall of the conduit. 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 ARRANGEIVIENT FOR AN ELECTRICAL STORAGE DEVICE TECHNICAL FIELD The present disclosure relates to cooling arrangements, particularly liquidcoolant-based cooling arrangements and cooling arrangements for electricalstorage devices.

BACKGROUND Battery packs of electrical energy storage devices need cooling to operate ina preferred temperature span, which enables, i.a., the highest efficiency andthe lowest wear. Liquid cooling is a common type of heat management systemfor electrical energy storage devices. Such systems generally operate bypumping a coolant along a coolant path in a conduit. Heat is transferred fromthe batteries to the coolant. At least one problem of liquid coolant-basedcooling systems is that the coolant is heated up as it is pumped through thecoolant 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 anelectric automobile battery pack which employs a cooling passage with agradually increasing cross-sectional area, rather than a uniform cross- sectional area.

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

SUMMARY lt is an object of the present disclosure to provide an efficient coolingarrangement for an electrical energy storage device.

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

By varying the heat conduction property in dependence of the configuration ofthe electrical energy storage device, the rate of heat conduction through theconduit 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 wallincreases along the coolant path starting from the inlet. Due to the heat transferfrom the electrical energy storage device to the coolant, the temperature of thecoolant fluid increases along the coolant path, which can lead to a lower rateof heat conduction near the end of the coolant path. With the heat conductionproperty increasing along the coolant path this effect can be compensated for,promoting a substantially constant temperature of the electrical energy storagedevice along the coolant path.

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

According to aspects, the heat conduction property of the conduit wall isarranged to comprise one or more local maxima along the coolant path,configured in dependence of a configuration of the electrical energy storagedevice. For example, a local maximum of the heat conduction property can bearranged in proximity to a part of the electrical energy storage device that isanticipated to generate more heat than other parts of the electrical energystorage device. Advantageously, this enables efficient cooling of the part thatgenerates more heat.

According to some aspects, the wall of the conduit comprises a thermalinsulator associated with a thickness and a thermal conductivity. The thicknesscan then be arranged to vary the heat conduction property of the conduit wallalong the coo|ant path. The thermal conductivity of the thermal insulator canalso be arranged to vary the heat conduction property of the conduit wall alongthe coo|ant path.

According to aspects, the conduit wall comprises fins, wherein the fins arearranged to vary the heat conduction property of the conduit wall along thecoo|ant path. Advantageously, the fins increase the contact area between theconduit wall and the coo|ant, thereby increasing the heat conduction propertywith minimal effects on the cross-sectional area of the conduit.

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

According to some aspects, the coo|ant path is arranged into branches,wherein the branches are arranged to vary the heat conduction property of theconduit wall along the coo|ant path. The branches can be arranged to beopened or closed off dynamically in dependence of local temperatures on theheated surface. An advantage of this arrangement is that the heat conductionproperty of the conduit wall can be changed during operation of the coolingsystem.

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

An advantage of this method is that the cooling system can be adapted tochanges in the local temperature of the electrical energy storage device duringoperation.

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

Generally, all terms used in the claims are to be interpreted according to theirordinary meaning in the technical field, unless explicitly defined otherwiseherein. All references to "a/an/the element, apparatus, component, means,step, etc." are to be interpreted openly as referring to at least one instance ofthe element, apparatus, component, means, step, etc., unless explicitly statedotherwise. The steps of any method disclosed herein do not have to beperformed in the exact order disclosed, unless explicitly stated. Furtherfeatures of, and advantages with, the present invention will become apparentwhen studying the appended claims and the following description. The skilledperson realizes that different features of the present invention may becombined 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 tothe 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 i||ustrates a conduit with piecewise varying wallthickness Figure 4 schematically i||ustrates a conduit with piecewise varying wall thicknessFigure 5 schematically i||ustrates a conduit with piecewise varying wall material Figure 6 schematically i||ustrates a conduit where the inner conduit wall isarranged with fins Figure 7 schematically i||ustrates a conduit that is arranged into branches Figure 8 schematically i||ustrates a conduit where one section of the conduit wall comprises a different material Figure 9 is a block diagram showing a method for contro||ing a cooling arrangement DETAILED DESCRIPTION Aspects of the present disclosure will now be described more fully withreference to the accompanying drawings. The different devices and methodsdisclosed herein can, however, be realized in many different forms and shouldnot be construed as being limited to the aspects set forth herein. Like numbersin the drawings refer to like elements throughout.

The terminology used herein is for describing aspects of the disclosure onlyand 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 thecontext clearly indicates otherwise.

A heat transfer rate Q between the walls of the coolant conduit and the coolantdepends on, among other parameters, a temperature difference AT betweenthe walls and the coolant, a flow velocity v of the coolant and a contact area Abetween the wall and the coolant. This can be expressed by the following equation: Q = c A UO-SAT, where a proportionality constant C is determined i.a. by the thermal andviscous properties of the coolant fluid. ln the prior art, increasing the cross-sectional area of the conduit increases the contact area, which increases theheat transfer rate. However, the flow velocity is inversely proportional to thecross-sectional area and will therefore decrease as the cross-sectional area is increased, Iowering the heat transfer rate.

Control over the heat transfer rate can also be achieved through control overthe temperature difference between the inner conduit wall and the coolant fluid.The temperature of the inner conduit wall depends on a second heat transferrate from the surroundings through the conduit wall, which in turn depends onseveral characteristics of the conduit wall. Such characteristics are for examplea thermal conductivity of the wall material and a thickness of the wall material.A combination of such characteristics resulting in a heat transfer rate betweenthe surroundings and the inner conduit wall is referred to as a heat conduction property of the wall of the conduit.

Figure 1 shows a top view of cooling arrangement 100 for cooling a heatedsurface of an electrical energy storage device. The cooling arrangementcomprises 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 toexhaust the coolant, thereby forming a coolant path 120 between the inlet 121and the outlet 122. The conduit 110 is configured to transfer heat from theheated surface to the coolant along the coolant path 120 with an associatedheat 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 temperaturedifference between the heated surface and the coolant, the thermalconductivity of the coolant, the velocity of the coolant, and the kinematicviscosity of the coolant. The heat transfer rate may also be expressed in termsof the flow, e.g. the Reynolds numbers and/or the Prandtl number. Thetemperature 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. ln anexample electrical energy storage device comprising a plurality of equalbattery packs equally distributed on a cooling arrangement, a decreasing heattransfer rate along the coolant path 120 results in higher operatingtemperatures of the battery packs closer to the outlet 122 compared to thebattery packs further away from the outlet. The varying operating temperaturesresult in the battery packs operating under different efficiencies and differentwear. Extra care must be taken such that the battery packs closest to the outletdo not become too hot, which can be very challenging indeed. Furthermore, ifsufficient cooling is managed for the battery packs closest to the outlet, thebattery packs closest to the inlet are exposed to excessive cooling, which canbe seen as an unnecessarily costly and inefficient solution.

The disclosed cooling arrangement 100 is arranged with the wall of the conduitarranged with a variable heat conduction property, where the heat conductionproperty varies in dependence of a configuration of the electrical energystorage device. For example, the heat conduction property of the conduit wallmay be arranged to increase along the coolant path 120 starting from the inlet121. As such, the battery packs in an electrical energy storage devicecomprising a plurality of substantially equal battery packs distributedsubstantially equally on a cooling arrangement may be kept at a substantiallysimilar temperature, despite the coolant heating up along the coolant path. lnsuch example, the heat conduction property of the conduit wall may or maynot be piecewise constant. ln other words, the heat conduction property of theconduit 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 deviceis not necessarily equal. For example, the discharge rate of each battery packmay differ. l\/loreover, the external environment of the battery pack may affectthe heat output. The isolation of the battery packs may differ, as in, e.g.,isolation to the outside environment. Furthermore, the battery packs in thecenter of the electrical energy storage device may be affected by adjacentbattery packs. Some battery packs may be arranged close to other heat sources, as in, e.g., a turbo. Therefore, the disclosed cooling arrangement 100may be arranged with the heat conduction property of the conduit wallcomprising one or more local maxima along the coolant path 120, configuredin dependence of a configuration of the electrical energy storage device. Thisway, the cooling arrangement comprises one or more local sections along thecoolant path where the heat transfer rate from the heated surface to the coolantis larger compared to the average heat transfer rate. A local maximum is amaximum 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 twoto four battery packs.

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

The heat conduction property of the conduit wall is dependent on thedimensions, geometry, and thermal conductivity of the wall. For instance, thewall 111 of the conduit 110 may comprise a thermal insulator associated witha thickness and a thermal conductivity. This way, the thickness may bearranged to vary the heat conduction property of the conduit wall 111 alongthe coolant path 120. The larger the thickness, the lower the heat transfer ratebetween the heated surface and the coolant. By thermal insulator is meant amaterial with a low thermal conductivity, substantially a material with a thermalconductivity lower than 0.1 W/mK, preferably a material with a thermalconductivity below 0.05 W/mK. As an example, the material could be analuminum 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. Figure2 shows a conduit comprising a wall with a gradually decreasing thicknessalong the coolant path 120 starting from the inlet 121. lf the wall comprises a thermal insulator, the heat transfer rate between the heated surface and thecoolant increases along the coolant path starting from inlet 121 (if all otherfactors affecting the heat transfer rate remain constant). Thus, the heat transferdecrease resulting from the coolant heating up along the coolant path can becompensated for. Figure 3 shows a conduit comprising a wall with a step wisedecreasing thickness along the coolant path 120. Figure 4 shows a conduitcomprising a wall with a local minimum of the thickness along the coolant path120. lf the wall comprises a thermal insulator, the heat transfer rate betweenthe heated surface and the coolant is increased at the local minimum of thethickness. This way, local hot spots may be cooled sufficiently.

The required variation in wall thickness along the conduit will depend onseveral factors, e.g. the length of the conduit and the distribution of local hotspots. As an example, the optimal thickness could be determined bymathematical calculation or numerical simulation of the heat flow in the coolingsystem. l\/lethods for calculating or simulating heat flow are well known. Asanother example, the wall thickness could be decreased, gradually orstepwise, to between one half and one third of its starting value over the lengthof the conduit. As a third example, the wall thickness could be reduced tobetween 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 theheat conduction property of the conduit wall 111 along the coolant path 120.For example, different sections of the conduit wall may comprise differentmaterials with different thermal conductivities. Figure 5 shows a conduitcomprising a wall where the middle section 501 comprises a different materialto other sections of the conduit, giving this section a different heat conductionproperty. According to an example, the section 501 can consist of a materialwith a higher thermal conductivity than other sections of the conduit wall.According to another example, the section 501 can consist of a material witha lower thermal conductivity than other sections of the conduit wall. A sectionof the wall is taken to mean a continuous part of the wall extending a finitelength along the conduit.

The conduit wall 111 may comprise fins, as shown in figure 6, where the fins601 are arranged to vary the heat conduction property of the conduit wall 111along the coolant path 120. Thus, a varying geometry of the wall varies theheat conduction property of the conduit wall. The fins 601 increase the contactsurface area between the coolant and the conduit wall without changing thecross-sectional area of the conduit.

The presence of fins may affect the type of flow of the coolant liquid. ln fluiddynamics a distinction is made between laminar and turbulent flow of a fluidsuch as a liquid. During laminar flow the individual particles of the fluidgenerally follow smooth paths in the direction of the flow, essentially confinedto narrow regions or layers in the fluid. ln contrast, turbulent flow frequentlyinvolves particles moving in a direction other than the overall flow direction, forexample as part of an eddy or swirl in the flow, leading to a higher degree ofmixing in the fluid. Whether a fluid displays laminar or turbulent flow isdependent on i.a. the viscous properties of the fluid and the size and shape ofthe conduit. ln the context of liquid cooling, turbulent flow can lead to a higher degree ofmixing between the fluid near the conduit wall and the fluid near the middle ofthe conduit, resulting in more efficient cooling. lt may therefore be anadvantage 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 dependon several factors, e.g. the length of the conduit and the necessary conditionsfor producing turbulent flow. As an example, the optimal size and placementcould be determined by mathematical calculation or numerical simulation ofthe flow of liquid in the cooling system. l\/lethods for calculating or simulatingthe flow of liquids are well known in the art.

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

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

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

A design for the cooling arrangement could for example be found throughnumerical simulations. System properties to be simulated may include theestimated heat flow from different parts of the energy storage device, the heatflow thought the conduit walls, mechanical strain in the system, and the flowrate of the coo|ant liquid. l\/lethods for numerical simulation of heat flow,mechanical strain and fluid dynamics are well known. According to anotherexample, a design of the cooling arrangement could be found through experimentation.

There is also disclosed herein a method for dynamically controlling localcooling in a cooling arrangement 100 for cooling a heated surface of anelectrical energy storage device. The cooling arrangement comprises aconduit 110 with a length, a wall, an inlet 121 and an outlet 122, wherein theinlet is configured to receive a coo|ant and the outlet is configured to exhaustthe coo|ant, thereby forming a coo|ant path 120 between the inlet 121 and theoutlet 122. The conduit 110 is configured to transfer heat from the heated surface to the coolant along the coolant path 120 with an associated heattransfer rate, the heat transfer rate being dependent on a heat conductionproperty of the wall of the conduit.

The method, shown in Figure 9, comprises arranging S1 the conduit intobranches to vary the heat conduction property of the conduit wall along thecoolant path 120 in dependence of a configuration of the electrical energystorage device, arranging S2 the branches to be in either of an opened or aclosed 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 applicableregardless of the coolant used. As an example, coolants based on ethyleneglycol or propylene glycol can be used. As another example, water can beused as a coolant fluid.

Claims

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

2. The cooling arrangement (100) according to claim 1, wherein the heatconduction 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 heatconduction property of the conduit wall (111) is piecewise constant.

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

5. The cooling arrangement (100) according to any previous claim, whereinthe 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 thethickness 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 thermalconductivity of the thermal insulator is arranged to vary the heat conductionproperty of the conduit wall (111) along the coolant path (120).

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

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

10. The cooling arrangement (100) according to any previous claim, whereinthe coolant path (120) is arranged into branches (701), wherein the branchesare 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 thebranches are arranged to be opened or closed off dynamically in dependenceof local temperatures on the heated surface.

12. A method for dynamically controlling local cooling in a coolingarrangement (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), whereinthe inlet is configured to receive a coolant and the outlet is configured toexhaust the coolant, thereby forming a coolant path (120) between the inlet(121) and the outlet (122), wherein the conduit (110) is configured to transferheat from the heated surface to the coolant along the coolant path (120) withan associated heat transfer rate, the heat transfer rate being dependent on aheat conduction property of the wall of the conduit, the method comprising: arranging (S1) the conduit into branches (701) to vary heat conductionproperty 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 closedstate; contro||ing (S3) the states of the branches (701) in dependence of local temperatures on the heated surface.