WO2013144829A1

WO2013144829A1 - Cell stack heat sink panel with integral heat dissipating fin

Info

Publication number: WO2013144829A1
Application number: PCT/IB2013/052384
Authority: WO
Inventors: Wilhelm Franz Fuls
Original assignee: The Technology Innovation Agency
Priority date: 2012-03-30
Filing date: 2013-03-26
Publication date: 2013-10-03
Also published as: ZA201407909B

Abstract

A heat sink panel for a cell stack or other multiple cell battery module is provided in which the heat sink panel has an integral heat dissipating fin extending along one edge of a cell area thereof that is operatively to be in contact with, or immediately adjacent, an individual cell. The heat dissipating fin has at least one leading end edge towards which coolant air is to flow, in use, and a coolant air departure region spaced from the leading end edge of the fin. The heat dissipating fin has a portion thereof nearer the leading end edge removed to render the surface area of the heat dissipating fin asymmetric about a position in between the leading end edge and the coolant air departure region of the heat dissipating fin. The coolant air departure region may be an opposite end edge or a central region of the heat dissipating fin.

Description

CELL STACK HEAT SINK PANEL WITH INTEGRAL HEAT DISSIPATING

FIN

FIELD OF THE INVENTION

This invention relates to a heat sink panel for a cell stack or other multiple cell battery module wherein multiple heat sink panels, typically forming parts of cell trays, cooperate with each other to envelope individual cells and locate multiple cells relative to each other. More particularly, the invention relates to a heat sink panel and a cell tray embodying same wherein the heat sink panel has an integral heat dissipating fin.

BACKGROUND TO THE INVENTION

In battery cell stacks and other battery modules, individual cells are typically located between two adjacent heat sink panels with the individual cells being grouped into stacks and the stacks being grouped into battery modules. In all of those assemblies, the heat sink panels are generally parallel to each other and the integral heat dissipating fins project beyond the confines of the cells and extend from one side of the cell group to the other side. Coolant air enters at one end edge of the fins, herein referred to as the leading end edge, and leaves in the region of the opposite end edge of the fins, often changing direction upwards because of buoyancy effects.

The efficiency of the absorption of heat from the cells by the heat sink panels and the dissipation of this heat by way of the integral heat dissipating fins has given cause for concern and further investigation. A computational fluid dynamics (CFD) study was conducted to simulate the flow of air around and thermal energy through the solid components of one form of present heat sink and fin arrangement made of aluminium plate, a cell tray embodying same being illustrated in Figure 1 . In this instance a moulded plastic frame (A) is attached to a thermally conductive heat sink in the form of an aluminium plate (B) with the frame defining the outer perimeter of a housing for a pouch cell and an integral heat dissipating fin (C) projecting outwards beyond the frame along one side, the upper side in this instance. The heat dissipating fins have symmetrically positioned gaps [D] extending inwardly from the free edge [E] of the heat sink panel with the gaps terminating short of the fourth and nearest side of the rectangular frame so that the heat dissipating fin is effectively divided into three adjacent sections along its length. The leading edge of the fin is indicated by the letter (F) and the other end of the fin is indicated by the letter (G).

In the study under discussion, it was found that under natural convection conditions the heat transfer characteristics of the fin geometry illustrated in Figure 1 are not very effective as no significant heat transfer takes place from the horizontal midpoint of the fin to the other end of the fin (G), being the extreme left hand side of the cell tray as illustrated in Figure 1 .

Published international patent application number WO 20091 146196 describes a variety of different configurations of heat dissipating fins but none of these, in applicant's view, is able to combat the temperature variations and gradients occasioned by the flow of coolant air from a leading end edge of the heat dissipating fin to the other end edge. There is, accordingly, a need for a heat sink panel that has an integral heat dissipating fin wherein the heat sink panel is able to more evenly absorb heat from a cell and dissipate the heat by way of the heat dissipating fins. SUMMARY OF THE INVENTION

In accordance with a first aspect of this invention there is provided a heat sink panel for a cell stack or other multiple cell battery module, the heat sink panel being heat conductive and having an integral heat dissipating fin extending along one edge of a cell area of the heat sink panel that is operatively to be in contact with, or immediately adjacent, an individual cell, wherein the heat dissipating fin has at least one leading end edge towards which coolant air is to flow, in use, and a coolant air departure region spaced from the leading end edge of the fin, the heat sink panel being characterised in that the heat dissipating fin has a portion thereof nearer the leading end edge removed to render the surface area of the heat dissipating fin asymmetric about a position in between the leading end edge and the coolant air departure region of the heat dissipating fin.

Further features of this first aspect of the invention provide for the coolant air departure region to be either an opposite end edge region of the heat dissipating fin or a generally centrally located region along the length of the fin in which instance the opposite end edge of the fin forms a second leading end edge of the heat dissipating fin; for the removed portion to be of generally rectangular shape with a lower boundary of the rectangle preferably lying on or close to a boundary between the heat dissipating fin and the cell area of the heat sink panel with the removed portion preferably forming a rectangular aperture through the heat dissipating fin; for the rectangular removed portion to have a length of from about one quarter to about one half of the length of the heat dissipating fin, and for the height of the removed portion to be at least about one half of the height of the heat dissipating fin.

A still further feature of the invention provides for a lower edge of the heat dissipating fin corresponding to the removed portion to be covered with non- heat conductive material either in the form of a separate insert or an integrally moulded part of a surrounding frame of the cell area of a cell tray; and for the heat sink panel to be made of a suitable aluminium plate material.

In accordance with a second aspect of the invention there is provided a cell tray incorporating a heat sink panel as defined above and having a rectangular moulded plastic frame defining a cell area of the heat sink panel from which an integral heat dissipating fin projects outwards.

A further feature of this second aspect of the invention provides for the rectangular moulded plastic frame to be moulded directly onto the heat sink panel such that the heat sink panel is permanently captive relative thereto.

The above and other features of the invention will become more apparent from the following more detailed description of the invention and different embodiments thereof in which reference is made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:-

Figure 1 is an elevation of a prior art cell tray showing the design of the heat dissipating fin;

Figure 2 is an elevation of one embodiment of heat sink panel according to the invention;

Figure 3 is an elevation of a cell tray embodying the heat sink panel illustrated in Figure 2;

Figure 4 is a reverse elevation of the cell tray illustrated in Figure 3 from the opposite side thereof; Figure 5 is the same as Figure 3 but illustrating one variation thereof;

Figure 6 is a perspective illustration of a battery module made up of multiple cell stacks embodying cell trays as illustrated in Figures 3 and 4;

Figure 7 is a perspective view showing the cell trays of two cell stacks opened out in the manner of a book and showing one face of one cell tray and the opposite face of the other cell tray and a pouch cell in exploded relationship relative thereto;

Figure 8 is an elevation similar to Figure 2 but illustrating an alternative embodiment of the invention;

Figure 9 is an elevation similar to Figure 2 but illustrating a further alternative embodiment of the invention; and,

Figure 10 is an elevation similar to Figure 2 but illustrating a still further embodiment of the invention in which the heat dissipating fin of the heat sink panel is arranged to have a central coolant air departure region and two leading end edges of the heat dissipating fin. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

Figures 2 to 5 of the accompanying drawings illustrate one embodiment of heat sink panel (1 ) and cell tray (2) according to the invention; and Figures 6 and 7 illustrate cell trays made up into a battery module (3) that is composed of a plurality, in this instance six, series connected cell stacks (4) each of which is composed of a plurality, in this instance five, individual pouch cells (5) and associated cell trays, the general arrangement of which is well known.

Each of the heat sink panels is formed from a heat conductive metal, in this instance a suitable aluminium plate, and has an integral heat dissipating fin

(6) projecting upwards from a surrounding injection moulded plastic frame (7) that, in this instance, is moulded onto the heat sink panel so as to become permanently attached to it to form the cell tray. The plastic frame defines the cell area and provides a surround for the relevant pouch cell (5). As the heat dissipating fin and heat sink panel are integral with each other, the line of the upper edge of the plastic frame, as indicated by numeral (8) in Figure 2, may be considered to be the lower edge of the heat dissipating fin as it is along this line that heat can commence being dissipated into the air with which it is in contact.

As shown in Figure 3, in the installed position, a ceiling (1 1 ) is present over the battery modules so that the one end edge of the heat dissipating fin forms a leading end edge (1 2) towards which coolant airflow flows in use in the general direction indicated by arrow "X". The opposite end region (1 3) of the heat dissipating fin forms the coolant air departure region, in this instance in which coolant air leaves the heat dissipating fin after flowing from the leading end edge along the fin. The direction of the departure of the coolant air may be somewhat transverse to the length of the heat dissipating fin such as in the general direction indicated by arrows "Y" as a result of changing direction upwards because of buoyancy effects.

The heat dissipating fin has a portion thereof nearer the leading end edge removed to form an aperture (1 5) and render the surface area of the heat dissipating fin asymmetric about a position in between the leading end edge and the coolant air departure region of the heat dissipating fin. In this instance the aperture (1 5) is of generally rectangular shape with a lower boundary of the rectangle approximately coincident with the outer periphery of the plastic frame.

The rectangular aperture has a length that is just short of one half of the length of the heat dissipating fin, and a height of about one half of the height of the heat dissipating fin and is located a short distance, of the order of 5 mm, inwards from the leading end edge (1 2) of the heat dissipating fin. This leaves a narrow pillar formation (1 6) connecting an elevated part (1 7) of the heat dissipating fin with the heat sink itself in order to contribute significantly to the robustness of the heat dissipating fin and heat sink. The fin thus consists of a single fin located predominantly towards one side of the heat sink so that coolant the air travels firstly across the aperture section and then along the uninterrupted fin.

The configuration described above is presently preferred from a practical point-of-view as the fin is protected and not easily damaged. However, it is important to note that the computational fluid dynamics (CFD) study indicated that the further the rectangular aperture is from the leading end edge of the fin, the worse the thermal performance appears to become, possibly because the air heats up as it flows across the aluminium pillar created between the leading end edge and the rectangular aperture.

It is to be mentioned that the height of the ceiling in the instance mentioned above was 30 mm and the computational fluid dynamics (CFD) study also indicated the ceiling height is critical to the efficiency of the heat dissipating fin. The vertical height of the leading end edge of the fin is also indicated as playing a vital role in the thermal performance of the fin. The longer the leading edge the better should be the performance. A reduction in the ceiling height dramatically is indicated as reducing fin thermal performance. It is also to be noted that the presence of the ceiling above the fin positively affects the thermal performance due to a tunnel effect that it creates for the flow of coolant air.

The fin design described above, when applied to a heat sink panel measuring about 207 mm wide by about 160 mm high (including a heat dissipating fin height of 25 mm), has been estimated in the computational fluid dynamics (CFD) study to yield a reduction of about 7.3 ^QC in the average cell contact surface temperature when compared to that of the prior art fin design. However, it was also estimated that a more significant reduction of about 13.5 ^QC in the average cell contact surface temperature could be brought about if it were possible to raise the ceiling height from 30 to 45mm in the instance described above.

The temperature distribution within the cell contact surface is also more uniform. Since temperature uniformity across the cell is improved, charging and discharging of the cells are also more uniform making cell management more efficient. Temperature uniformity furthermore results in more uniform cell aging, a factor that is highly significant.

Of course, cooling efficiency is sensitive to total surface area of the fin, and if the fin is too small, it may not be sufficiently effective.

The thermal performance can be further improved by thermally insulating the lower edge of the aperture (removed fin section). This is to try and ensure that the cold air remains cold for longer until it reaches a central section of the heat sink where heat is drawn out. As illustrated in Figure 5, the lower edge of the aperture may be covered with a non-heat conductive material that is illustrated in the form of a separate insert (18). The lower edge of the aperture may, in this instance, be lower than the lower edge (20) of the heat dissipating fin such that the upper surface of the insert is on a level with that lower edge of the heat dissipating fin which corresponds to the upper edge of the frame, as indicated in Figure 5.

Such a non-heat conductive cover for the lower edge of the aperture may, alternatively, be formed by allowing an integrally moulded part of a surrounding plastic frame of the cell area of a cell tray to flow around the lower edge of the aperture to attach a transverse side (1 9) of the plastic frame to the reverse side of the panel as shown in Figure 3. There are a number of alternative possibilities, not all of which are equally effective or practical. In particular, the heat sink panel itself could be of a somewhat different shape to provide the required asymmetry occasioned by a removed section. As shown in Figure 8, it is possible for an entire one half of the length of the heat dissipating fin (21 ) to be removed thereby effectively presenting a leading end edge (22) that is displaced from its normal position and is located about halfway along the length of the heat sink panel (23). As a further alternative, and as shown in Figure 9, the pillar formation (1 6) that is shown in Figures 2 to 7 could be omitted with a slot (25) extending into the heat dissipating fin from the leading end edge (26) thereof for about one half of the length of the fin. The difficulty with this arrangement is that it may not be sufficiently robust for practical use.

It will be noted that air is, in the embodiments of the invention described above, only drawn into a battery module from one end, namely that corresponding to the leading end edge of the heat dissipating fins, and consequently only one aperture or removed section is necessary towards the leading end edge of the fin facing the incoming air. However, as illustrated in Figure 10 the heat dissipating region and coolant air departure region (31 ) of the heat dissipating fin could alternatively be located in the central region of the heat sink panel with rectangular apertures (32) being provided towards each of the two opposite ends of the fin so that air can travel from both ends of the fin with both ends serving as leading end edges (33). In each instance air would first pass over the aperture sections and then across the central heat dissipating region of the fin to form a plume of hot air rising from the centre of the fin.

However, to utilize this fin design the arrangement of battery modules in a battery pack may need to be changed so that the two leading edges can now face two streams of incoming air. It was estimated in the computational fluid dynamics (CFD) study that about a 24.4 ^QC reduction in the average cell contact surface temperature could be effected by not installing battery modules in side-by-side pairs but allowing a battery module to draw in air from both directions parallel to the heat dissipating fins.

Numerous variations may be made to the embodiments of the invention described above without departing from the scope hereof.

Claims

A heat sink panel for a cell stack or other multiple cell battery module, the heat sink panel being heat conductive and having an integral heat dissipating fin extending along one edge of a cell area of the heat sink panel that is operatively to be in contact with, or immediately adjacent, an individual cell, wherein the heat dissipating fin has at least one leading end edge towards which coolant air is to flow, in use, and a coolant air departure region spaced from the leading end edge of the fin, the heat sink panel being characterised in that the heat dissipating fin has a portion thereof nearer the leading end edge removed to render the surface area of the heat dissipating fin asymmetric about a position in between the leading end edge and the coolant air departure region of the heat dissipating fin.

A heat sink panel as claimed in claim 1 in which the coolant air departure region is an opposite end edge region of the heat dissipating fin.

A heat sink panel as claimed in claim 1 in which the coolant air departure region is a generally centrally located region along the length of the fin in which instance the opposite end edge of the fin forms a second leading end edge of the heat dissipating fin.

A heat sink panel as claimed in any one of the preceding claims in which the removed portion of the heat sink panel is of generally rectangular shape with a lower boundary of the rectangle lying on or close to a boundary between the heat dissipating fin and the cell area of the heat sink panel.

A heat sink panel as claimed in claim 4 in which the removed portion forms a rectangular aperture through the heat dissipating fin.

6. A heat sink panel as claimed in any one of the preceding claims in which the removed portion has a length of from about one quarter to about one half of the length of the heat dissipating fin. 7. A heat sink panel as claimed in any one of the preceding claims in which the height of the removed portion is at least one half of the height of the heat dissipating fin.

A heat sink panel as claimed in any one of the preceding claims in which a lower edge of the heat dissipating fin corresponding to the removed portion is covered with non-heat conductive material either in the form of a separate insert or an integrally moulded part of a surrounding frame of the cell area of a cell tray.

A heat sink panel as claimed in any one of the preceding claims in which the heat sink panel is made of a suitable aluminium plate material.

A cell tray incorporating a heat sink panel as claimed in any one of the preceding claims and having a rectangular moulded plastic frame defining a cell area of the heat sink panel from which the integral heat dissipating fin projects outwards.

A cell tray as claimed in claim 10 in which the rectangular moulded plastic frame is moulded directly onto the heat sink panel such that the heat sink panel is permanently captive relative thereto.