Immersed battery pack thermal management system

Abstract

The invention provides an immersed battery pack heat management system, which comprises a battery pack box body filled with a heat exchange medium; the plurality of single batteries are arranged in the battery pack box body and are immersed in the heat exchange medium; the cooling box body is fixedly arranged on one side of the battery pack box body, a liquid inlet and a liquid outlet are formed in the cooling box body, and the liquid inlet and the liquid outlet are used for circularly introducing a cooling medium into the cooling box body; the plurality of heat pipes are provided with evaporation sections and condensation sections, the evaporation sections of the plurality of heat pipes are uniformly arranged in the battery pack box body, the evaporation sections are immersed in the heat exchange medium, and the condensation sections extend into the cooling box body and are immersed in the cooling medium. The single batteries are immersed in the static heat exchange medium, so that the temperature gradient is reduced, and uneven heat dissipation is avoided. The evaporation section of the heat pipe is arranged in the battery pack, and the condensation section is in contact with the dynamic cooling medium, so that efficient heat dissipation of the single battery can be realized, mechanical impact of the cooling medium on the single battery is avoided, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of battery thermal management, and in particular to an immersion battery pack thermal management system. Background Art

[0002] With the development of the new energy vehicle industry, the performance of power batteries also has an important impact on the market share of new energy vehicles. New energy vehicles have put forward higher requirements for the safety, reliability and driving range of power batteries, which requires the thermal management system of power batteries to be safer and more reliable. The commonly used cooling method for the thermal management system of power batteries is to achieve heat exchange through a liquid cooling plate structure. This cooling method has a long heat transfer path, large thermal resistance, low heat exchange efficiency, and relatively high weight and processing costs.

[0003] As a new cooling method, immersion cooling of batteries directly fills the battery pack with cooling medium and completely immerses the single battery in the cooling medium for heat exchange cooling. The current immersion cooling method removes the heat of the battery by circulating coolant into the battery pack. However, the flow speed and direction of the coolant in the box are uneven, which will cause the batteries in some areas to dissipate heat faster, while other areas will dissipate heat more slowly, resulting in a temperature gradient. Therefore, the current immersion cooling method is difficult to achieve stable and uniform heat dissipation of the battery. In addition, the fluid pressure generated when the coolant circulates in the battery box and the long-term direct impact of the coolant on the single battery will cause certain damage to the single battery. Summary of the invention

[0004] In view of this, the present invention proposes an immersion type battery pack thermal management system to solve the problems of insufficient uniformity of battery heat dissipation temperature and damage to the battery cell caused by the impact of coolant on the single battery in the traditional immersion type thermal management system.

[0005] The technical solution of the present invention is achieved in this way:

[0006] The present invention provides an immersion battery pack thermal management system, comprising:

[0007] A battery pack box, wherein the battery pack box is filled with a heat exchange medium;

[0008] A plurality of single cells are arranged in a battery pack box and immersed in a heat exchange medium;

[0009] The cooling box is fixedly arranged on one side of the battery pack box, and is provided with a liquid inlet and a liquid outlet, and the liquid inlet and the liquid outlet are used to circulate the cooling medium into the cooling box;

[0010] A plurality of heat pipes are provided, each having an evaporation section and a condensation section. The evaporation sections of the plurality of heat pipes are evenly arranged in the battery pack box, and the evaporation sections are immersed in the heat exchange medium, and the condensation sections extend into the cooling box and are immersed in the cooling medium.

[0011] On the basis of the above technical solution, preferably, it also includes a plurality of static fins vertically arranged in the battery pack body, a plurality of single cells are vertically arranged to form a plurality of battery groups, a static fin is arranged on both sides of each row of battery groups, and the side of the static fin away from the battery group is in contact with the evaporation section of the heat pipe, and the heat pipe is a flat plate structure.

[0012] Further, preferably, enclosing fins are vertically arranged on both sides of the single cells in the battery pack, and the enclosing fins are respectively vertically fixedly connected to the static fins on both sides of the battery pack.

[0013] Based on the above technical solution, preferably, the liquid inlet and the liquid outlet are respectively located on both sides of the length direction of the cooling box, and the liquid inlet is located below the condensation section, and the liquid outlet is located above the condensation section, and the flow direction of the liquid inlet and the liquid outlet is perpendicular to the surface of the heat pipe.

[0014] On the basis of the above technical solution, preferably, it further comprises a fin heat sink, wherein the fin heat sink is fixedly arranged between two adjacent condensation sections.

[0015] On the basis of the above technical solution, preferably, a plurality of condensing sections of the heat pipe are arranged at equal intervals along the height direction of the evaporating section, and the fin heat sink is fixedly arranged between two adjacent condensing sections in the horizontal direction.

[0016] On the basis of the above technical solution, preferably, the fin heat sink includes fixed fins and dynamic fins, the fixed fins are fixedly connected to the side wall of the condensation section, and a plurality of dynamic fins are provided, and the plurality of dynamic fins are vertically arranged between two fixed fins at equal intervals along the width direction of the cooling box.

[0017] On the basis of the above technical solution, preferably, the cooling box body is provided with upper and lower fixing plates, and the fixing plates are provided with positioning grooves for fixing the single battery in the axial direction.

[0018] Preferably, the static fins and the enclosure fins are integrally formed.

[0019] Preferably, the heat exchange medium is a coolant made of insulating material.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) By immersing the single cell in a static heat exchange medium, the heat exchange medium provides a uniform heat conduction path on the surface of the single cell. The heat from different parts of the battery can be quickly transferred to the heat exchange medium and diffused in the heat exchange medium, reducing the temperature gradient, so that the temperature on the surface of the battery tends to be uniform, avoiding the uneven heat dissipation problem caused by uneven coolant flow rate and direction. By evenly arranging the evaporation section of the heat pipe in the battery pack box, it can effectively absorb the heat from each area. At the same time, the condensation section of the heat pipe extends into the cooling box and contacts the cooling medium. The circulating cooling medium can efficiently take away the heat released by the single cell into the heat exchange medium through the heat pipe, thereby improving the heat dissipation performance of the single cell. Due to the use of heat pipes, the cooling medium is prevented from directly contacting the single cell, thereby avoiding the mechanical impact of the cooling medium on the single cell and extending the service life of the battery.

[0022] (2) Through the synergistic effect of heat pipes and static fins, the submerged battery pack thermal management system can significantly improve the temperature uniformity of the single battery. The static fins separate the battery pack, limiting the flow area of ​​the heat exchange medium, making the temperature distribution in each area more uniform. The heat pipe provides an efficient heat conduction path, quickly transferring heat from the battery pack to the circulating cooling medium.

[0023] (3) The grid structure formed by the enclosure fins and the static fins limits the flow of the heat exchange medium, so that the heat in each grid is evenly distributed. When combined with the heat pipe, the efficient heat transfer of the heat pipe further improves the uniform temperature heat dissipation effect, ensuring that the temperature of each single battery remains consistent.

[0024] (4) By arranging a finned heat sink between two adjacent condensing sections, the finned heat sink increases the heat exchange area and enhances the efficiency of heat dissipation from the condensing section to the cooling medium. The addition of the finned heat sink makes the heat evenly distributed between adjacent condensing sections, avoids local overheating, and improves the stability and safety of the system.

[0025] (5) The condensing section of the heat pipe is arranged at equal intervals along the height direction of the evaporating section to ensure uniform distribution of heat in the vertical direction of the heat pipe and avoid local overheating.

[0026] (6) By configuring the fin heat sink to consist of fixed fins and dynamic fins, the fixed fins are fixedly connected to the side wall of the condensing section of the heat pipe, providing a stable heat conduction path, and heat can be efficiently transferred to the dynamic fins and the cooling medium. The equidistant arrangement of the dynamic fins ensures that the cooling medium flows evenly between the dynamic fins, increasing the surface area for heat exchange. The dynamic fins form multiple cooling channels between the fixed fins, ensuring that the coolant can fully contact the fin surface, achieving efficient heat transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 It is a schematic diagram of the three-dimensional structure of the battery pack disclosed in the present invention;

[0029] Figure 2 It is a schematic diagram of an exploded view of the battery pack disclosed in the present invention;

[0030] Figure 3 A top view from a first perspective of the battery pack disclosed in the present invention;

[0031] Figure 4 It is a schematic diagram of the assembly structure of the heat pipe, single battery, static fin, enclosure fin and fin radiator disclosed in the present invention;

[0032] Figure 5 A top view of the battery pack disclosed in the present invention from a second perspective;

[0033] Figure 6 for Figure 5 Plane section view at AA in the middle;

[0034] Reference numerals:

[0035] 1. Battery pack box; 20. Single cell; 2. Battery pack; 3. Cooling box; 31. Liquid inlet; 32. Liquid outlet; 4. Heat pipe; 41. Evaporation section; 42. Condensation section; 5. Static fin; 6. Enclosure fin; 7. Fin radiator; 71. Fixed fin; 72. Dynamic fin; 8. Fixed plate; 81. Positioning groove. DETAILED DESCRIPTION

[0036] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] like Figure 1 As shown, combined Figure 2-6 The present invention discloses an immersed battery pack thermal management system, including a battery pack box 1, a plurality of single cells 20, a cooling box 3 and a heat pipe 4.

[0038] Among them, the battery pack box 1 is used to accommodate the single battery 20, and the battery pack box 1 is filled with a heat exchange medium. This heat exchange medium is used to directly contact the single battery 20 to achieve heat exchange. In this embodiment, the heat exchange medium in the battery pack box 1 is a coolant made of insulating material, and the above-mentioned heat exchange medium is sealed inside the battery pack box 1 and does not circulate to the outside.

[0039] Multiple single cells 20 are arranged in the battery pack box 1 and immersed in the heat exchange medium. This arrangement allows the single cells 20 to directly exchange heat with the heat exchange medium. Since the heat exchange medium does not flow inside the battery pack box 1, this helps the single cells 20 to dissipate heat evenly.

[0040] However, since the heat exchange medium is not circulated to the outside, the heat exchange medium inside the battery pack case 1 will be thermally saturated, resulting in reduced heat dissipation efficiency of the single battery 20. In the prior art, in order to improve the heat dissipation efficiency of immersion liquid cooling, a heat exchange medium is usually circulated into the battery pack case 1. Although this method can improve the heat dissipation efficiency of the single battery 20, the flow speed and direction of the heat exchange medium in the case are uneven, which will cause the batteries in some areas to dissipate heat faster, while other areas will dissipate heat more slowly, thereby causing a temperature gradient, resulting in insufficient uniformity of heat dissipation of the single battery 20 inside the battery pack case 1. At the same time, the fluid pressure generated when the heat exchange medium circulates in the battery pack case 1 and the long-term direct impact of the heat exchange medium on the single battery 20 will cause certain damage to the single battery 20.

[0041] To this end, this embodiment solves the above problem by arranging a cooling box 3 and a heat pipe 4 to cooperate with each other.

[0042] Specifically, the cooling box 3 is fixedly arranged on one side of the battery pack box 1, and a liquid inlet 31 and a liquid outlet 32 ​​are provided on the cooling box 3, and the liquid inlet 31 and the liquid outlet 32 ​​are used to circulate the cooling medium into the cooling box 3. In the actual working process, the liquid inlet 31 and the liquid outlet 32 ​​are connected to the coolant circulation system, so that the cooling medium is circulated into the cooling box 3. The heat exchange efficiency of the battery can be improved by setting the cooling box 3 and cooperating with the heat pipe 4. In this embodiment, the cooling medium can be the same as the heat exchange medium in the battery pack box 1, or cooling water can be directly used.

[0043] There are multiple heat pipes 4, each of which has an evaporation section 41 and a condensation section 42. The evaporation sections 41 of the multiple heat pipes 4 are evenly arranged in the battery pack box 1, and the evaporation sections 41 are immersed in the heat exchange medium. The evaporation section 41 is used to absorb the heat released by the heat exchange medium. The condensation section 42 extends into the cooling box 3 and is immersed in the cooling medium, and is used to transfer the absorbed heat to the cooling medium. The cooling medium circulates and can quickly take away the heat, thereby achieving efficient heat dissipation of the single battery 20.

[0044] Specifically, when the single battery 20 is working, the heat generated is absorbed by the evaporation section 41 of the heat pipe 4, the working liquid in the heat pipe 4 evaporates and absorbs heat, the vapor quickly moves along the heat pipe 4 to the condensation section 42, releases heat in the condensation section 42, and condenses into liquid under the action of the cooling medium, and the liquid flows back to the evaporation section 41 by capillary action or gravity. This cycle process can conduct heat quickly and efficiently.

[0045] In this embodiment, the single cell 20 is immersed in a static heat exchange medium, and the heat exchange medium provides a uniform heat conduction path on the surface of the single cell 20. The heat from different parts of the battery can be quickly transferred to the heat exchange medium and diffused in the heat exchange medium, thereby reducing the temperature gradient and making the temperature on the surface of the battery tend to be uniform, thereby avoiding the uneven heat dissipation problem caused by uneven coolant flow rate and direction.

[0046] By evenly arranging the evaporation section 41 of the heat pipe 4 in the battery pack box 1, the heat of each area can be effectively absorbed. At the same time, the condensation section 42 of the heat pipe 4 extends into the cooling box 3 and contacts with the cooling medium. The circulating cooling medium can efficiently take away the heat released by the single battery 20 to the heat exchange medium through the heat pipe 4, thereby improving the heat dissipation performance of the single battery 20. Due to the use of the heat pipe 4, the dynamic cooling medium is prevented from directly contacting the single battery 20, thereby avoiding the mechanical impact of the cooling medium on the single battery 20 and extending the service life of the battery.

[0047] In order to improve the uniformity of heat dissipation of the single cell 20 in the battery pack box 1, the battery pack of this embodiment also includes a plurality of static fins 5 vertically arranged in the battery pack box 1. The plurality of single cells 20 are vertically arranged to form a plurality of battery groups 2. A static fin 5 is arranged on both sides of each row of battery groups 2, and the side of the static fin 5 away from the battery group 2 is in contact with the evaporation section 41 of the heat pipe 4. The heat pipe 4 is a flat plate structure.

[0048] By adopting the above technical solution, the static fins 5 evenly divide the space inside the battery pack box 1 into several independent areas. The heat exchange medium in each area is confined to its own space, effectively reducing the flow and interference of the heat exchange medium between different areas. Since the heat exchange medium is confined to independent areas, the conduction of heat between different areas is reduced, thereby ensuring the uniformity of heat exchange of each battery group 2 and avoiding thermal management problems caused by excessive temperature gradients.

[0049] The static fins 5 fit the evaporation section 41 of the heat pipe 4, increasing the heat conduction path so that the heat generated by the battery can be transferred to the heat pipe 4 more quickly through the static fins 5. Since the flat heat pipe 4 has a larger contact area, it can transfer heat to the cooling medium more efficiently and evenly, thereby improving the heat dissipation efficiency of the entire system.

[0050] Through the synergistic effect of the heat pipe 4 and the static fins 5, the submerged battery pack thermal management system can significantly improve the temperature uniformity of the single battery 20. The static fins 5 separate the battery pack 2, limiting the flow area of ​​the heat exchange medium, making the temperature distribution in each area more uniform. The heat pipe 4 provides an efficient heat conduction path, quickly conducting heat from the battery pack 2 to the circulating cooling medium.

[0051] The solution disclosed in the above embodiment can improve the heat dissipation uniformity of multiple battery packs 2. In order to further improve the heat dissipation uniformity of the single battery 20, this embodiment adopts the following technical solution.

[0052] Specifically, enclosure fins 6 are vertically arranged on both sides of the single battery 20 in the battery pack 2, and the enclosure fins 6 are respectively vertically fixedly connected to the static fins 5 on both sides of the battery pack 2. With the above technical solution, the enclosure fins 6 and the static fins 5 enclose a plurality of independent grid areas, each grid surrounds a single battery 20, and the heat exchange medium in the grid is restricted from flowing, so that the heat of each single battery 20 will not be easily transferred to other single batteries 20. The independent grid structure ensures that the temperature distribution of each single battery 20 is more uniform, reducing the temperature difference of the single batteries 20 in the battery pack 2.

[0053] The grid structure formed by the enclosure fins 6 and the static fins 5 limits the flow of the heat exchange medium, so that the heat in each grid is evenly distributed. After being combined with the heat pipe 4, the efficient heat transfer of the heat pipe 4 further improves the uniform temperature heat dissipation effect, ensuring that the temperature of each single battery 20 remains consistent.

[0054] As some preferred embodiments, the static fins 5 and the enclosure fins 6 are integrally formed, which improves the structural strength and stability of the fins inside the battery pack box 1 on the one hand, and facilitates installation inside the battery pack box 1 on the other hand.

[0055] As some preferred embodiments, the liquid inlet 31 and the liquid outlet 32 ​​are respectively located on both sides of the length direction of the cooling box 3, and the liquid inlet 31 is located below the condensation section 42, and the liquid outlet 32 ​​is located above the condensation section 42, and the flow direction of the liquid inlet 31 and the liquid outlet 32 ​​is perpendicular to the surface of the heat pipe 4.

[0056] With the above technical solution, the liquid inlet 31 is located below the condensation section 42. After the cooling medium enters the cooling box 3, it directly contacts the area below the condensation section 42, begins to absorb heat and flows upward. When the cooling medium completely fills the cooling box 3, the entire cooling section of the heat pipe 4 is completely immersed in the cooling medium. After absorbing heat, the density of the cooling medium decreases, forming natural convection, passing through the condensation section 42 from bottom to top, and taking away heat. The cooling medium flows from bottom to top, ensuring uniform cooling of the entire condensation section 42, avoiding local overheating, and improving the uniformity of heat distribution.

[0057] The condensation section 42 of the heat pipe 4 is located on the flow path of the coolant, and the cooling medium can efficiently absorb the heat released from the condensation section 42 of the heat pipe 4, further enhancing the heat transfer effect of the heat pipe 4. Since the flow direction of the cooling medium is perpendicular to the surface of the heat pipe 4, the vertical flow path of the cooling medium is in vertical contact with the surface of the heat pipe 4, which greatly increases the contact area between the cooling medium and the surface of the condensation section 42, thereby improving the cooling effect.

[0058] In order to further improve the heat exchange efficiency between the heat pipe 4 and the cooling medium, the present embodiment further provides a finned heat sink 7, which is fixedly arranged between two adjacent condensing sections 42. With such a technical solution, the finned heat sink 7 increases the efficiency of heat dissipation from the condensing section 42 to the cooling medium by increasing the heat exchange area. The addition of the finned heat sink 7 allows the heat to be evenly distributed between adjacent condensing sections 42, avoiding local overheating and improving the stability and safety of the system.

[0059] As some preferred embodiments, the condensing sections 42 of the heat pipe 4 are arranged at equal intervals along the height direction of the evaporating section 41 to ensure uniform distribution of heat in the vertical direction of the heat pipe 4 and avoid local overheating. The finned heat sink 7 is fixedly arranged between two adjacent condensing sections 42 in the horizontal direction. The finned heat sink 7 acts as a bridge between the condensing sections 42, and quickly transfers heat to the cooling medium through a horizontal heat exchange path. The fin structure increases the heat exchange area and improves the efficiency of heat dissipation to the cooling medium and the external environment.

[0060] The present embodiment discloses a preferred structural mode of the fin heat sink 7. Specifically, the fin heat sink 7 includes a fixed fin 71 and a dynamic fin 72. The fixed fin 71 is fixedly connected to the side wall of the condensation section 42. A plurality of dynamic fins 72 are provided. The plurality of dynamic fins 72 are vertically arranged between two fixed fins 71 at equal intervals along the width direction of the cooling box 3.

[0061] By adopting the above technical solution, the fixed fins 71 are fixedly connected to the side wall of the condensing section 42 of the heat pipe 4, providing a stable heat conduction path, and heat can be efficiently transferred to the dynamic fins 72 and the cooling medium. The equidistant arrangement of the dynamic fins 72 ensures that the cooling medium flows evenly between the dynamic fins 72, increasing the surface area of ​​heat exchange, and the dynamic fins 72 form multiple cooling channels between the fixed fins 71, ensuring that the coolant can fully contact the fin surface to achieve efficient heat transfer.

[0062] As some preferred embodiments, fixing plates 8 are arranged above and below the cooling box 3, and positioning grooves 81 are provided on the fixing plates 8 for fixing the single battery 20 in the axial direction. The fixing plates 8 arranged as above can stably support and fix the single battery 20 in the battery pack box 1, thereby ensuring the overall structural stability of the battery pack.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An immersion battery pack thermal management system, characterized in that: include: A battery pack box (1), wherein the battery pack box (1) is filled with a heat exchange medium; A plurality of single cells (20) are arranged in a battery pack box (1) and immersed in a heat exchange medium; A cooling box (3) is fixedly arranged on one side of the battery pack box (1), and a liquid inlet (31) and a liquid outlet (32) are provided on the cooling box (3), wherein the liquid inlet (31) and the liquid outlet (32) are used to circulate a cooling medium into the cooling box (3); A plurality of heat pipes (4) are provided, each heat pipe (4) having an evaporation section (41) and a condensation section (42), the evaporation sections (41) of the plurality of heat pipes (4) being evenly arranged in a battery pack box (1), the evaporation sections (41) being immersed in a heat exchange medium, and the condensation sections (42) extending into a cooling box (3) and being immersed in the cooling medium.

2. The submerged battery pack thermal management system according to claim 1, characterized in that: It also includes a plurality of static fins (5) vertically arranged in a battery pack box (1); a plurality of single batteries (20) are vertically arranged to form a plurality of battery groups (2); a static fin (5) is arranged on both sides of each row of battery groups (2); and a side of the static fin (5) away from the battery group (2) is in contact with an evaporation section (41) of a heat pipe (4); and the heat pipe (4) is a flat plate structure.

3. The submerged battery pack thermal management system according to claim 2, characterized in that: Enclosing fins (6) are vertically arranged on both sides of the single battery (20) in the battery pack (2), and the enclosing fins (6) are respectively vertically fixedly connected to the static fins (5) on both sides of the battery pack (2).

4. The submerged battery pack thermal management system according to claim 3, characterized in that: The liquid inlet (31) and the liquid outlet (32) are respectively located on both sides of the length direction of the cooling box (3), and the liquid inlet (31) is located below the condensation section (42), and the liquid outlet (32) is located above the condensation section (42), and the flow directions of the liquid inlet (31) and the liquid outlet (32) are perpendicular to the surface of the heat pipe (4).

5. The submerged battery pack thermal management system according to claim 4, characterized in that: It also includes a fin heat sink (7), wherein the fin heat sink (7) is fixedly arranged between two adjacent condensation sections (42).

6. The submerged battery pack thermal management system according to claim 5, characterized in that: A plurality of condensing sections (42) of the heat pipe (4) are arranged at equal intervals along the height direction of the evaporating section (41), and the fin heat sink (7) is fixedly arranged between two adjacent condensing sections (42) in the horizontal direction.

7. The submerged battery pack thermal management system according to claim 5 or 6, characterized in that: The fin heat sink (7) comprises a fixed fin (71) and a dynamic fin (72), wherein the fixed fin (71) is fixedly connected to the side wall of the condensing section (42), and a plurality of dynamic fins (72) are provided, wherein the plurality of dynamic fins (72) are vertically arranged at equal intervals along the width direction of the cooling box (3) between two fixed fins (71).

8. The submerged battery pack thermal management system according to claim 1, characterized in that: Fixing plates (8) are arranged above and below the cooling box (3), and positioning grooves (81) for fixing the single battery (20) in the axial direction are provided on the fixing plates (8).

9. The submerged battery pack thermal management system according to claim 3, characterized in that: The static fins (5) and the enclosure fins (6) are integrally formed.

10. The submerged battery pack thermal management system according to claim 1, characterized in that: The heat exchange medium is a cooling liquid made of insulating material.

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