Coolant for immersion cooling system and immersion cooling system including the same

Abstract

To provide a coolant for an immersion cooling system, which includes cooling oil that is low-viscosity polyalphaolefin (PAO) heat transfer oil having electrical insulation properties and high heat transfer efficiency, and an immersion cooling system including the same.SOLUTION: A coolant for an immersion cooling system comprises polyalphaolefin (PAO) cooling oil polymerized via oligomerization of C5 to C15 alpha olefin monomers (α-olefin monomers), wherein the polyalphaolefin cooling oil has kinematic viscosity at 40°C of less than 10.0 cst, density at 20°C of 800 kg / m3 or lower, a specific heat capacity at 40°C of 1.5 kJ / kg K or greater, and thermal conductivity at 40°C of 0.10 W / m K or greater.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a coolant for a liquid immersion cooling system and a liquid immersion cooling system including the same, and more particularly, to a coolant for a liquid immersion cooling system including a cooling oil which is a low-viscosity polyalphaolefin (PAO) heat transfer oil having electrical insulation and high heat transfer efficiency, and a liquid immersion cooling system including the same.

Background Art

[0002] In recent years, with the rapid development of the information technology (IT) industry, a huge amount of data has been generated, and data centers, which are buildings or facilities that store and manage digital data and provide server computers and network lines for storing IT infrastructure, have been increasing.

[0003] With the development of advanced data services such as cloud and artificial intelligence (AI) technologies, the power used in data centers has increased, and the resulting heat generation phenomenon has become severe. When the servers in the data center are overloaded and overheated, the heat sinks and cooling fans of the computers cannot sufficiently cool the central processing unit (CPU) or the graphic processing unit (GPU), which may cause accidents such as the server malfunctioning or shutting down, and may even lead to the problem of data center fires due to excessive heat generation.

[0004] Therefore, in most data centers, a constant temperature and humidity control equipment is separately installed and controlled in the server room where the server rack is installed. However, in large-scale data centers, due to the large amount of heat generated, more constant temperature and humidity control equipment is required. When a large number of the constant temperature and humidity control equipment are installed, not only does the cost increase rapidly, but also the cost for driving them is high, and energy is consumed.

[0005] In addition to computer servers, storage devices used in data centers, network switches, and batteries used in various energy storage systems (ESS) generate a large amount of heat during operation. Therefore, a cooling system must be separately installed to sufficiently cool this heat.

[0006] In addition to this, conventionally, there is a system that compares the temperature and humidity of the internal air and external air of a data center, and either allows external air to flow into the interior or circulates the internal air to cool the interior of the data center. However, there is a limit to the efficiency of cooling, and there is also a problem that precise temperature and humidity control is difficult depending on the external environment.

[0007] In recent years, the immersion cooling method, which is a technology for directly immersing heat-generating electronic devices such as servers and batteries in a data center in an electrically non-conductive (non-conductive) liquid coolant for cooling, has attracted attention. The immersion cooling method can reduce the energy consumed compared to existing methods that use air cooling, has high energy efficiency, can prevent the inflow of contaminants in the air, simplifies the thermal design, and has the advantage of reducing the number of operating parts. In order to implement an excellent cooling system by the immersion cooling method, it is an important technical issue to develop a liquid coolant for immersion that has high thermal conductivity while maintaining electrical insulation.

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a coolant for an immersion cooling system containing a low-viscosity polyalphaolefin (PAO) heat transfer oil having high heat transfer efficiency, and an immersion cooling system containing the same.

[0009] The object of the present invention is not limited to the objects mentioned above. Other objects and advantages of the present invention not mentioned can be understood from the following description and can be more clearly understood from the embodiments of the present invention. Also, it can be easily understood that the objects and advantages of this specification can be achieved by the means and combinations thereof shown in the claims.

Means for Solving the Problems

[0010] According to one aspect of the present invention for achieving the above object, it includes a polyalphaolefin (PAO) cooling oil polymerized by oligomerization of a C5-C15 alpha-olefin monomer. The polyalphaolefin cooling oil has a kinematic viscosity at 40°C of less than 10.0 cst, a density at 20°C of 800 kg / m 3 The following, a heat capacity at 40°C of 1.5 kJ / kg·K or more, and a heat transfer coefficient at 40°C of 0.10 W / m·K or more, a coolant for a liquid immersion cooling system can be provided.

[0011] The flash point of the polyalphaolefin cooling oil may be 120 to 300°C.

[0012] The appearance of the polyalphaolefin cooling oil can show a bright and vivid hue.

[0013] The coolant for the liquid immersion cooling system may further include one or more additives selected from antioxidants, antifoaming agents, and corrosion inhibitors.

[0014] Based on 100% by weight of the coolant for the liquid immersion cooling system, the polyalphaolefin cooling oil may be contained in an amount of 99.0 to 99.9% by weight, and the additive may be contained in an amount of 0.1 to 1.0% by weight.

[0015] According to another aspect of the present invention, a liquid immersion cooling system including the coolant for the liquid immersion cooling system can be provided.

Advantages of the Invention

[0016] The polyalphaolefin (PAO) cooling oil according to the present invention is a heat transfer medium oil, which has high thermal conductivity and low viscosity. Therefore, the heat transfer efficiency is greatly improved, and it can exhibit excellent characteristics as a coolant for a liquid immersion cooling system.

[0017] The polyalphaolefin (PAO) cooling oil according to the present invention has excellent insulation properties and a high flash point, so when used as a coolant for a liquid immersion cooling system, it can ensure safety against various accidents and fires. In addition, it can show a bright and vivid hue in appearance.

[0018] The above-mentioned effects and the specific effects of the present invention will be described and described while explaining the embodiments for carrying out the following invention.

Brief Description of the Drawings

[0019]

Figure 1

Embodiments for Carrying Out the Invention

[0020] The above-mentioned objects, features and advantages will be described in detail below, so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement the technical idea of the present invention. When explaining the present invention, if it is determined that a specific description of the known technology related to the present invention obscures the gist of the present invention, the detailed description will be omitted. The terms described later are terms described in consideration of the functions and actions in the present invention, and the meaning of each term must be interpreted based on the content throughout this specification.

[0021] The singular expressions used in this specification include plural expressions unless the context clearly indicates otherwise.

[0022] As used herein, unless the context clearly dictates otherwise, the singular forms also include the plural referents. As used in this specification and the appended examples, the term "or" is generally used in the sense of including "and / or" unless the context clearly dictates otherwise.

[0023] As used herein, references to numerical ranges by endpoints are to be construed to include any numbers subsumed within that numerical range unless otherwise limited.

[0024] Terms such as "comprising" and "containing" in this specification are not to be construed as necessarily including all of the various components described in the specification. Some of these components may not be included, or it may be construed that additional components may be further included.

[0025] Hereinafter, the present invention will be specifically described.

[0026] The coolant for a liquid immersion cooling system according to an embodiment of the present invention includes polyalphaolefin (PAO) cooling oil. The polyalphaolefin cooling oil can be polymerized by oligomerization of C5-C15 alpha-olefin monomers, for example, by oligomerization of C8-C12 alpha-olefin monomers, or by oligomerization of C10 alpha-olefin monomers. The alpha-olefin, which is a monomer used in synthesizing the polyalphaolefin of the present invention, is an olefin having a double bond at the alpha position, and its molecular weight can be determined according to the number of carbon atoms of the alpha-olefin monomer, whereby the viscosity can be adjusted.

[0027] In the present invention, the selection of polyalphaolefin oil as the cooling oil has the advantage that the viscosity can be adjusted to be lower and the synthesis using monomers is easier compared to mineral or paraffin-based oil, which has been used as the immersion cooling material oil.

[0028] The immersion cooling oil must have electrical insulation properties, a high flash point, and it is necessary to ensure the heat transfer coefficient. In the present invention, as factors for determining the heat transfer coefficient, four factors of density, thermal conductivity, specific heat capacity, and kinematic viscosity, and the relationship between these heat transfer coefficients were organized as shown in the following relational expression 1.

[0029]

Equation

[0030] In the above relational expression 1, k represents the heat transfer coefficient, ρ represents the density, λ represents the thermal conductivity, Cp represents the specific heat capacity, and ν represents the kinematic viscosity.

[0031] As can be seen from the above relational expression 1, in order to improve the heat transfer coefficient, the kinematic viscosity (ν) must be lowered, and materials with high thermal conductivity (λ), density, and specific heat capacity are required. As a result of the physical property evaluation of the main candidate materials and the prediction of the heat transfer coefficient based on this, it was confirmed that the kinematic viscosity among the four factors has the greatest influence. In the present invention, a coolant having a high heat transfer coefficient was developed by adjusting the kinematic viscosity and thermal conductivity of the polyalphaolefin cooling oil.

[0032] Therefore, the polyalphaolefin cooling oil according to the present invention preferably has a kinematic viscosity at 40°C of less than 10.0 cst, for example, it may be 9.0 cst or less, for example, it may be 8.0 cst or less, for example, it may be 7.0 cst or less, for example, it may be 6.0 cst or less, for example, it may be 5.0 cst or less. The "kinematic viscosity" in the present invention is measured based on the method according to ASTM D445 / D7042 with reference to 40°C.

[0033] Also, the polyalphaolefin cooling oil according to the present invention may have a heat transfer coefficient at 40°C of 0.10 W / m·K or more, preferably 0.10 to 0.15 W / m·K, for example, it may be 0.12 to 0.14 W / m·K. The heat transfer coefficient in the present invention is measured based on the method according to ASTM D7896 with reference to 40°C. Considering that the heat transfer coefficient of air used in conventional data center cooling systems is 0.020 to 0.03 W / m·K, the immersion cooling oil according to the present invention has high thermal conductivity and can exhibit excellent characteristics as an immersion coolant.

[0034] The density (ρ) of the polyalphaolefin cooling oil according to the present invention may be 800 kg / m 3 or less based on 20°C, for example, it may be 600 to 800 kg / m 3 or less. The density in the present invention is measured based on the method according to ASTM D7042.

[0035] The specific heat capacity (Cp) of the polyalphaolefin cooling oil according to the present invention may be 1.5 kJ / kg·K or more based on 40°C, preferably 1.5 to 3.5 kJ / kg·K, for example, it may be 2.0 to 3.0 kJ / kg·K. The specific heat capacity in the present invention is measured based on the method according to ASTM E1269.

[0036] The flash point of the polyalphaolefin cooling oil according to the present invention is preferably 120 to 300 °C, more preferably 130 to 250 °C, still more preferably 140 to 220 °C, and even more preferably 150 to 200 °C. Considering that the flash point of gasoline, a commonly used oil, is about -42 °C and the flash point of diesel is 52 to 96 °C, the flash point of the polyalphaolefin cooling oil according to the present invention is at a considerably high level, and it is possible to suppress the heat generation phenomenon in the data center and accidents caused thereby.

[0037] The lower the acidity of the polyalphaolefin cooling oil according to the present invention, the less it affects the object to be immersed. Therefore, the acid number (AN) is preferably 0.01 mgKOH / g or less.

[0038] The appearance of the polyalphaolefin cooling oil according to the present invention is measured based on the method according to ASTM D5386 and shows a clear and bright color.

[0039] The breakdown voltage of the polyalphaolefin cooling oil according to the present invention, measured based on the method according to ASTM D149, is about 40 kV, and the volume resistivity, measured based on the method according to ASTM D991, is about 1.0×10 13 Ω·cm, so it can exhibit excellent electrical insulation properties.

[0040] The coolant for the liquid immersion cooling system according to an embodiment of the present invention may further comprise one or more additives selected from antioxidants, antifoaming agents, and corrosion inhibitors. The coolant for the liquid immersion cooling system in the present invention is also simply referred to as "liquid immersion coolant", and in order to clarify that it is in a state of being mixed with polyalphaolefin cooling oil, it is also referred to as "liquid immersion cooling oil composition".

[0041] While it is important for the immersion cooling material to maintain electrical insulation in addition to its heat transfer physical properties, most additives tend to reduce electrical insulation during compounding. Therefore, it is preferable to minimize the use of additives and also minimize the types of additives.

[0042] Therefore, according to one embodiment of the present invention, with respect to 100% by weight of the coolant for the immersion cooling system, the polyalphaolefin cooling oil is preferably contained in an amount of 99.0 to 99.9% by weight, and the additive is preferably contained in a small amount of 0.1 to 1.0% by weight.

[0043] The antioxidant reacts with radicals generated during the oxidation process in the immersion cooling material, plays a role in suppressing the chain reaction of radicals, imparts a function of improving the oxidation stability of the PAO cooling oil in a high-temperature environment, and can improve the service life. For example, toluene-based antioxidants, phenol-based antioxidants, etc. can be used. In a specific example, it may include butylated hydroxytolune (BHT), phenol alkyl ester, phenol amine, etc., but is not limited thereto. From the perspective of further enhancing the oxidation stability, a toluene-based antioxidant, for example, dibutylhydroxytoluene, can be used.

[0044] The defoaming agent plays a role in weakening the surface tension in order to suppress the generation of bubbles that may occur during the circulation of the immersion cooling material. In a specific example, it may include polyacrylates, polydimethylsiloxane, bis-(nonylphenyl)amine, etc., but is not limited thereto.

[0045] The corrosion inhibitor functions as a reducing agent to prevent oxidation of the metal material in contact with the liquid immersion coolant. For example, a triazole-based corrosion inhibitor can be used. Specifically, it may include, but is not limited to, benzotriazole.

Examples

[0046] Hereinafter, the present invention will be described in more detail with reference to production examples and experimental examples. However, the following production examples and experimental examples are only illustrative of the present invention, and the content of the present invention is not limited thereto.

[0047] <Production Example> As shown in Table 1 below, PAO cooling oils with different characteristics of Example 1, Comparative Examples 1 and 2 were produced.

[0048]

Table 1

[0049] As can be seen from Table 1 above, Example 1 showed a very low level of kinematic viscosity compared to Comparative Examples 1 and 2. This was achieved by inducing a dimer reaction instead of a trimer or tetramer formation reaction of 1-decene, which is the raw material (feedstock) during PAO synthesis, so as to adjust the viscosity downward.

[0050] <Experimental Example 1> As shown in Table 2 below, antioxidant A (butylated hydroxytoluene), B (phenol alkyl ester), and C (phenol amine) were respectively added to the PAO produced in Example 1 above to produce the liquid immersion coolant compositions (= liquid immersion coolants) of Example 2, Comparative Examples 3 to 5, and their service lives were evaluated by the evaluation method according to ASTM D6186.

[0051] The evaluation according to ASTM D6186 is a method for measuring the time required until the oxidation reaction of PAO starts under severe conditions where high temperature and oxygen are supplied, and it is a method capable of evaluating the service life of the cooling oil product. It was confirmed that by applying an antioxidant to the PAO cooling oil, the time required for the oxidation reaction to start can be delayed.

[0052] [Table 2]

[0053] <Experimental Example 2> As shown in Table 3 below, immersion cooling oil compositions were respectively produced such that the presence or absence of the defoaming agent "polyacrylate" in the PAO produced in Example 1 above was different, and it was evaluated whether bubbles were generated by the evaluation method according to ASTM D892.

[0054] A continuously circulating fluid such as immersion cooling oil generates bubbles in the process, and the generated bubbles can impose a load on equipment such as heat exchange and pumps. The evaluation according to ASTM D892 is a method for measuring the amount of bubbles generated by artificially generating bubbles and measuring the amount of bubbles again after 30 minutes to evaluate the generation of bubbles. It was confirmed that when a defoaming agent is applied to the PAO cooling oil of the present invention, the generation of bubbles can be suppressed.

[0055] [Table 3]

[0056] <Experimental Example 3> As shown in Table 4 below, immersion cooling oil compositions were respectively produced such that the presence or absence of the corrosion inhibitor "benzotriazole" in the PAO produced in Example 1 above was different, and the corrosion prevention performance by metal change evaluation was evaluated by the evaluation method according to ASTM D130.

[0057] For electronic device products such as servers to which immersion cooling water is applied, when corrosion occurs, it can cause damage to the equipment, so a corrosion prevention function is necessary. The evaluation according to ASTM D130 is a method of evaluating the metal change due to corrosion after impregnating copper metal in a liquid, and it was confirmed that this improved corrosion prevention.

[0058]

Table 4

[0059] <Experimental Example 4> To the PAO cooling oil obtained in Example 1, Comparative Examples 1 and 2 above, antioxidant dibutylhydroxytoluene 0.05 wt%, antifoaming agent polyacrylate 0.02 wt%, and corrosion inhibitor benzotriazole 0.02 wt% were added at the mixing ratio, and the final immersion cooling oil compositions (total content 100 wt%) of Example 5, Comparative Examples 8 and 9 were respectively produced.

[0060] In an environment where a server for a data center was immersed in the produced immersion cooling oil composition, the CPU load was maintained at 90%, and the memory ram load was maintained at 10 - 90%, and it was confirmed that it drove normally. At this time, although the immersion cooling oil composition was circulated at a constant flow rate sufficient for the server for the data center to be fully immersed, when the temperature rose (when exceeding 27 - 30 °C), the cooling fan was driven to maintain the temperature of the immersion cooling oil composition constant while evaluating the performance as a coolant in the data center, and it is shown in Table 5 below.

[0061]

Table 5

[0062] As can be seen from Table 5 above, in the case of Example 5 using the immersion cooling oil composition containing PAO according to Example 1, it can be seen that the average temperature of the CPU is maintained lower than that in Comparative Examples 8 and 9 using PAO of Comparative Examples 1 and 2. Thus, while having excellent cooling effect, the immersion cooling oil composition containing PAO according to Example 1 (Example 5) also has a much lower cooling power consumption compared to the immersion cooling oil compositions of Comparative Examples 8 and 9, and it was confirmed that it is very excellent also from the aspect of energy efficiency.

[0063] 0.01% by weight of dibutylhydroxytoluene, which is an antioxidant, was blended into the PAO cooling oil obtained in Example 1 above to produce the final immersion cooling oil composition (total content 100% by weight).

[0064] Regarding the above immersion cooling oil composition, in order to evaluate the actual use stability and life when applied to a data center, after immersing a data center server in the immersion cooling oil composition, the data center server was continuously operated for about 2,000 hours (12 weeks), the physical property changes of the immersion cooling oil were evaluated, shown in Table 6 below, analyzed by Fourier transform infrared spectroscopy (FT-IR), and the resulting graph is shown in FIG. 1. FT-IR analysis is a method that utilizes the principle that chemical substances absorb specific infrared wavelengths, and when changes in chemical substances occur, the absorbed wavelengths change.

[0065] The main physical properties of the immersion cooling oil before immersing the data center server and the immersion cooling oil after operating the server for 2,000 hours were compared and shown in Table 6 below and FIG. 1 (graph by Fourier transform infrared spectroscopy). The horizontal axis of FIG. 1 represents the wave number and the vertical axis represents the absorbance, and it has a specific graph according to the structure and functional groups of the chemical substance. The immersion cooling oil composition of the present invention maintains the specific graph of the chemical substance even as time passes, which means that the immersion cooling oil composition stably maintains its chemical structure even in an environment where the server is immersion-cooled.

[0066] The graph in Figure 1 shows, from the bottom up, starting from the bottommost graph, the cases of Fresh Fluid (state where no time has passed), 1 week (after 1 week), 2 weeks (after 2 weeks), 3 weeks (after 3 weeks), 4 weeks (after 4 weeks), 6 weeks (after 6 weeks), and 12 weeks (after 12 weeks).

[0067] From the results in Table 6 and Figure 1, it was confirmed that there is almost no change in the physical properties of the server for the data center before and after operation. Thus, it was also confirmed that when applying to an actual data center server, the physical properties of the immersion cooling oil composition can be stably maintained and have a long lifespan.

[0068]

Table 6

[0069] As described in more detail above with reference to the embodiments of this specification, this specification is not necessarily limited to these embodiments, and various modifications can be made within the scope that does not deviate from the technical idea of this specification. Therefore, the embodiments disclosed in this specification do not limit the technical idea of this specification, but are for the purpose of explanation, and the scope of the technical idea of the present invention is not limited by these embodiments. Therefore, it must be understood that the embodiments described above are exemplary in all aspects and not restrictive. The protection scope of this specification and the present invention should be interpreted according to the scope of the claims, and any technical idea within the equivalent scope should be interpreted as being included in the scope of rights of this specification and the present invention.

Claims

1. The present invention relates to a polyalphaolefin (PAO) refrigerant oil, the polyalphaolefin (PAO) refrigerant oil being polymerized by oligomerization of C5-C15 alpha-olefin monomers; The polyalphaolefin cooling oil is The kinematic viscosity at 40°C is less than 10.0 cst; Density at 20°C is 800 kg / m ３ is as follows: The specific heat capacity at 40°C is 1.5 kJ / kg K or more, The thermal conductivity at 40°C is 0.10 W / m K or more. Coolant for immersion cooling systems.

2. 2. The coolant for an immersion cooling system according to claim 1, wherein the polyalphaolefin coolant oil has a flash point of 120 to 300°C.

3. 2. The coolant for an immersion cooling system according to claim 1, wherein the polyalphaolefin coolant oil is polymerized by oligomerization of C8-C12 alphaolefin monomers.

4. 2. The coolant for a liquid immersion cooling system according to claim 1, wherein the polyalphaolefin coolant oil has a bright and vivid appearance.

5. 10. The coolant for use in an immersion cooling system according to claim 1, further comprising one or more additives selected from antioxidants, antifoaming agents and corrosion inhibitors.

6. For 100% by weight of the coolant for the immersion cooling system, The polyalphaolefin cooling oil is contained in an amount of 99.0 to 99.9% by weight, The coolant for use in an immersion cooling system according to claim 5 , wherein the additive is contained in an amount of 0.1 to 1.0% by weight.

7. An immersion cooling system comprising a coolant for an immersion cooling system according to any one of claims 1 to 6.

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