Coolant for immersed liquid cooling system and immersed liquid cooling system comprising same

Abstract

The present invention relates to a coolant for an immersed liquid cooling system and an immersed liquid cooling system comprising the same, and more particularly, to a coolant for an immersed liquid cooling system comprising a cooling oil which is a low-viscosity poly-alpha-olefin (PAO) heat transfer oil having electrical insulating properties and also having high heat transfer efficiency, and an immersed liquid cooling system comprising the same.

Description

Technical Field

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

[0002] Recently, 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 provide server computers, network lines, etc. for storing and managing digital data and maintaining information technology infrastructure, have also increased accordingly.

[0003] With the development of high-level data services such as cloud and artificial intelligence (AI) technologies, the power consumed in data centers has also increased, and the resulting heat generation phenomenon has become serious. When the servers in the data center overheat due to excessive load, the heat sinks or cooling fans of the computers cannot sufficiently cool the central processing unit (CPU) or the graphic processing unit (GPU). Therefore, the servers may experience failures or outages, and furthermore, a fire problem in the data center may be caused by excessive heat.

[0004] Therefore, most data centers are controlled by setting separate constant temperature and humidity devices in server rooms equipped with server racks. However, due to the large amount of heat generated in large-scale data centers, more constant temperature and humidity devices are required. When a large number of the above constant temperature and humidity devices are installed, not only does the cost increase significantly, but more expenses and energy are also consumed to drive these devices.

[0005] In addition to computer servers, storage devices, network switches, and batteries used in various energy storage systems (ESS: Energy Storage System) used in data centers generate a large amount of heat during operation. Therefore, an additional cooling system for strongly cooling the above heat should be provided.

[0006] In addition, there has been a system in the past that cools the inside of a data center by comparing the temperature and humidity of the inside air and the outside air of the data center to allow the outside air to flow into the inside or circulate the inside air, but there are limitations in that it cannot effectively cool, and there is a problem in that it is difficult to precisely control the temperature and humidity according to the external environment.

[0007] Recently, the immersion liquid cooling method, as a technology for directly immersing heat-generating electronic devices such as servers and batteries in a data center in an electrically insulating (non-conductive) liquid coolant without power supply, has been on the rise. Compared with the conventional air cooling method, the immersion liquid cooling method can reduce the energy consumption, so it has advantages such as high energy efficiency, can block the inflow of pollutants in the air, and simplifies the thermal design to reduce operating parts. In order to achieve an excellent cooling system through the immersion liquid cooling method, it has become an important technical issue to develop an immersion liquid coolant for liquid cooling with high thermal conductivity while maintaining electrical insulation. Summary of the Invention

[0008] Technical Problem

[0009] An object of the present invention is to provide a coolant for an immersion liquid cooling system including a low-viscosity poly-α-olefin (PAO) heat transfer oil having a high thermal conductivity, and an immersion liquid cooling system including the same.

[0010] The object of the present invention is not limited to the above-mentioned object, and other objects and advantages of the present invention not mentioned can be understood through the following description, and will be more clearly understood through the embodiments of the present invention. And it is obvious that the objects and advantages of the present invention can be achieved by the means shown in the claims of the invention and their combinations.

[0011] Technical Solution

[0012] In order to achieve the above object, according to an embodiment of the present invention, a coolant for an immersion liquid cooling system can be provided, including a poly-α-olefin cooling oil obtained by oligomerization polymerization of C5-C15 α-olefin monomers, and the poly-α-olefin cooling oil satisfies the following conditions: the kinematic viscosity at 40 °C is less than 10.0 cst, and the density at 20 °C is 800 kg / m 3 Hereinafter, the specific heat capacity at 40 °C is 1.5 kJ / Kg·K or more, and the heat transfer coefficient at 40 °C is 0.10 W / m·k or more.

[0013] The flash point of the above poly-α-olefin cooling oil can be 120-300 °C.

[0014] The appearance of the above poly-α-olefin cooling oil can show a clear and bright color.

[0015] The coolant for the immersion liquid cooling system may further include one or more additives selected from antioxidants, defoamers, and corrosion inhibitors.

[0016] With respect to 100 weight percentages of the coolant for the above-mentioned immersion liquid cooling system, it may contain 99.0 to 99.9 weight percentages of the above-mentioned poly-α-olefin cooling oil and 0.1 to 1.0 weight percentages of the above-mentioned additive.

[0017] According to another embodiment of the present invention, an immersion liquid cooling system containing the coolant for the above-mentioned immersion liquid cooling system can be provided.

[0018] Effects of the Invention

[0019] The poly-α-olefin cooling oil of the present invention, as a heat transfer oil, significantly improves the heat conduction efficiency due to the advantages of high thermal conductivity and low viscosity, and thus can exhibit excellent characteristics as a coolant for an immersion liquid cooling system.

[0020] The poly-α-olefin cooling oil of the present invention has excellent insulation properties, shows a high flash point, can ensure safety against various safety accidents and fires when used as a coolant for an immersion liquid cooling system, and the appearance can show a clear and distinct color.

[0021] The specific effects of the present invention will be described together with the above effects in the process of explaining the specific embodiments. Description of the Drawings

[0022] Figure 1 It is a graph showing the chemical property changes evaluated by Fourier transform infrared spectroscopy in Experimental Example 5 of the present invention. Figure 1 The horizontal axis represents the wave number (cm -1 ), and the vertical axis represents the absorbance (%T). Detailed Description of the Invention

[0023] Hereinafter, the foregoing objects, features, and advantages will be described in detail, and those of ordinary skill in the technical field to which the present invention pertains can easily implement the technical idea of the present invention based on this. In the process of describing the present invention, when it is determined that the specific description of the well-known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. The following terms are terms described after considering the functions and roles in the present invention, and the meanings of the respective terms should be interpreted based on the content of the entire specification.

[0024] Unless otherwise specified in the context, the singular expressions used in this specification include the plural expressions.

[0025] In this specification, unless otherwise clearly indicated, the content in the singular form includes the plural indicated objects. In this specification and the accompanying embodiments, unless otherwise clearly indicated, the term "or" generally uses the meaning including "and / or".

[0026] In this specification, unless otherwise specifically restricted, a numerical range referred to by an endpoint shall be construed as including all numbers within the said numerical range.

[0027] Terms such as "comprising" and "containing" in this specification shall not be construed as necessarily including the various structural elements described in the specification, but rather as possibly not including some of the structural elements, or as possibly including additional structural elements.

[0028] Hereinafter, the present invention will be specifically described.

[0029] The coolant for the immersion liquid cooling system according to an embodiment of the present invention contains poly-α-olefin cooling oil. The above poly-α-olefin cooling oil can be polymerized by the oligomerization of C5-C15 α-olefin monomers. For example, it can be polymerized by the oligomerization of C8-C12 α-olefin monomers, or by the oligomerization of C10 α-olefin monomers. The monomer α-olefin used in synthesizing the poly-α-olefin of the present invention is an olefin having a double bond at the α-site. The molecular weight can be determined according to the number of carbon atoms of the α-olefin monomer, and the viscosity can be adjusted thereby.

[0030] In the present invention, poly-α-olefin series oil is selected as the cooling oil. Compared with the mineral series or paraffin series used as immersion liquid coolant oil in the past, it has the advantages that the viscosity can be reduced by adjustment and the synthesis using monomers is relatively easy.

[0031] The immersion liquid cooling oil should have electrical insulation properties, and while having a high flash point, it is necessary to ensure the heat transfer coefficient. In the present invention, the relationships between the four factors of density, thermal conductivity, specific heat capacity, and kinematic viscosity, which are the factors for determining the heat transfer coefficient, and their heat transfer coefficients are organized into the following relational expression 1.

[0032] Relational expression 1:

[0033] In the above relational expression 1, κ represents the heat transfer coefficient, ρ represents the density, λ represents the thermal conductivity, Cp represents the specific heat capacity, and υ represents the kinematic viscosity.

[0034] As can be seen from the above relational expression 1, in order to increase the heat transfer coefficient, the kinematic viscosity (υ) should be reduced, and materials with high thermal conductivity (λ), density, and specific heat capacity are required. Evaluating the physical properties of the main candidate materials and predicting the heat transfer coefficient based on this, it is confirmed that the influence of low viscosity among the four factors is the greatest. The poly-α-olefin oil of the present invention is developed into a coolant with a high heat transfer coefficient by adjusting the kinematic viscosity and thermal conductivity.

[0035] Therefore, preferably, the poly-α-olefin cooling oil of the present invention has a kinematic viscosity of less than 10.0 cst at 40 °C. For example, it can be 9.0 cst or less, for example, it can be 8.0 cst or less, for example, it can be 7.0 cst or less, for example, it can be 6.0 cst or less, for example, it can be 5.0 cst or less. In the present invention, the "kinematic viscosity" is based on 40 °C and is measured according to the American Society for Testing and Materials D 445 / D 7042 (ASTM D 445 / D 7042) method.

[0036] Moreover, the thermal conductivity of the poly-α-olefin cooling oil of the present invention at 40 °C can be 0.10 W / m·k or more, preferably 0.10 - 0.15 W / m·k. For example, it can be 0.12 - 0.14 W / m·k. In the present invention, the thermal conductivity is based on 40 °C and is measured according to the American Society for Testing and Materials D 7896 (ASTM D 7896) method. Considering that the thermal conductivity of air used in the cooling systems of conventional data centers is 0.020 - 0.03 W / m·k, the immersion liquid cooling oil of the present invention can exhibit excellent characteristics as an immersion liquid coolant due to its high thermal conductivity.

[0037] The density (ρ) of the poly-α-olefin cooling oil of the present invention, based on 20 °C, can be 800 kg / m 3 or less. For example, it can be 600 - 800 kg / m 3 . In the present invention, the density is measured according to the American Society for Testing and Materials D 7042 (ASTM D 7042) method.

[0038] The specific heat capacity (Cp) of the poly-α-olefin cooling oil of the present invention, based on 40 °C, can be 1.5 kJ / Kg·K or more, preferably 1.5 - 3.5 kJ / Kg·K. For example, it can be 2.0 - 3.0 kJ / Kg·K. In the present invention, the specific heat capacity is measured according to the American Society for Testing and Materials E 1269 (ASTM E 1269) method.

[0039] Preferably, the flash point of the poly-α-olefin cooling oil of the present invention is 120 to 300 °C, preferably 130 to 250 °C, more preferably 140 to 220 °C, and even more preferably 150 to 200 °C. Considering that the flash point of gasoline, which is a commonly used oil, is about -42 °C and the flash point of diesel is 52 to 96 °C, the flash point of the poly-α-olefin cooling oil of the present invention is at a relatively high level, which can suppress the heat generation phenomenon in the data center and the resulting safety accidents.

[0040] The lower the acidity of the poly-α-olefin cooling oil of the present invention, the less impact it has on the submerged object. Preferably, the acid number (AN) is 0.01 mg KOH / g or less.

[0041] The appearance of the poly-α-olefin cooling oil of the present invention is determined according to the ASTM D5386 method, showing a clear and bright color.

[0042] The breakdown voltage of the poly-α-olefin cooling oil of the present invention measured by the American Society for Testing and Materials D 149 (ASTM D149) method is about 40 kV, and the volume resistivity measured by the American Society for Testing and Materials D 991 (ASTM D 991) method is about 1.0×10 13 Ω·cm, which can exhibit excellent electrical insulation.

[0043] The coolant for the immersion liquid cooling system according to an embodiment of the present invention may further include one or more additives selected from antioxidants, defoamers, and corrosion inhibitors. In the present invention, the coolant for the immersion liquid cooling system is simply referred to as "immersion liquid coolant", and in order to clearly represent the state of mixing with the poly-α-olefin cooling oil, it is also referred to as "immersion liquid cooling oil composition".

[0044] In addition to the heat conduction physical properties, it is also important for the immersion liquid coolant to maintain electrical insulation. Most additives will reduce the electrical insulation when compounded. Therefore, preferably, the additives are used in a minimized manner and the types of additives are minimized.

[0045] Therefore, according to an example of the present invention, relative to 100 parts by weight of the above-mentioned coolant for the immersion liquid cooling system, preferably, it contains 99.0 to 99.9 weight percentages of the above-mentioned poly-α-olefin cooling oil, and preferably, it contains 0.1 to 1.0 weight percentages of the above-mentioned additives.

[0046] In an immersion liquid coolant, the above antioxidant plays a role in inhibiting the chain reaction of free radicals by reacting with the free radicals generated during the oxidation process, endowing the PAO cooling oil with the function of improving oxidation stability in a high-temperature environment and increasing its service life. For example, toluene-based antioxidants and phenol-based antioxidants can be used. Specific examples may include butylated hydroxytoluene (BHT), phenolalkyl ester, phenol amine, etc., but are not limited thereto. From the perspective of further improving oxidation stability, toluene-based antioxidants can be used. For example, butylated hydroxytoluene can be used.

[0047] To inhibit the bubbles that may be generated during the circulation of the immersion liquid coolant, the above defoamer plays a role in weakening the surface tension. Specific examples may include polyacrylates, polydimethylsiloxane, bis-(nonylphenyl)amine, etc., but are not limited thereto.

[0048] The above corrosion inhibitor acts as a reducing agent to prevent the oxidation of the metal material in contact with the immersion liquid coolant. For example, triazole-based corrosion inhibitors can be used. Specific examples may include benzotriazole, etc., but are not limited thereto.

[0049] Hereinafter, the present invention will be described in more detail through preparation examples and experimental examples. However, the following preparation examples and experimental examples are only used to illustrate the present invention, and the content of the present invention is not limited thereto.

[0050] Preparation Examples

[0051] As shown in Table 1 below, PAO cooling oils with different characteristics were prepared for Example 1, Comparative Example 1, and Comparative Example 2.

[0052] Table 1

[0053]

[0054] As can be seen from Table 1 above, compared with Comparative Example 1 and Comparative Example 2, the kinematic viscosity of Example 1 shows a very low level. This is because during the synthesis of PAO, the dimerization reaction of 1-decene as the feedstock was induced instead of the trimer formation reaction or the tetramer formation reaction, thereby reducing the viscosity by adjustment.

[0055] Experimental Example 1

[0056] As shown in Table 2 below, antioxidant A (dibutylhydroxytoluene), B (alkylphenol ester), and C (phenylamine) were respectively incorporated into the PAO prepared in Example 1 above to prepare the immersion liquid-cooled oil compositions (i.e., immersion liquid coolants) of Example 2 and Comparative Examples 3 to 5, and the service life was evaluated by the American Society for Testing and Materials D6186 (ASTM D6186) evaluation method.

[0057] The ASTM D6186 is a method for measuring the time required for PAO to start the oxidation reaction under severe conditions of high temperature and supplied oxygen, and it is a method capable of evaluating the service life of a cooling oil product. It can be confirmed that the time required for the start of the oxidation reaction can be delayed by using antioxidants in the PAO cooling oil.

[0058] Table 2

[0059]

[0060] Experimental Example 2

[0061] As shown in Table 3 below, immersion liquid-cooled oil compositions were respectively prepared based on the difference in whether the defoaming agent "polyacrylate" was incorporated into the PAO prepared in Example 1 above, and whether bubbles were generated was evaluated by the American Society for Testing and Materials D892 (ASTM D892) evaluation method.

[0062] In an immersion liquid-cooled oil, bubbles are generated during the continuous circulation of the fluid, and the generated bubbles will increase the load on equipment such as heat exchangers and pumps. The ASTM D892 is evaluated as a method for artificially generating bubbles and measuring the amount of generated bubbles, and then re-measuring the amount of bubbles after 30 minutes to evaluate bubble generation. It was confirmed that when a defoaming agent is used in the PAO cooling oil of the present invention, bubble generation can be suppressed.

[0063] Table 3

[0064]

[0065] Experimental Example 3

[0066] As shown in Table 4 below, immersion liquid-cooled oil compositions were respectively prepared based on the difference in whether the corrosion inhibitor "benzotriazole" was incorporated into the PAO prepared in Example 1 above, and the corrosion protection function evaluated by metal change was evaluated according to the American Society for Testing and Materials D130 (ASTM D130) evaluation method.

[0067] When electronic instrument products such as servers using immersion liquid-cooled oil are corroded, equipment damage will occur, so a corrosion protection function is required. The ASTM D130 is evaluated as a method for immersing metallic copper in a liquid and evaluating the change of the metal with corrosion, and through this, it was confirmed that the corrosion protection was improved.

[0068] Table 4

[0069]

[0070] Experimental Example 4

[0071] To the PAO cooling oils obtained in the above Example 1, Comparative Example 1, and Comparative Example 2, 0.05 wt% of dibutylhydroxytoluene as an antioxidant, 0.02 wt% of polyacrylate as an antifoaming agent, and 0.02 wt% of benzotriazole as a corrosion inhibitor were added to prepare the final immersion liquid cooling oil compositions of Example 5, Comparative Example 8, and Comparative Example 9 (total content is 100 wt%).

[0072] In an environment where a data center server was immersed in the immersion liquid cooling oil composition prepared above, with the CPU load maintained at 90% and the load of the memory random access memory maintained at 10 - 90%, normal operation was confirmed. In this case, the immersion liquid cooling oil composition was circulated at a specified flow rate capable of fully immersing the server for the data center. When the temperature rose (when exceeding 27 - 30°C), the immersion liquid cooling oil composition was maintained at a specified temperature by starting a cooling fan, and its performance as a coolant for the data center was evaluated and shown in Table 5 below.

[0073] Table 5

[0074]

[0075] As can be seen from Table 5 above, compared with Comparative Example 8 and Comparative Example 9 using the PAO of Comparative Example 1 and Comparative Example 2, the average temperature of the CPU of Example 5 using the immersion liquid cooling oil composition containing the PAO of Example 1 was maintained at a lower level. While having such excellent cooling effects, the cooling power consumption of the immersion liquid cooling oil composition containing the PAO of Example 1 (Example 5) was also significantly lower than that of the immersion liquid cooling oil compositions of Comparative Example 8 and Comparative Example 9, and it can be confirmed that it is also excellent in terms of energy efficiency.

[0076] 0.01 wt% of dibutylhydroxytoluene as an antioxidant was incorporated into the PAO cooling oil obtained in the above Example 1 to prepare the final immersion liquid cooling oil composition (total content is 100 wt%).

[0077] To evaluate the safety and lifespan during actual use of the above-mentioned immersion liquid cooling oil composition when applied in a data center, after immersing a server for the data center in the immersion liquid cooling oil composition, the server for the data center was kept running for about 2000 hours (12 weeks), the physical property changes of the immersion liquid cooling oil were evaluated and shown in Table 6 below, and Fourier transform infrared spectroscopy (FT-IR) analysis was carried out. The resulting curve graph is as Figure 1 shown. FT-IR analysis is a method that utilizes the principle of the inherent infrared wavelength absorption of chemical substances. When the chemical substance changes, the absorbed wavelength is different.

[0078] Comparing the main physical properties of the immersion liquid cooling oil before immersing the server for the data center with the immersion liquid cooling oil after the server has run for 2000 hours after being immersed in the immersion liquid cooling oil, the results are as shown in Table 6 below and Figure 1 (the curve graph of Fourier transform infrared spectroscopy method). Figure 1 The horizontal axis of represents the wave number, and the vertical axis represents the absorbance, and has an inherent curve according to the structure and functional groups of the chemical substance. The immersion liquid cooling oil composition of the present invention still maintains the inherent curve even after the passage of time, which indicates that the immersion liquid cooling oil composition stably maintains its chemical structure in the environment of immersing the server for immersion liquid cooling.

[0079] In Figure 1 's curve graph, taking from bottom to top as the reference, from the bottommost curve upwards in turn represent fresh fluid (state without the passage of time), 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), 12 weeks (after 12 weeks).

[0080] Through the results of Table 6 and Figure 1 , it was confirmed that there was almost no change in the physical properties before and after the operation of the server for the data center. Through this confirmation, when actually applied to the data center server, the physical properties of the immersion liquid cooling oil composition can be kept stable and can have a high lifespan.

[0081] Table 6

[0082]

[0083]

[0084] As described above, the description has been made in more detail with reference to the embodiments of the present specification. However, the present specification is not limited to the above embodiments, and various modifications can be made without departing from the technical idea of the present specification. Therefore, the embodiments disclosed in the present specification are only for explaining the present invention, rather than limiting the technical idea of the present invention. The scope of the technical idea of the present invention is not limited to the above embodiments. Therefore, it should be understood that, in any aspect, the above-described embodiments are only illustrative and not restrictive. The scope of protection of the present specification and the present invention should be interpreted by the scope of the claims of the invention, and all technical ideas within the same scope should be interpreted as being included in the scope of rights of the present specification and the present invention.

Claims

1. A coolant for an immersion liquid cooling system, characterized in that: Contains polyalphaolefin cooling oils polymerized by oligomerization of C5-C15 alpha-olefin monomers, The above poly-alpha-olefin cooling oil meets the following conditions: The kinematic viscosity at 40°C is less than 10.0cst. The density at 20°C is 800 kg / m 3 the following, The specific heat capacity at 40°C is above 1.5 kJ / Kg·K. The thermal conductivity at 40°C is 0.10 W / m·K or more.

2. The coolant for the immersion liquid cooling system according to claim 1, characterized in that: The flash point of the poly-α-olefin cooling oil is 120-300°C.

3. The coolant for the immersion liquid cooling system according to claim 1, characterized in that: The poly-α-olefin cooling oil is polymerized by oligomerization of C8-C12 α-olefin monomers.

4. The coolant for the immersion liquid cooling system according to claim 1, characterized in that: The appearance of the above-mentioned poly-α-olefin cooling oil shows a clear and bright color.

5. The coolant for the immersion liquid cooling system according to claim 1, characterized in that: It also contains one or more additives selected from antioxidants, defoamers and corrosion inhibitors.

6. The coolant for the immersion liquid cooling system according to claim 5, characterized in that: With respect to 100 weight percent of the coolant for the immersion liquid cooling system, 99.0 to 99.9 weight percent of the poly-α-olefin cooling oil and 0.1 to 1.0 weight percent of the additive are included.

7. An immersion liquid cooling system, characterized in that: A coolant for an immersion liquid cooling system comprising the coolant according to any one of claims 1 to 6.

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