A saturated fatty acid based binary phase change material for implementing temperature zoned segmentation

Abstract

The application discloses a kind of saturated fatty acid-based binary phase change materials for realizing segmented temperature control, including two non-eutectic proportions of saturated fatty acid, thereby melt blending forms two-peak clear binary phase change material of limit.The conventional solid-liquid phase change material usually only has one endothermic peak, only in single temperature interval shows good temperature control performance, difficult to adapt to the change of environmental temperature and the fluctuation of battery heating power, and saturated fatty acid-based binary phase change material in the application can form two endothermic peaks under specific ratio, so as to realize temperature control effect in two temperature intervals.When the material has two temperature control intervals, segmented temperature control can be realized, thereby improving the thermal adaptability of thermal management system.Simultaneously saturated fatty acid has the advantages of stable property, cheap price and the like, is conducive to realizing large-scale application.

Description

Technical Field

[0001] This invention relates to the field of phase change cooling technology, specifically to a saturated fatty acid-based binary phase change material for achieving segmented temperature control. Background Technology

[0002] With the rapid expansion of the global electric vehicle market, power batteries, as the power source of electric vehicles, are required to provide greater power and capacity, posing new challenges to battery technology. It is well known that power batteries release a large amount of heat during operation. If this heat cannot be dissipated into the environment in time, the battery temperature will continue to rise, leading to overheating, decreased battery performance, shortened lifespan, and in extreme cases, even explosion. To ensure the normal operation of power batteries, effective battery thermal management technologies are needed. Common battery thermal management technologies include air cooling, liquid cooling, heat pipe cooling, and PCMs (phase change materials) cooling, as well as the coupling of these technologies. PCMs cooling technology, as a passive cooling technology, has the advantages of system simplicity, low cost, and low energy consumption, and therefore has attracted much attention.

[0003] However, past research on PCMs cooling technology has mainly focused on the synthesis of composite phase change materials and system structure design, aiming to achieve higher cooling efficiency. This has largely neglected the influence of the power battery's thermal load and ambient temperature, two crucial factors in practical applications. Studies have shown that, under different heating powers, using PCMs with higher melting points can extend the operating time of the target device within its normal temperature range and facilitate cooling recovery; conversely, using PCMs with lower melting points can provide timely protection for the target device. Therefore, the selection of PCMs with appropriate melting points is strongly dependent on the applied thermal conditions.

[0004] However, in real-world applications, the thermal load on power batteries and the ambient temperature can vary significantly. If a single PCM (Power Management System) is chosen for its thermal management system, it will inevitably be unable to adapt to these constantly changing thermal loads and environments. Therefore, developing a PCM capable of adapting to different thermal loads and environments is crucial. Summary of the Invention

[0005] Purpose of the invention: To address the above-mentioned shortcomings, this invention provides a saturated fatty acid-based binary phase change material for achieving segmented temperature control. The binary bimodal phase change material is prepared using stable and inexpensive saturated fatty acids, thereby achieving better temperature control performance in multiple temperature ranges and enhancing the adaptability of the phase change material under different thermal environments and heat loads.

[0006] Technical solution: To achieve the above objectives, the present invention provides a saturated fatty acid-based binary phase change material for segmented temperature control, comprising two non-eutectic ratios of saturated fatty acids, thereby melt-blending to form a binary phase change material with clearly defined bimodal boundaries.

[0007] Specifically, one of the saturated fatty acids is lauric acid, and the other saturated fatty acid is one of myristic acid, palmitic acid, stearic acid, and arachidic acid.

[0008] Preferably, the mass fraction of lauric acid is 0.2 to 0.5. Tests show that when the mass fraction of lauric acid is in the range of 0.2 to 0.5, it is beneficial to form a clearly defined bimodal peak shape, and therefore more suitable for segmented temperature control.

[0009] Specifically, the method for calculating the bimodal temperature of the binary phase change material includes:

[0010] The phase transition onset temperature and molar enthalpy of two saturated fatty acids were obtained by calorimetry. Then, the eutectic temperature and liquidus temperature of the binary phase change material were calculated using the Schrader equation, thereby predicting the extrapolated onset temperature of the first endothermic peak and the peak temperature of the second endothermic peak.

[0011] Specifically, the method for calculating the total enthalpy of the binary phase change material includes the following steps:

[0012] S1. The heat flow curves (including heat flow-temperature and heat flow-time curves) of two saturated fatty acids, components A and B, were determined using calorimetry to obtain the phase transition initiation temperatures T of components A and B. o,A T o,B and mass enthalpy H A H B ;

[0013] S2. Calculate the eutectic temperature and eutectic ratio of binary phase change materials using the Schrader equation:

[0014]

[0015] Among them, T E X represents the eutectic temperature. A and X B These represent the mole fractions of components A and B in the eutectic system, respectively.

[0016] X A +X B =1, R is the gas constant, ΔH m,A and ΔH m,B Let ΔH represent the molar enthalpy of components A and B, respectively. m,A =H A M A ,

[0017] ΔH m,B =H B M B ;

[0018] S3. Calculate the mass enthalpy of the eutectic system:

[0019]

[0020] Among them, H E The mass enthalpy of the eutectic system, m E,A and m E,B Let m represent the mass fractions of components A and B in the eutectic system, respectively. E,A +m E,B =1;

[0021] S4. Let the mass fractions of components A and B in the binary phase change material be m and m, respectively. A and m B m A +m B =1, then the total enthalpy of the binary phase transition material is:

[0022]

[0023]

[0024] Furthermore, in step S1, the test atmosphere is air, the test temperature is room temperature to 90°C, and the heating rate is 0.2K / min.

[0025] Beneficial effects: Traditional solid-liquid phase change materials typically have only one endothermic peak and exhibit good temperature control performance only within a single temperature range. This indicates that their temperature control capability is only good within this specific temperature range and is difficult to adapt to changes in ambient temperature and fluctuations in battery heating power.

[0026] In contrast, saturated fatty acid-based binary phase change materials can form two endothermic peaks under specific ratios, thereby achieving temperature control within two temperature ranges. When the material has two temperature control ranges, segmented temperature control can be achieved, thus improving the thermal adaptability of the thermal management system. At the same time, saturated fatty acids have advantages such as stable properties and low price, which are conducive to large-scale applications. Attached Figure Description

[0027] Figure 1 (a) and (c) are respectively the temperature control principle diagram and heat flow curve diagram of the single-peak phase change material;

[0028] Figure 1 (b) and (d) are respectively the temperature control principle diagram and heat flow curve diagram of the bimodal phase change material;

[0029] Figure 2 (a) to (d) are heat flow-temperature curves of four sets of binary bimodal PCMs in the embodiments of the present invention.

[0030] Figure 3 (a) to 3(d) are binary phase diagrams of four sets of binary bimodal PCMs in the embodiments of the present invention;

[0031] Figure 4 (a) to 4(d) are the total enthalpy prediction error diagrams of the four groups of binary bimodal PCMs in the embodiments of the present invention;

[0032] Figure 5 (a) to (d) are the bimodal enthalpy distribution diagrams of the four groups of binary bimodal PCMs in the embodiments of the present invention. Detailed Implementation

[0033] To make the objectives, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0034] This invention provides a saturated fatty acid-based binary phase change material for achieving segmented temperature control, comprising two non-eutectic ratios of saturated fatty acids, which are melt-blended to form a binary phase change material with clearly defined bimodal boundaries.

[0035] like Figure 1 As shown, traditional solid-liquid phase change materials typically possess only one endothermic peak, thus exhibiting good temperature control performance only within a single temperature range. In contrast, saturated fatty acid-based binary phase change materials can form two endothermic peaks under specific ratios, thereby achieving temperature control within two temperature ranges. When a material possesses two temperature control ranges, segmented temperature control can be achieved.

[0036] This embodiment utilizes five common saturated fatty acids, namely lauric acid (LA, C... 12 H 24 O2 (98% purity), myristic acid (MA, C) 14 H 28 O2 (99% purity), palmitic acid (PA, C) 16 H 32 O2 (98% purity), stearic acid (SA, C) 18 H 36 O2 (98% purity) and arachidic acid (ArA, C) 20 H 40Binary phase change materials (PCMs) were prepared using O2 (99% purity), and their thermal storage properties were tested using CALVET, with the patterns summarized. Finally, suitable binary bimodal PCMs were selected based on enthalpy and temperature to achieve segmented temperature control.

[0037] Specifically, in this embodiment, four series of binary PCMs were prepared by melt blending: LA-MA, LA-PA, LA-SA, and LA-ArA. The specific preparation methods are as follows:

[0038] First, weigh the two fatty acids in the predetermined mass ratio into a beaker. Then, place the beaker into a heat-collecting, constant-temperature magnetic stirrer at 90°C. After the fatty acids are completely melted, turn on the stirrer and continue stirring for 1 hour to ensure uniform mixing. Finally, pour the binary mixture into a mold and cool to room temperature. The mass fraction of LA in each series is 0.1, 0.2...0.9, and the binary mixture is named according to the mass fraction of the raw materials, such as LA20-MA80, which represents a mixture consisting of 20% LA and 80% MA by mass.

[0039] The thermal storage performance of four groups of binary bimodal PCMs was characterized using Calvet calorimetry, as follows: Figure 2 As shown, the heat flux peak types of these 51 PCMs are mainly divided into three categories: clearly defined single peaks, double peaks, and double peaks with a tendency to merge. In common solid-liquid PCMs, the heating heat flux curve of a pure substance usually shows a single peak, which indicates that the substance has undergone a solid-liquid transition, such as... Figure 2 The heat flow curves of LA and MA shown in the figure both exhibit only one endothermic peak. While binary PCMs typically exhibit bimodal peaks, under eutectic ratios, structurally stable systems emerge, where the heat flow curves also show a single peak. For example, combinations such as LA60-MA40, LA80-PA20, LA90-SA10, and LA90-ArA10 all show a single peak because the mass ratios of these combinations are extremely close to the eutectic ratio, forming a eutectic system. Unlike the aforementioned eutectic systems, combinations such as LA20-MA80, LA30-PA70, and LA40-SA60 exhibit distinct and clearly defined bimodal peaks in their heat flow curves, meeting the objectives mentioned earlier.

[0040] Besides exhibiting distinct and clearly defined bimodal peaks, the process of segmented temperature control using phase change materials places special demands on the positional distribution of the two endothermic peaks. This requires considering both the battery's operating temperature and variations in the external ambient temperature. Therefore, understanding the temperature distribution patterns of bimodal phase change materials is extremely important.

[0041] In determining phase transition temperatures using DSC and Calvet methods, the thermal scanning rate significantly affects peak shape, especially when the heating rate is too rapid. This causes the peak shape to shift towards higher temperatures, which greatly influences the peak temperature and the extrapolated termination temperature. However, the extrapolated onset temperature remains relatively unchanged and is quite close to the actual phase transition temperature. Therefore, for bimodal PCMs, the extrapolated onset temperature (T0) of the first peak can be determined. m The peak temperature (T0) is used as the solidus temperature in the binary phase diagram. Meanwhile, in determining the liquidus temperature of metallic crystals, the peak temperature in the heat flow curve is usually taken as the liquidus temperature, and it is assumed that the lower the scan rate, the smaller the error. However, the Calvet calorimetry used in this embodiment has a scan rate of 0.2 K / min, which is much lower than the heating rate of ordinary DSC tests, giving it the advantage of high accuracy in peak shape determination. Therefore, this embodiment uses the peak temperature of the second peak (T0) as the solidus temperature. l This is used as the liquidus temperature in the binary phase diagram. In this way, the phase diagrams (including solidus temperature, liquidus temperature, and theoretical liquidus temperature calculated using the Schrader equation) for these four series of binary PCMs were obtained, such as... Figure 3 As shown.

[0042] like Figure 3 As shown, the solid-state temperatures of the five systems are highly consistent, and since the solid-state temperature is the extrapolated onset temperature of the first peak, it can be inferred that the binary PCMs in all proportions contain partially identical crystal structures. Variations in these identical parts cause the consistency of the solid-state temperature. Furthermore, the solid-state temperatures of these four series are very close to the eutectic temperatures calculated by the Schrader equation. In summary, the first peak of the binary bimodal PCMs is caused by the initial melting of the portion with the same structure as the eutectic system. Meanwhile, due to… Figure 3 It is evident that the experimentally obtained liquidus temperature agrees very well with the liquidus temperature calculated by the Schrader equation. This indicates that Calvet calorimetry can determine the liquidus temperature of binary bimodal PCMs at very low heating rates, while the Schrader equation can theoretically calculate the liquidus temperature of binary bimodal PCMs. Combining these two methods, one can first test the thermal properties of the two raw materials using Calvet calorimetry, and then calculate the liquidus temperature of binary bimodal PCMs with arbitrary proportions using the Schrader equation. This approach can provide a basis for predicting the position of the second peak in such materials.

[0043] Specifically, the methods for calculating the bimodal temperature of binary bimodal PCMs include:

[0044] (1) The thermal properties of components A and B were tested by Calvet calorimetry, and the heat flow-temperature and heat flow-time curves of components A and B were obtained. The test atmosphere was air, the test temperature was room temperature to 90℃, and the heating rate was 0.2K / min.

[0045] (2) Based on the heat flow curves of components A and B, the phase transition initiation temperatures T of components A and B can be obtained. o,A T o,B and mass enthalpy H A H B Then, the eutectic temperature and eutectic ratio are calculated using the Schrader equation:

[0046]

[0047] Among them, T E X represents the eutectic temperature. A and X B X represents the mole fractions of components A and B in the eutectic system, respectively. A +X B =1; R is the gas constant, R = 8.314 J / (mol·K); ΔH m,A and ΔH m,B Let ΔH represent the molar enthalpy of components A and B, respectively. m,A =H A M A ΔH m,B =H B M B ;

[0048] (3) Further utilize the Schrader equation to obtain the liquidus temperature of the binary bimodal PCMs:

[0049]

[0050] Among them, T L X represents the liquidus temperature. o X represents the mole fraction of component A in binary bimodal PCMs. A This represents the mole fraction of component A in the eutectic system obtained from the aforementioned calculations.

[0051] The process of using bimodal PCMs for battery thermal management requires not only specific requirements on the melting temperature of the PCMs, but also a reasonable total enthalpy and enthalpy distribution. Therefore, understanding the laws governing total enthalpy and enthalpy distribution is essential. The preceding section demonstrated that the first peak is caused by the partial melting of the binary bimodal PCMs with a structure consistent with the eutectic system. Therefore, it is reasonable to believe that the remaining peak is caused by the melting of a single part excluding the eutectic system. Thus, the total enthalpy of fusion should be the sum of the enthalpies of the eutectic structure and the remaining portion in the binary bimodal PCMs.

[0052] Specifically, the method for calculating the total enthalpy of the aforementioned binary bimodal PCMs includes the following steps:

[0053] S1. Similarly, the Calvet calorimetry was used to test the heat flow-temperature and heat flow-time curves of the two saturated fatty acids, namely components A and B, to obtain the phase transition initiation temperatures T of components A and B. o,A T o,B and mass enthalpy H A H B ;

[0054] S2. Calculate the eutectic temperature and eutectic ratio using the Schrader equation:

[0055]

[0056] Among them, T E X represents the eutectic temperature. A and X B X represents the mole fractions of components A and B in the eutectic system, respectively. A +X B =1, R is the gas constant, ΔH m,A and ΔH m,B Let ΔH represent the molar enthalpy of components A and B, respectively. m,A =H A M A ΔH m,B =H B M B ;

[0057] S3. Calculate the mass enthalpy of the eutectic system:

[0058]

[0059] Among them, H E The mass enthalpy of the eutectic system, m E,A and m E,B Let m represent the mass fractions of components A and B in the eutectic system, respectively. E,A +m E,B =1;

[0060] S4. Let the mass fractions of components A and B in the binary phase change material be m and m, respectively. A and m B m A +m B =1, then when m A <m E,A When the eutectic structure proportion depends on the proportion of component A, that is:

[0061]

[0062] Therefore, the mass enthalpy of the first peak is:

[0063]

[0064] The remaining portion is now component B, therefore the mass enthalpy of the second peak is:

[0065]

[0066] The total enthalpy is then:

[0067]

[0068] When m A >m E,A When the eutectic structure proportion depends on the proportion of component B, that is:

[0069]

[0070] Therefore, the mass enthalpy of the first peak is:

[0071]

[0072] The remaining portion is now component A, therefore the mass enthalpy of the second peak is:

[0073]

[0074] The total enthalpy is then:

[0075]

[0076] Combined with m B =1-m A and H E The calculation formula yields:

[0077]

[0078] Figure 4 The variation in the total enthalpy prediction error for these four series of binary PCMs is shown. It can be seen that the relative errors between the experimental and calculated values ​​are all within 10%, with the errors for the LA-PA, LA-SA, and LA-ArA systems remaining within 5%. This proves that the equation can effectively calculate the total enthalpy of the aforementioned binary PCM systems. Furthermore, since this set of equations is based on the theoretical derivation that the total enthalpy equals the sum of the enthalpy values ​​of the eutectic portion and the remaining portion, its accuracy further confirms the correctness of this theory.

[0079] Besides total enthalpy, the distribution pattern of enthalpy is equally important. Since the peak shape varies with different proportions, we will only focus on the case of a double peak, as shown in the distribution results below. Figure 5As shown in the figure, in the four series of binary bimodal PCMs, the enthalpy values ​​of both peaks exhibit a clear linear trend with changes in composition. Furthermore, in these four systems, when the mass ratio of LA is within the range of 0.2–0.5, the enthalpy values ​​of the two peaks are close, which is conducive to forming a clearly defined bimodal peak shape. At the same time, the total enthalpy value is also at a relatively high level within the entire system. Therefore, a mass ratio of LA within the range of 0.2–0.5 is more suitable for segmented temperature control.

[0080] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A saturated fatty acid-based binary phase change material for achieving segmented temperature control, characterized in that, It is formed by melt blending lauric acid and arachidic acid in a non-eutectic ratio, wherein the mass fraction of lauric acid is 0.2~0.

5. The binary phase change material has two endothermic peaks with clear boundaries and no tendency to merge, and can achieve segmented temperature control in two independent temperature ranges.

2. The saturated fatty acid-based binary phase change material according to claim 1, characterized in that, The method for calculating the bimodal temperature of the binary phase change material includes: using Calvet calorimetry in an air atmosphere, at a test temperature of room temperature to 90°C and a heating rate of 0.2 K / min, the phase change initiation temperature and molar enthalpy of lauric acid and arachidic acid are measured; then, the eutectic temperature and liquidus temperature of the binary phase change material are calculated using the Schrader equation, thereby predicting the extrapolated initiation temperature of the first endothermic peak and the peak temperature of the second endothermic peak.

3. The saturated fatty acid-based binary phase change material according to claim 1, characterized in that, The method for calculating the total enthalpy of the binary phase change material includes the following steps: S1. Using Calvet calorimetry, heat flow curves of lauric acid and arachidic acid were tested in an air atmosphere, at a test temperature of room temperature to 90°C, and at a heating rate of 0.2 K / min. The phase transition initiation temperatures of lauric acid and arachidic acid were thus obtained. , and mass enthalpy , ; S2. Calculate the eutectic temperature and eutectic ratio of binary phase change materials using the Schrader equation: in, Indicates the eutectic temperature. and These represent the mole fractions of lauric acid and arachidic acid in the eutectic system, respectively. , It is the gas constant. and These represent the molar enthalpies of lauric acid and arachidic acid, respectively. , ; S3. Calculate the mass enthalpy of the eutectic system: ， in, This represents the mass enthalpy of the eutectic system. and These represent the mass fractions of lauric acid and arachidic acid in the eutectic system, respectively. ; S4. Let the mass fractions of lauric acid and arachidic acid in the binary phase change material be respectively... and , The total enthalpy of the binary phase transition material is: ， 。

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