Phase change energy storage concrete and preparation method thereof

Abstract

The invention is suitable for the technical field of materials, and provides phase change energy storage concrete and a preparation method thereof.The preparation method of the phase change energy storage concrete comprises the steps that n-decanoic acid and methyl stearate are subjected to melt blending, and a binary eutectic mixture is obtained; carrying out packaging treatment on the binary eutectic mixture by using a hollow metal material to obtain a phase change material aggregate; the preparation method comprises the following steps: uniformly mixing the cement, the fine aggregate, the coarse aggregate, the phase-change material aggregate and the human hair fiber, adding water, uniformly mixing, pouring into a mold, vibrating and compacting, standing and curing to obtain the phase-change energy-storage concrete. The thermal performance of the concrete can be improved, and meanwhile the mechanical performance of the concrete is kept. Compared with common concrete, the phase change energy storage concrete prepared in the invention has excellent thermal performance and mechanical performance, the energy storage efficiency is improved by 27.2%-38%, the phase change energy storage concrete has good applicability in the field of energy piles, and a solid foundation is laid for efficient development of geothermal energy.

Description

Technical Field

[0001] This application belongs to the field of materials technology, and particularly relates to a phase change energy storage concrete and a preparation method thereof. Background Technique

[0002] In the context of the rapid global economic growth, energy shortage and environmental pollution are becoming increasingly serious. This has led to energy becoming an important factor restricting social and economic development. Geothermal energy is highly favored for its wide distribution, large storage capacity, and environmental friendliness. As an important technology for extracting shallow geothermal energy, the heat transfer efficiency is the core factor for evaluating the working performance of energy piles.

[0003] Previous studies have improved the heat transfer efficiency of energy piles by changing the pipe burying method, operation-stop ratio, and introducing phase change materials (PCMs). Among them, the introduction of PCMs is relatively efficient in improving the heat transfer efficiency of energy piles. Phase change materials can effectively limit the temperature fluctuation of concrete under temperature loads and improve the thermal performance of energy piles by absorbing or releasing latent heat during the phase change process. Elkezza et al. used paraffin-based PCMs in energy piles and energy geo-diaphragms respectively. The experiments found that both the energy piles and energy geo-diaphragms with PCMs showed good heat transfer performance during both heating and cooling cycles. Qu et al. developed a micro-encapsulated PCM (microPCM). Introducing microPCM into energy piles can significantly improve their heat transfer efficiency. The experimental results show that the heat transfer efficiency of phase change energy piles is greater than that of traditional energy piles. In addition, the computational and experimental studies by Yang et al. have also confirmed that introducing PCMs can improve the heat transfer efficiency of energy piles. So far, many scholars have carried out a large number of studies on phase change energy storage concrete.

[0004] Although the introduction of PCMs can effectively improve the thermal performance of concrete materials. However, some studies have shown that the introduction of PCMs will lead to a reduction in the bond strength between aggregates, affect the mechanical properties of concrete, and cause a reduction in the bearing capacity of the energy pile structure. Summary of the Invention

[0005] The purpose of the embodiments of this application is to provide a preparation method of phase change energy storage concrete, aiming to improve the energy storage efficiency of phase change energy storage concrete and solve the problems that the existing concrete with PCMs has a reduction in the bond strength between aggregates, affects the mechanical properties of concrete, and causes a reduction in the bearing capacity of the energy pile structure.

[0006] The embodiments of this application are implemented as follows. A preparation method of phase change energy storage concrete includes:

[0007] Melting and blending n-decanoic acid and methyl stearate to obtain a binary eutectic mixture;

[0008] Using a hollow metal material to encapsulate the binary eutectic mixture to obtain an aggregate of phase change materials;

[0009] After uniformly mixing cement, fine aggregate, coarse aggregate, phase change material aggregates, and human hair fibers, water is added and uniformly mixed, then poured into a mold and vibrated densely. After standing and curing, phase change energy storage concrete is obtained.

[0010] Preferably, the mass ratio of water, cement, fine aggregate, coarse aggregate, phase change material aggregates, and human hair fibers is 190:375:560:(896 - 924):(146.5 - 167.5):(1.13 - 1.88).

[0011] The embodiment of the present application also provides a kind of phase change energy storage concrete, and the phase change energy storage concrete is prepared by the preparation method of the above-mentioned phase change energy storage concrete.

[0012] In the embodiment of the present application, capric acid and methyl stearate are first melt-blended, and then encapsulated with hollow metal materials to obtain phase change material aggregates. Furthermore, the phase change material aggregates are uniformly mixed with cement, fine aggregate, coarse aggregate, human hair fibers, and water to prepare phase change energy storage concrete. The present application can improve the thermal performance of concrete while maintaining its mechanical properties. Compared with ordinary concrete, the phase change energy storage concrete prepared by the present application is superior in thermal performance and mechanical properties, and the energy storage efficiency is increased by 27.2% - 38%. It has good applicability in the field of energy piles, laying a solid foundation for the efficient development of geothermal energy. Description of the Drawings

[0013] Figure 1 It is the theoretical phase diagram of the DA / MS-PCMs binary eutectic mixture provided by the embodiment of the present application;

[0014] Figure 2 It is the theoretical prediction phase diagram of the fatty acid binary eutectic provided by the embodiment of the present application;

[0015] Figure 3 It is the DSC curve diagram of the DA / MS-PCMs eutectic mixture provided by the embodiment of the present application;

[0016] Figure 4 It is the schematic diagram of the PCMs-HSB preparation process provided by the embodiment of the present application;

[0017] Figure 5 It is the test result of the compressive strength of the DA / MS-HF concrete provided by the embodiment of the present application;

[0018] Figure 6 It is the test result of the thermal conductivity of the DA / MS-HF concrete provided by the embodiment of the present application;

[0019] Figure 7The test results of the specific heat capacity of DA / MS-HF concrete provided by the embodiments of the present application;

[0020] Figure 8 The CTE test results of DA / MS-HF concrete provided by the embodiments of the present application;

[0021] Figure 9 The numerical model of DA / MS-HF concrete provided by the embodiments of the present application;

[0022] Figure 10 The temperature change curve of the center point of the concrete provided by the embodiments of the present application;

[0023] Figure 11 The internal temperature change of DA / MS-HF concrete provided by the embodiments of the present application;

[0024] Figure 12 The energy storage efficiency of DA / MS-HF concrete provided by the embodiments of the present application;

[0025] Figure 13 Regression analysis of the energy storage efficiency of DA / MS-HF concrete provided by the embodiments of the present application: (a) Heating condition (b) Cooling condition. Detailed implementation manners

[0026] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0027] The embodiments of the present application provide a preparation method of phase change energy storage concrete, including:

[0028] Melting and blending n-decanoic acid and methyl stearate to obtain a binary eutectic mixture;

[0029] Using a hollow metal material to encapsulate the binary eutectic mixture to obtain a phase change material aggregate;

[0030] After uniformly mixing cement, fine aggregate, coarse aggregate, phase change material aggregate and human hair fiber, adding water and uniformly mixing, then pouring into a mold, vibrating and compacting, and after standing and curing, phase change energy storage concrete is obtained.

[0031] Among them, the n-decanoic acid (DA) with a purity of 98% and methyl stearate (MS) with a purity of 99% used in the specific embodiments of the present application are provided by Shanghai Macklin Biochemical Co., Ltd. and Guangdong Daxiao Chemical Co., Ltd. respectively. Table 1 below lists their chemical compositions and theoretical thermal property data.

[0032] Table 1. Chemical composition and thermal properties of PCM

[0033] Material Molecular formula Molecular weight Density (g / ml) Melting point (°C) Latent heat (J / g) DA <![CDATA[C 10 H 20 O 2 > 172.26 0.893 27-32 142.5 MS <![CDATA[C 19 H 38 O 2 > 298.5 0.84 37-41 189.2

[0034] Among them, according to Chinese standard ISO R679, in the specific embodiments of this application, 32.5-grade ordinary Portland cement and river sand with a fineness modulus of 2.5 are used as fine aggregates. The coarse aggregates are selected as continuously graded limestone gravel with a particle size of 20 - 25 mm. The human hair fiber (HF) is selected as human hair with a length of 20 mm.

[0035] In the embodiments of this application, the mass ratio of water, cement, fine aggregate, coarse aggregate, phase change material aggregate, and human hair fiber is 190:375:560:(896 - 924):(146.5 - 167.5):(1.13 - 1.88), preferably 190:375:560:896:167.5:1.88.

[0036] In the embodiments of this application, in the step of melting and blending n - decanoic acid and methyl stearate to obtain the DA / MS - PCMs binary eutectic mixture, the molar ratio of n - decanoic acid to methyl stearate is (71 - 75):(25 - 29); 5. The temperature of melting and blending is 19.8 - 22.4 °C, and the time is 20 - 30 min. The phase diagram and theoretical data of the eutectic mixture predicted by the following formulas (1) and (2) are as Figure 1 shown. The theoretical eutectic point of the DA / MS - PCMs binary eutectic mixture is a molar ratio of 73 / 27, the phase change temperature is 21.85 °C, and the phase change latent heat is 151.99 J / g.

[0037] The prediction formulas for the phase change temperature and phase change latent heat of the binary eutectic mixture are as follows:

[0038]

[0039] Among them, T m is the predicted phase change temperature (K) of the eutectic mixture, T i is the phase change temperature (K) of each phase change material, R is the universal gas constant (=8.31 J / mole·K), X i is the molar percentage of the i - th component, H i is the latent heat (J / mole) of the i - th component. H m is the predicted phase change latent heat of the eutectic mixture, C PLi and C PSi are the specific heats (J / mole·K) of the i - th component in the solid phase and liquid phase under constant pressure.

[0040] As shown in Table 2, Figure 2As shown, the phase change temperatures of different fatty acid binary eutectics vary. The DA / MS-PCMs prepared in this application exhibit a phase change temperature more suitable for the operation of the energy pile system compared to other binary eutectic PCMs. The DSC curve of the DA / MS-PCMs eutectic mixture is as shown in Figure 3 , as shown in Table 3

[0041] Table 2. Predicted data of fatty acid binary eutectics

[0042]

[0043] Table 3. DSC test results of the DA / MS-PCMs eutectic mixture

[0044] Operating condition DA / MS (molar ratio) Phase change temperature (°C) Latent heat (J / g) 1 77 / 23 24.2 166.4 2 75 / 25 22.4 163.9 3 73 / 27 21.1 161.2 4 71 / 29 19.8 158.1 5 69 / 31 18.6 155.6

[0045] In the embodiment of this application, the step of encapsulating the binary eutectic mixture with a hollow metal material to obtain a phase change material aggregate includes:

[0046] Drill holes in the non-welded area of the hollow metal material to completely fill the drilled holes of the hollow metal material with the liquid binary eutectic mixture by means of vacuum adsorption, seal the drilled holes with rivets, and fill the voids with adhesive to obtain a phase change material aggregate (PCMs-HSB).

[0047] Optionally, the hollow metal material is a hollow steel ball (HSB) made of stainless steel. The HSB parameters are shown in Table 4. The preparation process of PCMs-HSB is shown in Figure 4 .

[0048] Table 4. Physical properties of HSB

[0049] Item Value Inner diameter (mm) 18 Outer diameter (mm) 19 <![CDATA[Density (g / cm 3 )]]> 7.93 <![CDATA[Specific heat capacity (kJ·kg -1 K -1 )]]> 0.5 <![CDATA[Thermal conductivity (W·m -1 K -1 )]]> 16.3 <![CDATA[Coefficient of linear expansion (10 -6 ·K -1 )]]> 17.2

[0050] In the embodiment of this application, the step of mixing cement, fine aggregate, coarse aggregate, phase change material aggregate, and human hair fiber evenly, adding water for uniform mixing, pouring the mixture into a mold, vibrating it densely, and then obtaining phase change energy storage concrete after standing and curing includes:

[0051] After mixing cement, fine aggregate, coarse aggregate, phase change material aggregate, and human hair fiber evenly, add water for uniform mixing, pour the mixture into a mold, vibrate it densely, cover the mold with plastic wrap and store it at a temperature of 20°C ± 2°C for 24 - 48 h at room temperature. After demolding, cure for 7 - 28 d to obtain phase change energy storage concrete.

[0052] The preparation method of phase change energy storage concrete is described in detail below with specific examples as follows. The experimental methods used in the following examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial sources unless otherwise specified.

[0053] Example: Preparation of DA / MS-HF Phase Change Energy Storage Concrete

[0054] Caprylic acid and methyl stearate were melt-blended to obtain a binary eutectic mixture (DA / MS-PCMs); among them, the molar ratio of caprylic acid to methyl stearate was 73:27, the phase change temperature was 21.10 °C, and the phase change latent heat was 161.2 J / g.

[0055] A hand drill with a drill bit diameter of 2.5 mm was used to drill holes in the non-welded area of a stainless-steel hollow steel ball (HSB). The liquid DA / MS-PCMs was introduced into the HSB by vacuum adsorption. When no bubbles overflowed, it was considered that the HSB was completely filled. Finally, the drilled holes were sealed with rivets of the same size, and the voids were filled with AB adhesive. The encapsulated samples were called PCMs-HSB. 100 PCMs-HSB samples were randomly selected and weighed, and their density and adsorption rate were calculated to be 1364 kg / m 3 and 49.2%, respectively.

[0056] Referring to the concrete (P0H0) design, the strength grade C30 was selected, which meets the requirements of the concrete strength grade for building pile foundations. The concrete mix ratio was designed according to the volume method in Chinese standard (JGJ55-201). The calculation formulas are shown in Equations (3) and (4). To ensure the workability of the concrete, the water-cement ratio was controlled at 0.50. The test results of the concrete compressive strength showed that the compressive strength of P0H0 was 31.7 MPa, reaching the standard value of the compressive strength of C30 concrete.

[0057] To evaluate the mechanical properties and thermal characteristics of DA / MS-HF concrete, the coarse aggregate in the concrete was replaced by PCMs-HSB of equal volume, and four groups of PCMs-HSB replacement ratios (15%, 17.5%, 20% and 22.5%) were adopted. The introduction of PCMs-HSB reduced the bond strength between the aggregates, thus affecting the strength of the concrete. To compensate for the strength reduction caused by the introduction of PCMs-HSB, HF was directly incorporated at 0.2%, 0.3%, 0.4%, 0.5% and 0.6% of the cement weight. Table 5 lists the detailed mix ratios of DA / MS-HF concrete.

[0058] The preparation process of DA / MS-HF concrete includes the following steps. First, put cement, HF, coarse aggregate (including PCMs-HSB), and fine aggregate into an electric concrete mixer and stir well for 1 min. Subsequently, add water to the mixture and stir well for another 2 min. After mixing, they will be poured into plastic molds of 100 mm×100 mm×100 mm and 300 mm×300 mm×40 mm. Place the molds filled with the mixture on a vibrating table and vibrate for 1 min to achieve a dense state. Then, cover the molds with plastic wrap and store them in a laboratory at room temperature of 20℃±1℃ for 48 h. Finally, demold the samples, mark their numbers, and place them in the laboratory for curing for 28 d.

[0059]

[0060] Among them, m c0 is the cement dosage per cubic meter of concrete in the calculated mix ratio (kg / m 3 ), m f0 is the mineral admixture dosage per cubic meter of concrete in the calculated mix ratio (kg / m 3 ), m g0 is the coarse aggregate dosage per cubic meter of concrete in the calculated mix ratio (kg / m 3 ), m s0 is the fine aggregate dosage per cubic meter of concrete in the calculated mix ratio (kg / m 3 ), m w0 is the water dosage per cubic meter of concrete in the calculated mix ratio (kg / m 3 ), ρ c is the cement density (kg / m 3 ), ρ f is the mineral admixture density (kg / m 3 ), ρ g is the apparent density of fine aggregate (kg / m 3 ), ρ s is the apparent density of coarse aggregate (kg / m 3 ), ρ w is the density of water (kg / m 3 ), α is the air content percentage of concrete, and α can be taken as 1. β s is the sand ratio (%).

[0061] Table 5.1 Mix ratio design of m 3 DA / MS-HF concrete

[0062]

[0063] Compressive strength, thermal conductivity, specific heat capacity, CTE tests and error analysis were carried out on each of the concrete samples prepared in the above embodiments. Among them, the compressive strength of the concrete samples was measured according to Chinese standard (GB / T50081 - 2002); a HFM300 thermal conductivity tester produced by German Linseis Company was selected to measure the thermal conductivity of the concrete; the specific heat capacity of the concrete samples was measured by the method proposed by Cui et al. based on the law of conservation of energy; the CTE of the concrete samples was measured by the method proposed by Poore et al.; the experimental results were affected by environmental error and measurement error. The heat exchange between the model water tank and the ambient air led to environmental error. An insulating film was used to control the thermal boundary conditions of the model water tank to achieve the best heat insulation effect. Therefore, the instrument measurement error is the main source of error in this application. The relative measurement error was used to evaluate the accuracy of the test results. Table 6 lists the instrument accuracy parameters used in this application. The relative error was calculated according to Equation (5).

[0064] Table 6. Instrument Parameter Description

[0065]

[0066]

[0067] Among them, δRx i is the maximum relative error, indicating the accuracy of the test instrument, K i is the scale range of the test instrument, x i is the minimum value measured.

[0068] Test Results and Analysis:

[0069] (1) Mechanical Properties of DA / MS-HF Concrete

[0070] The test results of the compressive strength of DA / MS-HF concrete are as Figure 5 shown. The compressive strength of DA / MS-HF concrete decreases with the increase of the PCMs-HSB replacement ratio. It was observed that the compressive strength of P15H0.5 was 35.6 MPa, while the compressive strengths of P17.5H0.5, P20H0.5 and P22.5H0.5 were 2.5%, 6.7% and 14% lower than that of P15H0.5 respectively. When the PCMs-HSB replacement ratio reached 22.5%, its compressive strength was significantly insufficient compared with P0H0. Such a PCMs-HSB replacement ratio is no longer suitable for engineering applications. Therefore, it will not be considered in the subsequent thermal performance analysis of this application.

[0071] On the one hand, the introduction of PCMs-HSB reduces the bonding force between aggregates, which directly affects the integrity of concrete and results in a decrease in compressive strength. On the other hand, it can be clearly observed that the cracks developed during the failure of the samples and the spalled concrete fragments are all generated around PCMs-HSB. This indicates that during the load transfer process, stress tends to concentrate near PCMs-HSB.

[0072] Compare the effects of different HF content levels on the compressive strength of DA / MS-HF concrete. Obviously, when the HF incorporation amount is in the range of 0.2% - 0.5%. The compressive strength of DA / MS-HF concrete increases with the increase of HF content. The compressive strengths of P15H0.3, P15H0.4, and P15H0.5 are increased by 2.4%, 4.5%, and 5.6% respectively compared to P15H0.2. This shows that the addition of HF plays a certain role in connecting the crack surface of concrete, thus improving its compressive strength. However, it is observed that the compressive strength of P15H0.6 is 35.3 MPa, which is 0.8% lower than 35.6 MPa of P15H0.5. The excessive addition of HF leads to a decrease in the compressive strength of concrete. The excessive HF content level may cause HF aggregation, generating voids that are not conducive to resisting stress in the concrete, thereby further complicating the stress distribution in the concrete.

[0073] 2) Thermal properties of DA / MS-HF concrete

[0074] 2.1) Thermal conductivity

[0075] Figure 6 The test results of the thermal conductivity of DA / MS-HF concrete are shown. Compared with P0H0, the thermal conductivities of P15H0.2, P17.5H0.2, and P20H0.2 are reduced by 16.3%, 18.4%, and 23% respectively. This is because DA / MS-PCMs undergoes a phase change within the temperature range set by the HFM300 heat flux method thermal conductivity meter. And the heat energy absorbed by DA / MS-PCMs during the phase change is proportional to the addition amount of DA / MS. Therefore, the thermal conductivity of DA / MS-HF concrete decreases with the increase of the replacement rate of PCMs-HSB.

[0076] It is not difficult to find that the increase in the HF content level also reduces the thermal conductivity of DA / MS-HF concrete. However, the degree of its influence is much smaller than that of PCMs-HSB. Compared with P15H0.2, the thermal conductivities of P15H0.3, P15H0.4, P15H0.5, and P15H0.6 are reduced by 4.1%, 13.3%, 17.5%, and 25.6% respectively. This is because the incorporation of HF promotes the formation of more voids inside the concrete. On the one hand, the existence of these voids slows down the heat transfer rate. On the other hand, the irregular distribution of these voids complicates the heat flow path. Therefore, the above reasons jointly lead to the reduction of the thermal conductivity of DA / MS-HF concrete.

[0077] 2.2) Specific heat capacity

[0078] The test results of the specific heat capacity of DA / MS-HF concrete are as Figure 7 shown. The specific heat capacities of P15H0.2, P15H0.4, and P15H0.6 are 1176.3 (J·kg -1 K -1 ), 1176.5 (J·kg -1 K -1 ), and 1176.6 (J·kg -1 K -1 ), respectively. The slight changes in these values indicate that the influence of the HF content level on the specific heat capacity of DA / MS-HF concrete can be ignored.

[0079] When the initial temperature of DA / MS-PCMs > 10 °C, DA / MS-PCMs is in a liquid state at this time. When the initial temperature of DA / MS-PCMs < 10 °C, DA / MS-PCMs is in a solid state at this time. DA / MS-PCMs in different phases exhibits different specific heat capacity values. When the test condition is that DA / MS-PCMs is in a liquid state, compared with P0H0, the specific heat capacities of P15H0.2, P17.5H0.2, and P20H0.2 are increased by 13.6%, 19.2%, and 36.6% respectively. This shows that DA / MS-PCMs can effectively increase the specific heat capacity of concrete. And, with the increase of the PCMs-HSB replacement rate, the specific heat capacity of the concrete increases significantly. When DA / MS-PCMs is in a solid state, it is further increased by 11.5% - 16.5% compared with the specific heat capacity value under the liquid test condition. This is because the molecular motion modes of DA / MS-PCMs are different in the solid and liquid phases. When DA / MS-PCMs transforms from the solid phase to the liquid phase, the constraint of the molecular lattice structure gradually weakens, which enables the molecules to have greater freedom of movement. When DA / MS-PCMs transforms from the liquid phase to the solid phase, the constraint of the molecular lattice structure gradually strengthens, and the freedom of molecular movement becomes smaller. Therefore, the specific heat capacity of the concrete measured under the experimental condition of solid DA / MS-PCMs is larger.

[0080] 2.3) CTE

[0081] Figure 8 The CTE test results of DA / MS-HF concrete are shown. When the replacement rate of PCMs-HSB ranges from 15% to 20%, the overall CTE of the concrete shows a downward trend. The CTEs of P15H0.6, P17.5H0.6 and P20H0.6 decrease by 2.1%, 3.3% and 4.6% respectively compared with that of P0H0. First of all, compared with the concrete, the HSB CTE of stainless steel material is lower. Therefore, the introduction of PCMs-HSB reduces the overall CTE of the concrete. Secondly, the DA / MS-PCMs inside the PCMs-HSB absorb heat during the phase change process, providing a thermal buffering effect. This enhances the thermal stability of the concrete, thus reducing the expansion when heated.

[0082] The observed CTE of P15H0.2 is 9.04 (×10 -6 / ℃). The CTEs of P15H0.3, P15H0.4, P15H0.5 and P15H0.6 increase by 0.1%, 0.3%, 0.7% and 0.9% respectively compared with that of P15H0.2. It can be seen that the CTE of DA / MS-HF concrete will increase with the increase of the addition amount of HF. However, the influence effect is not as significant as that of PCMs-HSB. It is considered that the introduction of HF will increase the micro-pores in the concrete, and these tiny pores will make the expansion behavior of the concrete more obvious when heated. Thus, the CTE of the concrete is increased.

[0083] 4) Evaluation of energy storage efficiency

[0084] 4.1) Numerical modeling and verification

[0085] DA / MS-HF concrete will store / release heat under thermal load. The energy storage capacity of DA / MS-HF concrete is evaluated by numerical simulation. A numerical model of DA / MS-HF concrete is constructed using finite element numerical simulation software. This numerical model uses the same physical parameters as the DA / MS-HF concrete in this application. PCMs-HSB is randomly placed inside the concrete by means of built-in programming in the software ( Figure 9 ). After careful consideration, a balance is achieved between the model complexity and the objectives of this application. The following assumptions are made in this application:

[0086] (1) It is assumed that the physical properties of the material are isotropic and remain constant;

[0087] (2) The contact thermal resistance between parts is ignored;

[0088] (3) The concrete is assumed to be a two-phase composite material composed of PCMs-HSB and concrete.

[0089] To verify the accuracy of the numerical model, the test results were compared with the numerical simulation. The concrete sample wrapped with a waterproof membrane was placed in a water bath and heated to 40°C at a temperature rise rate of 10°C per hour, and then maintained for 2 hours. The temperature change curve of the center point of the concrete sample was plotted. The initial temperature of the numerical model was set to the laboratory room temperature (20°C). A temperature function matching the heating rate of the water bath was applied to the surface of the numerical model. The transient heat transfer module built into the software was used to solve the model. Equation (6) is the control equation for solid heat transfer. The numerical simulation and the test results are as Figure 10 shown.

[0090]

[0091] where ρ is the density of the material (kg / m 3 ), C p is the specific heat capacity of the material (J·kg -1 K -1 ), is the gradient operator, T, t, and u represent temperature (K), time (s), and velocity vector (m / s) respectively, k represents the thermal conductivity of the material (W·m -1 K -1 ), and Q represents the heat source (J).

[0092] Although the numerical model adopted the same parameters as the test, the differences in the test materials and the complex environmental effects led to errors in the numerical simulation. Considering a reasonable error range, it was observed that the trends of the numerical simulation and the test results were in good agreement. This verified the accuracy of the numerical model.

[0093] 4.2) Energy storage efficiency

[0094] The initial temperature of the numerical model was set to 20°C, and the size was the same as the DA / MS-HF concrete cube size of this application (100 mm × 100 mm × 100 mm). A temperature load of ΔT = 15°C was applied to one surface of the model. Figure 11 Shows the temperature distribution of the internal cross-section of DA / MS-HF concrete under heating and cooling conditions at different times. The software was used to output the average body temperature of the concrete within 4 hours, and the energy storage efficiency of the concrete was calculated using Equation (7).

[0095] Q s = C p mΔT / t (7)

[0096] where Q s represents the energy storage efficiency of the material (W), m represents the mass of the material (m), ΔT represents the temperature increase / decrease of the material (°C), and t is the heat exchange duration (s).

[0097] Figure 12 The energy storage efficiency of DA / MS-HF concrete during heating / cooling is shown. Obviously, regardless of the change in the replacement rate of PCMs-HSB, the energy storage efficiency of DA / MS-HF concrete continuously decreases and gradually stabilizes after 1 hour. During the heating condition, it is observed that the energy storage efficiency of P0 at 1 h is 4.67 W. In contrast, P15, P17.5, and P20 are 21%, 30%, and 38% higher than P0. During the cooling condition, the energy storage efficiency of P0 at 1 h is -4.67 W. P15, P17.5, and P20 are 9.2%, 13.3%, and 27.2% higher than P0. Thus, it can be seen that the DA / MS-HF concrete developed in the embodiments of the present application significantly improves the energy storage capacity of the concrete. Since the phase change temperature of DA / MS-PCMs is closer to the temperature range of the heating condition, this also results in the energy storage efficiency of the cooling condition being 10.8% - 16.7% lower than that of the heating condition.

[0098] 4.3) Regression analysis

[0099] The degree of agreement between the predicted value and the actual value can be evaluated by the non-linear fitting determined by R square. As Figure 13 shown, the R square of the curve of the energy storage efficiency of DA / MS-HF concrete varying with time is obtained by fitting with the Expdecay1 function. The fitting equation is shown in Equation (8). Under the heating condition, when the replacement rate of the phase change aggregate is 20%, the R square is the minimum value of 0.956. Obviously, Figure 13 the R square of each curve is above 0.95, which proves the reliability of the relevant results.

[0100]

[0101] where y 0 is the offset of y, x 0 is the offset of x, A 1 is the amplitude, and t 1 is the time constant.

[0102] In summary, in the embodiments of the present application, DA / MS-PCMs is prepared with DA / MS as the raw material, DA / MS-PCMs is encapsulated by HSB and replaces part of the coarse aggregate in the concrete, and at the same time HF is directly incorporated as a reinforcing material to develop a DA / MS-HF concrete. The thermal and mechanical properties of DA / MS-HF concrete with 4 kinds of PCMs-HSB replacement rates (15%, 17.5%, 20%, and 22.5%) and 5 kinds of HF content levels (0.2%, 0.3%, 0.4%, 0.5%, and 0.6%) are studied. The conclusions are as follows:

[0103] (1) The raw materials (DA and MS) for preparing the binary eutectic mixture are non-toxic and harmless, and have good economic feasibility. The binary eutectic composed of 73% DA and 23% MS in molar ratio is the DA / MS-PCMs with the best thermal performance. DA / MS-PCMs have a phase change temperature suitable for the energy pile system. Under such conditions, the high latent heat of DA / / MS-PCMs can be fully exerted.

[0104] (2) The addition of PCMs-HSB will reduce the compressive strength of concrete, and the introduction of HF can make up for this defect to a certain extent. However, a high content of HF (0.6%) will reduce the compressive strength of concrete. The compressive strength of the concrete with a PCMs-HSB aggregate replacement rate of 22.5% is lower than that of P0H0 and is no longer suitable for engineering applications. The compressive strength of P15H0.5 reaches a peak of 35.6 MPa, which is 12.3% higher than that of P0H0.

[0105] (3) The introduction of PCMs-HSB and HF can effectively reduce the thermal conductivity of concrete. The thermal conductivity of P20H0.6 is 0.787 W·m -1 ·K -1 , which is only 55.2% of that of P0H0. The specific heat capacity of DA / MS-HF concrete is positively correlated with the PCMs-HSB replacement rate. And HF does not affect the specific heat capacity of concrete. When the PCMs-HSB replacement rate is 20%, the specific heat capacity of DA / MS-HF concrete is 1391.1 (J·kg -1 K -1 ), which is 49.8% higher than that of P0H0. It can be seen that DA / MS-PCMs can significantly improve the specific heat capacity of concrete, which ensures the potential application of DA / MS-HF concrete in the energy pile system.

[0106] (4) P20H0.2 concrete exhibits the best CTE performance. After balancing the thermal performance and mechanical properties, the optimal mix ratio of DA / MS-HF concrete is considered to be P20H0.5. DA / MS-PCMs show excellent thermal performance, and HF significantly improves the influence of PCMs-HSB on the compressive strength of concrete. At the same time, the analysis of the energy storage efficiency also provides insights into the thermal performance of DA / MS-HF concrete. The energy storage efficiency of DA / MS-HF concrete is increased by 27.2% - 38% compared with ordinary concrete.

[0107] (5) This application confirms that the combined application of DA / MS-PCMs and HF in concrete can improve the thermal performance of concrete while maintaining its mechanical properties. Different proportions of incorporation content are analyzed to give the optimal mix ratio of DA / MS-HF concrete. The thermal and mechanical properties of DA / MS-HF concrete show excellent applicability in the field of energy piles. Exploring better thermal performance materials is the future research direction. Improve the heat exchange efficiency of energy piles to make efficient use of shallow geothermal energy.

[0108] The above-described embodiments merely represent several implementation manners of this application, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of this application. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several modifications and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of the patent of this application shall be subject to the appended claims.

[0109] The above is only the preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of this application shall be included in the protection scope of this application.

Claims

1. A method for preparing phase change energy storage concrete, characterized in that: include: The n-decanoic acid and methyl stearate are melt-blended to obtain a binary eutectic mixture; The binary eutectic mixture is packaged by a hollow metal material to obtain a phase change material aggregate; After cement, fine aggregate, coarse aggregate, phase change material aggregate and human hair fiber are uniformly mixed, water is added for uniform mixing, and then poured into a mold, vibrated to make it dense, and after standing and curing, phase change energy storage concrete is obtained.

2. The method for preparing phase change energy storage concrete according to claim 1, characterized in that: The mass ratio of water, cement, fine aggregate, coarse aggregate, phase change material aggregate and human hair fiber is 190:375:560:(896-924):(146.5-167.5):(1.13-1.88).

3. The method for preparing phase change energy storage concrete according to claim 1, characterized in that: The mass ratio of water, cement, fine aggregate, coarse aggregate, phase change material aggregate and human hair fiber is 190:375:560:896:167.5:1.

88.

4. The method for preparing phase change energy storage concrete according to claim 1, characterized in that: The molar ratio of n-decanoic acid to methyl stearate is (71-75):(25-29).

5. The method for preparing phase change energy storage concrete according to claim 1, characterized in that: In the step of melt-blending n-decanoic acid and methyl stearate to obtain a binary eutectic mixture, the melt-blending temperature is 19.8-22.4° C. and the time is 20-30 min.

6. The method for preparing phase change energy storage concrete according to claim 1, characterized in that: The step of encapsulating the binary eutectic mixture with a hollow metal material to obtain a phase change material aggregate comprises: Holes are drilled in non-welding areas of the hollow metal material to completely fill the liquid binary eutectic mixture into the drilled holes of the hollow metal material by vacuum adsorption, and the drilled holes are sealed with rivets and the gaps are filled with adhesives to obtain phase change material aggregates.

7. The method for preparing the phase change energy storage concrete according to claim 1 or 6, characterized in that: The hollow metal material is a hollow steel ball made of stainless steel.

8. The method for preparing phase change energy storage concrete according to claim 7, characterized in that: The inner diameter of the hollow steel ball is 18 mm, the outer diameter is 19 mm, and the density is 7.93 g / cm 3 , specific heat capacity is 0.5 kJ·kg -1 K -1 , thermal conductivity is 16.3W·m - 1 K -1 , the linear expansion coefficient is 17.2×10 -6 ·K -1 .

9. The method for preparing phase change energy storage concrete according to claim 1, characterized in that: The steps of uniformly mixing cement, fine aggregate, coarse aggregate, phase change material aggregate and human hair fiber, adding water for uniform mixing, pouring into a mold, vibrating and compacting, standing and curing to obtain phase change energy storage concrete include: After cement, fine aggregate, coarse aggregate, phase change material aggregate and human hair fiber are evenly mixed, water is added for uniform mixing and then poured into a mold, vibrated to compact, the mold is covered with plastic wrap and stored at a temperature of 20℃±2℃ for 24-48h. After demolding, it is cured for 7-28d to obtain phase change energy storage concrete.

10. A phase change energy storage concrete, characterized in that: The phase change energy storage concrete is prepared by the preparation method of the phase change energy storage concrete according to any one of claims 1-9.

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