Preparation method of composite heat exchange fluid for medium-deep geothermal energy heat removal
By preparing a composite heat exchange fluid containing 2-methyl-1,3-propanediol, water, surfactant, and nanoparticles, the problems of insufficient working fluid stability and heat transfer performance in medium-deep geothermal systems were solved, achieving efficient heat extraction and transfer.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-08
- Publication Date
- 2026-04-03
AI Technical Summary
Existing geothermal heat extraction fluids in medium-deep geothermal systems suffer from problems such as low boiling point, high evaporation, poor chemical stability, and insufficient heat capacity, making them difficult to adapt to complex wellbore and reservoir conditions. Furthermore, there is insufficient research on the synergistic effect of base fluid formulation control and nanoparticle enhancement.
A binary mixed base liquid was constructed using 2-methyl-1,3-propanediol and water, and surfactants, MWCNT, Al2O3, and SiO2 nanoparticles were added. The composite heat exchange fluid was prepared by ultrasonic vibration to improve its stability and heat transfer performance under high temperature and high pressure.
It improves the boiling point and thermal conductivity of the composite heat exchange fluid, enhances its efficiency in extracting heat from medium and deep geothermal energy, and provides a design concept for high-performance heat transfer working fluids applicable to other complex energy systems.
Smart Images
Figure CN121780139A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of geothermal energy development technology, specifically relating to a method for preparing a composite heat exchange fluid for extracting heat from medium-deep geothermal energy. Background Technology
[0002] Geothermal energy, as a renewable energy source with abundant reserves and low carbon footprint, plays a crucial supporting role in optimizing the energy structure and achieving the "dual-carbon" strategic goals through its efficient development and utilization. In geothermal energy systems, the working fluid is the key heat transfer medium used to extract heat from underground reservoirs and transfer it to the Earth's surface during geothermal energy utilization. Its performance directly determines the system's heat exchange efficiency, operational economy, and environmental friendliness. In recent years, improving the heat transfer performance of the working fluid through nanomaterial modification has become a research hotspot in the field of geothermal energy utilization.
[0003] Existing technologies have systematically studied the thermal properties, stability, and heat transfer performance of composite nanofluids, covering different combinations of nanoparticles, dispersion methods, and additive regulation, verifying their potential in enhancing heat transfer. However, existing research still has the following shortcomings: (1) Most studies use single or simple mixed base fluids (such as water, ethylene glycol, propylene glycol, etc.), which have problems such as low boiling point, high evaporation, poor chemical stability, and insufficient heat capacity under high temperature and high pressure environments, making it difficult to adapt to the complex wellbore and reservoir conditions of medium and deep geothermal systems; (2) Most current studies focus on the physical properties and heat transfer behavior of nanoparticles, while there is a significant lack of research on base fluid formulation regulation of the heat transfer upper temperature range and improvement of overall thermal properties, especially in the synergistic effect of base fluid boiling point regulation and nanoparticle enhancement. Summary of the Invention
[0004] To address the aforementioned problems, the present invention aims to provide a method for preparing a composite heat exchange fluid for extracting heat from medium-deep geothermal energy, thereby solving the problems of low boiling point and poor heat exchange performance of existing base fluids.
[0005] To achieve the above objectives, the technical solution adopted by the present invention includes: A method for preparing a composite heat exchange fluid for heat extraction from medium-deep geothermal energy includes the following steps: S1, 2-methyl-1,3-propanediol and pure water are mixed evenly to obtain a binary mixed base liquid; S2, add a surfactant to the binary mixed base liquid obtained in S1 and dissolve it to obtain the base liquid; S3, add the mixed nanoparticles to the base liquid obtained in S2 to prepare a nanoparticle suspension; S4. The nanoparticle suspension obtained in S3 is homogenized to obtain a composite heat exchange fluid for heat extraction from medium-deep geothermal energy.
[0006] Preferably, the mass ratio of 2-methyl-1,3-propanediol to water in S1 is less than or equal to 5:95.
[0007] Preferably, the surfactant in S2 is gum arabic, hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or polyvinylpyrrolidone.
[0008] Preferably, the volume concentration of the surfactant in S2 after dissolution is 0.2-1.5%.
[0009] Preferably, the mixed nanoparticles in S3 include MWCNT nanoparticles, Al2O3 nanoparticles, and SiO2 nanoparticles.
[0010] Preferably, the mass fraction of any one type of nanoparticle in the mixed nanoparticles is 5% to 90%.
[0011] Preferably, the volume concentration of the surfactant after dissolution is not higher than the volume concentration of the mixed nanoparticles in the nanoparticle suspension.
[0012] Preferably, the MWCNT nanoparticles have a diameter of 3-15 nm, a length of 15-30 μm, and a purity of >98%; the Al2O3 nanoparticles have a diameter of 10 nm and a purity of ≥99.9%; and the SiO2 nanoparticles have a diameter of 15 nm and a purity of ≥99.5%.
[0013] Preferably, the nanoparticle suspension is homogenized in an ultrasonic oscillator for 30-100 min; the ultrasonic oscillator has a power of 180 W and an ultrasonic frequency of 40 kHz.
[0014] A composite heat exchange fluid for extracting heat from medium-deep geothermal energy is prepared by the method for preparing the composite heat exchange fluid for extracting heat from medium-deep geothermal energy disclosed in this application.
[0015] Compared with the prior art, the present invention has the following technical advantages: (1) A binary mixed base liquid constructed from water and 2-methyl-1,3-propanediol is used. The high boiling point of the binary mixed base liquid can expand the liquid phase stability range of the heat exchange working fluid under high temperature conditions. (2) The three nanomaterials introduced, MWCNT (high thermal conductivity), Al2O3 (high specific surface area) and SiO2 (stable dispersion), work together to improve the thermal conductivity and density of the composite heat exchange fluid, thereby improving the heat carrying capacity of the composite heat exchange fluid. (3) The "functional mixed base liquid + composite nanoparticle" design concept proposed in this invention produces a composite heat exchange fluid with good heat exchange performance for medium-deep geothermal energy extraction. It provides a general design method and research paradigm for the subsequent development of high-performance heat transfer working fluids suitable for other complex energy systems (such as high-temperature solar heat exchange, industrial waste heat recovery, etc.). Attached Figure Description
[0016] Figure 1 This is a SEM image of the composite heat exchange fluid in Example 1; Figure 2 This is a comparison chart of density data for the composite heat exchange fluid in Example 1; Figure 3 This is a comparison chart of the thermal conductivity of the composite heat exchange fluid in Example 1; Figure 4 This is a comparison chart of density data for the composite heat exchange fluid in Example 2; Figure 5 This is a comparison chart of the thermal conductivity of the composite heat exchange fluid in Example 2; Figure 6 This is a comparison chart of the boiling points of the binary mixed base liquids in Example 1 and Example 2; Figure 7 The graph shows the heat extraction of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and the binary mixed base liquid. Detailed Implementation
[0017] In this invention, only certain exemplary embodiments have been simply described. As those skilled in the art will recognize, the described embodiments can be modified in various ways, such as by adding, deleting, or altering, without departing from the scope of the invention. Therefore, the drawings and descriptions are considered to be exemplary in nature and not restrictive. Specific embodiments of the invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the invention.
[0018] The 2-methyl-1,3-propanediol, Al2O3 nanoparticles, and SiO2 nanoparticles of this invention were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and the MWCNT nanoparticles were purchased from Shenzhen Suiheng Graphene Technology Co., Ltd.
[0019] Example 1 This embodiment provides a method for preparing a composite heat exchange fluid for mid-deep geothermal energy extraction, specifically including the following steps: S1, 2-methyl-1,3-propanediol is added to pure water at a mass ratio of 5:95 and mixed evenly to obtain a binary mixed base liquid; like Figure 6 In this embodiment, a binary mixed base liquid constructed from water and 2-methyl-1,3-propanediol has good thermal stability, which solves the problem of easy decomposition of traditional base liquids under medium-deep geothermal high temperature and high pressure conditions. S2, sodium dodecylbenzenesulfonate is added to the binary mixed base liquid obtained in S1 and dissolved. The volume concentration of the surfactant after dissolution is 0.6%, and the base liquid is obtained. S3, obtain mixed nanoparticles. In this embodiment, the mixed nanoparticles are composed of MWCNT nanoparticles, Al2O3 nanoparticles and SiO2 nanoparticles in a mass ratio of 1:8:1. The mixed nanoparticles are added to the base liquid obtained in S2 to prepare a nanoparticle suspension. The volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. In this embodiment, the MWCNT nanoparticles have a diameter of 3-15 nm, a length of 15-30 μm, and a purity >98%; the Al2O3 nanoparticles have a diameter of 10 nm and a purity ≥99.9%; and the SiO2 nanoparticles have a diameter of 15 nm and a purity ≥99.5%. S4. The nanoparticle suspension obtained in S3 was placed in an ultrasonic oscillator for homogenization for 60 min. The power of the ultrasonic oscillator was set to 180 W and the ultrasonic frequency was set to 40 kHz to obtain a composite heat exchange fluid for heat extraction from medium-deep geothermal energy.
[0020] like Figure 2 As shown, at a temperature of 60℃, the density of the composite heat exchange fluid prepared for medium-deep geothermal energy extraction is 1016.86 kg / m³. 3 Compared to binary mixed base liquids, the density increased by 7%, and the density of nanofluids decreased reasonably with increasing temperature. For example... Figure 3 As shown, at a temperature of 90℃, the thermal conductivity of the composite heat exchange fluid used for medium-deep geothermal energy extraction was 0.62 W / (m·K), which is 26% higher than that of the binary mixed base fluid. Furthermore, the thermal conductivity of the composite heat exchange fluid used for medium-deep geothermal energy extraction increases reasonably with increasing temperature.
[0021] This embodiment uses Ansys Fluent software to establish a geometric model, which includes the internal fluid computational domain of the pipe and the pipe wall structure. A pipe segment of fixed length is selected to simulate the heat extraction process of the nanofluid at a given depth. The numerical simulation employs an Eulerian-Lagrange two-phase flow model, which can describe the motion behavior of nanoparticles and their interaction with fluid heat transfer. Boundary conditions are set as a velocity inlet and a pressure outlet, and the pipe wall is set to a constant wall temperature. Momentum and energy exchange between nanoparticles and the base fluid are achieved through a bidirectional coupling method. The thermophysical parameters of the nanoparticles and the base fluid are set independently in the discrete and continuous phases, respectively.
[0022] The heat extraction of different fluids was simulated through simulation experiments, and the results are as follows: Figure 7 As shown, the heat output of the composite heat exchange fluid in this embodiment is 17559.40W per year, and the heat output of the base liquid obtained by S2 is 16414.20W per year.
[0023] Example 2 This embodiment provides a method for preparing a composite heat exchange fluid for mid-deep geothermal energy extraction, specifically including the following steps: S1, 2-methyl-1,3-propanediol is added to pure water at a mass ratio of 5:95 and mixed evenly to obtain a binary mixed base liquid; S2, sodium dodecylbenzenesulfonate is added to the binary mixed base liquid obtained in S1 and dissolved. The volume concentration of the surfactant after dissolution is 0.6%, and the base liquid is obtained. S3, obtain mixed nanoparticles. In this embodiment, the mixed nanoparticles are composed of MWCNT nanoparticles, Al2O3 nanoparticles and SiO2 nanoparticles in a mass ratio of 8:1:1. The mixed nanoparticles are added to the base liquid obtained in S2 to prepare a nanoparticle suspension. The volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. In this embodiment, the MWCNT nanoparticles have a diameter of 3-15 nm, a length of 15-30 μm, and a purity >98%; the Al2O3 nanoparticles have a diameter of 10 nm and a purity ≥99.9%; and the SiO2 nanoparticles have a diameter of 15 nm and a purity ≥99.5%. S4. The nanoparticle suspension obtained in S3 was placed in an ultrasonic oscillator for homogenization for 60 min. The power of the ultrasonic oscillator was set to 180 W and the ultrasonic frequency was set to 40 kHz to obtain a composite heat exchange fluid for heat extraction from medium-deep geothermal energy.
[0024] like Figure 4 As shown, at a temperature of 60℃, the density of the composite heat exchange fluid prepared for medium-deep geothermal energy extraction is 1005.96 kg / m³. 3 Compared to binary mixed base liquids, the density increased by 6%, and the density of nanofluids decreased reasonably with increasing temperature. For example... Figure 5 As shown, at a temperature of 90℃, the thermal conductivity of the composite heat exchange fluid used for medium-deep geothermal energy extraction was 0.74 W / (m·K), which is 47% higher than that of the binary mixed base fluid. Furthermore, the thermal conductivity of the composite heat exchange fluid used for medium-deep geothermal energy extraction increases reasonably with increasing temperature.
[0025] The heat extraction simulation experiment in this embodiment is conducted under the same conditions as the simulation experiment in Example 1. The simulation experiment simulates the heat extraction of different fluids, and the results are as follows: Figure 7 As shown, the composite heat exchange fluid prepared in Example 2 has a heat output of 17328.98 W per year.
[0026] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that only SiO2 was used as the nanomaterial, and the density of the heat exchange fluid obtained at a temperature of 60°C was 1019 kg / m³. 3The thermal conductivity of the heat exchange fluid obtained at a temperature of 90°C is 0.50 W / (m·K), which is lower than that of Example 1.
[0027] The heat extraction simulation experiment in this comparative example is conducted under the same conditions as the simulation experiment in Example 1. The simulation experiment simulates the heat extraction of different fluids, and the results are as follows. Figure 7 As shown, the heat output of the composite heat exchange fluid prepared in Comparative Example 1 is 17298.46 W per year.
[0028] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that only Al2O3 was used as the nanomaterial, and the density of the heat exchange fluid obtained at a temperature of 60°C was 1117 kg / m³. 3 The thermal conductivity of the heat exchange fluid obtained at a temperature of 90°C was 0.51 W / (m·K), which was lower than that of Example 1.
[0029] The heat extraction simulation experiment in this comparative example is conducted under the same conditions as the simulation experiment in Example 1. The simulation experiment simulates the heat extraction of different fluids, and the results are as follows. Figure 7 As shown, the heat output of the composite heat exchange fluid prepared in Comparative Example 2 is 17274.57 W per year.
Claims
1. A method for preparing a composite heat exchange fluid for heat extraction from medium-deep geothermal energy, characterized in that, Includes the following steps: S1, 2-methyl-1,3-propanediol and pure water are mixed evenly to obtain a binary mixed base liquid; S2, add a surfactant to the binary mixed base liquid obtained in S1 and dissolve it to obtain the base liquid; S3, add the mixed nanoparticles to the base liquid obtained in S2 to prepare a nanoparticle suspension; S4. The nanoparticle suspension obtained in S3 is homogenized to obtain a composite heat exchange fluid for heat extraction from medium-deep geothermal energy.
2. The method for preparing the composite heat exchange fluid for medium-deep geothermal energy extraction as described in claim 1, characterized in that, The mass ratio of 2-methyl-1,3-propanediol to water in S1 is less than or equal to 5:
95.
3. The method for preparing the composite heat exchange fluid for medium-deep geothermal energy extraction as described in claim 2, characterized in that, The surfactant in S2 is gum arabic, hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or polyvinylpyrrolidone.
4. The method for preparing the composite heat exchange fluid for medium-deep geothermal energy extraction as described in claim 3, characterized in that, The volume concentration of the surfactant in S2 after dissolution is 0.2-1.5%.
5. The method for preparing the composite heat exchange fluid for medium-deep geothermal energy extraction as described in claim 4, characterized in that, The mixed nanoparticles in S3 include MWCNT nanoparticles, Al2O3 nanoparticles, and SiO2 nanoparticles.
6. The method for preparing the composite heat exchange fluid for medium-deep geothermal energy extraction as described in claim 5, characterized in that, The mass fraction of any one type of nanoparticle in the mixed nanoparticles is 5% to 90%.
7. The method for preparing the composite heat exchange fluid for medium-deep geothermal energy extraction as described in claim 6, characterized in that, The volume concentration of the surfactant after dissolution is not higher than the volume concentration of the mixed nanoparticles in the nanoparticle suspension.
8. The method for preparing the composite heat exchange fluid for medium-deep geothermal energy extraction as described in claim 7, characterized in that, The MWCNT nanoparticles have a diameter of 3-15 nm, a length of 15-30 μm, and a purity >98%; the Al2O3 nanoparticles have a diameter of 10 nm and a purity ≥99.9%; and the SiO2 nanoparticles have a diameter of 15 nm and a purity ≥99.5%.
9. The method for preparing the composite heat exchange fluid for medium-deep geothermal energy extraction as described in any one of claims 1-8, characterized in that, The nanoparticle suspension was homogenized in an ultrasonic oscillator for 30-100 minutes. The ultrasonic oscillator has a power of 180W and an ultrasonic frequency of 40kHz.
10. A composite heat exchange fluid for extracting heat from medium-deep geothermal energy, characterized in that, It is prepared by the method for preparing composite heat exchange fluid for medium-deep geothermal energy extraction as described in any one of claims 1-9.