A seawater-based nanofluid enhanced offshore geothermal heat exchanger system

Abstract

The present invention proposes a seawater-based nanofluid enhanced offshore geothermal heat exchanger system, which includes a seawater-based nanofluid preparation module: used to prepare nanofluids with seawater as the base fluid and regulate the nanofluid concentration; a seawater-based nanofluid buried pipe circulation module: used to extract shallow offshore geothermal energy, which includes a buried pipe loop buried in the constant temperature formation of the seabed and a nanofluid peristaltic pump for driving the nanofluid circulation; a phase change heat exchange module: coupled with the buried pipe circulation module and used to convert low-grade heat energy into high-grade heat energy, which includes a nanofluid heat exchange chamber connected to the buried pipe, a heat exchange pipeline, a heat pump working fluid, etc.; an energy storage / output module: used to convert high-grade heat energy into other forms of energy and store or output it. The present invention locally uses seawater as the base fluid to prepare nanofluids, with adjustable nanofluid concentration, avoiding nanoparticle aggregation, overcoming the problem of unbalanced cold and heat loads in the formation, and effectively realizing the efficient and stable development of offshore geothermal energy.

Description

Technical Field

[0001] The present invention relates to the technical field of marine energy engineering, and particularly to a seawater-based nanofluid enhanced offshore geothermal heat exchanger system. Background Art

[0002] Geothermal resources come from the temperature difference between the shallow strata and the sea surface, and can be extracted through heat exchange between a heat exchanger and the strata. At present, the development of shallow geothermal energy is concentrated on land, but the shallow geothermal energy in the sea is richer. However, there are problems such as complex environmental conditions in the sea, being far from the intensive energy demand areas, and low efficiency of geothermal heat exchangers, which restrict the development and utilization of shallow geothermal energy in the sea.

[0003] Nanofluids are a new type of heat transfer enhancement medium. By dispersing nanoparticles with high thermal conductivity (such as metals, oxides or carbon materials) in traditional base fluids (such as water, ethylene glycol, etc.), the thermal conductivity of the fluid is significantly improved, thereby enhancing the heat transfer efficiency. It has been widely used in fields such as chemical engineering and electrical engineering, but due to its long-term stability and economic problems, it has not been applied to the field of geothermal development. Geothermal heat exchangers often require long-term stable operation for decades, but the agglomeration and sedimentation of nanoparticles will lead to a decrease in their heat transfer performance. At winter and summer temperatures, the thermal conductivity and viscosity of nanofluids will also change. The operation of a single nanofluid throughout the year in a geothermal heat exchanger will also cause an imbalance in the cold and heat loads of the strata. In a marine environment, conventional nanofluids will also change their components due to mixing with seawater, affecting the overall stability and thus reducing the performance. Therefore, it is necessary to regularly replace the fluid at sea, and the cost is very high. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above problems and provide a system that can efficiently and stably develop and utilize offshore geothermal energy.

[0005] To achieve the above purpose, the present invention proposes a seawater-based nanofluid enhanced offshore geothermal heat exchanger system, including:

[0006] A seawater-based nanofluid preparation module: used to prepare seawater-based nanofluids with adjustable concentrations using seawater as the base fluid, including a seawater filter, a feed controller, a nanofluid mixing tank, and a concentration meter;

[0007] A seawater-based nanofluid buried pipe circulation module: used to extract offshore shallow geothermal energy using seawater-based nanofluids, including a buried pipe loop buried in the constant temperature strata of the seabed and a nanofluid peristaltic pump for driving the nanofluid circulation;

[0008] A phase change heat exchange module: coupled and connected to the seawater-based nanofluid buried pipe circulation module, used to convert low-grade thermal energy obtained through the seawater-based nanofluid buried pipe circulation module into high-grade thermal energy, including a nanofluid heat exchange tank connected to the buried pipe, a heat exchange pipeline, a heat pump working fluid, a compressor, and an expansion valve;

[0009] Energy storage / output module: Connected to the phase change heat exchange module, for converting the high-grade thermal energy into other forms of energy and storing or outputting it.

[0010] Furthermore, in the seawater-based nanofluid preparation module,

[0011] The seawater filter is arranged at the top opening of the feed controller, for filtering seawater impurities to obtain seawater clear liquid as the nanofluid base liquid;

[0012] The nanofluid mixing tank is arranged below the feed controller. A stirrer and an ultrasonic vibrator are arranged in the mixing tank, for uniformly mixing the base liquid, nanoparticles and dispersant to prepare a seawater-based nanofluid with high fluidity; The seawater-based nanofluid preferably uses inert nanoparticles that do not react with substances in seawater, facilitating the formation of a highly dispersed nanofluid; The inert nanoparticles include nano-aluminum oxide, nano-graphene oxide and carbon nanotubes;

[0013] The mixing tank, stirrer and ultrasonic vibrator are all made of seawater corrosion-resistant materials;

[0014] The concentration meter is installed on the buried pipe, for measuring the concentration of the seawater-based nanofluid in the buried pipe and connecting to the feed controller, so that the feed controller can flexibly adjust the nanofluid concentration in the buried pipe according to the nanofluid concentration measured by the concentration meter and the preset seasonal target concentration by discharging part of the nanofluid and injecting seawater clear liquid, nanoparticles and dispersant to ensure the balance of the formation cooling and heating loads.

[0015] Furthermore, in the seawater-based nanofluid buried pipe circulation module, ultrasonic vibrators are installed at the inlet and outlet of the buried pipe to increase the dispersibility of the seawater-based nanofluid; The power of the nanofluid peristaltic pump changes periodically in a pulsed manner to create turbulent flow and avoid precipitation.

[0016] Furthermore, in the phase change heat exchange module, an ultrasonic vibrator is installed in the nanofluid heat exchange tank, for continuously vibrating during the nanofluid circulation process to avoid particle precipitation; The nanofluid heat exchange tank is connected to the seawater-based nanofluid preparation module, for adjusting the nanofluid concentration in the buried pipe in real time to balance the formation cooling and heating loads; The heat exchange pipe is connected in the nanofluid heat exchange tank and is made of materials with high thermal conductivity, erosion resistance and effective resistance to seawater corrosion, including nickel-based alloy materials; The heat exchange pipe and the compressor and expansion valve form a heat pump working medium circulation loop, so that when the heat pump working medium flows in the heat exchange pipe, the low-grade thermal energy of the nanofluid is extracted in the seawater-based nanofluid heat exchange tank through the evaporation-compression-condensation-expansion process of the heat pump working medium and converted into high-grade thermal energy and transmitted to the energy storage / output module.

[0017] Furthermore, the specific regulation method for adjusting the concentration of the seawater-based nanofluid in the buried pipe in real time through a concentration meter is as follows: The total volume of the nanofluid circulating in the buried pipe loop of the seawater-based nanofluid can be calculated based on the pipe length, pipe diameter of the buried pipe, and the liquid volume of each component connected to the pipe. V Let the target concentration be C t , and the concentration of the nanofluid in the pipe measured by the concentration meter is C c (both are mass concentrations). In the seawater-based nanofluid preparation module, to ensure the fluidity of the seawater-based nanofluid, the concentration of the prepared nanofluid cannot be too high, and the maximum adjustable concentration is set as C max .

[0018] 1) When C t > C c , it is necessary to increase the concentration of the nanofluid in the pipe. First, drain a part of the low-concentration nanofluid in the pipe, and prepare a high-concentration nanofluid with a concentration of C max in the nanofluid preparation module and inject it into the pipe to increase the concentration of the nanofluid in the pipe. The drained volume and the injected volume of the nanofluid should be equal, set as V io , and calculate according to the following formula:

[0019] ;

[0020] 2) When C t < C c , it is necessary to reduce the concentration of the nanofluid in the pipe. First, drain a part of the nanofluid in the pipe, and then inject seawater of the same volume. Let the injection and drainage volume be V io , and calculate according to the following formula:

[0021] ;

[0022] Furthermore, the energy storage / output module is adapted to a variety of energy storage devices or thermal energy utilization systems, including but not limited to thermal energy storage tanks, generator sets, or seawater desalination devices.

[0023] Furthermore, the buried pipe is a continuous slender pipe loop filled with seawater-based nanofluid and buried in a stable stratum with a constant temperature throughout the year.

[0024] Furthermore, the nanofluid peristaltic pump is used to drive the seawater-based nanofluid to circulate in the buried pipe.

[0025] Both the buried pipes and the heat exchange pipes are made of high thermal conductivity materials to enhance the heat exchange efficiency of the system; the remaining components are made of heat insulation materials to reduce heat loss.

[0026] Furthermore, the buried pipes, heat exchange pipes and the components in contact with seawater are all made of corrosion-resistant materials, which can effectively resist seawater corrosion.

[0027] Compared with the prior art, the advantages of the present invention are as follows:

[0028] The present invention directly uses seawater as the base fluid to prepare nanofluids on-site, solving the problem of scarce fresh water in the marine environment, reducing fresh water consumption and effectively reducing costs; at the same time, natural ions in seawater (such as chloride ions, sodium ions) are used to enhance the dispersibility and thermal conductivity of nanofluids, avoiding the aggregation of nanoparticles and further improving the heat exchange efficiency of nanofluids.

[0029] The present invention combines seawater-based nanofluids with a regulation technology. By real-time monitoring the nanofluid concentration and combining with the seasonal target value, the ratio of nanoparticles, dispersant and seawater clear liquid is controlled and adjusted, so that the nanofluid concentration can be flexibly regulated, overcoming the problem of unbalanced formation cold and heat loads caused by the differences in thermal conductivity and viscosity of nanofluids at different temperatures, achieving the annual cycle balance of formation cold and heat loads, and avoiding the system efficiency fluctuation caused by temperature changes.

[0030] The present invention integrates a seawater-based nanofluid preparation module, a seawater-based nanofluid buried pipe circulation module, a phase change heat exchange module and an energy storage / output module to form a complete closed-loop system. Through the coordinated cooperation of each module, the efficient development of marine geothermal energy is realized, which is conducive to sustainable development and provides a new solution for the large-scale development of marine geothermal energy.

[0031] The present invention uses nanofluids with high thermal conductivity as the circulating working medium of the geothermal heat exchanger, greatly improving the heat exchange efficiency of the system.

[0032] In the preparation process of the nanofluids of the present invention, inert nanoparticles (such as alumina, silicon carbide) are used, effectively avoiding their chemical reactions with seawater. Combined with concentration regulation and ultrasonic anti-precipitation, it is ensured that the nanofluids can operate stably for a long time in the marine environment, solving the long-term stability problem of traditional nanofluids and the frequent maintenance problems caused by aggregation or sedimentation. Brief Description of the Drawings

[0033] Figure 1 It is a schematic structural diagram of a seawater-based nanofluid enhanced marine geothermal heat exchanger system proposed by the present invention. Detailed Embodiments

[0034] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0035] This embodiment proposes a seawater-based nanofluid enhanced offshore geothermal heat exchanger system, as Figure 1 shown. The system structure includes a seawater-based nanofluid preparation module 1, a seawater-based nanofluid buried pipe circulation module 2, a phase change heat exchange module 3, and an energy storage / output module 4. Among them, the seawater-based nanofluid preparation module 1 is connected to the seawater-based nanofluid buried pipe circulation module 2, the seawater-based nanofluid buried pipe circulation module 2 is connected to the phase change heat exchange module 3, and the phase change heat exchange module 3 is connected to the energy storage / output module 4.

[0036] In this embodiment, the seawater-based nanofluid preparation module 1 is used to prepare seawater-based nanofluids with adjustable concentrations using seawater as the base fluid. Its device structure includes a seawater filter 101, a feed controller 102, a nanofluid mixing tank 103, and a concentration meter 104. Among them, the seawater filter 101 is arranged at the top opening of the feed controller 102 and is used to filter seawater impurities to obtain seawater clear liquid as the nanofluid base fluid; the nanofluid mixing tank 103 is arranged below the feed controller 102. A mechanical stirrer 105 and multiple ultrasonic vibrators 106 are arranged in the mixing tank 103 and are used to stir the base fluid, nanoparticles, and dispersant evenly to prepare nanofluids with high fluidity. In addition, the concentration meter 104 is installed on the buried pipe 201 and is used to measure the concentration of the seawater-based nanofluid 202 in the buried pipe 201 and is connected to the feed controller 102, so that the feed controller 102 adjusts the concentration of the nanofluid 202 in the buried pipe 201 according to the measured nanofluid concentration by the concentration meter 104 and the preset seasonal target concentration by discharging part of the nanofluid and injecting seawater clear liquid, nanoparticles, and dispersant to ensure the balance of the formation's cooling and heating loads. In this embodiment, the nanoparticles used in the seawater-based nanofluid are inert particle carbon nanotubes, which do not react with substances in seawater and are easy to form nanofluids with high dispersibility. In addition, the mixing tank 103, the stirrer 105, and the ultrasonic vibrator 106 are all made of seawater corrosion-resistant materials.

[0037] In this embodiment, the seawater-based nanofluid buried pipe circulation module 2 utilizes seawater-based nanofluids to extract shallow geothermal energy offshore. By directly exchanging heat with the formation through this module, low-grade heat energy is extracted. The device structure of the seawater-based nanofluid buried pipe circulation module 2 includes a buried pipe 201 loop buried in the constant-temperature formation under the sea and a nanofluid peristaltic pump 203 that drives the circulation of the nanofluid 202. In this embodiment, the buried pipe 201 is a continuous and slender pipe loop filled with seawater-based nanofluid 202, with a pipe diameter of 20 mm and a single U-shaped configuration. It is buried in a stable formation with a constant temperature throughout the year. At the same time, ultrasonic vibrators are installed at the inlet and outlet of the buried pipe 201 to increase the dispersion of the seawater-based nanofluid; the nanofluid peristaltic pump 203 is used to drive the seawater-based nanofluid 202 to circulate in the buried pipe 201, and the power of the nanofluid peristaltic pump 203 changes periodically in a pulsed manner to create turbulent flow and avoid precipitation.

[0038] In this embodiment, the phase change heat exchange module 3 is coupled to the seawater-based nanofluid buried pipe circulation module and is used to convert the low-grade heat energy obtained through the seawater-based nanofluid buried pipe circulation module 2 into high-grade heat energy. Its device structure includes: a nanofluid heat exchange chamber 301 connected to the buried pipe 201, a heat exchange pipe 302, and a heat pump working medium 303 disposed in the heat exchange pipe 302.

[0039] As Figure 1 shown, the heat exchange pipe 302 is connected to the inside of the chamber body of the nanofluid heat exchange chamber 301. Through heat exchange in the chamber, the heat of the seawater-based nanofluid 202 is transferred to the heat pump working medium 303. In this embodiment, the heat pump working medium 303 can be selected from R410A or R32. The heat exchange pipe 302 is made of a material with high thermal conductivity, resistance to erosion, and effective resistance to seawater corrosion, such as nickel-based alloy material.

[0040] At the same time, the heat exchange pipe 302, the compressor 304, and the expansion valve 305 form a heat pump working medium circulation loop, so that when the heat pump working medium 303 flows in the heat exchange pipe 302, the low-grade heat energy of the nanofluid 202 is extracted in the seawater-based nanofluid heat exchange chamber 301 through the evaporation - compression - condensation - expansion process of the heat pump working medium 303 and converted into high-grade heat energy and transmitted to the energy storage / output module 4.

[0041] In this embodiment, the nanofluid heat exchange chamber 301 is connected to the seawater-based nanofluid preparation module 1 through the injection / drainage device pipeline, which is convenient for real-time adjustment of the concentration of the nanofluid 202 in the buried pipe 201 to balance the formation cooling and heating loads; the injection / drainage device includes an injection pipe and a drain valve: the injection pipe is disposed between the seawater-based nanofluid preparation module 1 and the nanofluid heat exchange chamber 301, so that the nanofluid is injected from the preparation module 1 into the heat exchange chamber 301; the drain valve is provided on the heat exchange chamber 301 to control the liquid discharge.

[0042] In addition, as Figure 1 shown, a plurality of ultrasonic vibrators 306 are further installed in the nanofluid heat exchange chamber 301 to continuously vibrate during the circulation of the nanofluid 202 to avoid particle precipitation.

[0043] In this embodiment, the buried pipe 201 and the heat exchange pipe 302 are both made of high thermal conductivity materials to enhance the heat exchange efficiency of the system; the remaining components are made of heat insulating materials to reduce heat loss. At the same time, the buried pipe 201, the heat exchange pipe 302 and the components in contact with seawater are all made of corrosion-resistant materials, which can effectively resist seawater corrosion.

[0044] In this embodiment, the specific regulation method for adjusting the concentration of the seawater-based nanofluid 202 in the buried pipe 201 in real time through the concentration meter 104 is as follows: According to the pipe length, pipe diameter of the buried pipe 201, and the liquid volume of each component connected to the pipe, the total volume of the nanofluid circulating in the seawater-based nanofluid buried pipe circulation module 2 can be calculated V . Let the target concentration be C t , and the concentration of the nanofluid measured by the concentration meter 104 in the pipe is C c (both are mass concentrations). In the seawater-based nanofluid preparation module 1, to ensure the fluidity of the seawater-based nanofluid, the concentration of the prepared nanofluid cannot be too high, and the maximum adjustable concentration is set as C max .

[0045] 1) When C t > C c , it is necessary to increase the concentration of the nanofluid in the pipe. First, drain a part of the low-concentration nanofluid in the pipe, and prepare a high-concentration nanofluid with a concentration of C max in the nanofluid preparation module and inject it into the pipe to increase the concentration of the nanofluid in the pipe. The drained volume and the injected volume of the nanofluid should be equal, and set as V io , and calculate according to the following formula:

[0046] ;

[0047] 2) When C t < C c , it is necessary to reduce the concentration of the nanofluid in the pipe. First, drain a part of the nanofluid in the pipe, and then inject seawater of equal volume. Let the injection and drainage volume be V io [[ID=5l]], and calculate according to the following formula:

[0048] ;

[0049] In this embodiment, as Figure 1 shown, the energy storage / output module 4 is connected to the phase change heat exchange module 3, and is used to convert high-grade thermal energy into other forms of energy for storage or output. The energy storage / output module 4 is adapted to a variety of energy storage devices or thermal energy utilization systems, including but not limited to thermal energy storage tanks, generator sets, or seawater desalination devices.

[0050] The operation mode of the offshore geothermal heat exchanger system in this embodiment is specifically as follows:

[0051] The seawater-based nanofluid prepared by the seawater-based nanofluid preparation module 1 flows into the nanofluid heat exchange chamber 301 from the stirring chamber 103 through a pipeline, and then enters the buried pipe 201 through circulation.

[0052] In the summer working condition, the sea surface temperature is higher than the underground temperature. The seawater-based nanofluid 202 is driven by the nanofluid peristaltic pump 203 to circulate in the buried pipe 201 loop. After the high-temperature nanofluid cools down in the formation, it reaches the nanofluid heat exchange chamber 301, and cools the heat pump working fluid 303 in the heat exchange pipeline 302. The heat pump working fluid 303 absorbs heat in the energy storage / output module 4, becomes high-temperature steam through the compressor 304, cools down in the nanofluid heat exchange chamber 301, becomes low-temperature liquid through the expansion valve 305, and enters the energy storage / output module 4 to absorb heat, forming a refrigeration cycle.

[0053] In the winter working condition, the sea surface temperature is lower than the underground temperature. The seawater-based nanofluid 202 is driven by the nanofluid peristaltic pump 203 to circulate in the buried pipe 201 loop. After the low-temperature nanofluid heats up in the formation, it reaches the nanofluid heat exchange chamber 301, and heats the heat pump working fluid 303 in the heat exchange pipeline 302. The heat pump working fluid 303 releases heat in the energy storage / output module 4, becomes low-temperature liquid through the expansion valve 305, heats up in the nanofluid heat exchange chamber 301, becomes high-temperature steam through the compressor 304, and enters the energy storage / output module 4 to release heat, forming a heating cycle.

[0054] The above is only the preferred embodiment of the present invention, and it does not play any limiting role on the present invention. Any person skilled in the art within the technical field, without departing from the technical solution of the present invention, makes any form of equivalent substitution or modification and other changes to the technical solution and technical content disclosed by the present invention, all of which belong to the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A seawater-based nanofluid enhanced offshore geothermal heat exchanger system, characterized in that, Including: Seawater-based nanofluid preparation module: used to prepare seawater-based nanofluids with adjustable concentration using seawater as the base fluid, including a seawater filter, a feed controller, a nanofluid mixing tank, and a concentration meter; Seawater-based nanofluid ground pipe circulation module: utilizes seawater-based nanofluids to extract shallow geothermal energy offshore, including a ground pipe loop buried in the constant temperature formation at the seabed and a nanofluid peristaltic pump for driving the nanofluid circulation; Phase change heat exchange module: coupled and connected to the seawater-based nanofluid ground pipe circulation module, used to convert low-grade thermal energy obtained through the seawater-based nanofluid ground pipe circulation module into high-grade thermal energy, including a nanofluid heat exchange tank connected to the ground pipe, heat exchange pipes, a heat pump working fluid, a compressor, and an expansion valve; Energy storage / output module: connected to the phase change heat exchange module, used to convert the high-grade thermal energy into other forms of energy and store or output it; In the seawater-based nanofluid preparation module: The seawater filter is arranged at the top opening of the feed controller, used to filter seawater impurities to obtain seawater clear liquid as the nanofluid base fluid; The nanofluid mixing tank is arranged below the feed controller. A stirrer and an ultrasonic oscillator are arranged in the mixing tank, used to stir the base fluid, nanoparticles, and dispersant evenly to prepare seawater-based nanofluids with high fluidity; the seawater-based nanofluids use inert nanoparticles, and the inert nanoparticles include nano-aluminum oxide, nano-graphene oxide, and carbon nanotubes; The mixing tank, stirrer, and ultrasonic oscillator are all made of seawater corrosion-resistant materials; The concentration meter is installed on the ground pipe, used to measure the concentration of seawater-based nanofluids in the ground pipe, and is connected to the feed controller, so that the feed controller adjusts the concentration of nanofluids in the ground pipe by discharging part of the nanofluids and injecting seawater clear liquid, nanoparticles, and dispersant according to the measured nanofluid concentration by the concentration meter and the preset seasonal target concentration.

2. The seawater-based nanofluid enhanced offshore geothermal heat exchanger system according to claim 1, wherein In the seawater-based nanofluid ground pipe circulation module, Ultrasonic oscillators are installed at the inlet and outlet of the ground pipe to increase the dispersibility of seawater-based nanofluids; The power of the nanofluid peristaltic pump changes periodically in a pulsed manner to create turbulent flow and avoid precipitation.

3. The seawater-based nanofluid enhanced offshore geothermal heat exchanger system according to claim 1, characterized in that, In the phase change heat exchange module: An ultrasonic oscillator is installed in the nanofluid heat exchange tank, used to continuously vibrate during the nanofluid circulation process to avoid particle precipitation; The nanofluid heat exchange tank is connected to the seawater-based nanofluid preparation module, used to adjust the concentration of nanofluids in the ground pipe in real time to balance the cold and heat loads of the formation; The heat exchange pipes are connected in the nanofluid heat exchange tank and are made of materials with high thermal conductivity, erosion resistance, and effective resistance to seawater corrosion, including nickel-based alloy materials; The heat exchange pipes, compressor, and expansion valve form a heat pump working fluid circulation loop, so that when the heat pump working fluid flows in the heat exchange pipes, the low-grade thermal energy of the nanofluid is extracted in the seawater-based nanofluid heat exchange tank through the evaporation-compression-condensation-expansion process of the heat pump working fluid and converted into high-grade thermal energy and transmitted to the energy storage / output module.

4. The seawater-based nanofluid enhanced offshore geothermal heat exchanger system according to claim 1, characterized in that, The energy storage / output module is adapted to a variety of energy storage devices or thermal energy utilization systems, including but not limited to thermal energy storage tanks, power generation sets or desalination devices.

Images