A phase change energy storage tank
By preparing micron-sized graphite microsphere-based composite phase change materials, the problem of insufficient utilization of waste heat from industrial reclaimed water has been solved, achieving efficient storage and transfer of waste heat and improving energy utilization.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA UNIV OF GEOSCIENCES (WUHAN)
- Filing Date
- 2024-09-20
- Publication Date
- 2026-05-19
AI Technical Summary
Existing technologies fail to effectively utilize the waste heat in industrial reclaimed water, resulting in energy waste and hindering the sustainable development of industrial production.
A composite phase change material was prepared by mixing and milling nano-graphite and nano-cellulose into microspheres, which were then sprayed into microspheres and combined with the phase change material. The waste heat was stored and transferred using a heat exchange tube.
It has improved energy utilization, reduced energy waste, and promoted the sustainable development of industrial production.
Smart Images
Figure CN119197164B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of energy storage technology, and more particularly to a phase change energy storage box. Background Technology
[0002] In industrial production, the treated industrial waste gas and wastewater (reclaimed water) contain a large amount of heat. Because there is no mature technology to effectively utilize this heat, significant energy waste occurs, which not only hinders the sustainable development of industrial production but also wastes the financial and material resources of enterprises. Summary of the Invention
[0003] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing a phase change energy storage box that extracts, stores, and transfers waste heat from industrial reclaimed water, and then uses it as an energy source to heat domestic water, thereby achieving high energy utilization.
[0004] The present invention provides a phase change energy storage box, comprising a box body, wherein the box body is filled with a composite phase change material, and a heat exchange tube is embedded in the composite phase change material, wherein the inlet and outlet of the heat exchange tube extend to the outside of the box body.
[0005] The preparation method of the composite phase change material is as follows:
[0006] S1. Nanographite and nanocellulose are dispersed in deionized water and then ball-milled to obtain a nanographite-cellulose mixed solution.
[0007] S2. Use an electronic atomizer to spray the nano-graphite cellulose mixture into a container filled with liquid nitrogen, then sieve the microspheres in the container and freeze-dry the microspheres to obtain micron-sized graphite microspheres.
[0008] S3. After immersing micron-sized graphite microspheres in molten phase change material for a period of time, the composite phase change material is obtained by heat filtration.
[0009] Furthermore, the heat exchange tube is a U-shaped tube or a plate-type hollow tube.
[0010] Furthermore, the box body includes a stainless steel box and a foam box nested inside the stainless steel box, the inner wall of the foam box being adhered with an acrylic sheet.
[0011] Furthermore, multiple temperature sensors are spaced apart on the inner wall of the enclosure.
[0012] Furthermore, the mass ratio of nanographite to nanocellulose is 1-10:1.
[0013] Furthermore, the mass-to-volume ratio of nanographite to deionized water is 1-10:100g / ml.
[0014] Furthermore, the ball milling speed is 400-600 r / min, and the time is 2-4 h.
[0015] Furthermore, the phase change material is paraffin.
[0016] Further, the specific operation of step S3 is as follows: first, put the micron-sized graphite microspheres and phase change material into a container and then evacuate in a vacuum drying oven, and then react at 80°C for 2 hours to obtain micron-sized graphite microsphere-based composite phase change material, and then perform hot filtration in an oven at 80°C.
[0017] Furthermore, freeze-dry for 72 hours.
[0018] This invention involves ball milling and emulsifying a solution of nano-graphite and nano-cellulose to form an emulsion in the mixed solution. The sprayed droplets can then be cooled in liquid nitrogen to form microspheres. The nozzle of the electronic atomizer is at the micrometer level, ensuring that the sprayed droplets are also at the micrometer level, and the final microspheres are also at the micrometer level.
[0019] In preparing the composite phase change material, the present invention first evacuates the material to remove the air from the microspheres, so that the high-temperature molten paraffin liquid can flow smoothly into the pores of the microspheres. The microporous structure of the microspheres can bind the PW through capillary force to prevent the PW from leaking due to the molten phase change.
[0020] In this invention, microspheres are prepared by mixing and ball milling nano-graphite and nano-cellulose and then spraying them out using an electronic atomizer. Due to the formation of a micro-aerogel porous structure, the microspheres are better able to absorb phase change materials, thereby improving the loading rate. Moreover, because graphite is also used as the raw material for the microspheres, the heat storage capacity and thermal conductivity of the micron-sized graphite microsphere-based composite phase change material are greatly improved, and it still has a high phase change enthalpy value after multiple cycles.
[0021] This invention utilizes the properties of micron-sized graphite microspheres to combine them with phase change materials, which not only solves the problem of melting and leakage of phase change materials due to the phase change process, but also improves the thermal conductivity of the heat storage material, enabling timely and efficient heat transfer from the heat exchange tube and the composite phase change material.
[0022] This invention utilizes a composite phase change material with high energy storage and thermal conductivity to store the waste heat from reclaimed water as latent heat within the material via heat exchange tubes. This allows for the centralized storage and transfer of energy from wastewater to a specific application scenario, followed by release of the stored energy, thus enabling the reuse of waste heat from industrial reclaimed water. The use of this energy storage tank reduces energy waste, thereby improving energy utilization efficiency, lowering costs for industrial production, and contributing to the sustainable development of enterprises. Attached Figure Description
[0023] Figure 1A photograph of the micron-sized graphite microspheres prepared according to this invention.
[0024] Figure 2 A photograph of the micron-sized graphite microsphere-based composite phase change material prepared according to this invention.
[0025] Figure 3 These are the DSC diagrams for Examples 1-5.
[0026] Figure 4a -e is the BET diagram for Examples 1-5.
[0027] Figure 5 These are scanning electron microscope (SEM) images of Examples 1-5; where (a)-(b) are SEM images of Example 1, (c)-(d) are SEM images of Example 2, (e)-(f) are SEM images of Example 3, (g)-(h) are SEM images of Example 4, and (i)-(j) are SEM images of Example 5.
[0028] Figure 6 This is a schematic diagram of a U-shaped tube.
[0029] Figure 7 This is a schematic diagram of a plate-type hollow tube.
[0030] Figure 8 , 9 This is a schematic diagram of the internal structure of the energy storage tank.
[0031] Figure 10 This is a temperature-time curve of a U-tube heat exchanger heat storage box with a hot water source flow rate of 500ml / min at 70℃.
[0032] Figure 11 Temperature-time curves for heat release in a U-tube heat exchanger storage tank at a flow rate of 500 ml / min.
[0033] Figure 12 Temperature-time curves for heat release in a U-tube heat exchanger storage tank at a flow rate of 1000 ml / min.
[0034] Figure 13 The figure shows the temperature-time curve of the heat storage box of the hollow plate heat exchanger when the hot water source at 70℃ flows at a rate of 500ml / min.
[0035] Figure 14 Temperature-time curves for heat release in a hollow plate heat exchanger storage box at a flow rate of 500 ml / min. Detailed Implementation
[0036] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.
[0037] This invention employs the following technical solution to prepare composite phase change materials, comprising the following process steps:
[0038] (1) Preparation of micron-sized graphite microsphere precursor mixed solution
[0039] Add 30 g of 2% solids nanocellulose aqueous solution to a 100 ml beaker, then add 30 mL of deionized water to the beaker and mix. Add 0.6 g, 1.8 g, 3 g, 4.2 g and 5.4 g of nanographite to the mixture. Stir with a magnetic stirrer for 30 min, then place the solution in a planetary ball mill and ball mill for 3 h at a speed of 500 r / min. Pour the resulting mixed solution into a 100 ml beaker to obtain a nanographite cellulose mixed solution.
[0040] (2) Preparation of micron-sized graphite microspheres
[0041] Add 60ml of the obtained nano-graphite cellulose mixed solution to the purchased electronic atomizer for preparation. Pour 2L of liquid nitrogen into a Dewar flask for later use. Use the electronic atomizer to spray the nano-graphite cellulose mixed solution into the Dewar flask containing liquid nitrogen. After spraying 10ml, stop the electronic atomizer, wait five minutes, and then spray again. After all the solution has been sprayed, wait another five minutes. Pour the excess liquid nitrogen from the Dewar flask back into the liquid nitrogen storage bottle. Place a sieve between the Dewar flask and the liquid nitrogen storage bottle, pour the prepared microspheres onto the sieve, transfer them to a beaker, seal with filter paper, and dry in a freeze dryer for 72 hours to obtain micron-sized graphite microspheres. Figure 1 As shown.
[0042] (3) Preparation of microsphere-based composite phase change materials
[0043] Weigh 1g of micron-sized graphite microsphere powder and 3g of paraffin wax into a beaker; place the beaker in a vacuum drying oven, evacuate the vacuum, and react at 80℃ for 2 hours to obtain a micron-sized graphite microsphere-based paraffin wax composite phase change material. Then, perform hot filtration in an oven at 80℃ to finally obtain the micron-sized graphite microsphere-based composite phase change material. Figure 2 As shown.
[0044] Example 1
[0045] Weigh 0.6g of nano-graphite powder, 30g of 2wt.% cellulose solution, and 30ml of deionized water into a 100ml beaker. Stir the solution in the beaker on a magnetic stirrer for half an hour. Then, place the mixture in the beaker into a ball mill and mill for 3 hours. Remove the mixture from the ball mill jar and use an electronic atomizer to spray 60ml of the solution into liquid nitrogen in a Dewar flask in six 10ml portions, with each portion spaced five minutes apart. Place the frozen microspheres into a vacuum freeze dryer and dry for 72 hours to obtain micron-sized graphite microspheres.
[0046] After hot filtration, micron-sized graphite microspheres and excess paraffin were combined to obtain a composite phase change material with a melting enthalpy of 117.3 J / g, a solidification enthalpy of 113.9 J / g, a thermal conductivity of 0.6235 W / (m·K), a specific surface area of 16.5332 m² / g, a pore volume of 0.318644 cm³ / g, and an average pore size of 28.8965 nm.
[0047] Example 2
[0048] Weigh 1.8g of nano-graphite powder, 30g of 2wt.% cellulose solution and 30ml of deionized water, and the rest is the same as in Example 1.
[0049] The obtained composite phase change material has a melting enthalpy of 137.2 J / g, a solidification enthalpy of 132.5 J / g, a thermal conductivity of 0.6772 W / (m·K), and according to BET testing, a specific surface area of 69.2373 m² / g, a pore volume of 0.668389 cm³ / g, and an average pore size of 35.3571 nm.
[0050] Example 3
[0051] Weigh 3g of nano-graphite powder, 30g of 2wt.% cellulose solution and 30ml of deionized water into a 100ml beaker. The rest is the same as in Example 1.
[0052] The obtained composite phase change material has a melting enthalpy of 121.7 J / g, a solidification enthalpy of 116.2 J / g, a thermal conductivity of 0.7325 W / (m·K), and according to BET testing, a specific surface area of 62.2777 m² / g, a pore volume of 0.533866 cm³ / g, and an average pore size of 31.8875 nm.
[0053] Example 4
[0054] Weigh 4.2g of nano-graphite powder, 30g of 2wt.% cellulose solution and 30ml of deionized water into a 100ml beaker, and follow the same procedure as in Example 1.
[0055] The obtained composite phase change material has a melting enthalpy of 127.9 J / g, a solidification enthalpy of 124.3 J / g, a thermal conductivity of 0.8023 W / (m·K), and according to BET testing, a specific surface area of 58.9647 m² / g, a pore volume of 0.507495 cm³ / g, and an average pore size of 31.9188 nm.
[0056] Example 5
[0057] Weigh 5.4g of nano-graphite powder, 30g of 2wt.% cellulose solution and 30ml of deionized water into a 100ml beaker, and follow the same procedure as in Example 1.
[0058] The obtained composite phase change material has a melting enthalpy of 102.3 J / g, a solidification enthalpy of 91.2 J / g, a thermal conductivity of 0.6323 W / (m·k), and according to BET testing, a specific surface area of 8.8841 m² / g, a pore volume of 0.149452 cm³ / g, and an average pore size of 25.7325 nm.
[0059] Comparative Example 1
[0060] Direct use of halloysite composite paraffin:
[0061] Weigh 3g of halloysite powder and combine it with paraffin wax, then heat filter it.
[0062] The obtained composite phase change material has a melting enthalpy of 72.2 J / g, a solidification enthalpy of -73.09 J / g, a thermal conductivity of 0.25 W / (m·K), and a loading rate of only 33.6%.
[0063] Comparative Example 2
[0064] The preparation of composite phase change materials involves replacing nano-graphite in the raw materials with halloysite.
[0065] Weigh 3g halloysite powder, 30g 2wt.% cellulose solution and 30ml deionized water into a 100ml beaker, and follow the same procedure as in Example 1.
[0066] The resulting composite phase change material has a melting enthalpy of -147.6 J / g, a solidification enthalpy of 150.8 J / g, an increased loading rate from 33.6% to 68%, and a thermal conductivity of 0.3266 W / (m·K).
[0067] Comparative Example 3
[0068] Directly using nano-graphite to composite paraffin:
[0069] Weigh 3g of nano-graphite and mix it with excess paraffin, then heat filter the mixture.
[0070] The obtained composite phase change material has a melting enthalpy of -77.53 J / g, a solidification enthalpy of 82.08 J / g, a thermal conductivity of 0.5022 W / (m·K), and a loading rate of only 38%.
[0071] Table 1. Enthalpy Comparison Table
[0072]
[0073] From the data in Table 1 and Figure 3 It can be seen that after microsphere preparation, the loading rate and thermal conductivity of the microsphere-based composite phase change material are significantly improved compared to the original composite phase change material. The heat storage performance of Example 2 is also the best among the five examples. Figure 4a The -e and BET test data show that the specific surface area, pore volume, and average pore size of Example 2 are the largest among the five examples. This can explain the highest adsorption rate of the phase change material in Example 2. From the above data, it can be seen that as the ratio of nano-graphite to cellulose increases, the thermal performance of the composite phase change material first increases and then decreases.
[0074] Energy storage tank manufacturing
[0075] This invention designs and manufactures two types of heat exchange tubes made of copper: U-shaped tubes and plate-type hollow tubes.
[0076] U-shaped tube, such as Figure 6 As shown, high thermal conductivity copper is used as the raw material, arranged in a 7-row, 7-column matrix. The inner diameter of the tube is 4mm, the outer diameter is 6mm, the total length is 13.34m, and the total volume is 0.38dm. 3 Heat exchange area 0.252m² 2 .
[0077] Plate-type hollow tubes, such as Figure 7 As shown, it consists of four rectangular plates, each 220mm x 220mm x 6mm, arranged in parallel at 60mm intervals and connected by a pipe with an inner diameter of 4mm, an outer diameter of 6mm, and a length of 60mm. The total volume is 1.23dm. 3 Heat exchange area 0.413m² 2 .
[0078] This invention uses a foam box with an outer volume of 390mm*390mm*390mm and an inner volume of 330mm*330mm*330mm as the body of the energy storage box. An acrylic sheet is glued to the inner wall of the foam box to allow the composite phase change material to come into direct contact with the foam box and corrode. The foam box is then placed in a custom-made stainless steel box to prevent the foam box from being damaged during daily use.
[0079] like Figure 8 , 9As shown, the heat exchange tubes were then placed in the chamber, and the composite phase change material was filled in, along with temperature sensors. The temperature sensors were selected from Kempsen ultra-fine T-type thermocouples, placed in seven positions within the chamber: bottom, middle, top, front, back, left, and right, to monitor the uniformity of the composite phase change material temperature change during the charging and discharging process of the energy storage tank.
[0080] Two energy storage tanks were fabricated, both using micron-sized graphite microsphere-based composite phase change material as the heat storage material. The first energy storage tank used a U-shaped tube as the heat exchanger, while the second energy storage tank used a plate hollow tube as the heat exchanger.
[0081] A test system simulating real-world conditions was built in the laboratory. Water containing waste heat from industrial reclaimed water was heated using an intelligent temperature-controlled heater. A peristaltic pump with intelligently adjustable water flow rate pumped hot water into the chamber through heat exchange tubes extending from the chamber's outlet. As the hot water flowed through the chamber, heat was transferred to the composite phase change material via the heat exchange tubes and stored. Temperature sensors placed inside the chamber allowed for real-time monitoring of temperature changes in the composite phase change material at different locations within the chamber, generating temperature-time curves on a computer.
[0082] Example 6
[0083] Investigating the effect of a flow rate of 500 ml / min on the heat storage and release performance of a U-tube accumulator:
[0084] Micron-sized graphite microsphere-based composite phase change material, U-shaped tubes, and seven temperature sensors were placed and compacted in a foam box with an outer volume of 390 mm * 390 mm * 390 mm and an inner volume of 330 mm * 330 mm * 330 mm, with an acrylic sheet adhered to the inner wall. The foam box was then placed in a custom-made stainless steel box. The two ends of the heat exchange tubes extended out of the box as inlet and outlet ports.
[0085] Figure 10 The U-tube heat exchanger storage tank was heated by a hot water source at a flow rate of 500 ml / min and a temperature of 70℃. After about 2 hours of heating, the composite phase change material reached its phase change temperature and began to undergo phase change, with the temperature change becoming more gradual. The phase change was completed in about 10 hours, after which the temperature rose to 65℃ via sensible heat. This process demonstrates that heating the storage tank with a hot water flow rate of 500 ml / min can be completed in about 10 hours.
[0086] A peristaltic pump with intelligent flow rate regulation introduces room temperature water into the heat exchange tubes at a flow rate of 500 ml / min. As the room temperature water flows through the chamber, it is heated by heat transfer from the composite phase change material via the heat exchange tubes. Seven temperature sensors placed inside the chamber monitor the temperature changes of the composite phase change material at different locations within the chamber in real time on a computer, generating temperature-time curves, such as... Figure 11 .
[0087] The composite phase change material cools to its phase change temperature after about 20 minutes, then enters the phase change process, completing the phase change in about 1.5 hours. It then cools to room temperature via sensible heat. The black line represents the temperature change of the outflowing water, and the water temperature change follows the same trend as the temperature change of the composite phase change material.
[0088] Example 7
[0089] Investigating the effect of a flow rate of 1000 ml / min on the heat storage and release performance of a U-tube accumulator:
[0090] Micron-sized graphite microsphere-based composite phase change material, a U-shaped tube, and seven temperature sensors were placed in a foam box with an outer volume of 390 mm * 390 mm * 390 mm and an inner volume of 330 mm * 330 mm * 330 mm, with an acrylic sheet adhered to the inner wall. The foam box was then compacted and placed inside a custom-made stainless steel box. The ends of the heat exchange tubes extended out of the box as inlet and outlet water inlets. A peristaltic pump with intelligent flow rate regulation introduced room temperature water into the heat exchange tubes at a flow rate of 1000 ml / min. As the room temperature water flowed through the box, it received heat transfer from the composite phase change material through the heat exchange tubes. The temperature changes of the composite phase change material at different locations inside the box were monitored in real time on a computer using the seven temperature sensors placed inside the box, and temperature-time curves were obtained, such as... Figure 12 .
[0091] The composite phase change material cools to its phase change temperature after approximately 20 minutes, then enters the phase change process, completing the phase change in about 1.5 hours. It then cools to room temperature via sensible heat. The black line represents the temperature change of the outflowing water, which follows the same trend as the temperature change of the composite phase change material. However, in this example, the water flow rate is faster than in Example 6, and the cold water has a shorter residence time in the heat exchanger, not having enough time to receive more heat transfer; therefore, the temperature of the outflowing water is lower than in Example 6.
[0092] Example 8
[0093] Investigating the effect of a flow rate of 500 ml / min on the self-storage and heat release performance of a plate-type hollow tube accumulator:
[0094] Micron-sized graphite microsphere-based composite phase change material, plate-type hollow tubes, and seven temperature sensors were placed in a foam box with an outer volume of 390 mm * 390 mm * 390 mm and an inner volume of 330 mm * 330 mm * 330 mm, with acrylic sheets adhered to the inner wall. The foam box was then compacted and placed inside a custom-made stainless steel box. The two ends of the heat exchange tubes extend out of the box as inlet and outlet ports.
[0095] A peristaltic pump with intelligent water flow rate regulation introduces 70°C water into the heat exchange tube at a flow rate of 500 ml / min. As the hot water flows through the tank, it transfers heat to the composite phase change material through the heat exchange tube, thus storing heat in the heat storage phase. Figure 13 The heat storage tank of the hollow plate heat exchanger was heated by a hot water source at a flow rate of 500 ml / min and a temperature of 70℃. After about 0.5 hours of heating, the composite phase change material reached the phase change temperature and began to undergo phase change, with the temperature change becoming gradual. The phase change was completed in about 1 hour and 40 minutes, after which the temperature rose to about 65℃ via sensible heat. This process demonstrates that heat storage in the heat storage tank at a hot water flow rate of 500 ml / min can be completed in about 1 hour and 40 minutes.
[0096] A peristaltic pump with intelligent flow rate regulation introduces room temperature water into the heat exchange tubes at a flow rate of 500 ml / min. As the room temperature water flows through the chamber, it is heated by heat transfer from the composite phase change material via the heat exchange tubes. Seven temperature sensors placed inside the chamber monitor the temperature changes of the composite phase change material at different locations within the chamber in real time on a computer, generating temperature-time curves, such as... Figure 14 .
[0097] After approximately 40 minutes, the composite phase change material reaches its phase change temperature and begins to undergo phase change, with the temperature change becoming relatively gradual. The phase change is completed in approximately 2 hours and 40 minutes, after which the temperature drops to room temperature via sensible heat. This process indicates that releasing heat to the heat storage tank at a flow rate of 500 ml / min at room temperature can be completed in approximately 2 hours and 40 minutes.
[0098] For any points not covered above, existing technologies shall apply.
[0099] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.
Claims
1. A phase change energy storage box, characterized in that: The device includes a housing, which is filled with a composite phase change material. A heat exchange tube is embedded in the composite phase change material, and the inlet and outlet of the heat exchange tube extend to the outside of the housing. The preparation method of the composite phase change material is as follows: S1. Nanographite and nanocellulose are dispersed in deionized water and then ball-milled to obtain a nanographite-cellulose mixed solution. S2. Use an electronic atomizer to spray the nano-graphite cellulose mixture into a container filled with liquid nitrogen, then sieve the microspheres in the container and freeze-dry the microspheres to obtain micron-sized graphite microspheres. S3. After impregnating micron-sized graphite microspheres in molten phase change material for a period of time, the composite phase change material is obtained by heat filtration. The mass ratio of nanographite to nanocellulose is 1-10:1; The specific operation of step S3 is as follows: first, put the micron-sized graphite microspheres and phase change material into a container and then evacuate in a vacuum drying oven. Then, react at 80°C for 2 hours to obtain the micron-sized graphite microsphere-based composite phase change material, and then perform hot filtration in an oven at 80°C.
2. The phase change energy storage box as described in claim 1, characterized in that: The heat exchange tube is a U-shaped tube or a plate-type hollow tube.
3. The phase change energy storage box as described in claim 1, characterized in that: The box includes a stainless steel box and a foam box nested inside the stainless steel box, with acrylic sheets adhered to the inner wall of the foam box.
4. The phase change energy storage box as described in claim 1, characterized in that: Multiple temperature sensors are spaced apart on the inner wall of the enclosure.
5. The phase change energy storage box as described in claim 1, characterized in that: The mass-to-volume ratio of nano-graphite to deionized water is 1-10:100 g / ml.
6. The phase change energy storage box as described in claim 1, characterized in that: The ball milling speed is 400-600 r / min, and the time is 2-4 h.
7. The phase change energy storage box as described in claim 1, characterized in that: The phase change material is paraffin.
8. The phase change energy storage box as described in claim 1, characterized in that: Freeze-dry for 72 hours.