HYDRATE ENERGY-STORAGE TEMPERATURE-CONTROL MATERIAL AND PREPARATION METHOD THEREFOR

Abstract

The present invention discloses a hydrate energy-storage temperature-control material and a preparation method therefor. The material includes a refrigerant hydrate and a cross-linked polymer. The preparation method comprises the following steps: first, preparing a refrigerant hydrate by using a high-pressure reactor, and conducting grinding, crushing and sieving to obtain hydrate particles; then, uniformly spraying polytetrafluoroethylene suspended ultrafine powder onto the surface of the hydrate particles by using an electrostatic spraying device, and putting the hydrate particles into a plasma instrument to modify polytetrafluoroethylene so as to allow free radicals to be formed on the polytetrafluoroethylene powder surface; finally, subjecting monomers to graft polymerization with the free radicals on the polytetrafluoroethylene surface under the irradiation of a high-pressure mercury lamp of UV lighting system to stabilize the structure of the material, preparing a final product. According to the present invention, a hydrate energy-storage temperature-control material with good stability is prepared. A method capable of preparing various types of refrigerant hydrate materials is provided. The product can give full play to the advantages of hydrate energy storage and temperature control, can be periodically used, and can be used in various fields such as building, refrigeration, etc.

Claims

1. A preparation method for a hydrate energy-storage temperature-control material, comprising the following steps: step 1. generating a refrigerant hydrate; step 2. crushing the hydrate: taking out the formed hydrate from a reactor, crushing, grinding and sieving by using a screen to obtain hydrate particles with a particle size of 180-250 μm and weighting same, and centrifuging by using a centrifugal machine at a revolving speed of not less than 2000 r/min for solid-liquid separation for 10-20 min; step 3. spraying polytetrafluoroethylene suspended ultrafine powder onto the hydrate particles by using an electrostatic spraying device: placing the hydrate particles crushed in step 2 on a conveyor belt (5), and adding a high-voltage electrostatic field between a nozzle (4) and the hydrate particles (7), so the polytetrafluoroethylene suspended powder is adsorbed and coated onto the hydrate particles under the action of electrostatic force and gravity; step 4. placing the hydrate particles (15) onto which the polytetrafluoroethylene powder is sprayed into a plasma instrument, and processing by using argon plasma so as to allow free radicals to be formed on the polytetrafluoroethylene surface; step 5. placing the hydrate particles wrapped by modified PTFE powder into a vacuum closed container, heating a monomer solution until steam evaporates, keeping an airflow pressure at 40-50 Pa by using a throttle valve (8), introducing into the closed container (14), cooling the closed container (14) by using a water bath of 25-30° C. and irradiating by using a high-pressure mercury lamp (11) of ultraviolet lighting system for 80-90 min, to promote graft polymerization of a monomer and free radicals; obtaining the hydrate energy-storage temperature-control material.

2. The preparation method for a hydrate energy-storage temperature-control material according to claim 1, wherein generating a hydrate in step 1 includes: {circle around (1)} cleaning and flushing the reactor by using deionized water, pouring the water into the reactor, and exhausting air from the reactor by using a vacuum pump; {circle around (2)} introducing refrigerant into the reactor, cooling the reactor to a temperature below the hydrate phase equilibrium temperature and above the freezing temperature by using a refrigeration cycle cooling system in which the reactor is placed according to the type of the refrigerant and the refrigerant hydrate phase diagram, pressurizing the reactor to the pressure point in a hydrate stabilization region corresponding to the temperature in the phase diagram after the temperature in the reactor is stabilized, and turning on a magnetic stirrer to initiate generation of the hydrate; {circle around (3)} judging whether the hydrate is initially formed through the increase of temperature in the reactor, if the temperature in the reactor suddenly increases, it is indicated that the hydrate formation reaction begins to release heat, and then if the temperature in the reactor gradually decreases until the temperature is stabilized at the original temperature within 1 h, it is indicated that a stable state is reached, and the hydrate is generated completely; measuring the temperature in the reactor by using a temperature sensor in the reactor, measuring the pressure in the reactor by using a pressure sensor, and gathering pressure and temperature signals by a data recording system and collecting same by a personal computer.

3. The preparation method for a hydrate energy-storage temperature-control material according to claim 2, wherein the hydrate refrigerant is a mixed liquid of one or more of tetrahydrofuran, cyclopentane and methylcyclohexane.

4. The preparation method for a hydrate energy-storage temperature-control material according to claim 2, wherein a magnetic stirrer is present in the reactor, and the magnetic stirrer has a revolving speed of 500-600 rpm, to initiate generation of the hydrate.

5. The preparation method for a hydrate energy-storage temperature-control material according to claim 1, wherein the polytetrafluoroethylene suspended ultrafine powder used in step 3 has a particle size of 2-12 μm, and is suitable for electrostatic spraying.

6. The preparation method for a hydrate energy-storage temperature-control material according to claim 1, wherein the electrostatic spraying device in step 3comprises: a storage bin (1), a coating propulsion device (2), a DC power supply (3), a nozzle (4), a conveyor belt (5) and a collection device (6), wherein the storage bin (1) is configured to internally store a spraying material, i.e. polytetrafluoroethylene suspended ultrafine powder; the coating propulsion device (2) is connected with a spraying device of the storage bin (1) and the nozzle (4) respectively; the nozzle (4) is made of a conductive material, configured to spray the polytetrafluoroethylene suspended ultrafine powder and connected with the negative electrode of the DC power supply (3), and dense negative charges are produced on the nozzle; the conveyor belt (5) of the spraying device is made of a conductive resin-based material and configured to place the hydrate particles (7), the conveyor belt (5) faces the nozzle, so that the suspended particles sprayed out from the nozzle (4) come into contact with the hydrate particles (7) to be sprayed; the conveyor belt (5) is connected with the positive electrode of the DC power supply (3), so that the hydrate particles carry positive charges, and then an electric field required for spraying is formed between the nozzle (4) and the conveyor belt (5).

7. The preparation method for a hydrate energy-storage temperature-control material according to claim 1, wherein the conveying speed of the conveyor belt (5) in step 3 is 0.5-2 m/s, the linear speed of spraying gas of the nozzle (4) is 100-200m/s, the powder content of the spraying gas is 1-2 kg/m.sup.3, the voltage of the high-voltage electrostatic field is 60-90 kV, and the distance between the nozzle (4) and the conveyor belt is 200-300 mm.

8. The preparation method for a hydrate energy-storage temperature-control material according to claim 1, characterized in that: wherein the monomer in step (5) is a monomer solution, which is one of a dopamine methacrylamide solution with a solution concentration of 10%, a 2-hydroxyethyl methacrylate solution with a solution concentration of 30% and a glycidyl methacrylate solution with a solution concentration of 30%, wherein the evaporation temperature of the dopamine methacrylamide solution is 109-110° C., the evaporation temperature of the 2-hydroxyethyl methacrylate solution is 95° C., and the evaporation temperature of the glycidyl methacrylate solution is 67° C.

9. The preparation method for a hydrate energy-storage temperature-control material according to claim 1, wherein the device in step 5 comprises: a throttle valve (8), a capacitance manometer (9), a gas distribution nozzle (10), a high-pressure mercury lamp (11) of ultraviolet lighting system, a water bath heating device (12), a vacuum pump (13) and a closed container (14), wherein the closed container (14) is connected to the throttle valve (8) and the capacitance manometer (9) at the inlet, to control the pressure of monomer steam entering the closed container; the closed container (14) is connected to the vacuum pump (13) at the outlet, and the gas distribution nozzle (10) is internally contained in the closed container to allow gas to be uniformly distributed in the closed container (14); the closed container is placed in the water bath heating device (12), to control the temperature in the closed container; and the high-pressure mercury lamp (11) of ultraviolet lighting system irradiates outside the closed container, to promote the reaction.

10. A hydrate energy-storage temperature-control material prepared by means of the method of claim 1, wherein a core of the material is made of a mixture of refrigerant and water, and a shell thereof is made of a cross-linked polymer.

Description

DESCRIPTION OF DRAWINGS

[0024] FIG. 1 is a system schematic diagram of an electrostatic spraying device of the present invention;

[0025] In the figure: 1. storage bin; 2. coating propulsion device; 3. DC power supply; 4. nozzle; 5. conveyor belt; 6. collection device; 7. hydrate particle;

[0026] FIG. 2 is a schematic diagram of a device used in the process of graft polymerization of monomer and free radicals of the present invention;

[0027] In the figure: 8. throttle valve; 9. capacitance manometer; 10 gas distribution nozzle; 11. high-pressure mercury lamp of ultraviolet lighting system; 12. water bath heating device; 13. vacuum pump; 14. closed container; 15. hydrate particle wrapped by modified PTFE powder.

DETAILED DESCRIPTION

[0028] Specific embodiments of the present invention are further described below in combination with the drawings and the technical solution.

[0029] Taking a cyclopentane hydrate as an example, a preparation method for a hydrate energy-storage temperature-control material, comprising the following steps:

[0030] (1) Generating a hydrate: cleaning and flushing a reactor for three times by using deionized water, pouring the water into the reactor and sealing, evacuating a top space, vacuumizing the reactor for 30 min by using a vacuum pump to exhaust air from the reactor, and then turning off the vacuum pump. Measuring the temperature in the reactor by using a temperature sensor in the reactor, measuring the pressure in the reactor by using a pressure sensor, and gathering pressure and temperature signals by a data recording system and collecting same by a personal computer. Injecting cyclopentane refrigerant into the reactor first as liquid refrigerant, i.e. cyclopentane is used, to allow the mole ratio of the cyclopentane refrigerant to water to be 1:17, and then cooling the reactor to a required temperature, i.e. 2° C. by using a refrigeration cycle water bath system in which the reactor is placed. Pressurizing the reactor to a required pressure, i.e. 0.2 MPa after the temperature in the reactor is stabilized, and turning on a magnetic stirrer (having a stirring speed of 550 rpm) to initiate generation of the hydrate. Judging whether the hydrate is formed through the increase of temperature or decrease of pressure observed in the reactor. In this specific embodiment, judging whether the hydrate is initially formed through the increase of temperature in the reactor, if the temperature in the reactor suddenly increases, it is indicated that the hydrate formation reaction begins to release heat, and then if the temperature in the reactor gradually decreases until the temperature is stabilized at the original temperature, i.e. 2° C. within 1 h, it is indicated that a stable state is reached, and the hydrate is generated completely. After the hydrate is generated completely, opening a reduction valve, and taking out the hydrate from the reactor rapidly.

[0031] (2) Crushing the hydrate: taking out the formed hydrate from the reactor, crushing, grinding, and sieving by using a screen to obtain hydrate particles with a particle size of 180-250 μm, and centrifuging by using a low-speed centrifugal machine at a revolving speed of not less than 2000 r/min for solid-liquid separation for 10-20 min. Taking out solid hydrate particles, and weighing same by using an electronic analytical balance.

[0032] (3) Spraying polytetrafluoroethylene suspended ultrafine powder onto the hydrate particles 7 by an electrostatic spraying device. The storage bin 1 is configured to internally store a spraying material i.e. polytetrafluoroethylene suspended ultrafine powder. The coating propulsion device 2 is connected with a spraying device of the storage bin 1 and the nozzle 4 respectively, and the spraying material in the storage bin 1 is pressurized, so that the polytetrafluoroethylene suspended ultrafine powder is sprayed out from the nozzle. The coating propulsion device 2 comprises a liquid propellant and carrier gas. The nozzle 4 is made of a conductive material, configured to spray the polytetrafluoroethylene suspended ultrafine powder and connected to the negative electrode of the DC power supply 3, and dense negative charges are produced on the nozzle. The conveyor belt 5 of the spraying device is made of a conductive resin-based material and configured to place the hydrate particles 7. The conveyor belt 5 faces the nozzle, so that the suspended particles sprayed out from the nozzle 4 come into contact with the hydrate particles 7 to be sprayed. The conveyor belt 5 is connected with the positive electrode of the DC power supply 3, so that the hydrate particles carry positive charges, and then an electric field required for spraying is formed between the nozzle 4 and the conveyor bel 5. After entering the electric field, the polytetrafluoroethylene suspended particles carrying charges may automatically fly towards the hydrate particles under the influence of the electric field force until the hydrate particles 7 are completely wrapped by the polytetrafluoroethylene suspended ultrafine powder and fall into the collection device 6.

[0033] (4) Placing the hydrate particles onto which the polytetrafluoroethylene powder is sprayed into a PMT100A plasma instrument with a power of 200 W, processing by using an argon plasma at a gas flow of 120 ppm and a pressure of 45 Pa for 6 min, to allow free radicals to be formed on the polytetrafluoroethylene surface; and irradiating by using an ultraviolet lamp to measure the concentration of the free radicals on the polytetrafluoroethylene surface.

[0034] (5) Placing the hydrate particles 15 wrapped by modified PTFE powder into the vacuum closed container 14, heating a monomer solution with a solution concentration of 10%, i.e. dopamine methacrylamide solution until steam evaporates, keeping an airflow pressure at 46.7 Pa by using a throttle valve 8, introducing into the closed container 14 by a capacitance manometer 9 through a gas distribution nozzle  Connecting the closed container 14 to the vacuum pump 13, cooling by using a water bath 12 of 30° C. and irradiating by using a high-pressure mercury lamp 11 of ultraviolet lighting system for 80 min (the power of the high-pressure mercury lamp 11 of ultraviolet lighting system is 1000 W, and the ultraviolet intensity is 6 mW/cm.sup.2), until the graft polymerization reaction is completed, obtaining a stable shell formed from PDMA-PS on the polytetrafluoroethylene surface. Cleaning by using methanol and drying under nitrogen flow, obtaining the hydrate energy-storage temperature-control material.

[0035] (6) Measuring product: measuring the mass of the hydrate energy-storage temperature-control material by the electronic analytical balance; measuring the particle diameter of the hydrate energy-storage temperature-control material by using an LA960 particle size analyzer of which the operating temperature is 25° C.; measuring the composition and latent heat of the hydrate energy-storage temperature-control material by using a differential scanning calorimeter, wherein all measurements are performed in a nitrogen environment, each of the heating rate and cooling rate is 5° C./min. Sealing about 6 mg of the particles of the hydrate energy-storage temperature-control material in a stainless steel crucible with an O-ring. Converting the refrigerant into hydrate completely through thermal cycle: cooling a sample to a low temperature T.sub.low which is usually −30° C.; heating and scanning the sample at −30° C. to 40° C., completing heating and scanning for the first time, and keeping the sample at each temperature for 5 min to reduce thermal effects before formal measurements.

[0036] Experimental Data Processing Method:

[0037] Because the measurement results directly obtained by means of the preparation device and method for a hydrate energy-storage temperature-control material are mass, volume and phase change latent heat, there is a need to perform thermodynamic calculation on the measurement results. By calculating the hydrate mass percentage M.sub.hydrate %, the encapsulation rate R, the encapsulation efficiency E and the heat Q transferred from a single microcapsule to the outside world, the performance of the hydrate energy-storage temperature-control material used in the phase-change temperature-control field is studied.

[0038] The theoretical hydrate mass percentage of the sample is represented by M.sub.hydrate %:

[00001]$\begin{array}{cc}{M}_{\mathrm{hydrate}}\%=\frac{M_{hydrate}}{M}\times 100\%& \left(1\right)\end{array}$

where M.sub.hydrate represents the hydrate particle mass of the crushed hydrate, and M represents the total mass of the hydrate capsule products.

[0039] The encapsulation rate of the sample hydrate is represented by R:

[00002]$\begin{array}{cc}R=\frac{\Delta H_{m,\mathrm{hydrate}}}{\Delta H_m}\times 100\%& \left(2\right)\end{array}$

[0040] The encapsulation efficiency of the sample hydrate is represented by E:

[00003]$\begin{array}{cc}E=\frac{\Delta H_{m,\mathrm{hydrate}}+\Delta H_{c,\mathrm{hydrate}}}{\Delta H_m+\Delta H_c}& \left(3\right)\end{array}$

where ΔH.sub.m,hydrate represents the phase change enthalpy in the melting process of decomposing the hydrate into liquid water and liquid refrigerant, ΔH.sub.c,hydrate the phase change enthalpy in the solidification process of synthesizing the liquid water and the liquid refrigerant into hydrate, and ΔH.sub.m and ΔH.sub.c respectively represent the phase change enthalpies in the melting process and the solidification process of the hydrate energy-storage temperature-control product measured by using the differential scanning calorimeter.

[0041] The heat transferred to the outside world in the phase change process of a single hydrate energy-storage temperature-control particle is represented by Q:

[00004]$\begin{array}{cc}Q=-kA\frac{\mathrm{dt}}{\mathrm{dr}}=-4\pi r^{2}k\frac{\mathrm{dt}}{\mathrm{dr}}& \left(4\right)\end{array}$

integral:

[00005]$\begin{array}{cc}{\int }_{t_1}^{t_2}\mathrm{dt}=-\frac{Q}{4\pi k}{\int }_{r_1}^{r_2}\frac{\mathrm{dr}}{r^2}& \left(5\right)\end{array}$

[0042] Where t.sub.1,t.sub.2respectively represent the temperature (phase change temperature) of the hydrate in the particles and the external ambient temperature, k represents the heat conductivity coefficient of the material shell, and r.sub.1 and r.sub.2 respectively represent the inside radius and outside radius of the single material particle.

[0043] r.sub.1 can be calculated by the following formula:

[00006]$\begin{array}{cc}{r}_1={\left(M_{\mathrm{hydrate}}/\frac{4}{3}\pi \rho \right)}^{1/3}& \left(6\right)\end{array}$

where M.sub.hydrate represents the hydrate particle mass of the crushed hydrate, and p represents the density of the hydrate.

[0044] ∅.sub.hydrate can be calculated by the following formula:

[00007]$\begin{array}{cc}{\varnothing }_{\mathrm{hydrate}}=M_{\mathrm{hydrate}}/\frac{4}{3}\pi r_2{ }^3\rho & \left(7\right)\end{array}$

where ∅.sub.hydrate represents the percentage of the hydrate in the total volume of the material particles, and r.sub.2 represents the mean radius of the material particles measured by a particle size measuring instrument.

[0045] The density ρ of the cyclopentane hydrate can be calculated by the following formula:

[00008]$\begin{array}{cc}\rho =\frac{N_{w}M{W}_{H_{2}O}+y_1{\alpha }_{1}M{W}_g+y_2{\alpha }_{2}M{W}_g}{N_{\mathrm{Avo}}{V}_{\mathrm{cell}}}& \left(8\right)\end{array}$

where for ρ, according to the assumption from Sloan (1998), assuming that guest molecules completely occupy the large cage of the hydrate, N.sub.w represents the number of water molecules per unit cell, N.sub.w=136; MW represents molecule mass, the molecule mass of MW.sub.H.sub.2.sub.O is 18, and the guest molecule mass of MW.sub.g is 70; y represents the partial occupancy rate of each cavity, α represents the number of cavities of each water molecule, subscripts 1 and 2 respectively represent small cavities and large cavities, the cyclopentane hydrate only occupies the large cavities, thus y.sub.1=0, y.sub.2=1, and α.sub.1=16, α.sub.2=8. V .sub.cell represents the volume which is (17.3×10-10).sup.3m.sup.3 of each unit cell, and N.sub.Avo represents Avogadro's constant. The density of 964.691 g/cm.sup.3 of the cyclopentane hydrate can be obtained through calculation.

[0046] The heat storage capacity of the hydrate energy-storage temperature-control material particles is represented by Q.sub.h:

[00009]$\begin{array}{cc}{Q}_h={\int }_{t_i}^{t_1}{M}_{\mathrm{hydrate}}{c}_p\mathrm{dt}+M_{\mathrm{hydrate}}fL+{\int }_{t_1}^{t_2}{M}_{\mathrm{hydrate}}{c}_p\mathrm{dt}& \left(9\right)\end{array}$

where t.sub.1 represents initial temperature, t.sub.2 represents final temperature, f represents melting fraction, L represents phase change latent heat, and c.sub.p represents specific heat capacity of hydrate. The phase change latent heat can be obtained according to experimental data, L=338.800 kJ/kg which is higher than 247 kJ/kg of phase change latent heat of formic acid and 186 kJ/kg of phase change latent heat of propylene glycol.

[0047] The constant pressure heat capacity c.sub.p can be calculated by the following formula:

c.sub.p=a+bT+cT.sup.2+dT.sup.3   (10)

where a, b, c, d represent the heat capacity parameters of the hydrate, for the cyclopentane hydrate, a=−124.33, b=3.2592, c=2×10.sup.−6 and d=−4×10.sup.−9.

[0048] The hydrate energy-storage temperature-control material is used to release cooling amount and adjust the temperature in a room. When the initial temperature t.sub.i of the material is 2° C. and the final temperature t.sub.2 (ambient temperature) thereof is 15° C. and the hydrate in the material melts completely, the cyclopentane hydrate can release 349.118 kJ/kg of heat which is higher than 279.45 kJ/kg of heat released by formic acid and 218.37 kJ/kg of heat released by propylene glycol under the same condition, thereby having good energy storage characteristics.

[0049] The phase change time of a single hydrate energy-storage temperature-control material particle is represented by τ:

[00010]$\begin{array}{cc}\tau =\frac{M_{\mathrm{hydrate}}}{m_H}& \left(11\right)\end{array}$

where m.sub.H represents the phase change rate of the hydrate energy-storage temperature-control material particle.

[0050] According to the hydrate thermal decomposition rate model studied by Kamath, the phase change rate m.sub.H of the hydrate energy-storage temperature-control material particle can be calculated by the following formula:

[00011]$\begin{array}{cc}\frac{m_H}{{\varnothing }_{\mathrm{hydrate}}A}=6.464\times 10^{-4}{\left(t_2-t_i\right)}^{2.05}.& \left(12\right)\end{array}$