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    Home > Coatings News > Paints and Coatings Market > General knowledge of coating: phase change energy storage technology

    General knowledge of coating: phase change energy storage technology

    • Last Update: 2020-04-03
    • Source: Internet
    • Author: User
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    The main results are as follows: 1

    The mechanism of PCMs When the phase change material changes from liquid state to solid state, it must undergo the change of physical state

    In these two phases, the material should absorb heat from the environment

    On the contrary, it should release heat to the environment

    The energy that can be stored or released when the physical state changes is called phase change heat, and the temperature range of phase change is very narrow

    When the physical state changes, the temperature of the material itself is almost unchanged before the completion of the phase transformation

    When a large amount of phase change heat is transferred to the environment, a wide temperature platform is formed

    The appearance of the temperature platform reflects the extension of the constant temperature time, and can be connected with sensible heat Application scope and advantages of roller ceramic coating Recommended introduction: the surface of ceramic rubber plate used for roller ceramic coating is cast into durable rubber plate by hundreds of independent small ceramic pieces

    Each ceramic piece has raised characteristics

    Under general conveyor belt pressure, thousands of unique cast bumps can produce positive traction, prevent slipping and extend the service life of conveyor belt roller

    At the same time, the bottom layer adopts high-quality rubber, which has strong elasticity and can play a good impact resistance role

    The scope of application of roller ceramic coating is one three six 83857180 (the same as V) 1

    Roller coating in extremely harsh working environment 2

    The belt joint is not suitable for fixing with iron buckle; 3

    It is suitable for leather Paint Home News: 1

    The mechanism of phase change energy storage materials

    When phase change from liquid to solid, phase change materials need to experience the change of physical state

    In these two phases, the material should absorb heat from the environment

    On the contrary, it should release heat to the environment

    The energy that can be stored or released when the physical state changes is called phase change heat, and the temperature range of phase change is very narrow

    When the physical state changes, the temperature of the material itself is almost unchanged before the completion of the phase transformation

    When a large amount of phase change heat is transferred to the environment, a wide temperature platform is formed

    The appearance of the temperature platform reflects the extension of constant temperature time, and can be distinguished from sensible heat and insulating materials

    Insulating materials only provide the gradient of heating temperature change

    The latent heat is stored or released during the thermal cycle of phase change materials

    The latent heat absorbed or released by the phase change material is quite large though the temperature is constant during the melting or solidification process

    Taking the ice water phase change process as an example, the latent heat absorbed by the phase change material and the heat absorbed under the ordinary heating conditions are compared

    When the ice melts, it absorbs 335j / g latent heat

    When the water is further heated, it only absorbs about 4 jars of energy for every 1 ℃ rise in temperature

    Therefore, the latent heat absorbed in the phase change process from ice to water is almost 80 times higher than that in the heating process outside the phase change temperature range

    In addition to ice water, more than 500 kinds of natural and synthetic phase change materials are known, and their phase change temperature and heat storage capacity are different

    By combining phase change materials with common building materials, a new type of composite energy storage building material can be formed

    This kind of building material has the advantages of both ordinary building materials and phase change materials

    At present, the latent heat of the phase change material is about 17oj / g, while the mass of the phase change material is 190 times of that of the ordinary building materials when the temperature changes 1 ℃

    Therefore, the composite phase-change material has the incomparable heat capacity of common building materials, which is very beneficial to the room temperature stability and the air conditioning system condition stability

    Phase change materials should have the following characteristics: narrow solidification melting temperature, high latent heat of phase change, high thermal conductivity, large specific heat, no supercooling or very small degree of supercooling during solidification, stable chemical properties, low vapor pressure at room temperature

    In addition, phase change materials should be compatible with building materials and can be absorbed

    2

    According to the form and process of phase change, phase change energy storage materials are mainly divided into solid-solid phase change and solid-liquid phase change energy storage materials; according to the temperature range of phase change, phase change energy storage materials are divided into high, medium and low temperature energy storage materials; according to its composition, phase change energy storage materials are roughly divided into inorganic materials and organic materials, including polymers)

    Generally, phase change materials are composed of many components, including main heat storage agent, phase change point regulator, anti supercooling agent, anti phase separation agent, phase change accelerator and other components

    2.1 at present, the solid-liquid phase change materials developed at home and abroad mainly include inorganic hydrated salts and organic matters

    2.1.1 high temperature phase change materials of inorganic energy storage materials mainly include pure salt (such as LIF, LiH), alkali (such as NaOH), metal and alloy (such as mg Cu) high temperature molten salt and mixed salt, etc

    High temperature molten salts are mainly fluorides, chlorides, nitrates, carbonates and sulfates

    The temperature range of mixed salts is wide, and the latent heat of melting is large

    They are mainly used in heat engine, solar power station, MHD power generation, artificial satellite and so on

    Because of its corrosiveness, high price, complex structure of heat exchanger and other reasons, they are seldom used

    (1) Pure salt: LiH has a small molecular weight and a very high melting heat of 2840j / g), which has been used as an energy storage material on artificial satellites

    LIF is also an ideal energy storage material

    Stirling heat engine is started with the sensible heat of 550-848 ℃ and the melting heat of 843 ℃, and vacuum sealed type is adopted

    The disadvantage is the high price, which can only be used in special occasions

    (2) Alkali: high specific heat of alkali, high melting heat and strong stability

    The steam pressure is very low at high temperature

    The price is cheap, and it is also a better energy storage material

    NaOH has phase transition at 287 ℃ and 318 ℃, and its latent heat is 330j / g

    (3) Metals and alloys: metals must be low toxic and cheap

    Aluminum is a good energy storage material because of its high melting heat, high thermal conductivity and low steam pressure

    The melting heat of mg Zn, Al Mg, Al Cu and mg Cu alloys is also very high, and they can also be used as energy storage materials

    (4) Mixed salt: all kinds of salts can be prepared into energy storage materials in the temperature range of 120-850% according to the needs

    The heat of melting is large, the volume change is small and the heat transfer is good

    Inorganic hydrated salts have a large melting heat and a fixed melting point, which is an important class of phase change materials at medium and low temperature

    There are mainly crystalline hydrated salts, molten salts, metals or alloys, etc

    Crystal hydrated salt provides nearly 7O kinds of phase change materials with melting point from several degrees Celsius to more than 100 degrees Celsius

    This kind of phase change material is usually the most important one of the medium and low temperature phase change materials

    This kind of material has the advantages of large melting heat, high thermal conductivity, small volume change during phase change and low price

    Most of them are halides, nitrates, sulfates, phosphates, carbonates and acetate of alkali and alkaline earth metals

    However, such materials are prone to "supercooling" and "phase separation"

    "Supercooling" means that the substance does not crystallize when it condenses to the condensation point of the towel, but starts to crystallize when the temperature below the "condensation point" is fixed, resulting in the fluctuation of the intersection temperature

    Supercooling phenomenon is related to material property, cooling speed, impurity type and content

    In order to prevent supercooling phenomenon, anti supercooling agent with small supercooling tendency, slightly higher melting point than phase change material and similar composition number property is often added

    "Phase separation" refers to the salt water separation often occurs in the process of repeated phase transformation

    Some salts are not soluble in the crystal water and sink at the bottom, and no longer combine with the crystal water to form a layered phenomenon, resulting in a significant decline in energy storage capacity and shortening the service life

    For this reason, thickener and crystal structure modifier are often used as phase separation inhibitor

    In order to meet the requirements of application, softener needs to be added

    Such as sodium silicate, polyacrylamide, glycerin, etc

    In order to adjust the phase change temperature, we can use mixed phase change materials, such as sodium sulfate hydrate and sodium carbonate hydrate with different molar ratio, which can adjust the phase change point at 24-32 ℃

    2.1.2 common organic phase change materials for organic energy storage materials include high-grade fatty hydrocarbons, fatty acids or their esters or salts, alcohols, aromatic hydrocarbons, aromatic ketones, amides, freon, polyhydroxycarbonic acids and polymers

    Polymers include polyolefins, polyols, polyols, polyacids and polyamides

    Paraffin is a mixture of straight alkanes

    The melting point of commonly used paraffin phase change materials is 12-75.9 ℃, and the melting heat is 150j / g to 250j / g

    The advantages are high melting heat, generally cold, non precipitation, stable performance, non corrosiveness and the lowest price in organic phase change materials

    The disadvantages are low thermal conductivity and low density

    Esters are also commonly used organic compounds, and their properties are similar to paraffin

    Polyolefin is also a common organic energy storage material

    The latent heat of polyolefin organic energy storage materials generally does not produce supercooling or phase separation phenomenon

    It can stably absorb and release heat for a long time, but the melting temperature of most products is above 100 ~ C

    If it is used in solar energy storage, it is generally difficult to reach this temperature, so its melting point should be appropriately reduced, so as to expand the scope of application

    The specific ways to reduce the melting point are: one is to add liquid additives to polyethylene, the more the amount is added, the greater the decrease of melting and crystallization temperature; the other is to mix different olefin components, such as polyethylene and polypropylene or polyethylene of different manufacturing methods

    The phase transition temperature and enthalpy of homologous organic compounds increase with the increase of carbon chain

    Therefore, energy storage materials with different phase change temperatures can be obtained by changing the length of carbon chain, but the increasing value of phase change temperature decreases with the increase of carbon chain

    Polymer phase change materials are mixtures with certain molecular weight distribution, long molecular chain and incomplete crystallization, so there is a melting temperature range in the process of phase change

    Organic phase change materials have the characteristics of good solid forming, difficult phase separation and supercooling, less corrosiveness and stable performance

    However, compared with inorganic phase change materials, they have poor thermal conductivity, low melting point, small heat of dissolution, volatile and easy to burn

    2.2 the solid-solid phase change energy storage materials are mainly composed of polyols, polymers and layered perovskites

    2.2.1 polyols are widely used in solid solid solid phase change energy storage materials

    Polyol phase change materials mainly include pentaerythritol PE), 2,2-dicarboxymethyl-1-propanol PG, neopentyl glycol NPG, tricarboxymethyl ethyl: TMP, tricarboxymethyl aminomethane, etc

    They take advantage of the transition from ordered to disordered crystal form to absorb and release heat

    In order to meet the different requirements of the actual situation for the phase change temperature, two or three polyols are generally mixed according to different proportions to adjust the phase change temperature

    The phase transition temperature and enthalpy of polyol mixtures with different kinds and proportions have great changes, among which the pk-tmp system formed by adding TMP is the best

    Polyol phase change materials have the characteristics of stable performance, long service life, large phase change enthalpy, no liquid phase and small volume change

    2.2.2 polyethylene is widely used in polymer phase change materials

    Polyethylene is cheap, easy to process, smooth surface, closely combined with the surface of the heating body, high thermal conductivity, and the crystallinity has a linear relationship with its thermal conductivity

    In particular, polyethylene with high structural regularity, such as high-density polyethylene and linear low-density polyethylene, has high crystallinity and high melting heat per unit weight

    2.2.3 layered perovskite is a kind of organic metal compound

    It is called layered perovskite because its crystal structure is layered

    The pure layered perovskite and its mixture have a high phase transition enthalpy of 42-146j / g and a small volume change of 5% - 10% when they are in solid-solid transition, which is similar to the mineral perovskite

    It is suitable for high temperature applications
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