Research On Preparation And Performance Of Stearic Acid-PCM Microcapsule

Energy resource crisis became a serious restriction to economic development. Energy storage technology can used to solve the out-tune-problem of power supply and need.This technique has a perspective usage in many fields such as solar energy utilization,electrical peak adjusting,waste heat recycling and air-conditioner energy storage for industrial and civil buildings and so on.Recently it become a active advancing research direction to study phase change material with a latent heat which can store and use energy to increase power efficiency and exploit renewable energy. This paper mainly study how to optimize the technique to wrap stearic acid with silicon-oxygen structure in water glass to produce core-shell-structured PCM.And how to strengthen its surface has also been studied.A thermal model and a experiment platform have been established to analyze the temperature-to-time response of the PCM and insulation material composite structure within a wallboard and study the initial way to use properly.Through the whole experiment in producing and surface strengthen process as well as the PCM put in wallboard research,some conclusion can be drew as follows:1.About the producing process and key parameter controlling:(1)The basic proportion of PCM microcapsule is as stearic acid:soluble glass: hydrochloric acid=1:1:0.24.Using chemically pure and industrial stearic acid can produce two types of PCM microcapsule according to the proportion..Industrial stearic acid can substitute chemically pure stearic acid to produce microcapsule in order to reduce cost when the using temperature is not specially requied.(2) Dilute both the soluble glass and hydrochloric acid with 5 times water can control the process nice and easily;The sequence of how to drop in the reacting matters has been comfirmed.The pH value of the system should be controlled within the range of 10-10.2 to make the shell wrapping up well.The best heat temperature is about 70℃which will get wrapped well and even size distributed PCM microcapsule.(3) When add some little alcohol as solvent(about 20%wt of stearic acid),the solute glass gelatin can be downsized to make the shell wrap well and increase the latent heat a little.But adding alcohol solvent more than 60%wt of stearic acid could make the core and shell distribute non-equally and cause phase-disengagement easily.2.About the surface strengthen technique of PCM mierocapsule:(1) When the abtained PCM capsules were soaked in hydrochloric acid and acetic acid(pH=3),the sodium stearate will restore to stearic acid with a volume expansion which will cause the breaking of Si-O structure to a bad wrap effect.So this PCM microcapsule can't be soaked in acid with a low pH value(pH≦3).(2) Using Fe³⁺ to strengthen the microcapsule surface will actually cause the shell breaking as a fierce action will happen between Fe³⁺ and the shell.While using Al³⁺ can have the microcapsule surface strengthened.(3) When using Ca²⁺ to strengthen the microcapsule surface,the stearic acid exposed in center part of the microcapsule could turn into calcium stearate which help to complete the shell to wrap well.3.About the initial way to use PCM properly in a wallboard:(1) A temperature-to-time-response experiment platform has been established for PCM and insulation material composite structure within a wallboard.Under the lab condition we found that when the PCM part was put in the third layer the system take a much longer time,about 600 min and 600 min to heat up and cool down, which prolonged a lot as that of a standard wallboard was 50 rain and 50 min.And also the PCM partact the best based on the temperature-to-time response relationship analyse of the innermost layer.The result is quite consistent with the thermal model.(2) A temperature-to-time-response experiment platform is established for PCM and insulation material composite structure in three dimensions.With the same kind of PCM substitute inner part of EPS insulation,the test result showed the inner peak temperature has dropped by 17℃and the total cool time has prolonged greatly to1000 min compared with the system without PCM which means the system thermal inertia has been improve greatly.