| The proportion of HVAC energy consumption in building energy consumption is increasing day by day.It is of vital importance to use energy more reasonably and efficiently.As a new type of building material,phase-change energy storage building material has both load-bearing and heat storage and temperature regulation performance.It can be used in building envelope structure to play the function of heat storage and temperature regulation as well as improve the indoor thermal environment,thus reducing the energy consumption of HVAC and achieving the purpose of energy saving.In this paper,by studying the thermal-physical properties of fatty acids and polyols,myristic acid(MA)lauric acid(LA)and myristic alcohol(TD)were selected as phase change materials of this subject.Based on the theory of eutectic low eutectic,the aim was to prepare ternary composite phase change materials suitable for this subject,while improving the utilization rate of phase change materials;the component ratio eutectic temperature and dissolution heat of the composite phase change material were predicted.Combined with the theoretical prediction and through the step cooling curve and differential scanning calorimetry(DSC)test,the ternary composite phase change material suitable for this topic was obtained,and it was characterized by DSC test Fourier infrared spectroscopy(FT-IR)test;in comparison to three kinds of material such as expanded perlite ceramsite diatomite adsorption performance,combined with subsequent pre-packaged test,choosing diatomite as adsorption material of this topic,the preparation of TD-MA-LA/diatomite finalize the design phase change materials,performance characterization of the phase change after absorption of diatomite,the phase change under different adsorption rate of diatomite seepage stability test,encapsulation effect through hot and cold cycle endurance test evaluation,combining with the packaging cost and process,choose good packaging way;the concrete was designed according to the strength grade of C25 concrete,and the three types of aggregate prepared were added into concrete instead of gravel respectively,hence studying the effect of aggregate content,type on the mechanical and thermal properties of concrete.The phase change cycle test was conducted to evaluate the phase change cycle stability;Two kinds of phase change concrete hollow block walls were designed according to the blending method of phase change aggregate.Furthermore,normal concrete hollow block wall was designed for comparison,and the steady state non-steady state non-periodic heat transfer test was carried out.The results showed that:(1)When myristic alcohol(TD): myristic acid(MA): lauric acid(LA)= 4.15: 2.05:3.80,the phase change temperature and latent heat of phase change materials prepared by TD-MA-LA ternary composite were 20.1℃ and 154.6J/g,which met the requirements of building energy conservation.FT-IR test showed TD,MA and LA did not react in the composite process,and the infrared spectra of TD-MA-LA after 500 phase transformation cycles were basically the same as before,that was to say,TD-MA-LA ternary composite phase change material had good thermochemical stability.(2)The adsorption results showed that the maximum adsorption rate of diatomite was54.5%,and the adsorption performance was excellent;DSC tests showed that the phase transition temperature of phase-change diatomite was basically unchanged,and it had a high latent heat of phase transition,and its thermal properties were stable after 50 cycles of phase transition;FT-IR test showed that diatomite did not react with phase-change materials in the adsorption process,which was pure physical adsorption.Seepage stability test showed that the adsorption rate was less than 30%,the phase transition of diatomite in the presence of phase change materials could be very stable in the surface of the diatomite or internal pore,when adsorption rate reached 40%,the existence of phase change materials instability,when reaching the maximum adsorption rate,the presence of phase change materials were in very unstable state.Therefore it was necessary to carry out its encapsulation.Hot and cold cycle durability test showed that the styrene acrylic emulsion and cement powder encapsulation mode shape of phase change materials in the circulation of hot and cold about 10 times that to achieve stable quality,almost no leak,mass loss rate was lesser,at 0.65%,packaging the most outstanding performance.In the end,integrated packaging cost and process,selection of cement powder was carried out on the phase transition of diatomite bulk packaging.(3)The greater the amunt of added aggregate,the worse the mechanical properties(compressive resistance and flexural resistance)of the concrete,and the lower the thermal conductivity;When the amount of added aggregate was constant,adding aggregate with higher adsorption rate would make the mechanical properties of concrete worse,and the addition of phase change diatomite aggregate would increase the thermal conductivity of concrete slightly higher than that of pure diatomite aggregate.After 30 phase transformation cycles,the compressive strength and thermal conductivity of all types of concrete were basically unchanged,and the stability of phase transformation cycle of concrete was great.(4)Under the steady-state heat transfer,the heat transfer resistance of the two phase-change walls was less different,the heat transfer resistance of direct-mixed and void-filled phase change concrete hollow block walls increases by 12.2% and 11.3%,respectively,compared with that of ordinary concrete hollow block walls,and the thermal insulation performance of the phase-change wall was more excellent.Under the unsteady heat transfer,the two kinds of phase-change walls showed excellent “peak cutting and valley filling” ability.In the time when there was sufficient phase change material,the final heat storage and temperature regulation effect of the two kinds of phase-change walls had little difference,and they were both suitable for building energy saving application. |
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