石墨填料的形態(tài)和面向尺寸對復(fù)合相變材料傳熱特性影響的實(shí)驗(yàn)研究
發(fā)布時(shí)間：2018-09-12 20:48
【摘要】：熱能存儲是應(yīng)對能源危機(jī)、提高熱能利用效率的有效手段。采用有機(jī)相變材料的相變潛熱進(jìn)行能量存儲具有安全穩(wěn)定、相變過程近似恒溫等優(yōu)點(diǎn),得到迅速發(fā)展。然而,有機(jī)相變材料導(dǎo)熱系數(shù)低(-0.2W/(m·K))的缺陷嚴(yán)重限制了其使用范圍。目前,將高導(dǎo)熱的顆粒添加到有機(jī)相變材料中制備復(fù)合相變材料是增強(qiáng)其傳熱能力最受關(guān)注的方法。石墨因其導(dǎo)熱系數(shù)高(100W/(m·K))、密度小等特點(diǎn),日益成為添加物的首選材料。 首先利用真空吸附法制備不同飽和吸附量膨脹石墨(EG)／十六醇復(fù)合相變材料,綜合運(yùn)用SEM、XRD、FT-IR等手段研究了材料的形態(tài)、結(jié)構(gòu)和化學(xué)穩(wěn)定性,對比研究了吸附量對導(dǎo)熱系數(shù)的影響。EG的多孔結(jié)構(gòu)對液態(tài)相變材料具有較強(qiáng)的吸附定型作用,吸附量越大,導(dǎo)熱系數(shù)越小。以十二酸為基體材料時(shí)變化趨勢相似。超聲震蕩(300W,10s)得到的石墨納米片(GNS)對導(dǎo)熱系數(shù)的強(qiáng)化效果優(yōu)于EG。在此基礎(chǔ)上,通過控制超聲震蕩時(shí)間得到不同面向尺寸的GNS,研究了GNS的添加量、尺寸和溫度對十六醇基復(fù)合相變材料導(dǎo)熱系數(shù)的影響。導(dǎo)熱系數(shù)隨著GNS添加量的增加均近似線性增長,面向尺寸越大,強(qiáng)化效果越好。Nielsen模型在形狀因子A取100至180時(shí)可以較好的預(yù)測實(shí)驗(yàn)值。導(dǎo)熱系數(shù)對溫度幾乎無依賴性。此外,對比研究了石墨的形狀和種類對復(fù)合物傳熱特性的影響,片層狀的鱗片石墨效果最好,多孔碳最差,二維平面結(jié)構(gòu)的石墨烯(GNP)強(qiáng)化效果優(yōu)于碳納米管。綜合對比以上各種石墨材料強(qiáng)化導(dǎo)熱效果,雖然基體材料不同,超聲震蕩30min得到的GNS-30導(dǎo)熱強(qiáng)化效果與GNP相當(dāng)。 其次,針對上述導(dǎo)熱強(qiáng)化效果最好的兩種石墨材料(EG、GNS),實(shí)驗(yàn)中利用DSC對相關(guān)樣品的相變溫度(T)、相變潛熱(L)進(jìn)行測試,并解釋了相變潛熱變小的原因。石墨的加入對相變溫度的的影響無明顯規(guī)律,相變焓減小,小于計(jì)算值。GNS的尺寸對相變溫度和相變焓的作用規(guī)律不明顯。 最后本文搭建了相變傳熱實(shí)驗(yàn)臺,采用時(shí)間-溫度法分別測試純十六醇及復(fù)合相變材料儲熱單元的相變傳熱過程,探究石墨的吸附量、尺寸、加載量和石墨種類對傳熱過程的影響。石墨材料的加入使得復(fù)合相變材料的吸、放熱速率得到很大提高,在有效提高復(fù)合相變材料導(dǎo)熱系數(shù)的同時(shí),增大粘度,減少相變傳熱過程中的自然對流,使得低加載量下的強(qiáng)化效果不明顯。
[Abstract]:Thermal energy storage is an effective means to deal with the energy crisis and improve the efficiency of thermal energy utilization. The use of latent heat of organic phase change materials for energy storage has the advantages of safety and stability, and the process of phase transition is similar to the constant temperature, so it has been developed rapidly. However, the low thermal conductivity (-0.2 W / (m K) of organic phase change materials severely limits its application range. At present, adding high thermal conductivity particles to organic phase change materials to prepare composite phase change materials is the most concerned method to enhance their heat transfer ability. Because of its high thermal conductivity (100W/ (m K), density, etc.), graphite is becoming the preferred additive material. Firstly, the expanded graphite (EG) / hexadecanol composite phase change materials with different saturated adsorption amounts were prepared by vacuum adsorption method. The morphology, structure and chemical stability of the materials were studied by means of SEM,XRD,FT-IR and so on. The effect of adsorption amount on thermal conductivity. The porous structure of EG has a strong adsorption setting effect on liquid phase change materials. The larger the adsorption amount, the smaller the thermal conductivity. The trend of change is similar when dodecanoic acid is used as base material. The enhancement of thermal conductivity of graphite nanocrystalline (GNS) obtained by ultrasonic oscillation (300W / 10s) is better than that of EG.. On this basis, the effects of GNS addition, size and temperature on the thermal conductivity of hexadecanol based composite phase change materials were studied by controlling the ultrasonic oscillation time and GNS, with different dimensions. The thermal conductivity increases linearly with the increase of GNS content. The larger the size is, the better the strengthening effect is. Nielsen model can predict the experimental value better when the shape factor A is between 100 and 180. The thermal conductivity is almost independent of temperature. In addition, the effects of graphite shape and type on the heat transfer characteristics of the composites were compared. The lamellar flake graphite had the best effect, and the porous carbon was the worst, and the two-dimensional graphene (GNP) was better than the carbon nanotube. Comprehensive comparison of the thermal conductivity of various graphite materials above, although the matrix material is different, the GNS-30 obtained by ultrasonic shock 30min is comparable to that of GNP. Secondly, for the two kinds of graphite materials (EG,GNS) with the best thermal conductivity strengthening effect, DSC was used to measure the phase transition temperature (T),) latent heat (L) of the related samples, and the reason why the latent heat of phase transition became smaller was explained. The effect of graphite addition on the phase transition temperature is not obvious, but the enthalpy of phase transition decreases, but the size of GNS is less than the calculated value, and the effect of the size of GNS on the phase transition temperature and enthalpy is not obvious. Finally, a phase change heat transfer test bench was set up. The phase change heat transfer process of pure hexadecanol and heat storage unit of composite phase change material was measured by time-temperature method, and the adsorption capacity and size of graphite were investigated. The effect of loading quantity and graphite type on heat transfer process. With the addition of graphite, the absorption and exothermic rate of the composite phase change material is greatly increased. The viscosity of the composite phase change material is increased while the heat conductivity of the composite phase change material is increased, and the natural convection in the process of phase change heat transfer is reduced. The enhancement effect under low load is not obvious.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TB34
本文編號：2240179
[Abstract]:Thermal energy storage is an effective means to deal with the energy crisis and improve the efficiency of thermal energy utilization. The use of latent heat of organic phase change materials for energy storage has the advantages of safety and stability, and the process of phase transition is similar to the constant temperature, so it has been developed rapidly. However, the low thermal conductivity (-0.2 W / (m K) of organic phase change materials severely limits its application range. At present, adding high thermal conductivity particles to organic phase change materials to prepare composite phase change materials is the most concerned method to enhance their heat transfer ability. Because of its high thermal conductivity (100W/ (m K), density, etc.), graphite is becoming the preferred additive material. Firstly, the expanded graphite (EG) / hexadecanol composite phase change materials with different saturated adsorption amounts were prepared by vacuum adsorption method. The morphology, structure and chemical stability of the materials were studied by means of SEM,XRD,FT-IR and so on. The effect of adsorption amount on thermal conductivity. The porous structure of EG has a strong adsorption setting effect on liquid phase change materials. The larger the adsorption amount, the smaller the thermal conductivity. The trend of change is similar when dodecanoic acid is used as base material. The enhancement of thermal conductivity of graphite nanocrystalline (GNS) obtained by ultrasonic oscillation (300W / 10s) is better than that of EG.. On this basis, the effects of GNS addition, size and temperature on the thermal conductivity of hexadecanol based composite phase change materials were studied by controlling the ultrasonic oscillation time and GNS, with different dimensions. The thermal conductivity increases linearly with the increase of GNS content. The larger the size is, the better the strengthening effect is. Nielsen model can predict the experimental value better when the shape factor A is between 100 and 180. The thermal conductivity is almost independent of temperature. In addition, the effects of graphite shape and type on the heat transfer characteristics of the composites were compared. The lamellar flake graphite had the best effect, and the porous carbon was the worst, and the two-dimensional graphene (GNP) was better than the carbon nanotube. Comprehensive comparison of the thermal conductivity of various graphite materials above, although the matrix material is different, the GNS-30 obtained by ultrasonic shock 30min is comparable to that of GNP. Secondly, for the two kinds of graphite materials (EG,GNS) with the best thermal conductivity strengthening effect, DSC was used to measure the phase transition temperature (T),) latent heat (L) of the related samples, and the reason why the latent heat of phase transition became smaller was explained. The effect of graphite addition on the phase transition temperature is not obvious, but the enthalpy of phase transition decreases, but the size of GNS is less than the calculated value, and the effect of the size of GNS on the phase transition temperature and enthalpy is not obvious. Finally, a phase change heat transfer test bench was set up. The phase change heat transfer process of pure hexadecanol and heat storage unit of composite phase change material was measured by time-temperature method, and the adsorption capacity and size of graphite were investigated. The effect of loading quantity and graphite type on heat transfer process. With the addition of graphite, the absorption and exothermic rate of the composite phase change material is greatly increased. The viscosity of the composite phase change material is increased while the heat conductivity of the composite phase change material is increased, and the natural convection in the process of phase change heat transfer is reduced. The enhancement effect under low load is not obvious.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TB34
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