相变微胶囊悬浮液中颗粒润湿性对导热系数的影响

Effect of Particle Wettability on Thermal Conductivity of Microencapsulated Phase Change Suspension( MPCS)

本工作的目的是通过实验研究相变微胶囊悬浮液中颗粒润湿性对悬浮液导热系数的影响。主要研究内容为:(1)实验研究了十六烷基三甲基溴化铵(CTAB)、十二烷基硫酸钠(SDS)两种不同种类表面活性剂及表面活性剂加入量对几种常用颗粒壁材润湿性(接触角)的影响;(2)借助Hot Disk 2500s型热物性分析仪测试常用质量分数为10%的相变微胶囊悬浮液静态导热系数,观察导热系数与接触角的关系。结果表明,随着表面活性剂质量分数的增加,材料与溶液的接触角越来越小,润湿性得到改善;在小质量浓度范围(0%~0.05%)内,CTAB的改性效果比SDS的改性效果好;当表面活性剂的添加量达到0.05%后,SDS的改性效果比CTAB的改性效果好;随着润湿性的改善(接触角的减小),无论是Maxwell模型理论值还是实验测试值,导热系数都有升高的趋势,实验测试值升高幅度更大;在接触角为45~95°范围内,导热系数的理论值与实验值吻合较好,接触角小于45°时,导热系数的测量值与实验值差距较大,所以Maxwell模型只在接触角45~95°范围内能较好地表示该相变微胶囊悬浮液的导热系数。接触角小于45°时,Maxwell模型需要进行修正,并给出了修正系数A的值,证实了湿润热阻的假设。

The effect of particle wettability on thermal conductivity of microencapsulated phase change suspension was studied experimentally.The wettability of the MPCS,characterized by contact angle between solid particles and carrying fluid,was modified by two selected surfactants,i.e.,cetyltrimethyl ammonium bromide(CTAB)and sodium dodecyl sulfate(SDS)combining changing their concentration in the suspensions.Meanwhile,the Hot Disk 2500s thermal analyzer was applied to test the static coefficient of thermal conductivity of the microencapsulated phase change suspension(the mass fraction is 10wt%)and obtain the relation between the thermal conductivity and contact angle.The conclusion are as follows:(i)when the additive amount of surfactants falls into the range of 0%—0.05%,the effect of the CTAB is more significant than SDS.When the mass fraction of surfactants reaches 0.05%,the effect of CTAB and SDS in influencing contact angle is opposite.(ii)the decrease in the contact angle leads to the growth in thermal conductivity for both Maxwell model’s theoretical value and experimental results.When contact angle falls into the range of 45—95°,the Maxwell model’s theoretical results of the thermal conductivity can match experimental value very well,but inversely when the contact angle is smaller than 45°,there is a big gap between the two results.To remove this gap a correction factor“A”which is associated with contact angle is proposed.