石蜡相变储热管放热时间的理论预测与验证

物料干燥是一个高能耗的过程,而且大多传统干燥都会产生环境污染,所以利用清洁,廉价的太阳能来干燥物料很有必要,但由于太阳能具有间歇性,使得储热材料成为了太阳能干燥过程中必不可少的部分.该文利用石蜡作为相变储热材料,对实际干燥过程中,石蜡放热过程中储热单元的一些特性进行了研究.结果表明,在实际干燥过程中,储热单元中的石蜡管中心和管壁一直存在温度差,而且换热介质的气流速度越大,管壁的温度减小得越快.与此同时,该试验还通过对干燥过程中石蜡管内部热量传递过程进行模拟,得到了石蜡凝固半径的理论表达式,通过理论表达式,得到了石蜡管放热时间的理论值,结果表明,放热时间理论值均高于试验实际得到的值,但是二者的误差都在5％以内,可以认为二者基本相符,所以这个理论放热时间公式可以用于预测物料干燥过程中储热单元中石蜡管的放热时间,既可以避免由于放热时间不够而浪费石蜡里面储存的能量,也可以避免由于时间过长而浪费时间.

Theoretic prediction and verification of heat release time for paraffin phase change heat storage tubes

Drying materials is an energy consumed process, which sometimes brings pollution to environment, therefore, it is necessary to use solar energy for material drying, which is clean and low cost. However, solar energy is intermittent, this makes heat storage materials involved in solar drying. Paraffin was taken as the phase change material in this paper to study the characters of paraffin units during drying process, the results showed that there was temperature difference between outside and inner paraffin tube. The wall temperature, which related to the air velocity, decreased more quickly along with the increase of air speed. Through simulating the heat transferring inner paraffin tubes, the theoretic expression of paraffin solidification radius (rx) was got, by which the theoretic values of heat release time were also got, the results indicated that though the theoretic values were higher than that of the practical, the errors were less than 5%, which showed that these two sets of values were correspond to each other. Thus, this theoretic heat release equation could be used to predict the heat release time during material drying, which could not only avoid wasting energy stored by paraffin because of the limited time, but also avoid wasting time.