茶叶导热系数的研究

对六种不同形状和制法的茶叶的导热系数用线性热源法作了测定和研究。这种方法可以在物料的密度和比热未知的条件下,迅速取得物料导热系数的资料。研究结果表明,茶叶的导热系数为0.0362～0.0486W/m·k,相当于工程隔热材料的热特性;因此,在茶叶加工中必须重视对流给热的作用。在同等密度条件下,茶叶的导热系数与含水率呈正相关;在含水率相同条件下,茶叶的导热系数随容重的增加而提高。茶叶的形状、含水率和揉捻紧度不同,其导热系数不同。红碎茶的导热系数高于条形茶,发酵茶的导热系数高于不发酵茶。各种茶叶的茶汤导热系数与水接近。试验采用的线性热源结构简单、应用方便、样品容易制作并且测定迅速,还可在现场取样测定,便于进行动态跟踪研究。

STUDY ON THERMAL CONDUCTIVITY OF TEAS

A new refined line-source technique is presented for rapid determination of thermal conductivity of teas. The technique is based on the temperature response of a point in an infinite solid near a line-source of heat, and adapted to finite samples for obtaining thermal conductivity. This transient test is very short in duration (under 5min) as comqared with several hours for steady-state devices. Conductivity results are presented for six kinds of Chinese teas. The broken shaped (granular shape) leaves have higher values of thermal conductivity than the eyebrow shaped. The fermented tea leaves have higher values of thermal conductivity than unfermented. The predictive models have been established for describe the relation between the moisture content and thermal conductivity of teas.