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ANALYSES OF TEMPERATURE AND MOISTURE PROFILES DURING APPLE DRYING.

机译：苹果干燥过程中的温度和水分特征分析。

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摘要

An experimental system has been designed to investigate the drying rate, temperature and moisture profiles developed within food materials during forced convective air drying. Moisture profiles were determined using the gamma ray densitometry, and embedded thermocouples were used to sense the local temperatures. The overall drying rate was measured using an electronic balance. A microcomputer and a computer front end were implemented for data acquisition and experimental control. An evaporation front was observed in a narrow region of the apple specimen, this front moved into the sample as drying progressed. The amount of apple shrinkage was determined to be linearly related to the receding distance of the evaporation front.;The experimental results from various drying conditions were collected and analyzed. The theoretical pseudo wet bulb temperature calculated from the drying air conditions agreed very well with the experimental results. The apple drying rate fell in the falling rate period when apples were dried at a relatively low humidity. The air humidity has the greatest influence of any of the drying conditions on the pseudo wet bulb temperature and on the time period of the first falling rate period. The temperature dependence of the drying rate followed an Arrhenius type of equation.;The heat and mass transfer coefficients were evaluated from the temperature profile, moisture profile and the drying rate curves. A linear relationship exists between the Nusselt number and the square root of the Reynolds number. A relationship of the Nusselt number, Prandtl number and Reynolds number in the drying period of 0 to 3 hours was developed, i.e., Nu = 0.719;A mathematical model based on the principles of heat and mass transfer in a porous solid was formulated to simulate the drying phenomena of apples. The Crank-Nicolson implicit finite difference scheme with the Tridiagonal Matrix Algorithm (TDMA) was employed to solve the parabolic partial differential equations.
机译：设计了一个实验系统来研究强迫对流空气干燥过程中食品材料内部的干燥速率，温度和湿度曲线。使用伽马射线密度测定法确定湿度曲线，并使用嵌入式热电偶感测局部温度。使用电子天平测量总干燥速率。实施了微型计算机和计算机前端以进行数据采集和实验控制。在苹果样品的狭窄区域中观察到蒸发前沿，随着干燥的进行，该前沿移至样品中。确定苹果的收缩量与蒸发前沿的后退距离成线性关系。收集并分析了各种干燥条件下的实验结果。根据干燥空气条件计算出的理论假湿球温度与实验结果非常吻合。当苹果在相对较低的湿度下干燥时，苹果的干燥速率在下降速率时期下降。在任何干燥条件下，空气湿度对假湿球温度和第一下降速率时间段的时间段的影响最大。干燥速率的温度依赖性遵循Arrhenius型方程。;传热和传质系数由温度曲线，水分曲线和干燥速率曲线评估。努塞尔数和雷诺数的平方根之间存在线性关系。建立了0至3小时干燥过程中的努塞尔数，普朗特数和雷诺数的关系，即Nu = 0.719；建立了基于传热和传质原理的多孔固体数学模型，用于模拟苹果的干燥现象。采用三对角矩阵算法（TDMA）的Crank-Nicolson隐式有限差分格式求解抛物型偏微分方程。

著录项

  • 作者

    CHIANG, WIN-CHIN.;

  • 作者单位

    Washington State University.;

  • 授予单位 Washington State University.;
  • 学科 Engineering Chemical.;Agriculture Food Science and Technology.
  • 学位 Ph.D.
  • 年度 1987
  • 页码 297 p.
  • 总页数 297
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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