Abstract

Rice (Oryza sativa L.) is one of the most produced and consumed cereals in the world, being characterized as the main food of more than half of the world population, since it is source of energy, protein, vitamins and minerals. Freshly harvested rice from the field generally has a high moisture content to be stored safely and, therefore, a suitable drying process needs to be conducted to decrease the physical-chemical activity of the product and inhibit the associated microbial activities. In this work, experiments were carried out on the intermittent drying of rice grains, in order to evaluate the effects of different drying air temperatures (40, 50, 60 and 70 °C) and tempering times (30, 60, 120, 180 and 240 min). Intermittent drying was simulated by means of a new liquid diffusion model based on a prolate spheroid geometry. To validate the model, the solution was fitted to the experimental data for the drying air temperatures of 40 and 70 °C and tempering periods ranging from 0 to 180 min. The results show that, for all experiments of intermittent drying of rough rice, the effective operating time decreased compared to the continuous drying. In addition, intermittent drying produces lower temperature on the grain surface, which minimizes the thermal damages caused to the product during the process. Numerical simulations provide information on moisture distribution inside the rice grain during the periods of interruption in hot air application. After 15 min of drying at temperatures of 40 and 70 °C, followed by a 60-min pause at room temperature, it is possible to respectively reduce about 72 and 68% of the moisture content gradients inside the rice grain. With tempering of 180 min, it is possible to eliminate almost all moisture content gradients for the drying at 70 °C.

中文翻译：

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连续和间歇干燥稻谷粒的建模和实验

摘要

水稻（水稻L.）是世界上生产和消费最旺盛的谷物之一，被誉为世界一半以上人口的主要食品，因为它是能量，蛋白质，维生素和矿物质的来源。来自田间的新鲜收获的大米通常具有高水分含量以安全地存储，因此，需要进行适当的干燥过程以降低产品的物理化学活性并抑制相关的微生物活性。在这项工作中，对米粒的间歇干燥进行了实验，以评估不同干燥空气温度（40、50、60和70°C）和回火时间（30、60、120、180和180°C）的影响。 240分钟）。借助于基于长椭球形几何形状的新液体扩散模型来模拟间歇干燥。为了验证模型，该溶液符合40和70°C的干燥空气温度以及0至180分钟的回火时间的实验数据。结果表明，在所有间歇干燥糙米的实验中，与连续干燥相比，有效操作时间减少了。此外，间歇干燥会在谷物表面产生较低的温度，从而将过程中对产品造成的热损伤降至最低。数值模拟提供了在热风中断期间稻米内部水分分布的信息。在40和70°C的温度下干燥15分钟后，在室温下暂停60分钟后，可以分别减少稻米内部约72％和68％的水分含量梯度。回火180分钟