High-Quality Thawing of Frozen Food by Far-Infrared Radiation

(1)实验以冷冻金枪鱼为样本。样品被放置在恒温箱中，箱内设置风扇以控制空气流速，并由放置在箱上方的陶瓷加热器加热。用热电偶测量温度分布，并记录在软盘上。(2)数学模型采用表观比热模型预测冷冻食品的二维和三维传热。采用有限元方法求解基本方程和边界条件。热物性(表观比热、密度、导热系数)由Hakawa经验公式估算。(3)实验和数值计算结果我们进行了数值计算，考察了加热器温度、样品环境温度和样品厚度对解冻速度的影响。通过实验验证了该数学模型的有效性。使用热电偶测量了样品中的温度分布，与理论预测吻合较好。在这些实验中，由于样品表面温度上升到不可接受的水平，导致金枪鱼红色肌肉滴水损失或变色而导致的变质。然而，我们证明，通过将表面温度保持在10ﾟC以下，冷冻金枪鱼可以解冻而不会滴漏和变色。这是通过间歇照射能量或在表面温度达到7ﾟC时降低加热器温度来实现的。

(1) ExperimentFrozen tuna was used as a sample. The sample was placed in a constant temperature box, in which fans were set inside to control an air flow rate, and was heated by a ceramic heater placed above the box. The temperature distribution was measured by using thermocouples and was recorded on a floppy disk.(2) Mathematical modelAn apparent specific heat model was introduced to predict two dimensional and three dimensional heat transfer in frozen food. A finite element method was applied to solve the fundamental equation and boundary conditions. Thermal properties (apparent specific heat, density, thermal conductivity) were estimated by Hakawa's empirical equations.(3) Experimental and numerical calculation resultsWe performed some numerical calculations to examine the influence of the heater temperature, the ambient temperature of the sample and the sample thickness on thawing rate. Experiments were carried out to check the validity of the mathematical model. Temperature distributions in samples were measured by using thermocouples and they agreed well with the theoretical predictions.During these experiments, deterioration, which was caused by drip loss or discoloration of the red muscles of tuna, was occurred because the surface temperature of the sample increased to unacceptable levels. However, we demonstrated that frozen tuna could be thawed without drip loss and discoloration by keeping the surface temperature below 10ﾟC.This was performed by irradiation of the energy intermittently or by reducing the heater temperature when the surface temperature reached 7ﾟC.