冻融-热泵干燥机的设计与试验优化

Design and Experimental Optimization of Freeze Thaw Heat Pump Dryer

为探究冻融处理对香菇热泵干燥特性的影响,设计了一种冻融-热泵干燥机。依据自制冻融-热泵干燥机的结构特点,在干燥箱内的5个不同位置布置9个干燥床架,并在每个床架上均匀布置若干料盘。根据冷冻与融化速率对香菇物理性质的影响,设计快冻慢融的冻融干燥方法。重点考察新鲜香菇干燥品质的变化情况,主要指标有干基含水率、水分比、复水性、色差、干燥速率、有效水分扩散系数等,并结合4种典型薄层干燥模型,利用水分比进行数据拟合,从而建立干燥数学模型。结果表明:冻融香菇在干燥箱不同位置有效水分扩散系数在1.98×10^-7-2.36×10^-7m^2/s之间,色差、复水性差异性小,干燥后感官性较好,且复水值总体与色差L值呈正比;香菇冻融干燥各位置水分比和干燥速率变化情况基本一致,均匀性好。经过4次冻融处理,每次冻融后干燥速率短时间内有一定提高,随后下降,且随着冻融次数的增加,其对水分迁移速率的影响呈下降趋势,第4次冻融后干燥速率无明显变化,说明随着香菇含水率的下降,冻融处理对水分的剥离能力逐渐减弱。在20h进入单纯热泵干燥阶段,在30h基本达到平衡含水率,单纯热泵干燥过程存在加速与降速阶段,无明显恒速干燥阶段。冻融香菇在不同干燥条件下的干燥过程均满足HendersonandPabis方程,其中待定系数a,b,c,k,g,h与层架之间呈5次方关系,相关系数R2为0.998。本文为冻融-热泵干燥机的设计及香菇冻融干燥提供参考。

In order to explore the influence of freezing and thawing to the character of mushroom heat pump drying, designed a kind of freezing and thawing dryer. According to the structural features of freezing and thawing dryer, in five different positions of the drying box arrange nine drying bed, and in each frame are uniformly arrang some trays. In line with influence of the speed of frozen and thaw to physical property of mushroom, designed experiment scheme which fast frozen and slow melt. The experiment focused on the change of fresh letinous drying quality, leading indicator contain dry base moisture content, water ratio, rehydration, color difference, drying rate, effective moisture diffusion coefficient etc. and combine with four classic lamina dry model, taking advantage of water ratio to fit data, and establish dry mathematic model. The experimental results show that: the effective moisture diffusion coefficient of freeze-thaw of Letinous edodes in the drying box at different position is between 1.98×10-7 m2/s and 2.36×10-7 m2/s, color, rehydration of small differences, good sense of drying, and the rehydration value is proportional to L value. The change of moisture ratio and drying rate of Letinous edodes at different positions is consistent. After four times freeze-thaw treatment, each freeze-thaw after drying rate in short time has increased, then decreased. With the increase of freezing thawing times, the capacity of peel water is decline, increasing rate after the fourth freeze-thaw has no obvious change, manifestin the capacity of drive water migration has negative correlation with water content for Letinous edodes. At the time of twentieth, reaching pute heat pump drying stage, and the equilibrium moisture content is reached at the beginning of the 30th hour. There is a stage of acceleration and deceleration in the heat pump drying process, but don't exist obvious constant rate drying stage. The drying process of Letinous edodes under different drying conditions can be satisfied with the Henderson and Papis equation, and the undetermined coefficients a, b, c, k, g, h and the layer are 5 square relationship, the correlation coefficient R2 is 0.998. This paper provides a reference for the design of freeze thaw heat pump dryer and freeze thaw drying of Letinous edodes.