| High starch materials widely exist in agricultural products. And drying is one of the most important processing methods of agricultural materials. However, the current drying process for this high starch material has many shortcomings, such as difficult dehydration caused by starch gelatinization, easily crust, long drying time and serious color browning. In this work, process-based on temperature and humidity integration control drying (PTHICD) technology combined with tilted-tray air impingement drying (TAID) was applied to potato slices drying. The PTHICD combined with TAID characteristics and dried quality of the potato slices were investigated under different tilt angles (0,10,20and30°), spaces between trays and the nozzles (0,36,72,108and144mm), nozzle arrangement pitches (36,54and72mm), blanching times (0,30,45,60,75and90s), drying temperatures (50,60,70and80℃), air velocities (5,10,15and20m/s), slice thicknesses (5,10and15mm) and air humidity (10,20,30,40and50%RH) during its drying process.Based on PTHICD technology and TAID technology, a tilted-tray air impingement dryer based on PTHICD was designed. The technology was to make horizontal air flow impact at high speed to the surface of materials. Inclined multilayer structures were arranged in the dryer wagon, greatly increasing the loading capacity; material tray angles were flexible adjusted and it combined with the scour properties of hot and humid air flow, improving the uniformity of the drying process; the drying temperature, humidity and air velocity were regulated in real time by control system based on the material status, enhancing the heat transfer efficiency and the drying rate.The drying kinetics of potato slices indicated that all of the structural parameters including tilt material tray angles, spaces between trays and the nozzles, nozzle arrangement pitches, and processing parameters including drying temperature, air velocity, blanching time and slice thickness have significant effect on the drying uniformity coefficient, while the other parameters except tilt angles have significant effect on the drying time. The better structural parameter was the tilt tray angle for10°, spaces between trays and nozzles for72mm, nozzle arrangement pitch for36mm, which can get higher drying uniformity coefficient and shorter drying time. The whole drying process of potato slices occurred in the falling rate stage, and the internal moisture diffusion controls the entire dehydration process. The Fick’s second law of diffusion was used to determine the moisture effective diffusivity, which ranged from3.830×10-10m2/s to19.422×10-10m2/s with the increase of drying temperature, air velocity and significantly reduced with the increase of slices thickness. The drying activation energy of potato slices with10mm as its thickness was33.47kJ/mol, which was calculated by Arrhenius equation.The research of PTHICD characteristics and dried quality showed that it can shorten the drying process time effectively by enhancing the air humidity parameters at an appropriate time in the initial drying process; both of the air humidity parameters and the keeping time have a significant effect on the drying time and color of the dried product. The internal temperatures of potato slices treated by PTHICD were significantly higher than the continuous dehumidify controlled group. In the respect of contraction, it contributes to keep good volume after drying by holding high air humidity parameters at a longer period.Weibull distribution function can simulate the drying curves of potato slices based on the PTHICD precisely. It was found that the scale parameter (a) increased as the keeping time of air humidity parameters increased, while the shape parameter (β) showed a variation of fluctuation distribution. The calculated moisture diffusion coefficient (Dcal) of the potato slices were calculated, ranging from1.664×10-9m2/s to2.371×10-9m2/s and the geometric parameter (Rg) was fluctuated in a range of2.575-5.351. |
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