The Design And Experiment Of Hot-air Drying Equipment For Walnut

Drying is an essential processing step for walnut after its harvest. Walnut quality is not guarannteed by traditional drying method due to lacking of maturity drying equipments in domestic. Hot-air drying was applied to the walnut in this article and the equipment had been desiged. The drying experiments and model of walnut were investigated under different drying temperatures (35,40,45, and 50℃), air velocities(0.5,1.0,1.5, and 2.0 m/s)and varieties (Xinfeng, Xinxin 2, Zha 343, and Wen 185) during its hot-air drying process. At the same time, the quality of dried walnut was detected and analyzed.Based on the intrinsic characteristics of walnut, the equipment was designed and made. Single-chip microcomputer was employed to control the drying temperature and air velocities accurately and effectively. The angle between the screen and horizontal was 30° which could insure automatic discharge. The uniformity of wind field was increased by hyperboloid board.Walnut drying characteristics of hot-air was investigated. The whole hot-air drying process of walnut occurred in the falling rate period. Drying temperatures, air velocities and varieties had significant effect on its drying characteristics. The influence of these drying factors on on walnut drying time was in the following order:temperature> air velocity> variety. The moisture effective diffusivity and drying activation energy of walnut ranged from 5.7555 ×10-11 m2/s to 10.6508 ×10-11 m2/s and 32.20 kJ/mol to 37.89 kJ/mol, respectively. Dried walnut quality was evaluated by acid value and peroxide value which increased with the increase of drying temperature. The dried walnut quality was met the national food hygiene standards in this experiment. Experiment parameters that used for drying walnut were feasible. In order to improve the quality of dried walnut, the drying temperature should not be set too high. The drying process need adjust with walnut itself characteristics.Weibull distribtion function could simulate the drying curves of walnut precisely. Scale parameter (a) related with the temperature, air velocity and variety and it decreased with increasing of drying temperature and velocity. In addition, scale parameter had some difference with varieties. Shape parameter (β) depended on the variety that had little impact on the temperature and velocity.The pilot scale test showed that the walnut moisture content was gradiently reduced from top to bottom in the whole drying process. The temperature in the cabinet reached to the set temperature after drying 11 h. The charging depth of walnut had little influence on drying time. Dried walnut should be placed in the normal temperature for 2～3 day to guarantee the uniformity of moisture content. Compared with the widely used hot air drying room in Xinjiang, the processing cost was reduced a third. At present, the hot-air drying equipment has been used in Hotan and Aksu in Xinjiang and Xiaoyi in Shanxi.The hot-air drying technology was applied to walnut dry in this article. Deep bed drying of hyperboloid board of screen inclined was used. The batch processing ability was increased greatly. The current work has great significance toimprove the mechanization level and increasethe market competitiveness of walnut.