Study On Drying Characteristics And Nutrition Of Alfalfa Based On Infrared Hot Air Drying

Alfalfa,which is rich in protein,vitamins,minerals and other nutrients,is used as one of the main forages in animal husbandry.The drying and modulation process of alfalfa is particularly important.The traditional alfalfa drying method has low efficiency and large nutrient loss,which is difficult to meet the current requirements for alfalfa quality.At present,infrared hot air combined technology has the advantages of low energy consumption,high efficiency and less nutrient loss in drying modulation,which is widely used in drying process.In this study,in order to improve the drying efficiency of alfalfa and reduce its nutritional loss in the drying process,the infrared hot air combined drying technology was used for the drying test of alfalfa.The specific research contents and results are as follows:（1）Temperature field simulation of infrared hot air combined dryerThe turbulent model and heat transfer model of the dryer were established by using the fluid module and heat transfer module based on RANS equation in Comsol Multiphysics 5.6 software.By analyzing the temperature field distribution of the key section under different wind speed,temperature and radiation distance,the influence of different levels of drying parameters on the temperature field was obtained.The results show that the increase of wind speed improves the drying uniformity and reduces the ambient temperature below the normal inlet.The temperature increases while maintaining the overall uniformity of the temperature field and reducing the local temperature difference caused by the wind field;on this basis,increasing infrared radiation can further optimize the uniformity of the overall temperature cloud.（2）Study on drying characteristics of alfalfaThe infrared hot air combined drying technology was applied to study the drying characteristics of alfalfa.The drying characteristics under different drying parameters were analyzed,and the drying rate diagram was drawn.The effective moisture diffusion coefficient Deff range of drying process at different temperatures was 1.829×10^-8～2.491×10^-8m²/min,and the regression equation was ln MR=-3.637×10^-2t-1.033;the range of effective moisture diffusion coefficient Deff under different wind speeds is 1.622×10^-8～2.018×10^-8m²/min,and the regression equation is ln MR=-2.946×10^-2t-1.030.the range of effective moisture diffusion coefficient Deff under different radiation distances is1.764×10^-8～2.610×10^-8m²/min,and the regression equation is ln MR=-3.381×10^-2t-1.181.（3）Study on drying model of alfalfaThe drying mathematical model was constructed in Minitab19 software,and the drying curves were fitted by combining the four commonly used classical mathematical models Lewis（Newton）,Page,Modified Page I and Logarithmic.The determination coefficient R2 was used to evaluate the fitting degree between the drying mathematical model and the drying test curve,and the optimal fitting models of alfalfa under infrared drying,hot air drying and infrared hot air combined drying were selected,which were all Page models.The average determination coefficient R²reached 0.9891 at different temperatures.the mean value of R²reached 0.9865 under different wind speeds,R²averaged 0.9826 at different radiation distances.（4）Effect of alfalfa drying on nutritional componentsThrough the single factor experiment,the different levels of hot air velocity,infrared radiation distance and drying temperature were analyzed.The process parameters that quickly reach the safe moisture content were as follows:temperature 95℃,wind speed 3m/s,radiation distance 50 mm.Taking the content of crude protein and crude fiber of alfalfa as the index,the three-factor Box-Behnken orthogonal rotation combination test was designed by Design-Expert 11 software,and the regression model was established.The response surface analysis of two-factor interaction was carried out.The results showed that the optimal combination of parameters was hot wind speed 3m/s,drying temperature77.36℃,radiation distance 75.9mm,alfalfa nutrient retention was 23.85%CP,25.68%ADF and 40.654%NDF,which effectively reduced the loss of alfalfa nutrients.In summary,the above experiments verified that the infrared hot air combined drying technology could effectively improve the drying efficiency,reduce the loss of nutrients in alfalfa,and provide quality assurance for the subsequent processing of alfalfa hay.