Study On Drying Characteristics And Process Matching Of Solar Energy Heat Pump For Alfalfa Bale

Based on the previous research,the uniformity of physical field distribution in drying chamber was improved by simulation and experiment.The effects of hot air temperature,hot air velocity and bales’density on the moisture ratio and drying rate of bales of alfalfa were studied by single factor experiment,and the drying characteristics of bales of alfalfa were analyzed.Combined with the four classical thin-layer drying models commonly used at present,the drying moisture ratio curve was fitted,and the optimal fitting model under the combined drying mode of solar-heat pump was selected.The improved fitting model was obtained by regression analysis of test parameters and model coefficients,and the accuracy of the improved model was verified by experiments.The range of each factor was determined by single factor test,and the response surface test was designed by Design-Expert11 software.The influence of each experimental factor on the SMER value and dehumidification amount per unit time was analyzed.The relevant mathematical model was established to obtain the optimal drying process parameters.The main conclusions are as follows:(1)The solar-heat pump combined drying technology was applied to study the drying characteristics of bales of alfalfa.The drying characteristics under different drying parameters were analyzed,and the curves of moisture ratio and drying rate during the drying process were drawn.When the hot air temperature increased from 45℃to 55℃,the effective water diffusion coefficient of alfalfa bales increased by 18.4%.When the hot air velocity increased from 2m/s to 6m/s,the effective water diffusion coefficient of alfalfa bales increased by 36.0%.When the bale density decreased from 120kg/m~3 to60kg/m~3,the effective water diffusion coefficient of alfalfa bales increased by 53.0%.(2)Four common drying kinetic models,such as Lewis,Page,Modified Page I and Logarithmic were fitted and compared by using the experimental data.By comparing the coefficient of determination R~2 in the model fitting results,the maximum mean value of the coefficient of determination R~2 of Page and Modified Page I models was 0.9682,and the Modified Page I model equation was obtained by multivariate nonlinear regression analysis of experimental parameters and model coefficients,which provided theoretical support for the application of solar-heat pump combined drying technology in the drying of bales of alfalfa.(3)Taking SMER value and dehumidification capacity per unit time as the index,the parameter optimization test of alfalfa bale was carried out.The regression model between each test factor and the index was obtained,and the interaction between the factors was analyzed.The best combination of drying process parameters was determined:hot air temperature 57℃～59℃,hot air speed 5m/s～6m/s,bales density 94kg/m~3～100kg/m~3,SMER value and dehumidification capacity per unit time can be maximized under this combination.