| In order to facilitate the storage and transportation of agricultural and sideline products,people often choose to use drying for their initial processing,while drying is also an indispensable and effective way in the product processing process.According to statistical data,the energy consumption of industrial drying accounts for 10%to 25%of the total energy consumption worldwide.In developed countries,the energy consumption of the drying industry accounts for 10%to 15%of the total energy consumption,while in China,the drying industry needs to consume 300 million tons of standard coal every year.Solar drying is one of the most traditional and energy-saving drying methods,but solar drying is easily affected by the outdoor environment,and intermittency has always been the biggest problem plaguing solar drying,resulting in the inability to promote it on a large scale in the drying industry.Heat pump drying can use the evaporator to recover waste heat to improve energy utilization,and has the characteristics of many drying varieties and relatively stable drying effect.To solve the intermittent problem of single solar drying,this article proposes a new type of solar-coupled heat pump drying system,combining the abundant solar energy resources in Kunming.The working principle and design method of the system are explained from the matching coupling and selection of components.The fluctuation of collector efficiency under different solar irradiance intensities is analyzed through theoretical analysis and experimental testing.The performance and energy efficiency relationship of the drying system under three modes are compared under different operating conditions,and the drying kinetics of the material during the drying process are analyzed,and a drying model for the material in the system is provided.The main research content and conclusions are as follows:(1)Based on the research results and status quo of various aspects of drying systems combining solar energy and other energy sources summarized by scholars at home and abroad,this paper complements the two heat sources and designs and builds a drying system coupled with solar vacuum tube collector and air source heat pump with a loading capacity of 800 kg,which can be operated in three modes according to different climatic conditions to achieve continuous drying of materials.(2)The efficiency of the vacuum tube collector will change with the fluctuation of solar irradiation intensity under the condition of constant collector inlet work mass flow.The solar radiation intensity varies in the range of 264 W/m~2 to 836 W/m~2,and the outlet temperature of the collector array shows a gradual increase with the increase of solar radiation intensity.The average efficiencies of collector array-1 and collector array-2 are 56.35%and 53.36%,respectively,while the average total thermal efficiency of the collectors is 58.04%,which is slightly higher than that of the collector sub-arrays.(3)Experimental tests were carried out for the performance of the solar coupled heat pump drying system operating under different operating conditions.The results showed that the system operated in solar drying mode alone,and the drying chamber temperature increased from 24.6°C to 51.3°C under load condition,and the relative humidity decreased from 68.3%to 20.1%.The temperature in the oven reached the target temperature of 45°C after 1.5 h,which was 1.17 h higher than the no-load condition;the system operated in the separate heat pump drying mode,and the average condenser heating power was 7.35 k W during the drying process,and the system COP fluctuated in the range of 1.77 to 3.6,with an average COP of 2.65,and the average condenser heating power was 11.88k W under the load condition,and the average system The average condenser heating power under load condition was 11.88k W,and the average system COP was 2.26,which was 15%lower than that of no-load;the system operated in solar-assisted heat pump mode,and the average system COP was3.36,which was 1.48 times higher than that of the former,compared with the separate heat pump drying mode,while the average power consumption of the drying system in this mode was 2.7 k Wh per hour,which was 35%lower.(4)The energy efficiency relationship of the system in different modes was analyzed separately from the perspective of energy.In the whole drying process the heating share of solar drying mode alone,heat pump drying mode alone and solar assisted heat pump drying mode were 37.9%,58.5%and 3.6%,respectively.The energy consumption shares were 21.2%,76.1%and 2.7%,respectively.According to the fitting results,the two models are the optimal drying kinetic models for drying grapes with solar collector-coupled heat pump system with R~2 value of 0.9986 and RMSE value of 0.01038.(5)METEONORM meteorological software was invoked to generate meteorological data for the Kunming area,and a simulation of the solar vacuum tube collector coupled heat pump drying system was established based on TRNSYS and analyzed for its annual operating characteristics and its operation law.The highest temperature of the solar collector outlet can reach 132.5℃and occurs in April,when the monthly accumulated irradiation intensity reaches 604 MJ/m~2,and the highest temperature is 5.2℃different from the actual experimental test temperature,which is in line with the model prediction.The collector efficiency varied from 45.8%to 58.9%throughout the year,with an average collector efficiency of 51.7%,while the experimentally measured average collector efficiency result was 58.4%,with a difference of 6.7%between the simulated and actual values;the annual heat pump heating performance coefficient COP ranged from 1.89 to 3.12,with an average value of 2.71.(6)Through experimental testing and theoretical analysis,the operation strategy of the drying system is optimized,and when the irradiation intensity is greater than386W/m~2,the system runs the separate solar drying mode;when the irradiation intensity is within the range of 225 W/m~2-386 W/m~2,the system runs the combined drying mode of solar energy and heat pump;when the irradiation intensity is less than225 W/m~2,the system runs the separate heat pump drying mode mode.When the irradiation intensity is less than 225 W/m~2,the system runs the individual heat pump drying mode.The solar coupled heat pump drying system can achieve continuous drying of materials under different weather conditions. |
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