Energy Saving Test And Optimization Of Combine Drying Of Special Fruits And Vegetables By Dehumidification Wheel And Heat Pump

The drying of characteristic fruits and vegetables is an important process for its storage and subsequent processing.Convection drying is currently the most widely used method,but it has problems such as high energy consumption,low efficiency and product difference.Dehumidification wheel of drying can achieve low-temperature and high-efficiency drying of fruit and vegetable,but problems such as high energy consumption for regeneration and unreasonable hot air circulation restrict industrial application.Based on the above problems,the research on the combined desiccant wheel dehumidification and heat pump drying technology(WHPD)for fruits and vegetables has beencarried out.A low temperature drying mode that was driven by low humidity low humidity to drive low temperature drying mode was established and dehumidification characteristics of WHPD was explored.Then the critical dehumidification mechanism has beening proved and the fractional condensation energy-saving regeneration technology has beensolved.The fruit and vegetable drying test was carried out,an optimized drying process was established.Finally,the high-quality,efficient and energy-saving drying of characteristic fruit and vegetable are achieved.The main research contents are as follows:(1)In terms of high energy consumption of desiccant wheel dehumidification,the research on the parameters matching and flow field distribution of drying system are carried out.The main parameters of the heat pump cycle are determined by the single drying output and drying time.On this basis,the main parameters of the desiccant wheel are determined and the optimized combined dehumidification and drying control system has been formulated.Then,focusing on the problem of uneven air output from the drying box of the WHPD system,the influence of the height of the bottom plate and the angle of the gentle slope on the flow rate and pressure of the drying medium was carried out,and the optimal angle of 6° was found.For the blind area of the inlet air duct,the equal-division gentle slope air duct was established and tested.And the results showed that,the air volume at each point is about 0.8m/s,which realize the even distribution of the air volume and the uniform flow of the front and rear air speeds.(2)In order to better realize the efficient matching of the WHPD and provide a theoretical reference for optimizing the drying process,the dehumidification performance of the heat pump and the dehumidification wheel wewe respectively studied and a prediction model was established.The adsorption characteristics of the dehumidification wheel and the COMSOL software were utilized to establish a desiccant wheel model,and the influences of dehumidification humidity,temperature,air speed,wheel speed and regeneration temperature on the dehumidification capacity and outlet temperature were discussed respectively.The optimal parameters were found as the wheel speed of 12r/h and the air speed of 2.5m/s.The relationship of heating capacity,cooling capacity,refrigerant flow rate and COP with the evaporating temperature and condensing temperature at the base frequency was analyzed by the compressor 10 coefficients.A inverter compressor model was established according to the "zero frequency" method and a interpolation verification proved that the refrigerant flow error was less than0.9%,and the input power error was less than 3%.The model was highly accurate and the results showed that it can be used to predict the output parameters of the compressor.(3)In order to solve the problem of efficient utilization of air energy and waste heat by WHPD,a research on the critical dehumidification process of the combined system was carried out,and the appropriate enthalpy conversion method for fresh air and return air was explored.The analysis of the combined dehumidification process of the heat pump and the wheel de-heat pump was carried out.The impact of the drying medium on the dehumidification efficiency was studied.The adiabatic drying and dehumidification efficiency of the WHPD in supersaturation,partial saturation and zero saturation stages.The relationship between the evaporation air and the dehumidification efficiency with the aid of the exergy analysis was studied.The critical conversion point of the system has beening proved and closed drying is rationality also been studied.The Pleurotus eryngii combined Pleurotus eryngii drying experiment was carried out by dehumidification wheel and heat pump.The mathematical numerical model between the dehumidification energy consumption ratio and the relative humidity of conversion point was established.The mechanism of the relative humidity of conversion point on the dehumidification energy consumption ratio was explored and further verified.When the relative humidity of conversion point was44%,the dried Pleurotus eryngii SPC was 0.679 k W·h/kg,the absolute error from the predicted value is less than 3%.(4)A regeneration technology using compressor exhaust gas fractional condensation was developed for the high regeneration regenerated energy consumption from desiccant wheel dehumidification.Fractional condensation refrigerant cycle process was analyzed,refrigerant and air-side models was builded,and the main factors that affect the regeneration effect was explored.A comparison test of the energy consumption between pure electric heating regeneration and fractional condensation regeneration was compared,which highlighted that the energy saving of fractional condensation mode was 29.5%.The response surface test between the regeneration inlet air temperature and speed,evaporation inlet air temperature and regeneration heating air temperature,regeneration condensation air volume and other indicators was established.It shows that when the evaporation inlet temperature was 34°C,the regeneration inlet air temperature was 32°C,and the air volume was 90% is the optimal process.Increasing the evaporation temperature and regeneration inlet air temperature at room temperature is beneficial to improve the effect of fractional condensation regeneration.(5)In order to further explore the advantages of WHPD.A composite experiment of the heat pump,the heat pump freeze-thaw and the WHPD for mushroom drying was carried out.The results showed that the WHPD rate was the highest(6h),and the rehydration rate and color difference were the best.It took only 36 hours for the macadamia nuts to be dried to a safe moisture of 1.5% at a low temperature below45? by the WHPD.The peroxide value(0.001g/100g)and acid value(0.37 mg/g)were far lower than the the national standard.