Optimization On Control System Of Heat Pump Dryer And Research On Drying Experiment

With worldwide energy shortage and environment degradation exacerbating, the importance of saving energy and protecting environment is more and more prominent. Heat pump is widely used in drying progress due to its advantages, such as low power consumption for each unit water removed, environmentally friendly, good quality product, accurate control of drying condition and saving drying time. In recent years, the developments and improvements on the heat pump drying can be mainly classified into four topics: heat recovery, use of phase change material, control of dryer and good drying strategies. Thus, it has very important practical significance to apply artificial intelligence control technology to the heat pump dryer for precise control of the drying parameters, automation of drying process and improvement in product quality.Moisture diffusion model of dried material is established and influence of drying medium temperature, relative humidity and initial moisture rate on drying rate is investigated based on green peas drying experiments. The results show that, increase in temperature of drying medium leads to faster average drying rate, shorter drying cycle and lower equilibrium moisture rate; the effect of drying temperature on drying rate is more obvious when moisture content is high; increase in relative humidity leads to lower average drying rate, longer drying cycle and higher equilibrium moisture rate; higher initial moisture rate is, faster average drying rate is, and average drying rate of initial stage is faster than entire process.In order to optimize the variable capacity control system of the heat pump dryer, parallel fuzzy control is proposed and the dynamic response process to fixed frequency control system, single-stage fuzzy control system and parallel fuzzy control system is investigated based on experiments. The performances under different working temperature are analyzed. The results show that, as parallel fuzzy control system is adopted in heat pump dryer,and when setting-temperature is 20?, the heating rate increases 75.263% and-10.228%,the upper limit overshoot rate drops 91.600% and 89.312%, the lower limit overshoot rate drops 83.631% and 76.514%; when setting-temperature is 25?, the heating rate increases 61.118% and-16.203%, the upper limit overshoot rate drops 90.607% and 85.868%, the lower limit overshoot rate drops 81.568% and 77.403%; when setting-temperature is 30?, the heating rate increases 54.327% and-21.195%, the upper limit overshoot rate drops 93.217% and 91.011%, the lower limit overshoot rate drops 78.177% and 70.235% compared with fixed frequency control system and single-stage fuzzy control system. From the above analysis, it is known parallel fuzzy control system has the lowest upper limit overshoot rate and lower limit overshoot rate. Meanwhile, the upper limit overshoot rate and the lower limit overshoot rate of parallel fuzzy control system are less influenced by drying temperature and more stable than the other two control strategies.