Research On Intelligent Defrosting Control Based On The Principle Of Parallel Plate Capacitors

With China’s commitment to achieve "carbon peak and carbon neutrality" in 2030 and the continuous increase of global greenhouse gases,reducing the consumption of fossil energy becomes increasingly important.With the development of human society,refrigeration and cold storage technology has been more and more widely used in life.More and more refrigeration equipment has been used to improve the quality of human life,and the energy consumption of refrigeration equipment has increased rapidly.Some of the energy has not generated the cooling capacity required by human beings,but is used to generate heat to eliminate the frost layer on the surface of the heat exchanger.How to reduce the energy consumption of defrosting,thereby reducing dependence on fossil fuels,and improving energy utilization efficiency has always been a hot research direction.To address such issues,this article provides a detailed analysis of the current development status and trends of defrosting methods and defrosting control technologies both domestically and internationally.A new intelligent defrosting control strategy based on the principle of parallel plate capacitors has been developed on the basis of existing work.In order to explore the feasibility of this new defrosting control method,this article first built a pre-test bench to study the influence of the distance between two parallel plates,the area of the opposite side,and the dielectric constant of the intermediate medium on the capacitance value of the parallel plate capacitor;Secondly,by building a test bench in the cold storage,the variation of capacitance values over time between two flat plates placed between the evaporator fins during the operation of the cold storage was explored.The thickness of the frost layer on the fins was observed using a CCD microscope and the capacitance values were recorded using an LCR digital bridge.Finally,the optimal starting and stopping points for defrosting in the cold storage were determined,corresponding to the capacitance values;Finally,a comparative analysis was conducted on the temperature,cold storage power consumption,and electric heating power consumption of the new intelligent defrosting control method and the timed defrosting method.The main research findings are as follows:(1)Theoretical analysis has been conducted on the impact of frost formation on heat transfer in evaporators.As the thickness of the frost layer increases,the frost layer density increases,the thermal conductivity decreases,the surface temperature difference between the frost layer and the environment decreases,the heat transfer performance of the system decreases,and energy consumption increases.Based on the mixed medium(air,water,ice)between fins during frosting,a theoretical computational mathematics model for calculating the capacitance value of parallel plate capacitor during frosting and defrosting was established.The results show that during the conventional refrigeration process,as the thickness of the frost layer increases,the capacitance value monotonically increases;During the defrosting process,the capacitance value first increases and then decreases.(2)Through conducting experimental research on intelligent defrosting of capacitors,it was found that the capacitance value was 11.2 p F at the beginning of refrigeration.When the optimal defrosting time was reached,the capacitance value reached 32 p F,and during the defrosting process,the maximum value reached 62.6 p F.After defrosting,the capacitance value decreased to 19 p F.Verify the correctness of the computational mathematics model of the parallel plate capacitor capacitance value theory.Based on the dual position adjustment algorithm of the PLC controller and the application of FStudio software,real-time monitoring of the intelligent defrosting process of the evaporator has been achieved.(3)Compared with conventional timed defrosting,the new capacitive intelligent defrosting control method combined with a closed hot air circulation structure design reduces defrosting time by about 4 minutes and improves efficiency by about 22%;The monthly electricity consumption for electric heating required for defrosting has decreased by 21.9 KW·h,and the central temperature fluctuation of the cold storage has decreased by14 ℃.The refrigeration efficiency of cold storage has been improved,and the consumption of fossil energy has also been reduced.