Numerical Analysis And Dynamic Characteristics Research Of Air-Water Direct Contact Humidity Machine

In the preservation and exhibition of cultural relics,the relative humidity is particularly important.To prevent the physical or chemical changes and reduce damage rate of cultural relics,it is significant to actively take measures such as active monitoring and control.At present,semiconductor refrigeration technology devices are widely used in small showcases at home and abroad,but they have disadvantages such as large heat dissipation devices,small cooling capacity and low efficiency.In contrast,the stirling refrigerator has the advantages of large refrigeration capacity,fast response,long life,safety and reliability,etc.,which is very promising in the field of cultural relic preservation.In view of this situation,this work designed an air-water direct contact type constant humidity device based on stirling refrigerant to achieve constant humidity and micro temperature rise control.At the same time,the experimental device also has the advantages of fast response and precise control.Aiming at the designed air-water direct contact constant humidity cultural relic displaycase,this article mainly carried out the researches in terms of the following three aspects:(1)First,an air-water direct contact constant humidity cultural relic device was designed: In view of the limited available space size of the cultural relic display case and the size of the PTC heater and the cold head of the cryocooler,a constant humidity cultural relic device adopting stirling cryocooler was optimized designed according to the working principle of the system.In the system,the cold head of the stirling cryocooler and heating rod were placed in the water tank to control the water temperature to achieve constant humidity,and the PTC heater was used to achieve temperature fine-tuning.Then the load of the small independent display case was calculated to choose an appropriate refrigerator.Besides,the cooling capacity of the selected cryocooler was measured based on heat balance method,and the relationship between cooling capacity and input power of the cryocooler and temperature of the cold head was fitted and analyzed.Moreover,the limit of the control voltage was determined experimentally.(2)Secondly,a numerical model of direct contact between air-water was established: The heat and mass transfer mechanism of air-water direct contact in the water tank heat exchanger in the constant humidity independent display cabinet system was studied.The evaporation-condensation UDF method was loaded by ANSYS to realize the coupling of flow and heat and mass transfer.Moreover,the grid independence analysis and experimental verification were performed,which validated the reliability of the model.In addition,the temperature field and flow field inside the water tank heat exchanger were analyzed,and the influence of air flow parameters and structural parameters on heat and mass exchange between air and water was studied.Furthermore,the uniform design method was adopted to optimize the deflector structure based on the proposed comprehensive evaluation index for later experiment and application guidance.(3)Finally,an air-water direct contact constant humidity cultural relic display case test bench was set up: The PLC method was used to realize system control.Then the preliminary tests were carried out to test and analyze the tightness of the showcase,and determined the system control plan.The results indicated that the use of PTC heaters can achieve a temperature rise of about 2.5 ℃ in the showcase.Moreover,it was found that compared with ordinary PID,the fuzzy PID had better control effect based on texperiments and simulations.Meanwhile,the stirling cryocooler and heating rod were controlled switching operation to achieve constant humidity in the showcase based on PID adjustment.Results showed that the constant humidity function can achieve the target value of 60 % in the showcase within 50 minutes to maintain stability when the ambient humidity is 30-80 %,and fluctuation of humidity in the cabinet less than ±1 %.Such results indicate the system can meet the requirements of preservation and display demand in independent showcase.At the same time,the experiment found that during the dehumidification process,the air temperature in the showcase had a certain degree of drop due to the large cooling capacity of stirling cryocooler,which could be used to reduce the influence of temperature fluctuations outside the showcase.Furthermore,the overall stability of the system was studied under the two working conditions,which were dehumidification and heating and humidification and heating,respectively.The results showed that the relative humidity and temperature fine-tuning control accuracy in the showcase were both within ±0.5 % and ±0.2 ℃.Such results indicate that it has good performance and meets the constant humidity demand of independent showcases.