| With the increasing attention to the protection of cultural relics in our country and the de-velopment of air-conditioning and control techniques,a large number of cultural relics preser-vation environment need to be improved urgently so as to better preserve the priceless and irre-placeable cultural relics.The main environmental factors affecting the long-term preservation of cultural relics are temperature,relative humidity,light intensity and concentration of harmful gases,among which relative humidity is the most basic and important factor,so it’s essential to provide constant humidity environment for cultural relics.For small independent display cases with the features of small volume,flexible distribution and removability,it is therefore not ap-propriate to adopt large centralized air handling unit to control relative humidity.At present,many domestic and foreign historical relics protection institutions have specially developed ac-tive constant humidity environment control devices mostly based on semiconductor refrigeration for small independent display cases.This kind of devices have the advantages of no noise and small footprint,but there are shortcomings of low cooling capacity and easy fouling.Focusing on these drawbacks and giving consideration to the above advantages,the following three main tasks are carried out in order to invent a novel kind of constant humidity environment control system for small independent display cases.(1)To meet the requirements of quiet environment in museum,a noiseless diffusion absorp-tion refrigerator was used as the cold source,and PLC modules were used as the controllers.The evaporator was placed underwater.Based on the principle that there are different state changes when air directly contact with water surface at different temperatures,the humidification and dehumidification process was combined together to control the humidity indirectly by control-ling the water temperature and a compact humidity control system was developed successfully.(2)Some preliminary experiments were conducted in order to determine the way to control the fan,the optimum generator heating power and the appropriate PLC control method.Accord-ing to the preliminary experimental results,the best way to control the fan is to keep it open when the program command is reached,the most suitable heating power range is 37W-80W,and PLC should adopt the PID analog output control method.Then experimental research was made on the controlling of relative humidity in display case,the results showed that the humidi-ty control system can regulate the relative humidity between 45%～65%continuously and main-tain the constant humidity condition.The maximum control deviation is within ±1.25%,which completely meets the diverse humidity demands of different cultural relics preservation.(3)In order to study the method of enhancing the heat and moisture exchange efficiency between air and water so as to accelerate the dynamic response of the humidity control system and improve its performance.A simplified CFD model was established based on the deep analy-sis of heat and mass transfer mechanism of the direct-contact method,the heat and mass transfer of the simplified model under steady state conditions were numerically simulated using ANSYS Fluent.The simulation results were compared with experimental date and correlations,and the comparison results verified the rationality and effectiveness of this simplified model.Next,the same model was used to simulate the air handling process in three water tanks with different structures,the simulation results indicated that supplying and returning air from the top has the highest heat and mass transfer efficiency,which provides a direction for optimizing the air han-dling process in water tank. |
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