Research On Humidity Control System Of Museum Relic Microclimate Based On Diffusion Absorption Refrigeration System

Cultural relic preservation and presentation requires precise and stable control of the temperature, humidity, light, noise and other factor. Thus, microclimate control system has become the focus of heritage conservation workers in the study. Furthermore, for those small, independent showcase which is scattered around the showroom, museums and heritage research institutions has been searching for a small, simple, noise-free microclimate control system. This paper describes a microclimate humidity control system based on Diffusion Absorption Refrigeration (DAR) system, which is quite, easy to control, and has no moving parts, making it very suitable for daily operation and maintenance in museum. Therefore, the following researches have been done in this paper:1. First, the required cooling capacity is calculated for a typical relic showcase, which is 15 W. Then a DAR system with cooling capacity of 21 W when evaporation temperature is 6.2 ℃ is chose as the cooling source. Combined with the requirements of showcase microclimate control, as well as the structure and working characteristics of the DAR system, a microclimate humidity control systems is designed. The system uses direct contact dehumidifier to handle the air circulating inside the system and showcase. Meanwhile, the condensation water is collected for humidification.2. Secondly, a simplified numerical model of the heat and mass transfer process between the moist air and water in the sink is established. The model is calculated in ANSYS FLUENT and verified with the empirical equation, of which the relative error is around 20%. Based on this model, the influence of the inlet air parameters, water temperature and geometric parameters on the condensation rate were discussed. It shows that given certain heat exchanger parameter, the efficiency is higher when the air flow rate is smaller. But, by decrease the area of the cross section, the efficiency can be greatly increased. It is also known that the efficiency reaches the highest if the water temperature is kept at a critical point, which is determined by inlet air temperature and humidity.3. The whole microclimate humidity control system is assembled and installed inside a box, as well as the control system, which consists of a Siemens S7-200 programmable logic controller, relays, and temperature and humidity sensors. The experiment is conducted under all kinds of environment condition. It shows that by controlling the start and stop of the fan, the relative humidity inside the showcase can be controlled at given any target value from 45% to 70% with an accuracy of 2.0% or smaller, when the ambient temperature is within 16～26 ℃. And by controlling the start and stop of the DAR system, the humidity can also be maintained within 2.0% around target, following a big temperature fluctuation in the water. By controlling the heating power or voltage of the DAR system consecutively, this situation can be improved. Meanwhile, the higher the heating power is, the lower humidity inside can be reached and maintained. Overall, these three control strategy can both achieve the goal of controlling the relative humidity of the relic microclimate in a large range with little float.