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Constant temperature and humidity theory and experimental analysis of constant temperature and humidity testing machine
November 10, 2015 source: navigation instruments Author: Network Editor
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The surface constant temperature and humidity phenomenon of the refrigeration system in the micro constant temperature and humidity test box affects the storage effect and consumption of the whole micro constant temperature and humidity test box. When the frost layer on the surface of the constant temperature and humidity testing machine reaches a certain thickness, the efficiency of the refrigeration unit will be reduced, and the flow will be hindered, which will affect the working efficiency of the fan; when the defrosting system is started, the storage temperature in the micro constant temperature and humidity test box will fluctuate, which will affect the storage effect. There are many effects on the research of constant temperature and humidity and refrigeration system, but the micro constant temperature and humidity test chamber has its own characteristics, that is, the unit does not work continuously in most cases, the constant temperature and humidity test machine is not continuous forced convection, and the previous research results, especially the increase of frost amount, are not suitable for working conditions. On the basis of experiment and theoretical analysis, this paper analyzes and discusses the constant temperature and humidity work, and summarizes the influencing factors and correlations of frost growth.

???? Humidity Chamber The frost formation process is a complex process. The shape of the frost is affected by the temperature of the cold wall, the moisture content and velocity of the incoming air. Hallet has proved that the shape of frost is mainly related to the temperature of the cold wall, but not to the supersaturation of the incoming air. Hallet thinks that with the decrease of the temperature of the cold wall, the frost morphology changes periodically, from plate to edge, and then from edge to plate. The frost conditions at different temperature stages are listed.
In this experiment, the surface temperature of evaporator is concentrated between - 22 ℃ and - 9 ℃, and the temperature of incoming air is between 2 ℃ and - 4 ℃. It can be considered that the main shape of frost appears in the form of flat plate in this experiment, which will also be used in the later macro equilibrium analysis. However, for the microscopic state of frost formation, it mainly refers to the condensation of water molecules, which depends on the collision frequency of water molecules. From this level, the microstructure of frost formation is spherical structure, which involves the critical radius of frost formation, which is of great significance to prevent constant temperature and humidity.
Frost formation process is essentially a phase change process of constant temperature and humidity test chamber in air. According to the phase law, there can only be one degree of freedom when the two phases are in equilibrium in a single element system. When one of the variables is changed, the state of two-phase coexistence will be destroyed; however, sometimes metastable system will be formed. For metastable system, if other substances are added, the metastable system will be easily destroyed, thus forming a stable substance. This metastable system is very important for crystal growth and will be discussed later. The phase diagram of water is shown.
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