Computer room refrigeration technology: adsorption refrigeration
(1) Intermittent adsorption refrigeration system
In the case of intermittent adsorption refrigeration, a solar-driven refrigerant is mainly composed of an adsorption bed, a condenser and an evaporator. During the daytime, the adsorption bed at ambient temperature is heated by solar energy. After the temperature of the adsorbent rises, the analysis begins, the refrigerant is desorbed therefrom, and the pressure of the refrigerant vapor in the system gradually increases. When the saturation pressure corresponding to the ambient temperature is reached, The refrigerant vapor condenses in the condenser while releasing latent heat, and the condensed liquid enters the evaporator for storage. At night, the adsorption bed is cooled, and the adsorption capacity of the adsorbent is increased, so that the refrigerant vapor in the evaporator is started to be adsorbed, and the gas pressure in the system is lowered. At this time, the refrigerant in the evaporator is continuously evaporated at a low temperature, and the absorption is absorbed. Cool the heat of the material to achieve the purpose of refrigeration. If other heat sources are used, as long as the adsorption bed is heated and cooled intermittently, the adsorbent periodically generates desorption and adsorption, which can also achieve the purpose of refrigeration. As can be seen from the above, adsorption refrigeration is also a liquid vaporization refrigeration. Compared with the vapor compression type refrigerator, the adsorption bed uses a change in temperature to cause a large change in the adsorption amount, resulting in a large change in the pressure in the closed system, thereby functioning as a compressor. However, the above adsorption system intermittently cools, the adsorber is in the adsorption process to produce a cold effect, and after the end of adsorption, there must be a desorption process to restore the state of the adsorbent, at which time the refrigeration will be stopped.
(2) Continuous adsorption refrigeration system
An adsorption refrigerating machine consisting of two (or more) adsorption beds only needs to alternately complete the adsorption and desorption processes, and continuous refrigeration can be achieved. Assume that the adsorption bed A is heated, the adsorption bed B is cooled, when the A bed is fully desorbed, the B bed is saturated, and then the adsorption bed A is cooled, the adsorption bed B is heated, and the two alternately operate to form a complete continuous refrigeration cycle. . At the same time, in the two process switching, it is also possible to use the exhaust heat of the hot bed just after the desorption to heat the cold bed which is just finished, so that the heat energy can be fully utilized and the efficiency of the refrigeration cycle is improved, thus forming a continuous heat recovery type. cycle.
(3) Adsorption refrigeration working fluid pair
The choice of the adsorbent refrigerant pair is one of the important factors affecting the performance of the adsorption refrigerator. The ideal working fluid pair is a refrigerant that requires strong adsorption performance, fast adsorption speed, good heat transfer effect, and large latent heat of vaporization and boiling point to meet the requirements. At present, the research on the adsorption working fluid is continuously deepening and developing. More mature are zeolite-water, silica gel-water, activated carbon-methanol, metal hydride-oxygen, chloride salts-ammonia, and the like. Since the latent heat of vaporization of water is relatively large and it is easy to freeze below 0 ° C, zeolite-water and silica gel-water are more suitable for an air-conditioning system having an evaporation temperature of 0 ° C or higher. The adsorption capacity of activated carbon for methanol is relatively large, and the adsorption capacity is sensitive to temperature changes. The latent heat of vaporization of methanol is large, the freezing point is low, the boiling point is higher than room temperature, and the metal materials such as copper steel are not corroded. Therefore, activated carbon is suitable for solar energy or other low temperature. Heat source driven general refrigeration system. However, since methanol is easily decomposed at about 150 ° C, its working temperature should be lower than 150 ° C.
(4) Characteristics of adsorption refrigeration
Compared to vapor compression refrigeration, adsorption refrigeration has the following advantages:
1 can be driven by various thermal energy. In addition to utilizing the heat generated by boiler steam and fuel gas, it can also use solar energy and various low-grade heat sources such as waste heat, waste gas and waste water.
2 can save a lot of electricity, reduce the peak load of the grid during the air conditioning season.
3 Simple structure, few running parts, safe and reliable.
4 Water, ammonia, methanol, etc. are used as refrigerants, which are harmless to the environment and the ozone layer.
Although adsorption refrigeration has great application prospects, some of its defects have greatly reduced its market competitiveness, mainly in the following: adsorption and desorption processes are relatively slow, refrigeration cycle is longer; and vapor compression and absorption Compared with the refrigerator, the cooling capacity is relatively small, and the thermal coefficient is generally 0.5 to 0.6.
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