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Research and Application of Wet Cool Storage Technology in Fruit and Vegetable Preservation
Abstract : The paper discusses the technology and theory of energy-storage refrigeration. It focuses on the application and research of wet-cooled cold-storage technology in the preservation of fruits and vegetables, and clarifies the technical characteristics, advantages and application prospects of the technology. Key words: wet cold storage and fresh-keeping technology application CLC: S37; TB6 Research and application of humidity cold with energy storage refrigeration technology in fresh fruit and vegetable holds Jia jun Hu wei Xiang junhong Ren changqing (Tianjin Farm Machine Bureau, Farm Machine Test (Appraisal Station Tianjin)Abstract: The paper showed detail of humidity cold with energy storage refrigeration technology and theory, to lay stress on the technology research and application in fresh fruit and vegetable holds, explain the technology characteristic, advantage and the expanding application in future Key words: Humidity cold, Energy storage, Cold storage technology Introduction At present, China's agricultural product storage and fresh food processing is at a stage of development, and it urgently requires a large number of various preservation and storage technologies and equipment. China's food experts have pointed out in the forecast of the food processing market: China The scale of the scale of agricultural products and food processing depends on the proportion of fresh storage technology and equipment used, and depends on the preservation capacity and the library. Turnover length of time. This shows that the level of fresh storage technology and equipment, the size of the application directly reflects China's agricultural products and food processing production scale and level. Namely: Regardless of whether fresh fruits and vegetables are sold or exported or finished products, it involves storage and preservation. It is not only a basic condition but also a crucial link. There are many kinds of technologies and methods for storage and preservation. Currently used are: wet and cold preservation technology, gas conditioning technology, micro-freezing technology, decompression technology and radiation treatment technology, air ion preservation technology, and chemical agent treatment technology. This article focuses on the principle of energy storage technology and analyzes and discusses the prospects for research and application of wet-cooled (cold storage) preservation technology. 1 The energy storage technology currently used in energy storage technology mainly utilizes the sensible latent heat effect or the chemical reaction process of the state change of the working medium to store energy. Each kind of material has a certain heat capacity. Under the condition that the material form is not changed, the material will absorb or release heat. In theory, all materials can be applied to energy storage technology, but in practice the specific heat capacity is larger. substance. At the beginning of the application of energy storage technology, the most widely used technology is cold and hot water storage technology. Cold and hot water storage is the use of low-cost, easy-to-use, specific heat capacity of water as an energy storage medium, the use of water cooling for energy storage. Its advantages are: low investment, simple equipment and easy maintenance. Disadvantages are: small temperature difference between energy storage, low density, can not achieve greater storage of energy. 1.1 Cold storage technology Cold storage technology is the use of the characteristics of the phase transition, the need to absorb or release heat to store or release energy, currently includes ice storage technology and eutectic salt storage technology two. Ice storage technology is one of the most widely used cold accumulating technologies. It uses the latent heat of phase change of ice to store and release the cold. As the transition from solid ice to liquid water, the latent heat of phase change reaches 335 kJ/kg. The unit mass energy density is much higher than water storage. Therefore, the cold storage tank required for ice storage is much smaller than water storage, and it is also easier to arrange in or around the cold storage. Due to the lower temperature of ice water, the supply of ice water and the air supply volume of the air-conditioning system can be reduced under the same air pressure load. The investment and operating costs of ice storage equipment systems are lower than that of water storage. The disadvantage of the ice storage system is that the freezing temperature of the water is 0°C. In consideration of the heat transfer temperature difference, the evaporation temperature of the refrigeration system must be below -8°C. For the ice storage system using indirect heat exchange of the refrigerant, the evaporation of the refrigeration system The temperature is even lower. Due to the low temperature of the cooling, ice storage tanks and ice water pipelines, the thickness of the insulation layer must be increased in order to avoid condensation on the outside of the ice tank and pipeline and to reduce the introduction of environmental heat. The technical requirements of the ice storage system are relatively high, especially the recently proposed ice storage refrigeration system, which makes the design and control of ice storage and refrigeration much more complicated than water storage and cooling. In order to satisfy the lower temperature requirements of stored materials, the ice storage refrigeration technology overcomes the disadvantages of lowering the energy consumption of the refrigeration due to the lower evaporation temperature and lowering the COP value, and may use a total temperature of the solid-liquid phase transition higher or lower than that of the water. Crystal salt to store energy. Eutectic salts consist mainly of inorganic salts, water, accelerators, and stabilizers. At present, eutectic salt materials with a phase transition temperature of about 8°C are used in the cold storage refrigeration system. Due to the high specificity of the eutectic salt phase transition temperature, the refrigeration capacity of the eutectic salt can be increased by 25% to 30%, and the COP value can be increased by about 15%. The cooling energy consumption is greatly reduced. The disadvantage of using eutectic salt is that the latent heat of phase change is low. When the same amount of cold is saved, the eutectic salt storage volume is larger than ice storage, but smaller than water storage. 1.2 Working principle When the work load of the grid is at a low level (that is, electricity at night), the ice storage and cooling system starts and the cold storage is started. According to the principle of the thermal working cycle, the cold storage technology can be divided into four due to different working media. A basic cycle. In Figure 1, the (a) cycle is mainly applied to the refrigeration storage refrigeration cycle with water or other high boiling point substances. Figure 1 (b) and (c) apply to working cycles with ammonia or other low boiling point refrigerant storage. Figure 1(d) is a working cycle that converts thermal energy into refrigeration and storage. Since the density of cold storage depends on the type of refrigerant and the concentration of the solution, the key to cool storage technology is the energy density of the working medium. The greater the energy storage density, the smaller the cold storage equipment, the less investment, and the ease of adoption. The energy storage density can be calculated using the following formula: CDEstor = CpΔt + PLIPF where: CP is the specific heat of the energy storage medium; Δt is the sensible heat storage available temperature difference; P is the density of the energy storage medium; L is the solid/liquid phase change Heat; IPF is originally intended for the ice-making rate, which is here extended to the crystallization rate. For cold water storage, reference temperature is only 6 ~ 11 °C, cold storage density is only 25 ~ 46kJ/kg. For ice storage, different storage systems have IPF values ​​between 20% and 75%. The available temperature difference is 10 to 12°C, and the storage density is 110 to 295 kJ/kg. The cold storage density of other cold storage methods is currently lower than the ice storage density. 2 Application of wet-cooled cold storage technology in fresh-keeping storage Cold-water storage technology, i.e., ice storage technology, is a new emerging fruit and vegetable preservation technology that has not been popularized in the 1980s, because it has better storage characteristics than atmospheric storage, ordinary cold storage and other storage methods. Because of its adaptability, it has been widely used in economically developed countries such as Europe and the United States. 2.1 Features and Advantages of Cold-Stored Cold Storage and Preservation Technology The wet-cooled storage and cold storage technology integrates pre-cooling, high-humidity, and low-temperature storage of fruits and vegetables, uses cold storage technology, and uses the price difference between peaks and valleys to exchange ice produced at night through heat and mass exchange. , water pumps, and blowers exchange the high-humidity cold air with the gas of the fresh-keeping warehouse for forced heat exchange, so as to realize the cooling of the cold storage and the preservation of fresh fruits and vegetables with high humidity, so as to maintain the original moisture of the fresh-keeping products, ie, the original fruits and vegetables. Quality, extended shelf life. Among many fresh-keeping technologies, the wet-cooled cold storage and fresh-keeping technology has a small installed capacity (the installed capacity is comparable to that of the same cold storage, and the storage capacity is reduced by 1/3), and the investment is small. Because the eutectic salt technology is adopted, the ice storage temperature can reach 8°C. That is to meet the temperature requirements of fresh fruits and vegetables, but also will not be frostbite. Fruits and vegetables are prone to mildew and rot in high-humidity environments. They can be treated with ozone water soaking before storage to achieve sterilization and disinfection, and to prevent mildew and rot. Jia Jun, Hu Wei, Xiang Junhong, Ren Changqing (Tianjin Agricultural Machinery Bureau Tianjin Agricultural Machinery Test and Evaluation Station)