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Research and development of solar refrigerator
- May 03, 2018 -

The current situation of solar refrigeration technology

Solar refrigeration is an important aspect of solar energy utilization. People have done a lot of research in this field. At present, there are two main forms of solar refrigeration: one is photoelectric conversion refrigeration. In fact, it is an application of solar power generation, which first realizes the photoelectric conversion, and then uses solar cells to drive the compressed refrigerating system of the refrigerator; the other is solar heat conversion refrigeration, and its research direction mainly includes solar energy absorption. Closed type refrigeration, solar adsorption refrigeration and solar ejector refrigeration.

1. absorption refrigeration system. The low pressure steam from the evaporator enters the absorber, absorbs strongly by the absorbent, and the heat released in the absorption process is taken away by the cooling water. The concentrated solution is sent into the generator by the pump, and then evaporated by the heat source, producing high pressure steam, entering the condenser to cool and reducing the dilute solution to the absorber. Cycle.

2. adsorption refrigeration system. The working process is composed of thermal desorption and cooling adsorption. The basic cycle process is to use solar energy or other heat sources to make the mixture (or complex) of adsorbents and adsorbents (or complexes) desorbed in the adsorber and release the refrigerant gas from high temperature and high pressure into the condenser, and the condensant liquid condenses into evaporation from the throttle valve. Apparatus. When the refrigerant is evaporated, it absorbs heat and produces the cooling effect. The evaporated refrigerant gas enters the adsorption generator and is adsorbed to form a new mixture (or complex), thus completing an adsorption refrigeration cycle.

3. ejector refrigeration system. The refrigerant is vaporized and supercharged after the heat exchanger is absorbed in the heat exchanger to produce saturated vapor, and the vapor enters the ejector. After the nozzle is spewed out at high speed, the vacuum is produced near the nozzle, and the low pressure vapour in the evaporator is inhaled into the ejector and the mixture of the ejector comes into the condenser to heat and condenses, and then the condensate is one of the condensers. Part of the refrigerant is evaporated through the throttle valve and evaporated after the heat is absorbed into the evaporator.

The principle of photoelectric conversion refrigeration is simple and easy to implement, but the cost of solar cells is high. The absorption refrigeration technology is the earliest and the technology is relatively mature. At present, the solar LiBr absorption chiller has been widely used in the field of large air conditioning. However, the absorption refrigeration system is large and complex, and the refrigerant is easy to crystallize, corrosiveness, and the evaporation temperature can only be above 0 centigrade. The pressure is high and it is dangerous. In the jet refrigeration technology, the circulating pump is the only part of the operation. The system is simple, stable and reliable, but the effect of the ejection refrigeration is low. In view of this, the main ways to realize solar energy for fridge technology are solar photovoltaic conversion refrigeration technology and solar adsorption refrigeration technology.

Solar optoelectronic refrigeration and refrigerator technology

Solar photovoltaic refrigerators mainly include solar photovoltaic fridge and solar semiconductor refrigerator. The solar photovoltaic refrigerator is developed on the basis of the traditional traditional compression refrigerator. It consists of solar cells, controllers, batteries and refrigerators. Because the internal structure of the solar photovoltaic refrigerator is the same as that of the traditional refrigerator, only the power supply unit is changed into a solar cell, so the realization is relatively simple.

The foreign literature reports show that many experimental results show that after converting the traditional AC refrigerator into a DC refrigerator suitable for photovoltaic solar system, the components can operate normally, and the refrigerator can work properly. In China, there are many researches on solar photovoltaic refrigerators, and some progress has been made. In 2007, the Journal of solar energy reported the results of Liu Qunsheng and other research results on the performance of a photovoltaic direct current refrigerator system. The only power source of the system was solar energy, a DC compressor, and a battery in the system. The experimental results show that the lowest temperature of the refrigerator freezer can reach -16 degrees Celsius, the refrigerated chamber can reach 0~10 C, and the operating rate is 48% when working at 25 C ambient temperature. As early as 1997, Huang Fulin applied the new digital SPWM modulation method to the frequency conversion circuit of the solar optoelectronic refrigeration refrigerator and realized the automatic control of the temperature of the refrigerator.

In the research of solar energy semiconductor refrigerator, Zou Jinping and Luo Bin of Gansu natural energy research institute have written the basic structure of the semiconductor refrigerator system driven by solar cells, established the theoretical model of the semiconductor refrigerator driven by solar cells, and analyzed the performance of the system by numerical simulation. The influence of solar radiation intensity and environmental wind speed on the performance of solar semiconductor refrigeration system is studied.

Technology of solar adsorption refrigeration refrigerator

In 2090s, China has begun to study solar adsorption refrigeration refrigerators, but most of them are still confined to the laboratory, which has not yet reached the desired level of practicality, mainly due to the effect of high temperature and time limitation of solar energy. At the same time, solar adsorption refrigeration refrigerator outdoor adsorption bed and indoor refrigerators between the need for pipeline connection, but also affect the solar adsorption refrigeration refrigerator into the bulk production stage of the main obstacle.

In order to solve the above defects, the domestic researchers have studied the solar solid adsorption refrigeration technology in many aspects, such as the system circulation mechanism, the selection of the adsorption refrigerant pair, the performance of the solar refrigerator, the internal and external characteristics analysis and the optimization design.Sun Changjiang, the research room of the thermal environment of the Shanghai Jiao Tong University, has made two solar adsorption refrigerators according to the process and process required by mass production. The experimental results show that the performance of the refrigerator is relatively stable, which proves that the solar refrigerator has ripe manufacturing conditions.

In the solar energy adsorption refrigerator, the choice of adsorption working pairs is very important. Domestic researchers tried to study the adsorption characteristics of different adsorbent materials, including CoF2-NH3, SrCl2-NH3, activated carbon methanol, activated carbon ethanol and so on. The experimental results show that the unit adsorption capacity of the CoF2-NH3 working substance is large, the maximum adsorption capacity is low, the adsorption period is short, and the adsorption refrigeration system is not lump and does not expand after repeated adsorption. It provides new energy for the miniaturization and application of the chemical adsorption refrigeration system, and the adsorption refrigeration capacity of the SrCl2-NH3 refrigerant pair The active carbon - methanol working substance is more suitable for the solar solid adsorption ice making machine than the active carbon - ethanol refrigerant.

The efficient solar collector is the key component of the solar refrigerator. It has two categories: the non focusing solar collector and the focused solar collector. The non focused solar collector is divided into three types: flat plate type, vacuum tube and CPC type. The three kinds of heat collector are not high in heat collecting temperature. Under 250, the solar collector belongs to low temperature or medium temperature solar collector; the focusing solar collector is divided into three kinds of trough type, dish type and tower type. In general, these three kinds of focusing heat collector are used. The collector temperature is above 300 C and belongs to the medium high temperature collector. For the solar refrigerator, the non focused solar collector is mainly used in the solar adsorption refrigeration refrigerator system, while the focused solar collector can be applied to the solar photovoltaic refrigerator system. At present, the research and utilization of solar collectors at home and abroad are mostly limited to the medium low temperature range.

Development and application of solar refrigerator

At present, solar energy refrigerator is the most widely studied solar refrigerator at home and abroad, and the research on solar adsorption refrigeration refrigerator is still on the basic theory of solar refrigeration and the development of experimental prototype.

Solar optoelectronic refrigerators usually use conventional solar power plants outside the refrigerator. The research focuses on the charging and discharging characteristics of the solar cells. Because of the less consideration of the photovoltaic characteristics of the refrigerator compressor, the research on the matching of each component of the solar optoelectronic refrigerators is not good enough, and the efficiency of the solar energy absorption device is also not enough. Very low, so the efficiency of the whole system can not be compared with that of the traditional refrigerator, and the cost is much higher than that of the traditional refrigerator. In the solar adsorption refrigeration refrigerator, the performance of the adsorbents - refrigerant refrigerant is most currently studied. How to further strengthen the heat transfer performance of the adsorption bed, how to effectively solve the relationship between the adsorption bed, the heat collector of the collector and the night heat dissipation, such as how to effectively store the night's refrigerating capacity Problems such as daytime use.

The author believes that the key technologies to be further solved in the application and development of solar fridge are as follows:

1. high efficiency solar collector technology

Solar collector is a device for converting solar energy into heat energy. It occupies an important position in the solar refrigerator system. Its efficiency and price will directly affect the efficiency and economy of the whole solar refrigerator. In order to improve the efficiency of the solar collector, the current research is mostly limited to the improvement of the structure of the absorber and the concentrator, but the research on the endothermic nature of the collector is less, and the essence of the heat absorption is the optical properties of the material, that is, the absorptive capacity of the light in a certain band. Therefore, the author believes that the development of the absorber and its surface absorbing coating material will be the key to improve the efficiency of the solar refrigerator collector. There are many places to improve and develop in technology, such as coating the solar radiation with high spectral absorptivity on the surface of the heat absorber, so as to keep the maximum amount of collection too.  The radiation absorptance of the heat absorbing material is reasonably selected according to the radiation characteristics of the material, so that its spectral absorption ratio is close to 1 in the wavelength range of 0.3~3 m.

2. high efficiency solar energy storage technology

In order to overcome the disadvantage that the time of the solar energy can not be consistent with the working conditions of the refrigerator during the day and night, a reasonable storage device should be designed to save the energy produced during the day for the night or rainy days, so as to realize the all-weather refrigeration so as to reach the conventional refrigerator. The effect of the sample. At present, the main types of solar photovoltaic storage are capacitor storage, lead-acid battery energy storage, nickel hydrogen battery storage and potassium ion battery storage. The application technology of all kinds of energy storage batteries is relatively mature, but the storage capacity is relatively small. How to improve the capacity of this type of battery is the research direction in the future.

The energy storage technology of solar adsorption refrigeration refrigerator is currently used and is being studied. It mainly uses the heat, latent heat effect or reaction heat of chemical reaction process to store energy in the process of changing the state of the working medium. The latent heat storage technology is the same as adsorption refrigeration, so the study of latent heat storage technology is of practical significance to the energy storage of the solar adsorption refrigeration refrigerator. In addition, the energy storage technology of solar energy adsorption refrigerators should be based on working fluids.