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　  Cold chain cold storage logistics affects food safety and supplyCold chain logistics is one of the important supports for transportation and food safety. Food cold chain logistics generally refers to a systematic project in which food is always in a prescribed low temperature environment from production, processing, storage, transportation, distribution, retail, to pre-consumption, in order to ensure food quality, reduce losses, and prevent pollution. Its scope includes primary agricultural products (fruits, vegetables, meat, poultry, eggs, aquatic products), processed foods (quick-frozen food, poultry, meat, aquatic products and other packaged cooked food, ice cream and dairy products, fast food raw materials), special commodities, and so on.Cold chain logistics runs through the entire chain of the food industry and serves as a bridge for the effective connection of various nodes in the food industry. Beginning in the upstream breeding or planting bases, refrigerated warehouses (cold storage), production and processing bases, frozen and refrigerated food production and processing enterprises, etc.; throughout the midstream of the food industry, refrigerated warehouses, wholesale markets of origin and wholesale markets, distribution centers, etc. Intermediaries and suppliers, etc.; linking farmers' markets, supermarkets, retailers, restaurants, households, etc. downstream of the food industry.　　The cold chain is closely related to the food industry. From the perspective of cold chain logistics customers, it can be divided into seven layers according to the pyramid type. The customers at the top of the tower are high value-added pharmaceuticals, catering chains, and fast-moving consumer goods, and cold chain logistics mostly adopts outsourcing; the middle is industrial products, processed dairy products, and quick-frozen rice and noodles, which is also the most competitive market for cold chain logistics. ; Then there are food-type poultry meat and aquatic products, and the bottom layer is fruits and vegetables, agricultural products, and the main form of transportation depends on social vehicles.　　 Cold chain cold storage has a profound impact on the development of agriculture and the food industry, and is vital to ensuring food safety and the quality of food ingredients.　　 For a long time, China’s fresh agricultural products have faced a series of serious problems such as an imperfect cold chain logistics system, high cost, low efficiency, and high loss.　　According to the research data of Asia Tung Shing's supply chain, China consumes more than 1 billion tons of perishable food each year, of which more than 50% require cold chain transportation. However, the current comprehensive cold chain circulation rate is only 19%, while the cold chain flow in Europe and the United States can reach more than 95%. The annual loss of fruits and vegetables alone can reach more than 100 billion yuan.Qin Yuming, secretary-general of the Cold Chain Logistics Committee of the China Federation of Logistics and Purchasing, said that under the impetus of the 2008 Beijing Olympics, China has truly ushered in the rapid development of food cold chain logistics. During this period, China's cold storage capacity and the number of refrigerated trucks increased by leaps and bounds, but due to long-term historical debts, many problems were still exposed. The state-owned cold storage warehouses, the main body of China's refrigeration industry, were constructed earlier, and most of them have been used for more than 15 years. Limited by the conditions at the time, the cold storage engineering design standards were low, the equipment quality had many problems and the degree of automation was low, and most of them had entered the period of overhaul. Moreover, there is a serious shortage of refrigerated transport vehicles in the domestic distribution market. In export and import trade, there is also a shortage of refrigerators and corresponding transport vehicles.The most prominent problem is the broken link.In foreign countries, cold chain transportation is uninterrupted. However, in China, the food cold chain started late, investment is low, the entire industry is low in concentration, and the strength of the enterprise is weak, making it impossible to achieve the entire cold chain.　　Even, most cold chain logistics belong to the state of chain disconnection. This not only leads to the high rate of corruption of fresh agricultural products and the inability to efficiently serve the huge food market, but also brings huge safety hazards to food companies and all sectors of society. At the same time, for companies, if food ingredients want to improve their bargaining power, they need to ensure that food ingredients maintain their freshness and taste to the greatest extent during the circulation process, which requires a whole cold chain guarantee system.　　Cold chain infrastructure promotes new formats and models of the food industry　　 In recent years, favorable national policies have continuously injected new vitality into the development of the industry, and the cold chain infrastructure has become more and more perfect. According to incomplete statistics, in 2019, there were more than 40 policies related to agricultural agricultural products and cold chain logistics issued by the government at the government level, providing sufficient conditions for the development of fresh agricultural products e-commerce, and a new retail that integrates online and offline logistics. The model is becoming more and more prosperous.On September 21, 2020, the General Office of the State Council formally issued the "Opinions on Leading the Accelerated Development of New Types of Consumption with New Business Forms and New Models", proposing to promote the two-way acceleration of online and offline integrated consumption, and accelerate the promotion of agricultural products "fresh e-commerce + cold chain home delivery" "And other new service models.　　 It can be seen that the development needs of China's cold chain logistics are gradually becoming mature.

Some customers have reported that the ice machine sometimes has operational problems because of refrigerant leakage. Let’s look at several refrigerant leak detection methods.1. Visual inspection: When oil stains are found somewhere in the system, this may be a leakage point. There is a big defect. Unless the system suddenly breaks and the system leaks a large leak and the system leaks liquid colored media, the visual leak cannot be located because the leak is usually very small, and many parts of the refrigeration system are almost invisible.2. bubble water or soapy water leak detection: Fill the system with 10-20kg/cM2 pressure nitrogen, and then apply soapy water to all parts of the system. The bubbling point is the leakage point. This method is the most common leak detection method for maintenance workers, but the human arm is limited, the human vision is limited, and in many cases the leak is not seen at all.3. Leak detection with nitrogen water: Fill the system with 10-20kg/cm2 pressure nitrogen, immerse the system in water, and the bubbling point is the leakage point. The obvious shortcomings of this method: the water used for leak detection is easy to enter the system, causing the materials in the system to be corroded. At the same time, high-pressure gas may also cause greater damage to the system, and the labor intensity for leak detection is also great.4. Fluorescence leak detection: It uses the principle that fluorescent leak detection agent emits bright yellow and green light under the irradiation of ultraviolet/blue leak detection lamp to detect fluid leakage in various systems. When in use, only a certain proportion of fluorescent agent is added to the system. After the system operates for 20 minutes, wear special glasses and illuminate the outside of the system with a leak detection lamp. The leak will show yellow fluorescence.5. Gas differential pressure leak detection: Using the pressure difference between the inside and outside of the system, the pressure difference is amplified by the sensor, and the leak detection result is expressed in the form of digital or sound or electronic signals. This method can only "qualitatively" know whether the system is leaking, but cannot accurately find the leak.6.Halogen lamp leak detection: Ignite the leak detection lamp and hold the air tube on the halogen lamp. When the nozzle is close to the leaking part of the system, the flame color changes to purple blue, which indicates that there is a large amount of leakage. In this way, open flames are generated, which is not only dangerous, but the combination of open flames and refrigerants will produce harmful gases, and it is also difficult to accurately locate leaks. So this method is hardly used by anyone now.7. Electronic leak detector for leak detection: Electronic leak detector is a reliable leak detector. Because of its accuracy in leak detection, it has quickly occupied the market in recent years. When using it, move the probe against the place where leakage is possible. When leak detection When the device sounds an alarm, it indicates that there is a leak. Leak detection with an electronic leak detector is currently the most scientific, simple and fast leak detection method. 

In the ice making machine industry, ammonia refrigeration and fluorine refrigeration have always been the focus of controversy. The choice of refrigeration method can maximize the economic, environmental and social benefits. This article objectively analyzes the nature of ammonia, fluorine refrigerants and ammonia and fluorine refrigeration systems, and summarizes the application status, existing problems, and research directions of the two refrigeration methods in the industry, which will help people have a clear understanding of these two refrigeration methods. To understanding.1. Comparison of properties of ammonia refrigerant (R717) and fluorine refrigerant (R22 and R404A)In terms of safety: the explosiveness and toxicity of ammonia greatly limit its application, and with the frequent news of ammonia refrigeration systems in recent years, people have a certain fear of ammonia refrigeration systems. The high safety of fluorine refrigerants is the main reason for the rapid development of fluorine refrigeration systems in recent years.Environmental protection: ODP of ammonia is zero, and GWP is also zero. R404A is a more environmentally friendly refrigerant, and R22 refrigerant due to its poor environmental performance, developing countries will restrict its application before 2020. At present, people in the industry are actively looking for alternative refrigerants that are more environmentally friendly.Material compatibility: When ammonia contains moisture, it is corrosive to copper. Therefore, copper and copper alloys cannot be used for the pipes and valves of the ammonia system. There are certain limitations in the selection of system equipment materials. Fluorine refrigerants have high chemical and thermal stability, and theoretically they are not corrosive to all metals. Interaction with water: the allowable water content of ammonia is less than 0.2%. Because ammonia is easily soluble in water, even if there is a trace amount of water, it will not appear "ice plug" like Freon, so it is necessary to dry the ammonia refrigeration system to the pipeline system. The requirements are not as strict as Freon. Freon is difficult to dissolve in water, so if there is water in the system, it is easy to cause ice clogging. Usually we have a filter drier in the system. Interaction with oil: At present, the lubricating oil of ammonia refrigeration system is mineral oil, which cannot be miscible with ammonia. Equipment such as oil separator and oil collector are usually installed to return the lubricating oil to the compressor through automatic or manual control. R404A is not miscible with mineral oil and alkylbenzene oil, but it can be miscible with polyester oil (POE). However, at high temperatures (around 50°C), there will be insoluble stratification, and R22 is also slightly soluble in lubricating oil. Therefore, large-scale fluorine refrigeration systems are usually equipped with oil and oil reservoirs. Take R404A as an example. The difference between the two compressors is only the refrigerant. Compare the cooling capacity of R717, R22 and R404A under the same evaporating temperature (-10°C), condensation temperature (45°C), liquid subcooling (0K) and suction superheating (10K). Ammonia has more advantages than fluorine in terms of cooling capacity, COP, and mass flow. However, the exhaust temperature of R717 is much higher than that of R22 and R404A, which will increase the configuration requirements of system components. Ammonia has a much larger refrigeration capacity per unit mass of fluorine, indicating that ammonia has a better refrigeration capacity. However, when the evaporation temperature reaches -33.33℃, the gauge pressure of ammonia is 0. In order to avoid the system working under negative pressure, ammonia is generally used For systems where the evaporation temperature is above -33.33°C.2. System complexityTube ice machine Ammonia refrigeration is a pump-supply system. Since the mineral lubricating oil used in the ammonia refrigeration system is not miscible with ammonia, the ammonia system is indispensable for oil separators, oil collectors and other equipment to ensure the oil return of the system and reduce the system temperature, so that the ammonia The oil system is very complicated. These make the ammonia system huge, many auxiliary machines, complicated pipelines, many valves, complicated construction, and long construction period. The fluorine system has a compact structure, a small footprint, and few accessories. The configuration of the unit has been very complete, and most of it can be completed in the factory of the unit supplier.3. Equipment investmentThe ammonia system includes a lot of equipment, mainly including compressors, evaporators, condensers, oil separators, high and low pressure storage tanks, intercoolers, recoolers, ammonia separators, low pressure circulation tanks, and emergency ammonia discharge devices. , Air vent, oil collector, ammonia pump and corresponding valve parts and bypass valve, etc., resulting in a lot of on-site installation workload. The main equipment of the fluorine system includes compressors, evaporators, condensers, oil separators, oil collectors, gas-liquid separators, liquid reservoirs and corresponding valves, etc. Generally, the fluorine system uses copper pipes or steel pipes, which is convenient to take over. , The pipe layout is simple, and the pipe consumption is less than that of the ammonia system. The cost of investment in ammonia and fluorine refrigeration equipment is at the same level of equipment quality and control methods. For small cold storage (compressors less than 50Hp), the price of fluorine is more than 10% lower than that of ammonia equipment. The prices of large and medium-sized cold storages are almost the same. If imported or imported domestically assembled fluorine refrigeration equipment is used, it is more than 30% cheaper than imported ammonia refrigeration equipment, but 20%-30% more expensive than domestic ammonia refrigeration equipment.4. Degree of automationBecause the valves of the domestic ammonia system are affected by valve material, processing equipment and processing technology, the leakage problem of the valves of the ammonia system is serious, and it is difficult to achieve a high degree of automatic control. Specialized personnel are required for 24-hour management (Note: There are also automated ammonia storages, but they are relatively few). The fluorine system is easy to realize highly integrated and relatively stable automatic control due to the mature products and stable performance of various components, and basically realizes the unattended operation of the system. Due to the hazards of Freon refrigerants to the atmospheric environment, the use of fluorine refrigeration has been restricted in recent years. Therefore, actively looking for more ideal refrigerants is the development direction of fluorine refrigeration. People have made positive progress in the search for alternative refrigerants of Freon. Some experts and scholars pointed out that the better refrigerants to replace R22 are R407C, R410A and R32.ConclusionA comparative analysis of the advantages and disadvantages of ammonia and fluorine refrigerants from the characteristics of refrigerants and current application characteristics shows that ammonia refrigeration has better refrigeration performance, and the toxicity and danger of ammonia are what we have to consider, so we need to continue Research and improve the objective problems of ammonia refrigeration system. The better safety and simplicity of fluorine refrigeration is widely used in small and medium-sized cold storage, and there is also a trend toward large-scale development. However, the hazards of Freon to the atmospheric environment have to be paid attention to. Therefore, it is still to find more ideal refrigerants. The focus and direction of future research.

      The ice making machine cooler is a type of heat exchange equipment used to cool fluids. Water or air is usually used as a coolant to remove heat. Mainly can be divided into tube cooler, plate cooler and air-cooled cooler. When the copper tube of the tube cooler is damaged and leaks, if the tube plug is used to block it, the total number of blockages shall not exceed 10% of the total number of tubes (or according to the requirements of the cooler product manual). According to the water quality and oil quality, carry out the inspection and cleaning of the fouling on the tube wall surface of the tube cooler.      The cleaning method of the tube cooler is as follows:　   1. Cleaning the water side of the tube cooler　   A. Trichloroethylene solution can be used for flushing, so that the cleaning liquid circulates in the cooler. The pressure of the solution is not greater than 0.63MPa, and the flow direction of the solution is preferably opposite to the direction of the oil flow in the cooler. The cleaning time depends on the dirt. After rinsing, introduce clean water into the cleaning until the water flowing out is clean by visual inspection.      B. You can also use carbon tetrachloride soak, pour the solution into the cooler, and watch the color of the solution after 15-20 minutes. If it is severely turbid, replace it with a new solution and repeat the soaking until the color of the solution after soaking is similar to that when it is clean. Then introduce clean water into the cleaning, until the outflow of water is clean by visual inspection.　  C.If there is no obvious structure in the water side pipeline, you can clean it with the corresponding brush according to the diameter of the pipeline, and then rinse it with clean water.　　2. After cleaning the tube cooler, perform a water pressure test. The cavity between the tubes of the tube cooler shall be tested for tightness with water according to its nominal pressure or 1.25 times the working pressure, and the pressure shall be maintained for 30 minutes, and there shall be no leakage at the expanded tube or welded joint. The water must be completely drained after the test.　　3. Check the heat exchange effect of the tube cooler. After the lubricating oil is cooled by the cooler, the temperature can generally be reduced by 5-10℃, and the temperature of the cooling water can be increased by 3-5℃.　　4. The connecting oil ports of the tube cooler must not be opened for no reason during the cleaning process, and must be sealed with bulkheads or flange covers.        Let us understand the difference between the cooler and the condenser of the ice maker:Condenser and cooler are also one of the important parts of heat exchange equipment in the heat exchange process. The main differences between the two are as follows:1. The cooler has no phase change, and the condenser has a phase change but the pipeline entering and exiting the cooler does not change. Generally, the pipe diameter is different from the inlet and the outlet, and the pipe diameter of the inlet and outlet of the condenser changes greatly, which is relatively easy. watch.2. The settings of the baffles of the two are different, the cooler is set up and down, and the condenser is set up and down, and the heat transfer coefficient is also different.3. There will be a liquid level gauge and a liquid level control port on the cooler, but the condenser does not. The air inlet and air outlet of the cooler are both at the upper part of the container and the pipe diameter is basically the same, while the air outlet of the condenser is at the bottom of the container, and the pipe diameter is different from the air inlet. The inlet and outlet of the intercooled ammonia liquid are under the container, while the water inlet and outlet of the condenser are not. The vertical type is generally one up and down, while the horizontal type is at one end of the container.