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Disinfection cabinet program
1. Comparison of drying and disinfection cabinets with other types of disinfection cabinets
1.1 Features of high temperature tableware disinfection cabinet
High-temperature disinfection is usually heated by milky white quartz heating tubes, and the objects and air in the cabinet are heated to above 120°C in the form of direct far-infrared radiation and air convection, and the holding time is greater than 15 minutes. In hot and dry air, bacteria and viruses are oxidatively destroyed and killed. High-temperature dry heat disinfection is only suitable for disinfection of items with a temperature resistance greater than 150°C, and is basically not suitable for plastic products. Due to the high disinfection temperature, in order to save energy and keep the temperature rise of the outer wall not exceeding the standard, the high-temperature disinfection cabinet adopts a sandwich-type insulation structure, so the cabinet material consumption is relatively large, and the foaming agent used for the insulation layer must also consider environmental protection issues.
1.2 Features of ozone tableware disinfection cabinet
The most notable feature of the ozone disinfection cabinet is the low working temperature, which is suitable for tableware made of various materials. Ozone disinfection usually uses an intermediate frequency or high frequency, high voltage discharge ozone generator, or an ozone source such as an ozone ultraviolet lamp to generate a certain concentration of ozone in a closed volume and keep the ozone concentration for a certain period of time. The strong oxidation of ozone fully destroys the tissues of bacteria, viruses and microorganisms to achieve the sterilization effect. The greater the air humidity, the better the disinfection effect. Ozone is a very unstable gas. The gas-phase half-life of ozone in the air at room temperature is 20-50 minutes. It begins to decompose at 30°C, and decomposes significantly at 40-50°C. Ozone also has certain toxicity, which is harmful to human body. The mucous membrane of the respiratory system has a stimulating effect and can coagulate the hemoglobin in the blood. After inhaling a certain amount of ozone, people will have symptoms such as coughing and dizziness. Therefore, the ideal working state of ozone disinfection is: reach the required concentration at room temperature with high humidity and keep it for a certain period of time, then turn the heating to above 50°C to completely decompose the ozone, dry the sterilized tableware, and eliminate bacteria again Conditions for reproduction. Due to the high cost of the ozone generator that meets the requirements of the wet and hot working environment of the disinfection cabinet, the cabinet body requires corrosion resistance and good sealing performance, and an ozone leakage protection safety device must be installed, but the control circuit is more complicated.
1.3 Features of Dry Tableware Disinfection Cabinet
Drying disinfection is a kind of thermal disinfection. Its working temperature can adapt to items of various materials. Generally, the cabinet body does not have an insulation layer, and there is no side effect in the process of drying tableware. If its disinfection effect can also meet the requirements, it will be an ideal disinfection method that can not only make up for the lack of high temperature disinfection and ozone disinfection, but also reduce costs and save electric energy. The research goal of the drying disinfection cabinet is what kind of heat source to use and how to achieve a satisfactory disinfection effect.
2. Analysis of the working principle and disinfection effect of the drying and disinfection cabinet
2.1 Disinfection effect requirements
The sensory indicators after the physical disinfection of tableware in the national standard GB14934-94 of the People's Republic of China "food (drink) utensil disinfection hygiene standard" are: no oil stains, no water stains, no peculiar smell on the surface; The number of coliform bacteria detected in 100cm2 filter paper is <3, and coliform bacteria cannot be detected by the paper method. For the quality inspection of disinfection cabinet products, the artificial contamination method is generally used to inspect the disinfection effect items, and the corresponding required indicators are: the killing rate of Escherichia coli ≥ 9919%.
2.2 Theoretical Basis of Low Temperature Disinfection
The principle of action or sterilization process of thermal sterilization is different under dry heat and moist heat. Under humid and hot conditions, such as saturated steam, the killing of microorganisms is due to the irreversible denaturation of enzyme structures and proteins, and the denaturation temperature is inversely proportional to the water content. For example, the albumin coagulation parameters of egg protein are as follows: albumin+50% moisture, freezing point 56°C; albumin+25% moisture, freezing point 74-80°C; albumin+0% moisture, freezing point 160-170°C . The reason why the temperature of dry heat disinfection with a moisture content of 0% is so high is that the sterilization process has undergone a fundamental change. It is generally believed that dry heat disinfection is an oxidation process of cell components. According to foreign relevant professional disinfection literature, reproductive organisms (such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, etc.) cannot survive at 80°C for 10 minutes and at 73°C for 15 minutes under humid and hot conditions. ℃, inactivation within 20min. In medical treatment, it is necessary to disinfect and clean heat-labile instruments with water at an appropriate temperature. To kill bacterial propagules or inactivate most viruses including hepatitis A (HIV), the water temperature is 70-100°C, and the soaking time is 5-5. Just 10 minutes.
2.3 Drying and disinfection test
(1) Disinfection effect of a dry disinfection cabinet with a foam insulation layer: the volume is 50L, a 130W heating tube is used, the heating time is 53min, and then the door is opened to pick up the objects when the temperature is kept at 80min, which can be divided into dry heat and damp heat. Before dry heat disinfection, the water on the tableware was completely wiped dry, and the humidity in the cabinet was 70% before disinfection. Five times of artificial infection and disinfection effect tests were carried out. The results showed that the highest working temperature was 8015°C, and the time above 60°C lasted 45 minutes. , Escherichia coli killing rate <9919%. During damp heat disinfection, the tableware is put into the cabinet after pouring out the accumulated water. The humidity before disinfection is 93%, and the humidity after disinfection is 85%. Extinction rate ≥ 9919%.
(2) The disinfection effect of the hot air external circulation dry bath disinfection cabinet: the volume is 56L, the heating power is 230W, the hot air blower inhales air from the outside, blows it to the tableware after heating, and the evaporated water vapor is discharged out of the cabinet through the crack of the door. After the tableware is cleaned, pour out the accumulated water and put it in the cabinet. The humidity in the cabinet is 90% before disinfection, and only 70% after disinfection. The continuous heating time is 90 minutes. Extinction rate <9919%. In addition, the defect that the pores of the outward exhaust passage are enough to crawl into insects such as cockroaches also makes the food have the risk of secondary pollution.
(3) The disinfection effect of the hot air internal circulation drying cabinet: Compared with the external circulation, the hot air internal circulation is characterized by no air exchange with the outside world, faster temperature rise, and a longer time in the high humidity environment in the cabinet, and eliminates Secondary pollution by insects. The water content of the tableware is eliminated by condensation on the vent hole and the lower temperature cabinet wall.
Test results in a 75L cabinet: heating power is 230W, tableware is washed and drained and put into the cabinet, the humidity before disinfection is 92%, the humidity after disinfection is 85%, the ambient temperature is 2315-27°C, and it works continuously for 60 minutes without stopping the machine , the maximum working temperature is 5917～7213°C, the holding time above 50°C is 40min, and the killing rate of E. coli in the three tests is ≥9919%.
Since there is no heat insulation layer, the temperature in the cabinet is still greatly affected by the ambient temperature. In order to ensure that the disinfection requirements can still be met under the extreme conditions of the standard detection temperature of 20±5°C, a margin must be left for the heating power. Increase the heating power to 350W, and set up a temperature controller so that the maximum temperature in the cabinet is lower than 85°C, and re-test the temperature rise and disinfection effect test. The three tests are carried out at room temperature 25-29°C, the humidity before disinfection is 92%, and the disinfection Finally, the humidity is 80%. As a result, when the temperature rises for 35-40 minutes, the temperature controller starts to jump, and the highest temperature in the cabinet is limited to 70-82°C, and the lowest temperature is limited to 60-68°C. The above holding time is 30 minutes, and the killing rate of E. coli at each point is ≥9919%. The test was carried out again in winter at a room temperature of 15°C. The humidity before disinfection was 92%, and the temperature was continuously heated for 60 minutes. The temperature controller did not operate. The maximum temperature in the cabinet was 60-70°C. The sterilization rate is still ≥9919%.
(4) Disinfection effect of windless natural convection heating drying and disinfection cabinet: the heating tube or heating sheet is placed at the bottom of the disinfection cabinet, and the biggest advantage of drying and disinfecting tableware by natural convection heat transfer is that the fan system is omitted , so that the product cost is significantly reduced. The disadvantage is that the heat transfer effect of natural convection is worse than that of hot air circulation, and the temperature difference between various parts of the cabinet is relatively large, resulting in that the two poles with the largest temperature difference may exceed the allowable temperature, or the sterilization and drying effects are not good.
Test results in a 75L cabinet: the heating power is 280W, and a special method is adopted to prevent the infrared radiation of the milky white quartz heating tube from directly irradiating the tableware, so as to reduce the temperature difference between various parts. Wash the tableware and pour out the accumulated water and put it into the cabinet. Before disinfection, the humidity in the cabinet is 95%, and it works continuously for 70 minutes. The temperature of each measuring point rises slowly in a small wave shape with the action of the temperature controller, reaching a maximum of 55-95°C. Keep above 50°C for 40 minutes, the humidity is still 90% when the work is completed, and the killing rate of E. coli is ≥9919%.
2.4 Analysis of disinfection effect
From the test results of the above four types of drying and disinfection cabinets, it can be seen that the temperature, holding time, and humidity of moderate temperature disinfection have the following relationship with the killing rate of E. , the sterilization rate is <9919%; ②When the humidity is 90-70%, and the temperature is maintained at 50-66°C for 60 minutes, the sterilization rate is <9919%; ③The humidity is 92-80%, and the temperature is maintained at 60-82°C for 30 minutes, the sterilization rate is The sterilization rate is ≥9919%; ④ When the humidity is 95-85% and the temperature is kept above 50°C for 40 minutes, the sterilization rate is ≥9919%.
3. Design of heating system of drying and disinfection cabinet
3.1 Heater
The heating system of the drying and disinfection cabinet is best to use a hot air blower, and the heat source is usually an electric heating wire or a PTC heating element. In order to keep the high humidity for a long time and improve the heating efficiency in the cabinet, it is better to use the hot air circulation heating method. The design of the hot air circulation duct must ensure that the temperature rise in the cabinet is relatively uniform, and there is no heating dead zone under full load conditions. The disadvantage is: the cost of components of the hot air blower system is relatively high, and the proportion of the cost in a small drying cabinet is relatively large.
3.2 Heating pipe
The milky white quartz heating tube used in the electric high-temperature tableware disinfection cabinet is an electric heating element with low cost, wide versatility, long life and convenient installation. Its far-infrared emissivity accounts for more than 60% of the output power, and the heated object can be directly It absorbs far infrared rays, so it heats up quickly and has high thermal efficiency. It is an ideal heating element for high-temperature dry disinfection. The maximum working temperature of the drying and disinfection cabinet is ≤95°C. If the milky white quartz heating tube is directly used, the high-efficiency heat radiation will heat up the items near the heating tube, while the items far away from the heating tube can only be heated by air convection heat transfer. There is a large temperature difference in various places, which is easy to damage the plastic products and cannot achieve the effect of disinfection and drying. At present, there are two ways of heating the heating tube: (1) using low far infrared heating tube: by reducing the surface temperature of the element, the radiation conversion efficiency is effectively reduced, and the convenient way to reduce the temperature is to reduce the power of the heating tube. (2) Set up a thermostat near the heating pipe, and limit the maximum temperature not to exceed the standard through repeated and frequent actions of the thermostat. The above two methods all reduce the input power per unit time, prolong the heating time, slow the temperature rise, and low thermal efficiency under the condition of a certain heat source layout.
3.3 New heating tube heating structure
The new heating tube heater is a heater for drying and disinfection cabinets designed for the above-mentioned advantages and disadvantages of milky white quartz heating tubes. It takes the advantages of low price and good quality of the milky white quartz heating tube, and makes up for the disadvantage of high far-infrared radiation rate.
Several heat pipes are installed in a metal heater which is closed on all sides, open on the top, and has an air inlet on the bottom. The top opening of the heater is covered with a metal cover densely covered with louvers, so that The infrared radiation is blocked and the hot air can be discharged smoothly. The cooler surrounding air enters the heater through the bottom air inlet, forming natural thermal convection of the air in the cabinet. The temperature controller located outside the heater can control the tableware in the cabinet. Do not overheat.
The arrangement density of the heating pipes in the heater must be limited so that the maximum internal temperature does not exceed the allowable temperature of the heating pipe material. The four sides of the heater are closed to block the influence of heat energy on the walls of the disinfection cabinet. The distance between the cabinet wall and the four walls of the heater must also be controlled to prevent the outer surface of the disinfection cabinet from overheating.
This kind of heat pipe heater is only suitable for vertical arrangement and all-metal cabinets. Limited by the arrangement density of heating pipes, in order to achieve better drying and disinfection effects, the volume of the disinfection cabinet it is suitable for is also limited by a certain upper limit.
Summarize
①Drying tableware disinfection cabinet is a tableware disinfection appliance that has a wider range of application than high-temperature tableware disinfection cabinets and lower cost than ozone tableware disinfection cabinets; ②Drying disinfection cabinets with correct disinfection temperature, humidity and holding time can The killing rate of Escherichia coli can reach a disinfection effect of over 99.9%; ③Heating tube heaters can meet the market demand for medium temperature and low cost of dry disinfection cabinets under certain conditions of use.
The above are the details of the disinfection cabinet solution introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have electronic function development needs for disinfection cabinets, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. Our development capabilities cover PCB design, single-chip microcomputer development, Bluetooth technology development, software customization development, APP customization development, WeChat official account development and other hardware and software design. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the development of electronic education products.
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