Development overview of microwave heating technology
Microwave technology is applied to communication, broadcast, TV technology at first. In these fields, the microwave is utilized as the carrier of a kind of information or the information. In microwave in using, find all the time following have one will cause microwave can loss, is it try prevent and factor of harmful toing that dispel to need decades in communication engineering Heat effect. As far back as 1945, U.S.A. is it utilize the heat effect of microwave is it go on idea that heat to material to come to put forward on someone. Many people heat this subject microwave afterwards Not going on, section is explored, tested and studied. Until the end of the sixties.
Microwave can is it utilize to come as one energy finally, heat, be dry, abate worm, sterilization, medical treatment,etc. at the industrial project. It is from food industry to initiate, the appearance of and the home microwave oven goes still one step further to expand the application of microwave heating technology. Now, the microwave is heated as already paying close attention to by every discipline domain and application and development of a new technology.
Can application study and academic exchange very much active and paying attention to straight to microwave abroad. The uncle was safe in A of Canada of North America in 1966 (Alberta) The city has set up international microwave power society ( Abbreviated as IMPI) ,Hold an academic discussion every year, and publish the quarterly " microwave power magazine " (" The Joural of Microwve Power ") regularly .
Our country begin microwave can use research work, begin microwave research and microwave, heating of application technology is it spend reseach of magnetron to heat on 1973 in the 1970s. Ministry of the Electronics Industry hold " national microwave popularize the exchanging meeting of application technology " 1974 and 1980, exchange microwave academy and application technology question. Transfered the scientific and technological strength of the unit subordinate to a ministry, established with the approval of four machine departments in March of 1981 China National Electronic Devices Industry Corp microwave can is it stand to popularize and apply, responsible for national microwave can organization, design research work of popularization and application. The Chinese institute of electronics held the first " the national microwave could use the seminar " in October of 1983. Each one has collections of thesis that are published, involve the application in such respects as the industry, agriculture, medicine, scientific research,etc..
At present, our country has been already in the leather, such trades as timber, colored printing, food, paper, chemical industry, pottery, medicines, tobacco leaf, building materials, rubber and medical treatment,etc. Dr.eye: adopt microwave technology gradually, have made the good economic benefits. Microwave can technology, as a kind of new processing means, the technological transformation and equipment of every profession and trade is it is it bludgon into greatly to form already to upgrade. Especially the present stage, it is a problem of solving product structure and social demand to be in front of every operator, meet the improvement to that the quality of the products, variety required of the social development. One of its focuses is achieved newly and insufficiently by technology, quality is upgraded and lagged behind. The appearance of microwave technology has offered the good condition that improve the product specification, keep up with the technological progress, achieve the high value added products.
1, food industry
Food is god for the people, the food industry is the pillar industry that our country emerged rapidly. Utilize microwave to bulk out, bakes the universe, takes off smelling of fish and keeps fresh to deal with to the food. Have already been used soybean,etc. Dr.eye: at present. Our company produces 50- 6 sets of microwave equipment to apply to the food industry every year.
2, wood processing
Microwave can carry on to 1-6 thick plank even baking the universe is dry to only take more than ten minutes fast, and does not fracture, out of shape and small, kill the ovum worms and larvas within the timber at the same time; Can deal with the plywood or the solidification of going all out to defeat the board glue and connecting; The bamboo article is dry and killing disinfecting mouldly.
3, rubber industry
Japan makes to the tire once heating with 2450MHz, 5- 10kw microwave heating device, intensifies and keeps warm with the hot wind after sulphurating temperature, can sulphurate the tire of weight of 3- tons; U.S.A. adopt 915MHz, 50kw loudspeaker aerial as radiate heater, utilize procedure is it rotate to scan to full-length tire to control, its advantage is heating evenly and sulphurating time to shorten by 1/3.
4th, kill worm's sterilization
Can sterilization abate worms under low temperature with microwave. Deal with food, medicines, tobacco, timber,etc.. Can play a role in killing worm's sterilization in 70- 8 degrees Centigrade. And intensification is fast, free of thickness of the supplies, form.
5, desulphurization
The sulphur in the raw coal appears in the form of pyrite, the pyrite has higher loss angle tangent than the coal, so utilize microwave to make the pyrite receive alternative heating and gas and react, carry on the desulphurization. The coal is not influenced. The ideal method is that the wave of pulse taking duration as 0.1 seconds heats the intermittence type, heat the yellow iron ore to high temperature of about 650 degrees Centigrade. This kind of method goes to the sulphur effectually, does not need expensive catalyst, saving the fund, the energy is with high efficiency, the environmental pollution is little.
6, microwave plasma technology
Have already adopted microwave plasma technology in the production technology of the semiconductor, carve losing, sputter, gaseous phase deposit, oxidize the silicon chip; Can also be used in the metal, alloy, nonmetal surface to deal with; Used in plasma spectral analysis, can measure more than ten kinds of elements.
7, medical treatment
The biological effect of microwave divides into the heat effect and not the heat effect. Heat effect its can carry on microwave physiotherapy, cooperate with radiotherapy and chemotherapy go on hot cancer of curing completely in medical treatment; Can also utilize microwave to heat the plasma, unfreeze and refrigerate the organ in addition; Can design microwave scalpel also, is it arrest blood soon, person who bleed little to operate on.
8, measurement
The microwave measures the precision high, is suitable for production to measure and automatically control in succession. Have already been used for respect of finding range, examining warmly, examining thick, testing the speed etc..
9th, the pottery frit
The microwave can carry on ceramic melting evenly and pre-pressingly and fritting, the maximum temperature can be up to 2000 degrees Centigrade, get meticulous pottery of the large size.
10, chemical industry
The microwave has extensive application in chemistry, for instance microwave clearing up, extracting, hydrolysising, catalysis promoter,etc..
Second, microwave heating principle and characteristic
1, some is microwave
Microwave, radiowave, TV signal, communication radar, infrared ray, visible light,etc. are the same, belonging to the electromagnetic wave, just the wavelength is not the same. The microwave is the frequency between 300 megahertzs and 300 gigahertz (GHz)s of electromagnetic waves ( 1 meter of wavelength- 1 mm.) ,Usually used in the TV, broadcast, communication technology, such as pursuing(1) . And regard microwave as a kind of energy in modern times, expand a branch technology again, heats, dry on the industry and agriculture; Chemical reaction of carrying on the catalysis, extracting etc. in the chemical industry and exciting the plasma; Wait a moment .
Dr.eye: It is becoming riper that the use of the home microwave oven marks microwave technology even more. Because the application of the electromagnetic wave is extremely extensive and popularizes, especially communication field, in order to avoid interfering each other, board of trustee has regulated specifically to the division of frequency the international radio. Giving the frequency that industry, science and medical science use has 433 megahertzs, 915 megahertzs, 2450 megahertzs, 5800 megahertzs, 22125 megahertzs, separated from communication frequency and used. It is 915 megahertzs and 2450 megahertzs to be used in the daily frequency that industry heats at home at present. Microwave frequency and choice of the power can be made according to heating the difference of forms, material, moisture content of the material.
2, microwave heating principle
The supplies medium is and not organized by polarity molecules by the polarity molecule, under electric magnetic field function, the polarity molecule transfers from the random distribution state to and carries on the orientation to arrange in accordance with the electric field direction. Under microwave electric magnetic field function, these orientation sports are changing constantly with the frequency of hundreds of millions of times per second, cause violent sports of the molecule to rub with colliding, thus produce heat, reach the electric energy to turn into the heat energy in the medium directly. It is obvious, it is that the medium material oneself losses electric field energy and generates heat that the microwave is heated. And it is different that medium constant ¦Å r and medium of different medium material loss angle tangent value tg¦Ä, so the heat effect under microwave electric magnetic field function is different. The material organized by polarity molecule, can absorb the microwave well. The moisture son presents extremely strong polarity, it is the best medium which absorbs the microwave, so all moisture members' goods and materials must absorb the microwave. Another from polarity member makes up, they do not absorb basically or seldom absorb the microwave, is this kind of material polytetrafluoroethylene (PTFE), polypropylene, polyethylene, gathered? Waiting for, plastic products, glass, pottery,etc., they through the microwave, and does not absorb the microwave. The container or supporting thing can be heated as the microwaved for this kind of material, or do the sealed material. Among microwave electric field, medium absorb all kinds of P direct radio, microwave of power on frequency f, intensity E the square of electric field have, dielectric constant ¦Å r and medium loss tangent value tg¦Ä.
P = 2πf•E2•εr•V•tgδ
V ----The supplies medium absorbs the effective volume of the microwave
In addition, will appear one phenomenon in practical application, but heating that have completely, some do not heat completely, this exist one throw ability and heating depth issue, what is pierces through ability? Pierce through ability whether electromagnetic wave penetrate ability to get medium, electromagnetic wave enter from the surface of the medium and when its inside spreads, because energy is being absorbed and turned into heat energy, the energy that it carries, with deepenning the distance on the medium surface constantly, decay in the form of index. The depth of transmission is defined: The density of power is 1 of the density of surface energy / e or 36.8% depth D regarded ases within the material, already
λ0 D = ----------------------- 2π√εr•tgδ
Can be found out from the type, heating depth of microwave than infrared to heat heavy much, because wavelength of microwave infrared close thousandfold of wavelength. It is heated that infrared but the surface is heated, the microwave is that the deepening inside is heated.
3, advantage that the microwave is heated
(1)Heating is fast in speed
The routine is heated (such as flame, hot wind, electric heat, steam) Utilize heat-conduction, convection, heat radiation is it give surface to heat the thing to transmit at first heat all, and then make the centre temperature rise progressively through the heat-conduction (outside that has already often claimed to add It is hot) . It should make the centre position reach necessary temperature, need certain heat-conduction time, and the time needed toward bad object of heat-conduction rate is longer. Microwave is it belong to inside heating way to heat, electromagnetic to can act on medium member change hotly directly, and transmission makes the medium heated at the same time, does not need the heat-conduction, so can reach heating evenly within short time.
(2)Heat evenly
While heating in outside heating way, in order to improve the speed of heating, need to raise external temperature, strengthen the gradient of difference in temperature. But apt to produce the burnt endogenous phenomenon outside thereupon. No matter how the form is when the microwave is heated, microwave can all permeate evenly, heat emerges, so the homogeneity is improved greatly.
(3)Energy-conservation is high-efficient
Different supplies have different absorption rate to microwave, with moisture content material apt to absorb microwave can. Glass, pottery, polypropylene, polyethylene, fluoroplastics,etc. seldom absorb the microwave, the metal will reflect the electric wave, these materials can't be heated by the microwave. When the microwave is heated, are having the supplies heated and usually putting with the heating room where the metal is being made into, it is a close of body for electromagnetic wave to heat the room, the electromagnetic wave can't be let out outside, can only be heated the object to absorb, will not be heated while heating the indoor air and corresponding container, so thermal efficiency is high. At the same time the environment temperature of the workplace will not rise because of this either, the production environment is obviously improved.
(4)Easy to control
The control of the microwave power is regulated by the switch, knob, namely open and already use, without hot inertia, the power is adjustable in succession, easy to automize.
(5)Sanitation and hygiene
While processing food, medicines,etc. drily, microwave heat effect and biological effect can kill worms and kill rapidly under lower temperature, can keep nutritional labeling and original color and luster maximumly, so the microwave is heated in the food industry widely usedly.
(6)Alternative heating
The absorption of the microwave of supplies of different nature losses differently, the characteristic of already alternative heating, this is useful to dry course. Because son's absorption of the microwave of the moisture losses biggest, so the position high in water content, absorb the microwave power rather than the position lower in water content, thus the dry speed trends towards unanimity. But some materials present and shoulder the coefficient of temperature, the higher temperature is, ¦Å r and tg¦Ä will increase, it is the better to absorb, causes the positive feedback to make the temperature of this parts rise sharply. Go on microwave notice making the processing technology to the material rationally just when being heated.
(7)Safe and harmless
Microwave can close to heat room, wave dish transmit in in charge ofing in whom metal make usually. The company collects the processing experience and technical equipment for many years, adopt the advanced person to design, make the microwave which passes in and out such places as the material mouth, viewing panel, furnace gate,etc. let out and control strictly in the national safety standard indicator, lower than the safety standard that the country makes greatly. And the microwave is not the radioactive ray, there is no harmful gas to discharge, it is a kind of very safe heating technology. The dry method that the microwave is heated is with heating the side commonly France (heat etc. such as the hot air, flame, electric heater, gas stove, infrared ray, high-frequency reaction) Compare, have a lot of characteristics. Mainly: Take heat transmission from outward appearance to inner essence, heat object directly, and hot temperature profile once is even often; Temperature can the attitude is controlled, control and heat time accurately temporarily; Necessary heating time is short; The quality of the products, output and labor productivity are raised; Suitable for the production process to automize; Environment-friendly, pollution problem. Begin with trial-production of the microwave therapeutic apparatus at first in our country, popularize to the processing of such light industrial products as the food, tea, tobacco, leather, medicines, paper, timber, rubber,etc. afterwards, and grain of agriculture bake such respects as the universe, seed treatment,etc..
Third, application in the food industry of microwave
At present, adopt microwave technology at most among food industry to is it " it is warm to answer " to unfreeze to apply abroad, the food is dry and bulking out and giving the cooking. " it go back it is the warm " mean unfreeze temperature of food unfreeze from depth state rise to -4- - 5 degrees Centigrades. There is certain hardness in although the food at this moment, can already cut into slices and cut apart. " it is warm to go back " with the microwave the food has a lot of outstanding advantages more than the routine method: Time shortens, apt to control greatly, products quality is good, color and luster and fresh degree can all keep such as processing, moisture and nutritional labeling are lost little, low in fungus, deals with and with high efficiency, with low costs, consumes energy little, the floor space is small, labour condition and environmental sanitation are improved etc.. Equipment of a 915MHz 25Kw, can deal with a ton of frozen meat, power consumptive about 40 degrees per hour. In order to adopt the microwave to go back warmly in a large amount now U.S.A. and Japan ( Or unfreeze) Frozen meat, fish and strawberry,etc.. It has already been used for producing that 915MHz 60Kw macaroni microwave which U.S.A. Microdry Company developed is dry. This machine uses hot air of 71- 8 degrees Centigrade first, drop the water content of the noodles to about 18% within 35 minutes, then adopt the microwave to be heated, accompany at the same time and regard temperature as 80- 9 degrees Centigrade, temperature is the hot-blast convection of 15- 20. This machine is 25% than original equipment energy-conservation, processing time shorten to 1.5 hours from 8 hours, process 4000 pounds of macaroni hour, bacterium's content of the products is 1/15 originally. Products color and luster, taste, mouthfeel are better than the traditional method, come into operation in a large amount at present. This machine can also be dry chips, onion slice,etc.. The international microwave Company of France, has designed the bulking device of the microwave vacuum dry instant tangerine powder. The diameter of the vacuum room is 1.5m, it is 12m to be long. Present into 2450MHz, the microwave power of 48kw, use the glass to strengthen the polytetrafluoroethylene (PTFE) to transmit and bring into the conduct conveying. It contain 63% firm tangerine thick liquid of shape release suck and coating on wide conveyor belt of 1.2m first, pile high 3- 7mm, to input microwave energy under being low-voltage 80-100T, heat 40 minutes, can bulk out to thickness 80- 100mm, dissolving the tangerine powder, its output 58kg/h promptly of 20% of water content, produce 220 tons per year. Products keep orange juice already existing color, smell and taste, but also Vc that keep to spray dry law impossible up to. A kind of microwave that Japan develops bulks the powder equipment of dry yolk out and uses 16 2450MHzs, magnetron of 5kw, total output power 90kW, method its first yolk thick liquid material on the conveyor belt coating, use and far preheat infraredly to 80 degrees Centigrade, then heat the microwave, it is thick to bulk out to 3- 5cm, cool to 40 degrees Centigrade rapidly, continue making yolk powder with the routine method after mincing, produce 1 ton daily. U.S.A. combines the microwave with the steam and cooks the salty meat slices or the chicken nugget in advance to use for industrial production. Its characteristic is: Processing speeds quickly, process quality to be fine broken can save 27% raw materialsing, has already put into industrial production in a large amount now, frequency is all 915MHz, power 150- 240kw, the biggest 300kw, adopts the tunnel type heater or the Model V heater. Is it cut apart chicken nugget after to punish with microwave, look at different position adopt such as wing, leg, chest, claw,etc. Dr.eye: different power level punish respectively. The equipment adopts microwave alone, microwave combined with steam, the microwave power is 50- 80kW, the adopting of frequency 915MHz, 2450MHz. Can improve the output, reduce lossing, save the workforce. Sweden adopts the microwave device of 2450MHz 30kw to produce the empanada. By the empanada that automatic machinery produced, finish microwave cooking course, is it make surface to be brown to take to heat with heating wire finally, the quality of the products obviously improves, the treatment time of each cake is 2 minutes, 16000 per hour. Tile, Lip river of Sweden, Company spend 80kW, 2450MHz microwave go on bread disinfect and defend mouldly, the bread used in 4400 pounds per hour is produced on-linely, after the microwave is dealt with, temperature rises to 80 degrees Centigrade from 20 degrees Centigrade, time only takes 1-2 minutes, extend to 30- 6 day from original 30- 6 days in quality guarantee period. In addition in production enema, the routine method takes 90 minutes. And adopt microwave technology, can use the mould processed in succession, less than 2 minutes altogether from pouring into the meat gruel, microwave and heating finalizing the design, drawing of patterns, have this kind leather enema is it is it makes or processes into the food in bags to smoke to send again. Can save the casing, has improved the output, has reduced the workforce, make the cost reduce greatly