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05.14.08 ЭНЕРГОУСТАНОВКИ НА ОСНОВЕ ВОЗОБНОВЛЯЕМЫХ ВИДОВ ЭНЕРГИИ
ОСОБЕННОСТИ СИНТЕЗА ФУНКЦИОНАЛЬНОЙ КЕРАМИКИ С КОМПЛЕКСОМ ЗАДАННЫХ СВОЙСТВ РАДИАЦИОННЫМ МЕТОДОМ
Часть 3
Рахимов Рустам Хакимович, д-р техн. наук, зав. лабораторией № 1 Института материаловедения научно-производственного объединения «Физика-Солнце» Академии наук Республики Узбекистан. E-mail: rustam-shsul@ yandex.com
Ермаков Владимир Петрович, старший научный сотрудник лаборатории № 1 Института материаловедения научно-производственного объединения «Физика-Солнце» Академии наук Республики Узбекистан. E-mail: labimanod@uzsci.net
Рахимов Мурод Рустамович, младший научный сотрудник лаборатории № 1 Института материаловедения научно-производственного объединения «Физика-Солнце» Академии наук Республики Узбекистан
Юлдашев Носиржон, д-р физ.-мат. наук, профессор Ферганского политехнического института, Узбекистан, Фергана. E-mail: uzferfizika@mail.ru
Исмоилов Каримжон, старший научный сотрудник Ферганского политехнического института, Узбекистан, Фергана. E-mail: uzferfizi- ka@mail.ru
Хатамов Солижон Охунжанович, канд. физ.-мат. наук, доцент Ферганского политехнического института, Узбекистан, Фергана. E-mail: uzferfizika@mail.ru
Аннотация. Разработана технология получения пленочно-керамического композита с активными микровключениями на основе функциональной керамики, максимально поглощающими энергию солнечного излучения и полиэтиленовой пленки для обогрева парников и теплиц. Изготовлены опытные образцы трехслойных композитных пленок с каскадным преобразованием солнечной энергии в инфракрасный диапазон заданной спектральной области с максимумами в окрестности длин волн 3,3 и 9,7 мкм. Натурными испытаниями в теплично-парниковых хозяйствах показано, что композитные пленки с содержанием функциональной керамики в 1,0 и 1,5 масс. % обеспечивают ночью положительные температуры 3-7 °С при отрицательной температуре 7-10 °С окружающей среды без дополнительного отопления.
Ключевые слова: пленочно-керамический композит, функциональная керамика, активные микровключения, трехслойная композитная полиэтиленовая пленка, обогрев теплиц и парников, эффективное преобразование солнечной энергии.
FEATURES OF SYNTHESIS OF FUNCTIONAL CERAMICS WITH A COMPLEX OF THE SET PROPERTIES BY A RADIATION METHOD
Part 3
RakhimovRustam Kh., doctor of technical Sciences, head of laboratory № 1 of Institute of materials science «Physics-sun» of Uzbekistan Academy of sciences, Uzbekistan
Yermakov Vladimir P., senior research associate of laboratory № 1 of Institute of materials science «Physics-sun» of Uzbekistan Academy of sciences, Uzbekistan
RakhimovMurodR., laboratory № 1 of Institute of materials science «Physics-sun» of Uzbekistan Academy of sciences, Uzbekistan
Yuldashev Nosirjon H., doctor of Science in Physics and Mathematics, professor of Fergana polytechnical institute, Fergana, Uzbekistan
Ismailov Karimjan, senior research associate of Fergana polytechnical institute, Fergana, Uzbekistan
HatamovSolijan O., the Ph.D in Physics and Mathematics, senior research associate of Fergana polytechnical institute, Fergana, Uzbekistan
Abstract. Is developed technology of receiving a film and ceramic composite with the active micro inclusions on the basis of functional ceramics which are most absorbing energy of sunlight and polyethylene film for heating of hotbeds and greenhouses. Prototypes of three-layer composite films with cascade transformation of solar energy to infrared range of the set spectral area with maxima in the vicinity of lengths of waves of 3.3 and 9.7 microns are made. By natural tests in hothouse and greenhouse farms it is shown that composite films with the maintenance of functional ceramics in 1.0 and 1.5 masses % provide at night positive temperatures 3-7 °C at a negative temperature - 7-10 °C environments without additional heating.
Key words: film and ceramic composite, functional ceramics, active components, three-layer composite polyethylene film, heating of greenhouses and hotbeds, effective transformation of solar energy.
Chapter I
Introduction
A method for heating greenhouses and hotbeds with the use of functional ceramics is proposed. Functional ceramics based on elemental oxides has been developed to convert the energy of sunlight into infrared radiation with given spectral and time characteristics [1-4]. It is shown that the use of a film-ceramic composite makes it possible to use solar energy more efficiently for heating greenhouses and hotbeds by shifting the spectrum to the long-wave region using photoluminescents as a dispersive micro inclusion. The researched three-layer film-ceramic composites proved to be 14-25 % more effective in using solar energy in comparison to the application of regular glass and by 10-15 % compared to the three-layer Turkish film.
Preliminary results were published in [5].
To ensure the maximum efficiency of conversion of solar energy using a ceramic-film composite, it turned out necessary to optimize not only the chemical composition, the structure of functional ceramics, but also the ceramics / polyethylene ratio. As a result of an experimental study of the properties of the composite, it was found that the best preservation of temperature at night at a low ambient temperature can be achieved using a three-layer composite in which the functional ceramics is contained only in the lower layer with a concentration of 0.5-1.5 wt %. Tellingly, that the thickness of the lower layer of ceramics in the range 15-40 |im practically does not affect the properties of the composite.
Experimental samples of three-layer composite films with a cascade conversion of solar energy into the infrared range of a given spectral region with maxima of 0.62-0.68 |im and 9.7-10 |im were fabricated.
The choice of wavelengths in the interval was carried out on the basis of the following position.
The absolute temperature T (K) is related to the emission wavelength X (|im) by the relation T = 2898/A.
Consequently, X = 9.7-10 microns corresponds to a temperature range of 290-299 degrees Kelvin or 17-26 degrees Celsius. It should be emphasized that from one high-energy photon of the UV and visible region, 10-20 photons are formed, with an energy corresponding to a temperature of 17-26 °C. This is equivalent to increasing the power of the light flux to maintain the temperature in the indicated interval by the same factor.
Full-scale tests in greenhouses showed that composite films with a functional ceramics content of 1.0 and 1.5 wt. % provide at night positive temperatures of 3-5 °C without additional heating, when outside temperature is at minus 7-10 °C.
At present, global warming is one of the main problems of mankind. Worldwide, the main focus in the field of energy is not only to create systems that allow more efficient use of traditional energy sources, but the development of new principles for the conversion of renewable energy sources (RES) - solar, wind, etc.
As it's known, in many countries of the world the heating season is problematic due to a shortage of fuel and other sources of energy. Natural energy reserves decreases with time. Therefore, many countries are in dire need of renewable cheap, environmentally friendly, non-traditional energy sources, in its careful use and in the development of efficient technologies for the purposeful conversion of solar energy.
It should be also said about high energy consumption, spent for air conditioning of rooms during hot period. For an equivalent reduction in temperature by the same amount, it is necessary to expend twice as much energy as heating. This means that while we are cooling the rooms, we further stimulate global warming.
Photovoltaic converters, solar air and water heaters, wind generators, solar power stations, using concentrating systems for obtaining superheated steam, etc., received wide development. A significant shortcoming of such systems is high material consumption, low efficiency and reliability, complexity of manufacture and operation.
Strictly speaking, it is necessary to take into account the energy that was expended on the production of metal and other components. There is such a paradox - many devices cannot fully recover even the energy spent on their manufacture. As a result, such systems are not able to compete with traditional ones.
If we talk about greenhouses, hotbeds and rooms, it should be said that some of the solar energy of the visible range passing through the transparent glass, reflecting from the inner surface of the wall of the room or the protected ground, goes back through the window or films outward without participating in the heating process, also like the ultraviolet part of sunlight, which is almost completely absorbed or reflected by a glass or a film.
In this regard, the creation of a heating and cooling system, the heating of greenhouses and eliminating these shortcomings, based on film-ceramic composites with active micro- and nanoclusters is one of the ways to effectively solve the energy and environmental problems.
The main objectives of this project are:
• the creation of functional ceramics without the use of solar energy, but with the basic characteristics similar to that one which was obtained on a large solar furnace, and which with maximum efficiency converts the energy of the Sun into radiation of the required spectral range (with a maximum of 0.62-0.68 |im and 9.7-10.0 |im);
• production of a film-ceramic composite based on functional ceramics and polyethylene film for effective heating of greenhouses and hotbeds;
• experimental study of the efficiency of a film-ceramic composite based on functional ceramics and polyethylene film for stabilizing the temperature of greenhouses depending on external conditions; carrying out full-scale field research.
Experimental samples of a film-ceramic composite based on functional ceramics and a polyethylene film for effective heating of greenhouses were made on a modern three-screw installation of Original Grand Plast Ltd. (Tashkent, Ukraine) -a three-layer polyethylene film with a functional ceramics content of 0.5; 1.0 and 1.5 wt. % in the lower layer of the composite.
1.1. Modern problems of using polyethylene films for heating greenhouses
The modern film for greenhouses is elastic, frost-resistant and water resistant. And, at the same time, oxygen and carbon dioxide easily pass through film, completely transparent to the ultraviolet and to the visible part of the solar spectrum. In addition, the film has a light scattering power, which is especially valuable for plants. Unlike glass, the film is permeable to ultraviolet waves with a wavelength of 280 nm, while for glass, the lower permeability limit is 315 nm. Despite its popularity, the film has not been sufficiently weatherproof since the first years of its exploitation for greenhouses. In this regard, after half a year of operation, it went out of order. In addition, it formed droplets, which is harmful to greenhouse plants, formed on its surface electrostatic charge, which attracted dust - and this decrease in its transparency by 24 %. And, finally, the film was constantly stretched, that created problem of fastening on a greenhouse without a sag among the gardeners.
In recent years, a new type of film for greenhouses, which are strikingly different from their predecessors, has appeared. It is antistatic, capable of well-holding heat, polyethylene films with a special ultraviolet stabilizer. Because of such coating, the microclimate significantly improves in the heifer, and the films of the new generation can last 2.5 years or more.
The choice of film for a particular greenhouse or a hotbed directly depends on the features of the greenhouse itself. For example, an ideal film for single-season use is polyethylene.
There were also films with special cells of 20-30 mm. Such bubble coatings are characterized by heat-retaining ability and durability. But, of course, the light passes less through such film.
Currently, the industry produces the following types of films for greenhouses.
1. Polyethylene unstabilized film.
Such film allows up to 80 % of thermal and ultraviolet radiation, and therefore it does not keep heat in the night hours. Its service life is about six months. To increase the strength in the composition of such film, light stabilizers are introduced.
2. Polyethylene stabilized hydrophilic film.
The main difference of this film is the formation of a flat-drop condensate on its surface. Droplets of water form and roll down, but without any drop. And special anti-static additives do not allow such a film to be quickly covered with dust; it remains sufficiently transparent throughout the life of the device. In addition, such film is impermeable to infrared rays. Because of this at night hours heat in the greenhouse is lost much less -this is facilitated by a layer of formed water on its inner surface. Harvest in a greenhouse with such coating is particularly rich due to the fact that it significantly reduces temperature fluctuations.
3. Polyethylene heat-retaining film.
Modern polyethylene film for greenhouses with increased absorption of thermal radiation is an ideal solution for those who are trying to save on heating. Therefore, in greenhouses with such coating, the temperature is higher by 1-3 °C than under the stabilized and unstabilized film. In addition, the heat-retaining film has valuable antistatic properties and a hydrophilic surface. The film has a matte-whitish shade, but does not possess such good durability as the previous types of films. But according to research data, the yield of vegetable crops in such greenhouse is 10-30 % more. The service life is about 9 months.
4. Polyethylene reinforced film.
Modern reinforced film for greenhouse has the highest operational reliability. It is produced on the basis of a conventional stabilized film, which is reinforced with polyethylene very dense yarns, the thickness of which is 0.29-0.32 mm. The film is very durable and does not break, so it can last up to 2 years. The reinforced film for greenhouses has a permeability of 1012 % lower than that of the stabilized film.
5. Copolymer ethylene vinyl acetate film.
This film for a greenhouse is especially strong. And at the same time, it is elastic, light-resistant and has permeability for the visible part of the spectrum up to 92 %, well detains valuable thermal radiation. The copolymer film is frost-resistant, especially resistant to punctures and wind loads and hydrophilic -the condensate in it, is formed by a continuous water layer. Its only drawback is a large light transmission, which can lead to an elemental overheating in a hot summer on especially hot days. The service life of such film is three years.
6. Polyvinyl chloride film.
Modern PVC film for the greenhouses is much more elastic and durable than all existing types of films.
To all, it also has less permeability in the infrared part of the spectrum, and therefore during frost periods and night hours in the greenhouse there will be higher temperatures. But in addition to infrared rays, the polyvinyl chloride transmits only a little amount of valuable ultraviolet rays - only 20 %, and therefore can not be applied in all areas.
Also, the PVC film is dusted quickly enough, however, dirt from it can easily be washed off with plain water. Polyvinyl chloride film sags and periodically requires pulling, otherwise because of the wind in places of sagging, it may quickly break. The life of PVC film is about 8 years.
In addition to the main ones, today less well-known films are used to cover greenhouses, and many new types are still in the experimental stage. So, just recently a new type of film was created, which converts short-wave ultraviolet radiation into long-wave red. And under such a film, photosynthesis is much more effective. The maturation of tomatoes is accelerated almost 2-fold, compared with polyethylene film.
Polyethylene films with additives of photoluminescents based on iron and chromium oxides with insignificant additions
of REE oxides (rare earth elements), including the film-ceramic composite, are now widely used for greenhouses in agriculture when growing vegetables in conditions of closed ground. The use of films here leads to a significant increase in the yield of many crops, shortening the time of their growing. Such an effect, called «multispectrum», is explained nowadays by the luminescent properties of films - the ability to change the solar radiation spectrum due to the absorption of its short-wavelength part and transformation into the red region of the spectrum. At the same time, data on the investigation of the luminescence features of such films are very limited. In connection with this, we conducted studies of such high-density polyethylene (HDPE) films with additives of 0.5-1.5 % by weight of functionally ceramic photoluminescers with rare-earth element oxides that have luminescence in the infrared region of the spectrum.
Films, now called «light-correcting», and made of high-pressure polyethylene by extrusion with blow-up technology.
The luminescence specters of the original phosphors and films with their additives can be obtained both by the typical methods for fluorescence spectroscopy (the SDL-1 spectrometer with the radiation source DRSh-250 and the UFS-6 lamp) and by a specially developed method for this purpose using the Solar radiation and acousto-optic spectrometer «Quartz 3102».
A feature of the films is dispersed, heterophase character of the distribution of photoluminescence in the polymer matrix. Such a character of the investigated composite materials is associated with the almost complete absence of solubility of phosphors based on the above compounds in the polymer matrix and is confirmed by luminescent microscopy data.
The heterophase character of the initial polymer composite materials determines the photo physical properties of the light-correcting films obtained from them.
1.2. Development of industrial technology for production of a three-layer ceramic polyethylene film using local raw materials of Uzbekistan
Polymeric materials containing in their composition luminophores of different chemical composition that convert the visible and ultraviolet parts of solar radiation into narrowband luminescent radiation are used, both in industry and in research work. They are widely used in agriculture, where a polyethylene film with additives of phosphors based on oxides of various elements, which activates the growth and development of plants, is used as the material to protect ground. The main physical properties of such films are determined by heterophasic, disperse characterizations of the distribution of phosphor additives in the polymer matrix, which allows to absorb and transform the radiation of the sun, which in turn led to the creation of multilayer and multifunctional polyethylene films.
At present, various polyethylene films, both domestic and foreign, are used in heating and protection against unfavorable weather conditions at greenhouses of our republic. Among them, three-layer films with protection from ultraviolet (UV) photo destruction are in great demand. However, there are still a number of significant problems concerning the physico-chemical properties of such films.
First, a low level of heat retention, especially in winter.
Secondly, at moderate temperatures (T < 20 °C) of the environment, due to the presence of saturated vapor in the greenhouses, condensation occurs on the inner surface of the film
and the formation of water droplets that fall on the plants and infect them.
Thirdly, insufficient weather resistance and accumulation of electrostatic charge, which reduces the transparency of films by more than 20 %.
Fourth, insufficient mechanical strength - the films are constantly stretched.
Although the modern heat-retaining polyethylene film for greenhouses with an increased level of absorption of thermal radiation allows saving on heating and in greenhouses with such a coating, the temperature is higher by 1-3 °C comparing to a stabilized and unstabilized film, however, unfortunately, such film does not possess good strength and will last about 9 months .
In connection with the foregoing, the purpose of this study was to develop an industrial technology for the production of a composite polyethylene film with sufficient heat retention properties, weather resistance and a low level of drop formation. This goal was achieved through the development of functional ceramics for mass-produced technology, as well as field research at greenhouse farms with a sufficient area. Moreover, functional ceramics must convert the energy of sunlight, even of low density, into pulsed infrared radiation with given spectral and time characteristics.
Synthesis of functional ceramics based on oxides of iron, chromium, copper, calcium, magnesium, aluminum and REE is carried out according to the following scheme.
The necessary components were thoroughly mixed in planetary mills in a water-alcohol medium, then dried and kept at a temperature of 800 °C. After that, the samples were placed in a special chamber with emitters based on functional ceramics, generating pulses in the 3.3 |im range for 1 hour. The resulting material, which is the basis of the ceramic-polymer composite, was ground in planetary mills in an aqueous medium up to 1-3 microns. Then, it was dried in IR driers.
The resulting fine powder was added to the raw material to produce a lower layer of a three-layer ceramic-polymer composite.
This researched film-ceramic composites proved to be more effective in the use of solar energy by 14-25 %, comparing to the regular glass and by 10-15 % compared to a three-layer polyethylene film with protection from UV-photo destruction. It is shown that three-layer composite films with a functional ceramics content of 1.0 and 1.5 wt. % provide at night positive temperatures of 3-7 °C without additional heating, while the temperature outside is minus 7-10 °C.
Multilayer polymer films are manufactured by co extrusion of melts of various polymers through an annular or flat multichannel head (the number of channels is determined by the number of layers); in the forming head, the flows of melts are combined without mixing, as a result of which a multilayer polymer film is formed at the exit from it.
To improve adhesion between heterogeneous polymer melts, synthetic adhesive can be used, which enters the channel of the molding head as a stream of polymer melt. One of the main advantages of the production of multilayer films by co extrusion is the savings due to the fact that the finished material is obtained directly from the granules of plastics in a single process.
Co-extrusion technology provides non-waste production of films. Equally, coastal cuttings and other waste products can be used to create the middle layer, including when the produced film is intended for direct contact with food.
As a result, it was possible to develop an industrial technology for the production of a film-ceramic composite for efficient
heating of greenhouses on the basis of functional ceramics and polyethylene film, using only local raw materials of the Republic of Uzbekistan. Due to the properties of the developed functional ceramics, a film-ceramic composite was obtained, which exceeds the foreign counterparts by the main operating parameters.
As a primary material for the synthesis of functional ceramics, multicomponent waste materials of the Almalyk Mining and Metallurgical Combine for the production of non-ferrous metals served. Polyethylene granules (crumbs) made in the Shurtan gas chemical complex (Karshi city) were used for the polymer matrix.
Industrial technology production of a three-layer composite polyethylene film included three stages:
1) process of preparation of multicomponent functional ceramics in the form of a powder with grain sizes of 1-3 |im;
2) the process of manufacturing primary raw materials in the form of composite crumbs with the help of a special installation - a granulator;
3) manufacture of finished products of a three-layer composite polyethylene film in rolls with the help of a special three-screw polyethylene installation.
Earlier, the group of scientists of the Institute of Materials Science of the NGO «Physics-Sun» headed by R.Kh. Rakhimov experimentally studied a film-ceramic composite based on functional ceramics, obtained on BSF(big solar furnace), and polyethylene film in laboratory conditions. Therefore, using the results obtained, at the first stage of the technology, work was carried out on the optimal choice of the chemical composition, the technology for the production of functional ceramics (without the use of BSF), its structure and grain composition based on the specific purpose of manufacturing a composite polyethylene film with improved optical and thermophysical parameters for efficient application of them in greenhouse farms.
Considering that the demand for films for greenhouse farms is high, and the possibilities of producing special functional ceramics on the BSF are limited in quantitative terms, a lot of work has been done to develop such a technology that would allow producing it in the required quantity.
After careful analysis of the results of previous studies and the known luminescence spectra of ceramic oxides for the synthesis of functional ceramics, it was concluded that the most expedient to use multicomponent compounds based on iron, copper, calcium, magnesium, aluminum and REE oxides.
At the second stage of industrial technology, film-ceramic composite pellets were prepared. For this purpose, the manufactured powder of functional ceramics with an average grain size of 1-3 |im was first introduced in an amount of 5.0-10.0 wt. % in dissolved polyethylene at a temperature of ~100 °C. The resulting composite slurry was thoroughly mixed to uniformly distribute the ceramic particles, and then passed through a granulator. As a result, composite crumbs (granules) with a radius of 1 mm and a length of 4 mm were obtained. For homogeneous distribution of ceramics in a polyethylene matrix, the granulation operation was repeated several times, dissolving again the composite crumbs with the added pure polyethylene chips of a new portion until the desired composition was achieved in the masses % of the ceramic. As a result, film-ceramic composite granules with a functional ceramics content of 0.5; 1.0; 1.5 and 2.0 wt. %.
At the final stage, the well-known method of extrusion blowing under the high pressure using the technology of three-layer film prototypes ceramic composite. It has been detected that to obtain micro- and nanocomposite films based on high-pressure polyethylene with a minimum porosity, it is necessary to provide a molding temperature of 110 °C. The total
thickness of the composite film was 100 |m, and the density was 990 ± 10 kg/m3.
The composite polyethylene film fabricated in this way with ceramic microinclusions consists of three layers, each of them having a thickness of 30 |im and cascading way to convert solar radiation. The first layer is a polyethylene film with additives that convert the ultraviolet range of solar radiation into visible. This allows not only to use more efficiently the energy of sunlight, but also protects the film itself from photodestruction, which significantly extends its service life. The second layer - a polyethylene film without additives, is hardening, and also reduces the back radiation of the visible spectrum converted by the third layer into IR radiation at night. The third layer contains a functional ceramics that absorbs solar energy over a wide range and converts it into radiation with maxima of 0.62-0.68 |m, which is necessary for photosynthesis and long-range IR radiation with a maximum of 9.7-10.0 |im to maintain optimal temperature. This is ensured by the fact that functional ceramics make it possible to create from one high-energy UV photon in the visible region, 10-20 photons, with an energy corresponding to a temperature of 17-26 °C.
The obtained results open the prospect of changing a number of basic physical macroscopic parameters of composite polyethylene films for heating greenhouses by changing the molding temperature, composition, percentage of functional ceramics and the thicknesses of individual layers.
Conclusions on Chapter I
1. The greatest demand at present, in three-layer polyethylene films with additives for protection against ultraviolet photodestruction. However, there are still a number of significant problems concerning the physico-chemical properties of such films.
First, the low level of heat conservation.
Secondly, at moderate temperatures (T < 20 °C) outside of greenhouse causing the process of drop formation on the inner surface of the film.
Thirdly, insufficient atmospheric stability and accumulation of electrostatic charge, which reduce the transparency of films by more than 20 %.
Fourth, insufficient mechanical strength, - the films are constantly stretched.
2. A new industrial technology has been developed for the production of a three-layer composite polyethylene film with a sufficiently high heat retention and reduced rate of drop formation, which includes three stages:
• process of preparation of multicomponent functional ceramics in the form of a powder with grain sizes of 1-3 |im;
• the process of making primary raw materials in the form of composite crumbs with the help of a special installation -a granulator;
• production of finished products - a three-layer composite polyethylene film by extrusion with blowing under high pressure in rolls with the help of a special three-screw polyethylene installation.
Such film differs from the known Turkish and other similar films by the composition and structure of the third lower layer in the installation - a layer of composite polyethylene crumbs with a certain percentage of functional ceramics.
3. Three-layer film-ceramic composites with a functional ceramics content of 1.0 and 1.5 wt. % use solar energy 14-25 % more efficiently comaparing to the regular glass and 10-15% compared to the standard three-layer polyethylene film with UV protection photodestruction.
Chapter II
Natural-field tests of the film-ceramic composite
in the system of heating greenhouses
Experimental and full-scale tests of thermophysical and agrotechnical parameters of a film-ceramic composite in real field conditions were carried out. Full-scale tests in greenhouse showed that three-layer composite polyethylene films with a functional ceramics content of 1.0 and 1.5 wt. % provide at night positive temperatures of 3-5 °C when outside temperature is negative 7-10°C without additional heating. A package of proposals for the serial production and operation of film-ceramic composites was recommended.
2.1. Results of research of thermophysical properties of the three-layer film-ceramic composite for heating greenhouses
One of the main tasks of this study is the experimental study of the thermophysical and agrotechnical properties of the film-ceramic composite based on functional ceramics and polyethylene. Below are the results of experimental studies of some thermophysical and biologically activating properties of the produced pilot samples of a film-ceramic composite obtained in the course of field field trials. The experiment took place in the greenhouse farm «Vody nihol umidi» in the city of Fergana, two fields were chosen with area 300 m2 plots with metal arc-shaped skeletons with a radius of 2.5 m and a length of 60 m. After appropriate preparation, the frames were covered with films in two layers with an air gap of 10 cm.
The lower layer on the first frame consisted of a composite film with a ceramic content of 0.5 mass. % (Film number 1), and on the second frame - similar film with ceramic in 1.5 wt. % (Film No. 2). A single-layer polyethylene film 30 |m thick was used for the top layer. Both greenhouse rooms were not heated.
Tomato seedlings were planted on 15 March 2015 under film No. 1 and on 22 March under film No. 2. In the evening of March 27, there was a strong hurricane at night with a wind speed of 20-25 m/s and the weather deteriorated until night frosts. The film No. 2 was torn off at both ends by 5 and 15 meters together with the metal wires holding them. We managed to strengthen the film only from one end, and the second end remained under the open sky, because On March 31, snow 40 sm thickly fell, the temperature dropped to -8 °C at night, and in the afternoon of April 1 it was still freezing. On the morning of April 2, they found out that the seedlings under the No. 1 film were completely preserved, where the temperature was constantly higher than +5 °C. Seedlings under Film No. 2 to a depth of 5 m from the open end was frozen and died, and in the rest part it was preserved completely the same as under the tightly closed film No. 1. This was a serious test of the composite film to maintain heat. At the same time, in the greenhouse located near, under the two-layered shelter of the regular glass and the usual polyethylene and also additionally heated, the seedlings were lost on about 50 %.
Further comparative observations in April and May of 2015 showed that the rate of growth of seedlings under composite films was almost two times higher than the development of seedlings under the open sky and 1.5 times the rate of development of seedlings under regular glass. The stems and leaves of each seedling were large and strong. The flowering period decreased 1.3 times. The number of flowers on each tier was at least 5-8 instead of 2-5. At night, under film No. 1, the temperature was higher 6-8 °C, and under film No. 2 8-10 °C than
the outside. In the afternoon, depending on the degree of solar radiation, these indicators were 15-20 °C and 17-25 °C. Composite films practically did not hang to outside temperatures +35 °C inclusive. At external temperatures below 20 °C, small droplets with a diameter of 1-2 mm were observed on the inner surface of composite films, and on film No. 2 the droplet size did not exceed 1 mm irrespective of the dew point and humidity under the film. It should be said that even such a weak drop formation can be completely eliminated if the thickness of the lower composite layer is reduced to 10-15 |m. We believe that all these new results are due to the presence of functional ceramics in the third - the inner layer of the composite film and, because of its infrared luminescence under the action of solar radiation.
The harvest of tomatoes from the Israeli ELPIDO sort was as follows. On each bush, up to 1.5-2 meters 20-30 tomatoes riped, which weighed 200-300 g. The yield from each bush averaged 6-8 kg, whereas under regular glass it reached a maximum of 4 kg.
The possible mechanism of observed phenomena is as follows. Ceramics converts a wide spectrum of solar radiation, not used for photosynthesis, into photons with a wavelength of 9.7-10.0 microns, which corresponds to a temperature of 17-26 °C.
From one high-energy photon is formed about 20 photons with the indicated energy:
• functional ceramics generates infrared radiation in pulsed mode. Taking into account that the energy density in the pulse can exceed many times the average value, the depth of warming up of the soil will also increase proportionately in the same amount;
• functional ceramics are contained in the lower layer of the composite. Through the upper layers, visible light passes with a slight attenuation, but the converted radiation at 9.7-10 |m is not passed through by the composite and all energy remains inside the greenhouse;
• at low ambient temperatures, the composite has a relatively high temperature. In this connection, there is no or little condensation of moisture on it;
• yield is significantly increased due to the fact that the composite generates radiation 0.62-0.68 |m - the most effective for photosynthesis. In addition, ceramics in the lower layer of the composite allow much better dispersion of incoming and generated light radiation. This also significantly affects the assimilation of light energy by plants.
Conclusions on chapter II
Complex natural-field tests of thermophysical and biologically activating properties of the produced prototypes of film-ceramic composite on the basis of functional ceramics and polyethylene films were carried out in order to stabilize the temperature of the greenhouses depending on the ambient temperature.
It is shown that three-layer composite polyethylene films with a functional ceramics content of 1.0 and 1.5 wt. % provide at night positive temperatures of 3-5 °C without additional heating while the outside temperature is negative 7-10 °C.
Comparative observations in April and May of the months of 2015 showed that the rate of growth of seedlings under composite films is almost twice more than under the regular glass. The stems and leaves of each seedling were large and strong. The flowering period decreased 1.3 times. The number of flowers on each tier was at least 5-8 instead
of 2-5 under glass. At night, under the composite film, the temperature was higher by an average of 6-10 °C than the outside temperature.
The best heating in the daytime at a low ambient temperature is the lower layer of a composite with a functional ceramics content of 0.5-1.0 % by weight, the top layer being conventional film. The worst is two layers of a composite coating with a functional ceramics content of 2.5 % by weight.
The best preservation of temperature at night at a low ambient temperature is two layers of a composite coating with a functional ceramics content of 2.0 %.
All the investigated three-layer film-ceramic composites proved to be more effective in using solar energy by 14-5 wt. %, relative to the application of the regular glass and by 10-15 % compared to the Turkish three-layer polyethylene film with UV protection of photodestruction.
Referens
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2. Rakhimov R.Kh.. Principles of the development of materials with a set of prescribed properties in the synthesis of BSP // Conference materials dedicated to the 90th anniversary of S.A. Azimova. Tashkent, 2004. Pp. 176-178.
3. Rachimov R.C., Ermakov V.P., John P., Rachimov M.R. Anwendung funktioneller keramiken fur tech nologien des trocknens mit impulsinfrarot. Freiberg exploratory folders // Journal of Mining Academy. Freiberger Forschungshefte. Published on 06/02/144. C. 1-44.
4. Rakhimov R.K., Kim E.V. US Patent No. 5,472,720 filed on December 5, 1995. Treatment of materials with infrared radiation.
5. Ermakov V.P., Ismoilov K., Rakhimov M.R., Khatamov S.O., Yulda-shev N.H. Composite polyethylene film with active ceramic microinclusions for stabilization of temperatures of greenhouses and greenhouses // Fundamental and applied questions of physics, the collection of abstracts of the international conference. November 6 Tashkent, 2015. P. 387-391.
