Investigation of changes in the spectral characteristics of lamps of ultraviolet and infrared radiation: a review

. The article describes the parameters of ultraviolet and infrared radiation, as well as their physical impact on organic and inorganic objects. The methods of using radiation, especially in agricultural activities, are characterized. The purpose of the study is to study the patterns of changes in the spectral characteristics of radiation depending on the choice of materials used. The parameters for finding IR radiation are given. Comparative results of radiation power depending on the brand of quartz glass are shown.


Introduction
Ultraviolet and infrared radiation have found great application in the processing of agricultural products and agricultural engineering. An example of the use of infrared (hereinafter IR) radiation is the industrial drying of various products: freshly painted cars, furniture, gunpowder, as well as fruits, vegetables, wet grain. Their distinguishing feature is that the air passes them without heating up, while the moisture contained in the object absorbs part of the spectrum, heats up and evaporates [2,9]. Ultraviolet (hereinafter referred to as UV) radiation in agriculture is used in several directions, this is the disinfection of organic products and the testing of agricultural machinery for susceptibility to the degradation process [4,8].
Solid materials absorb the radiation spectra under consideration by a thin surface layer. However, wet porous materials transmit radiation to some depth, and their transmittance depends on the moisture content.
When drying objects soaked with moisture, IR rays are absorbed by water and little is absorbed by the objects themselves. Water evaporates, and objects almost do not heat up, and therefore do not experience mechanical deformations or chemical transformations.
In general, food substances most effectively absorb the energy of long-wave infrared radiation through the mechanism of changing the vibrational state of molecules, which can lead to radiation heating. Water and organic compounds such as proteins and starches, which are the main components of food, absorb energy at wavelengths greater than 2.5 µm [15]. UV radiation, during the processing of food products, leads to a photochemical reaction of the protein part of the molecules, namely, to the inactivation of enzymes, as well as to the death of microorganisms, in general, the process is considered as positive, since this increases the shelf life [10].
The main advantage of drying with infrared rays is the rapid removal of moisture. This accelerated drying process is explained by the radiant heat flux, which partially penetrates into the capillary-porous bodies to a depth of 0.1-2.0 mm. Getting into the capillaries of the body, the rays are almost completely absorbed due to a series of reflections from the walls. Therefore, when drying with thermal radiation, the heat transfer coefficient has a large value, and much more heat can be transferred per unit of material surface per unit time than when drying with heated gases or contact drying. So, for example, the duration of drying textile materials with infrared rays is reduced by 30-100 times [7]. This occurs when drying other thin-layer materials. The intensity of absorption at different wavelengths depends on the components of the food when it comes to drying food.
As is well known, agricultural plant materials contain all the nutrients, vitamins and biologically active substances (BAS) necessary for the human body, but are perishable. Losses in raw materials of vitamins and biologically active substances significantly reduce its value; in the case of berries or medicinal and essential plants, they often reduce it to zero. According to the researched data, up to 30% of the daily collection of ripe raspberries, which are a "natural pantry" of ascorbic and salicylic acids, ketones and flavonoids, cannot be transported and sold in the trade network, and the lack of rapid processing of these berries leads to their damage during the day. The content of vitamins and biologically active substances in raw materials rapidly decreases over time due to chemical transformations in aqueous solutions of intra-and intercellular fluid of high-moisture raw materials under the influence of various factors, the main of which are temperature, light, degree of aeration of raw materials. Thus, the degree of preservation of vitamins and biologically active substances in the dried product is the main indicator of its quality. A significant increase in the degree of preservation of raw materials and their properties will allow the primary processing of vegetable raw materials directly by an agricultural producer in the places where raw materials are grown, that is, in a field, garden, vegetable garden, greenhouse or near them.
Processing methods aimed at preserving the native properties of plant raw materials, in addition to drying, include fortification, canting, and freezing [12]. At the same time, as a result of alcoholization and candling, a product is obtained that has restrictions for the consumer (children, nursing mothers, diabetics), and also creates additional difficulties in its further processing, for example, to obtain food powder [6]. Freezing requires the use of expensive equipment and significant energy costs, given that the canning process is carried out in summer or early autumn.
The most perfect drying method should be called freeze drying, however, the high cost of equipment and energy costs for the implementation of the process (as well as for freezing) do not yet allow us to consider this method as a mass one for use in agricultural enterprises [1,13].
For use in agricultural enterprises, it seems appropriate to use inexpensive compact modular drying devices that are highly efficient and allow the production of a high-quality product. The technologies implemented in such devices include infrared drying as a method of complex resource-saving processing of agricultural raw materials [5].
infrared drying for drying various vegetables and fruits has become increasingly interesting [3,11].
Infrared drying is carried out in chamber and conveyor type devices [14]. Both those and other devices can have single-tier and multi-tier versions. In devices, radiation sources are placed above the surface of a layer of wet raw materials. As radiation sources, tubular electric heating elements (TENY), spiral heating elements in quartz glass tubes (open type spirals) and gas-filled incandescent lamps are used.
In the subject under consideration, it is necessary to take into account the wavelength of various radiation spectra. Fig. 1 clearly defines the measurement ranges for ultraviolet and infrared radiation. In this article, ultraviolet rays are considered as an indicative radiation spectrum for the adaptation of materials in devices exposed to UV irradiation. The impact of IR radiation was mainly accentuated in a device with a radiation source in the form of a spiral heating element in a quartz glass tube.

Results
The aim of the study is to study the patterns of changes in the spectral characteristics of radiation depending on the choice of materials used in the construction of devices using the data of studies and the choice of heating temperature of the coil.
As you know, a heated body (the so-called gray body) emits electromagnetic waves in the wavelength range from zero to infinity (thermal radiation). The spectrum of this radiation is described by the Planck formula for grey bodies: Where r(λ,T) is the spectral density of gray body radiation; ε(λ,T) is the emissivity of a gray body for wavelength λ at temperature T.
Separately, consider an IR dryer with a heating element in the form of a nichrome spiral protected by quartz glass, then the radiation spectrum from the IR dryer will be determined by the following expression: Where τ(λ) is the transmittance of quartz glasses for the wavelength λ. Emissivity ε(λ,T) will be considered a constant value for the entire range of wavelengths λ, to wit ε(λ,T) =const. Dependence τ(λ) will be determined according to the table of transmission coefficients of quartz glasses for wavelengths λ from the book of Samarsky A.A.
To find the integral energy luminosity RT of a gray body (nichrome spiral) through quartz glass, one must find the integral: Where λmin and λmax, respectively, are the minimum and maximum values of the transmission range of electromagnetic waves of length λ in quartz glasses according to the table of transmission coefficients of quartz glasses for wavelengths λ.
The radiation power of the IR emitter is determined: Where S is the surface area of the heater. If we consider that emissivity ε(λ,T) =const, then to find the radiation power of the IR emitter: Thus, in this area of research, the issue of changing the spectral characteristics of IR radiation depending on the choice of materials used in the design of IR drying and the choice of heating temperature of the coil is revealed in more detail. In accordance with this statement, a comparison was made of the radiation power from emitters with the same values of the surface area of the heater S and the spectral coefficient of thermal radiation ε, i.e. the ratio of different powers will be found, which means that when comparing the powers, S and ε will be reduced.
Calculations by (5) were carried out in the Mathcad computer algebra system. Since the dependence τ(λ) for all five considered types of quartz glasses (KU1, KU2, KV, KV-R, KI) has a complex dependence over the entire range from λmin = 170 nm to λmax = 4400 nm, the integrand function in formula (5), will also have a complex dependence over the entire interval from λmin to λmax. Therefore, integration in the Mathcad system is carried out using the adaptive method of Kharitonov V.D., which allows you to calculate the value of the integral from a "non-smooth" function with a predetermined accuracy. As a rule, adaptive algorithms are just as efficient as traditional ones for "sufficiently smooth" integrands, but also inefficient for "bad" integrands, on which traditional algorithms fail, so we compared the results of integration by the Romberg method (it is used to integrate "smooth" functions with a predetermined accuracy) and an adaptive method. The calculation results showed that the difference in the results is visible at 4-5 decimal places, i.e. it can be assumed that this function is "relatively smooth", and the adaptive method gives the correct result with a predetermined accuracy. Also, the dependence τ(λ) is given in a table, and in order to integrate the integrand of formula (5), it is necessary to interpolate this dependence τ(λ) given in a table to obtain a functional dependence τ(λ). Since this dependence is "non-smooth", but at the same time "linear" in some parts of the interval from λmin to λmax, the best interpolation over the entire interval will be piecewise linear interpolation.

Discussion of the results
Comparison of the radiation power from radiators with the same values of the surface area of the heater S and the spectral coefficient of thermal radiation ε. were carried out for three temperatures of the nichrome coil T1=982, T2=938, T3=905. The calculation results are displayed in tables. Since, as previously noted that water and organic compounds such as proteins and starches, which are the main components of food, absorb energy at wavelengths greater than 2.5 µm, the radiation power was calculated for the wavelength range from λ = 2500 nm up to λmax = 4400 nm at the same temperature of the nichrome coil (the maximum value is taken as 100%) and radiation power for the wavelength range from λ = 2500 nm to λmax = 4400 nm at different temperatures of the nichrome coil (the maximum value is taken as 100%). Table 3. Radiation power for the entire wavelength range from λ = 2500 nm to λmax = 4400 nm at the same temperature of the nichrome coil (the maximum value as 100%).

Conclusions
The analysis performed shows that a small change in temperature leads to a strong change in the total radiation power. This is quite natural, since, according to the Stefan-Boltzmann law, the dependence of the energy luminosity Re~T 4 . However, as the presented calculations show, there is also a rather large dependence of the integral energy luminosity RT on which brand of quartz glass is used in the tube near the IR irradiator. The higher the transmittance τ has large values in the long-wavelength part of the IR spectrum, the greater the integral energy luminosity RT, and hence the total power of the IR drying radiation. Moreover, as studies have shown, these two dependences of the radiation power on the temperature of the spiral and the brand of quartz glass used in the long-wave part of IR radiation from λ =2500 nm to λmax = 4400 nm are even more pronounced.