CC BY
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Parpiev Azimdzhan, Tashkent Institute of textile and consumer goods industry, Doctor of Engineering Science, professor, E-mail: [email protected]. Kaiumov Abdul-malik, Tashkent Institute of textile and consumer goods industry, Senior research assistant - external doctoral candidate, E-mail: [email protected]. Akhmatov Nozimzhon, Tashkent Institute of textile and consumer goods industry, assistant, E-mail: [email protected].
Definition of area of soft temperature drying condition
Abstract: The question about the influence of temperature condition on uniformity of drying of components of raw cotton and on their quality in drum driers has not been studied thoroughly. In the article you can find practical recommendations on choosing the drying conditions depending on initial moisture of raw cotton, output of the dryable material, which guarantee maximal keeping of natural properties of fiber and seeds.
Keywords: drying, drier, raw cotton, fiber, seeds, moisture, uniformity.
The conditions of drying by means of hot air are characterized by three parameters: moisture content, speed of air movement and temperature. These parameters influence duration of process and quality of the dryable material. Therefore it is necessary to choose such drying conditions when with the smallest duration and with the smallest expense of heat the best technological properties of material can be received [1].
In case of using the technology of drying in drying drums the drying of raw cotton is carried out in variable conditions, i. e. moisture content of the drying agent increases at the expense of the moisture evaporated from raw cotton therefore it is impossible to regulate moisture content precisely. Speed and amount of the given drying agent can't be increased as with such increase normal operation of the dryer is interrupted and the dwell time of dryable material in the drying camera decreases. Therefore the speed of the heat transfer agent makes about 1,5 m/s (expenditure of the drying agent is about 20 thousand cub. m.). It follows therefrom that for achievement of desirable drying of raw cotton it is necessary to select the optimum temperature of the heat transfer agent.
At various intensity of heating and drying of raw cotton components in drum driers, and also at the subsequent ginning, the structure of fibers undergoes essential changes that, obviously, have to lead to change of structural and mechanical properties.
Academician of the Academy of Sciences of Uzbekistan M. A. Khadzhinova [2] at experimental studying of influence of temperature of the drying agent in the course of drying has proved that application of the drying agent with the temperature of 200 and 260 °C leads to decrease in durability of fiber respectively by 11 and 27%. It happens because of unevenness of heating and dehydration of components of raw cotton. At the same time the peripheral parts of fiber and hull are overdried, there occurs thermal destruction, and at the subsequent consumption the ends of fiber are broken off, the staple length decreases to 2 mm, and the increased breakage of seeds causes raise of fiber defects (hulls and fiber) and reduces the quality of seeds. Temperature condition of the drying process must be such that raw cotton isn't heated more than 100-110 °C. Heating at temperature higher than this leads to change of color of fiber and decrease in its durability.
According to the data from [3], durability of fiber decreases by 40% at its heating to 100 °C. Other author [4] specifies that heating of fiber at the temperature of220 °C with an exposition of 30 min. leads to increase in crystallinity of cellulose, and the increase of exposure time leads to destruction ofa crystal lattice. In the work [5] it is noted that even short-term influence (7-30 s) of the temperatures of 90, 180 and 200 °C leads to structural changes of fiber ofvarious degree, which is exposed to significant increase in density of cellulose.
Kucherova L. I. [6] has come to a conclusion that application of the drying agent with a temperature of 200 °C increases percentage of short fibers by a factor of 1,3-1,5 and fibration of waste — to 60%. It leads to increase in breakage at spinning by factor of 1,5-2.
Inconsistency of the characteristic received by various authors is explained, obviously, by the difference of drying conditions in the experiments (in thermostat, drying oven, special devices, etc.) and discrepancy of these conditions to conditions of the convective drying applied in the industry (considerable fluctuation of temperature and moisture content in the course of drying) that is proved by the large ranges of the revealed limit temperature conditions, and also by the fact that the influence of initial state of raw cotton (moisture, shredded state) on change of structure of fiber wasn't revealed, therefore, the choice of temperature conditions was not of prevailing significance.
Analyzing drying of raw cotton at ginning plants of the USA, the author [7] notes that temperature of the drying agent at the beginning of process of drying didn't exceed 70 °C. Most moisture is removed from raw cotton within the first 3 seconds of the influence of heated air therefore drying of raw cotton at a temperature of drying agent over 180 °C at the point of their mixing can make negative impact on quality of fiber. On the basis thereof the staff of the laboratory of cotton consumption equipment at the Department of Agriculture of the USA recommends that in one zone of drying installation temperature shouldn't exceed 180 °C. In practice the temperature needed is not more than 120 °C. In this regard they recommend applying multistage drying at lower temperatures instead of one-stage drying at high temperature.
Use of higher temperatures (200 °C) causes along with content reduction of impurities in raw cotton formation of such defects as bearded motes, small knots, which are the most harmful from the
Definition of area of soft temperature drying condition
standpoint of spinning and technology (transition to fabric). Besides the influence of high temperature leads to decrease in breaking strain to 12%, breaking extension to 11%, increase in short fibers on average by factor of 1,3-1,5, decrease in endurance limit to repeated stretching for 14-20%, increase in breakage at spinning 1,5-2 times. This work has big practical and scientific value. However the received characteristics are acquired only within the limits of moisture of raw cotton less than 16%. Besides, the frequency of drying process and influence of the frequency of drying process on quality of fiber have not been studied thoroughly.
Thus the study and the analysis of researches devoted to establishment of influence of drying on quality of fiber shows that change of quality of fiber caused by thermal impact was considered generally in stationary conditions, i. e. in the conditions which aren't describing raw cotton drying process under production conditions and in drum driers taking into account the subsequent impacts in
One-fold drying of raw cotton
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Pic. 1. Relation of the area of soft temperature condition to the initial moisture of raw cotton with output O = 3,5 t/h One-fold drying of raw cotton
course of consumption, cleaning and ginning of raw cotton. Therefore the received characteristics can't really reflect the influence of actual drying on quality of fiber and seeds.
Drum driers operate in the mode of alternate location of raw cotton in suspension under the influence of heat transfer agent and in heap on blades. Drying is carried out in variable parameters and moisture of the heat transfer agent. Therefore the recommended temperature of the drying agent (for example, T=200 °C) in laboratory conditions or layered driers doesn't change until the end of drying process, and in drum driers decreases already in two meters by 100 °C.
Our researches were conducted on the drier 2 CB-10 at the temperature of drying agent of T=100 and 200 °C, performance of 3,5 and 10 t/h on damp raw cotton. The object of our research was raw cotton C 6524, 2nd industrial grade, with initial moisture of W=10,5 and 22,3%.
One-fold drying of raw cotton
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Pic. 2. Relation of the area of soft temperature condition to the initial moisture of raw cotton with output O = 5 t/h One-fold drying of raw cotton
Pic. 3. Relation of the area of soft temperature condition to the initial moisture of raw cotton with output O =7 t/h
Pic. 4. Relation of the area of soft temperature condition to the initial moisture of raw cotton with output O =10 t/h
Two-fold drying of raw cotton
Two-fold drying of raw cotton
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Pic. 5. Relation of the area of soft temperature condition to the initial moisture of raw cotton with output O = 3,5 t/h
Two-fold drying of raw cotton
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Pic. 7. Relation of the area of soft temperature condition to the initial moisture of raw cotton with output O = 7 t/h
Experiments were made at one- and two-fold drying.
Experimental studies have shown that generally the overdried fiber has lower quality, as sorption activity of fibers decreases because of violation of orientation of structural elements. It is known that cotton fiber acquires increased strength while wet, as moisture getting in the inside layers of fiber, promotes formation of additional bonds between structural elements [6]. The overdried fiber (lower than 5,5%) becomes fragile and it breaks at additional mechanical influences (cleaning, ginning), damage and content of short fibers increase and the work of spinning and weaving factories worsen.
The obtained regression equations (at one-fold drying: for moisture of raw cotton — E1=12,8+4,75x1+0,97x2-1,10x3-0,47x1x3; for moisture of fiber — E2 = 7,98 + 3,07x1 + 1,3x2_1,66 x3 + 0,3 x1x2-
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Pic. 6. Relation of the area of soft temperature condition to the initial moisture of raw cotton with output O = 5 t/h
Two-fold drying of raw cotton
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Pic. 8. Relation of the area of soft temperature condition to the initial moisture of raw cotton with output O = 10 t/h
0,69 XjX3; at two-fold drying: for moisture of raw cotton — Ej = =9,81 + 3,85x1 + 1,54x2-1,68x3-0,66x1x3; for moisture offiber — E2 = 5,64 + 2,08x1 + 1,25x2-1,63x3-0,58x1x3) have been processed with ECM and various values of major factors have been defined. By trial method the borders of areas of soft and hard temperature conditions of drying at one- and two-fold drying have been determined depending on temperature of the drying agent and initial moisture of raw cotton with output of 3, 5; 5; 7 and 10 t/h; these borders are presented in the form of curves in pictures 1-8.
The graphs (pic. 1-4) show that at one-fold drying of raw cotton at moisture ofless than W , =11,6% raw cotton can not be dried
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with output less than 3,5 t/h, at W=11,0% less than 5 t/h, and at W =10% less than 7 t/h.
x/c
The investigation of invariance of the output of complex electric power system with application system's embedding approach
At two-fold drying of raw cotton (pic. 5-8) with output On the basis of the received results it is possible to make
P=3,5 t/h and moisture of raw cotton below Wx/c=15,8%, with practical recommendations on choosing the drying conditions
output P=5 t/h and moisture of raw cotton below Wx/c=14%, with depending on initial moisture of raw cotton, output of the dryable
output P =7 t/h and moisture of raw cotton below Wx/c=12,1% it is material, which guarantee maximal keeping of natural properties
not recommended to put raw cotton to two-fold drying. of fiber and seeds.
References:
1. Boltabaev S. D., Parpiev A. P. Drying of raw cotton. - Tashkent: «Ukituvchi», 1980.
2. Khadzhinova M. A. Research of properties and structure of cotton fiber in the course of drying. - Tashkent: Fan, 1966.
3. Alfei T. Mechanical characteristics of polymers. - M.: Inostrannaya literatura (Foreign literature), 1952. P. 305.
4. Bu m. G. Dobb and m. z.Safain. The effect of thermal treatment on the cruscerized cotton. J. of the textile Institute. - V. N 7/8. 1976, P. 229-234.
5. Edith Honold, Frederic R., Ondrers and James N. Crand Heating, Cleaning and mechanical procossing effect and cotton, Partil; Fiber chages as measured by achali Centuge Test. Text Reas. j. 1963, jannary, - N1, P. 51-60.
6. Kucherova L. I. Assessment of influence of drying on structure and properties of the cotton fiber and produced yarn and fabric: Ph. D. thesis in Engineering Science - M., 1981.
7. The "Cotton gin and oil mill Press" 22.11. 86. P. 8-9.
Mirzabaev Akram Makhkamovich, International Solar Energy Institute, Senior research assistant, the Faculty of PVSolar Plants E-mail: [email protected] Makhkamov Temur Akramovich, Tecon Group, Leading engineer, Research and Development Department, E-mail: [email protected]
The investigation of invariance of the output of complex electric power system with application system's embedding approach
Abstract: In article is considered the problem of providing the invariance of the output of dynamic system to external disturbances. As the dynamic system is considered the model of electric power system (EPS), provided for the small oscillation conditions. If the necessary and sufficient conditions of invariance required on the base of system's embedding approach are provided, then invariance of the exploring system's output to external disturbance is also provided. Keywords: Matrix approach, system's embedding approach, steady-state stability, invariance.
Invariance is one of the most important properties of the dynamic system. The problem of invariance, according to [1, 12], is the problem of identification structures and parameters of controlling system where the impact of spontaneous changes of the external disturbances and the system's own parameters to dynamic performance of the controlling process could be in part or in whole compensated.
This problem was formulated for the first time by G. V. S.C Hi-panov [2, 49-66] and the extensive discussions about its application have been going on up to now [3, 43-49; 4,21-29; 5, 34-41; 6, 61-67 etc.].
It must be noted that the different type of invariance systems are existed. They differ both in terms of functional capability and design concept [7, 23].
Below is considered the application of system's embedding approach to study the invariance of the output of controlled complex EPS at small disturbances as stationary determined multidimensional dynamic system. This is due to the fact that the input-output range of complex EPS are subjected to non-unique changings due to the existence of zero devisors and noncommutative operators [8,25], put in other words due to the algebraic singularity of the exploring system which is typical only for the multidimensional systems [9, 177].
In the case of representation of the exploring system in the state space [9, 185; 10, 23]:
x = Ax + Bu + Sw, (1)
u = -Kx, (2)
y = Cx, (3)
where x, u, y, and w are vectors of state, control, output and disturbance of the system, respectively; A, B, C, and S are matrices with constant digital elements of the respective size; K is regulator matrix, with constant digital elements. For invariance of the output of controlled system being studied, the transfer matrix from disturbance w(p) to the system output y(p) with the model in state space shall identically equal zero:
Fy (p) = C(pI„ - Ay )-1S = 0, (4)
where Ay = A + BK is matrix of dynamics of the system with the controller. The main problem is to find the controller (synthesis), ensuring the fulfillment of the condition (4). However, as indicated in [10, 25], solving this problem poses certain difficulties, as (4) has the operation of matrix inversion, and, as a rule, it is polynomial.
Necessary and sufficient conditions, under which the equality (4) is just, is ensured, when fulfilled the conditions of the theorem [10, 28], where established that the system (1)-(3) for specified matrices A, B, C and S is invariance to disturbances in the sense of
