Design and Practical Application of Thermal Humidity Converters for Liquid Materials

The paper considers quality indicators and morphological tables of the main elements of thermal converters of the moisture content of liquid materials on the basis of which the optimal structure of these converters is selected from the quality indicators, namely, sensitivity, accuracy, reliability, and performance.

The fourth morphological table (Table 4) presents the types of bridge measuring circuits with: 4.1) one active arm at Р h.e = const; 4.2 ) two active arms at Р h.e = const; 4.3) mode control at Т = const; 4.4) discrete switching the heating element on and off .
The fi fth morphological table (Table 5) contains the types of devices for stabilizing the fl ow rate of liquid materials: 5.1) constant level tank; 5.2) gear pump; 5.3) piston pump; 5.4) centrifugal pump.
The choice of the optimal structure of thermal converters of the moisture content of liquid materials is carried out according to the developed block diagram of the algorithm (see Fig. 1). This choice begins with the introduction of the requirements (block 1): sensitivity, accuracy, speed, reliability, error, etc., and the requirements themselves are formed at the request of the systems for monitoring and controlling the moisture content of liquid materials (block 2).
Further, in block 3, the optimal structure of thermal converters is selected according to the requirements. To do this, one should refer to the morphological tables of the main elements (block 4) which were synthesized on the basis of the analysis of the existing designs of thermal converters and those taken from the fund of scientifi c and technical information (block 10).  In block 5, the selected version of the thermal converter elements is checked regarding matching the requirements, and, if it is acceptable, the transition to the design layout of the thermal converter is carried out. Further, the obtained design of the thermal converter (block 9) is compared with the existing analogs and prototypes from the scientifi c and technical information fund (block 10). If there is no diff erence, applying the generalized methods of improving converters and varying their main elements (block 4), we change the design layout until a signifi cant diff erence from the known designs is achieved, and a new design is obtained (block 12) which can be protected by a patent.
The above generalized technique for improving thermal converters for the moisture content of liquid materials is a short rule for converting a prototype converter to obtain a new converter design. In the fi eld of thermal moisture converters, the following improvement methods can be used: combining functions of elements, changing separate functions of elements, changing the mutual arrangement of elements in the converter design, introducing new additional elements into the design and measuring circuit, expanding the function of elements to improve the metrological characteristics of converters, and so on. On the basis of the above methodology for the optimal structural design of thermal converters of the moisture content of liquid materials, a new design of a thermal converter was developed which was fi led with the patent offi ce for a patent [1].
Based on this technique, the optimal shape of the heat conductor, namely, 1.4 was selected from Table 1 fi rst of all in terms of the main quality indicators: sensitivity, accuracy, and speed. Further, the shape of the heating element 2.2 was chosen which also corresponded to the best accuracy, sensitivity, and speed indicators and was technologically installed on the surface of a cylindrical semiconductor resistance thermometer (see Table 3, position 3.4). As to the variant of the measuring circuit, the most eff ective was bridge measuring circuit 4.4 with discrete switching the heating element on and off , which corresponded to the best quality indicators: sensitivity, accuracy, and speed of operation. A constant level tank was selected as the device to stabilize the fl ow rate of a liquid material in position 5.1 which met the quality index for accuracy and was also the simplest and most reliable in design.
It is this design consisting of elements of morphological tables 1.4, 2.2, 3.4, 4.4, and 5.1 that was taken as the basis for research and refi nement based on comparison with analogs and prototypes and was brought to the level of meeting the patent requirements of the Republic of Uzbekistan. As shown above, the structure of a TCMCLM heat conductor is selected on the basis of the requirements formulated. The material of the heat conductor is selected with regard to the operational and design characteristics of a specifi c design of thermal converters of the moisture content of liquid materials.
At the same time, the material should have high thermal conductivity, resistance to mechanical stress, and heat capacity to ensure a high speed, as well as the ability to be machined and interchangeable. The most suitable shape of a heat conductor, as mentioned above, is a cylindrical tubular one inside which a cylindrical semiconductor resistance thermometer with a heating element is also placed. It is most advisable to use copper, brass, and aluminum as materials.
The choice of a heating element is carried out according to Table 2. As a heating element, a wire (nichrome and manganin) distributed heater is very eff ective, providing high accuracy of the specifi ed heating power, reliability, reproducibility of characteristics, small dimensions and weight. It should also be emphasized that this heating element ensures a constant specifi c heat fl ux on the heating surface of the cylindrical semiconductor resistance thermometer, which also corresponds to the mathematical models obtained with a uniform heating power of thermal converters of the moisture content of liquid materials.
Above, the main requirements for thermosensitive elements of thermal converters of the moisture content of liquid materials were indicated: high sensitivity, accuracy, high speed, convenience, and effi ciency of installation in a probe-type design joint with heating elements as well as small dimensions, weight, and price. Cylindrical semiconductor resistance thermometers of types MMT-1 and KTM-1 comply best to these requirements.
Among measuring circuits of thermal converters of the moisture content of liquid materials, with consideration for choosing semiconductor resistance thermometers as temperature-sensitive elements, bridge measuring circuits are the most common, where, depending on the operating mode of thermal converters, preliminary processing of signals in relation to the moisture content of the controlled fl ow of a liquid material occurs.
Taking into account the complexity of the measuring process in thermal converters of the moisture content of liquid materials and the possibility of a thermal control method that allows one to control the humidity and temperature, as well as the presence or absence of a liquid fl ow, it is possible to use microprocessor measuring systems for processing these signals. In general, the use of microprocessors complete with thermal converters of the moisture content of liquid materials will make it possible to carry out calibration, testing, verifi cation, nonlinearity correction, and temperature compensation.
The main objective of parametric designing thermal converters of the moisture content of liquid materials is to obtain the optimal parameters of all main elements and their characteristics that meet the stated requirements and criteria for their optimization.
One of the important problems in the optimal parametric design of TCMCLM is the choice of the optimality criterion ( ).
I a Typically, the initial data in the design of thermal converters of the moisture content of liquid materials are the following: conversion range of the moisture content [W min , W max ], parameters of the heating and thermosensitive elements, bridge circuit, and device for stabilizing the fl ow rate of a liquid material [2][3][4]. As a result of the optimal parametric design based on the studies of thermal converters, it is necessary to fi nd the optimal parameters U b0 , K 0 , P h.e0 , R h.e0 , d 0 , and V 0 which in the general case constitute the main parameters of the thermal converters under consideration: Above, U b is the power supply voltage of the bridge circuit, K is the symmetry coeffi cient of this circuit, P h.e is the heating power, R h.e is the resistance of the thermosensitive element, and the subscript zero corresponds to the optimal values. As a result of optimization, it is necessary to fi nd such parameters of thermal converters at which the optimal value of the optimality criterion is achieved, i.e., where Opt ( ) I a is the optimal value and Da is the region of feasibility.
For the -search area we have { : , 1, } , where b i and c i are the minimum and maximum values of a i . In the design process, it is necessary to take into account that thermal converters perform their functions and remain serviceable only if the input value is not outside the measurement range, i.e., where W min and W max are the minimum and maximum values of the input moisture content.
To search for the optimal parameters of thermal converters of the moisture content of liquid materials, mathematical models of such converters are used which should: 1) be informational; 2) be adequate to real measuring conversion processes (when the given experimental data well confi rm their adequacy); 3) use the output values and parameters accurately refl ecting the relationship between the varied parameters and the output infl uences; 4) be quite simple and easily implemented on a PC.
The largest number of problems in the optimal design of thermal converters for the moisture content of liquid materials is associated with an increase in sensitivity and accuracy, as well as linearity of the static characteristics and speed of response. The problem of designing such converters according to the criteria of linearity and sensitivity of the static characteristics is formulated as follows. The structure is selected and, therefore, the static characteristic of thermal converters is determined, for example, for the operating mode Р h.e = const in the form where U b is the power supply voltage of the bridge circuit. In the general case, the static characteristic can be represented as The problem of increasing linearity of the static characteristics of thermal converters of the moisture content of liquid materials is solved by approximating the determined real nonlinear static characteristics (Eq. (7) The problem of ensuring high sensitivity is easily solved after solving the problem of ensuring high linearity of the static characteristic, since these problems are very closely related. To solve the problem of increased sensitivity, it is necessary to determine the optimal value of the vector ( ) a y for which The accuracy of thermal converters of the moisture content of liquid materials is mainly determined on the basis of the entropy error ,  and the problem of the optimal parametric design according to the criterion of accuracy of converters can be solved by minimizing this error which is determined by the main components defi ned as the rms errors of the corresponding heating element, bridge circuit, thermosensitive element, and device for stabilizing the fl ow of a liquid material [5]. The necessary parameters of thermal converters of the moisture content of liquid materials are found so that for The calculation and selection of the optimal parameters of thermal converters of the moisture content of liquid materials is carried out according to the developed algorithm (see Fig. 2). We briefl y consider the main stages of the block diagram of this algorithm.
In module 1, the array of initial data is presented that is based on the requirements of control and management systems for liquid materials. In module 2, the temperature distribution along the heat conductor is calculated, and the specifi ed distributions are achieved with the use of modules 3 and 4. In module 5, the parameters of the resistance thermometer and measuring circuit are calculated, and the results are used to form the optimization criterion, restrictions, and choosing a method for fi nding the optimal design.
In module 6, the optimization criteria are selected. In module 7, choosing the initial approximations is carried out by the variable parameter In module 8, the defi nition of the fl ow area  is made. In module 9, we check whether the initial approximations a belong to the range of admissible values . a  In module 10, choosing a parametric optimization method is carried out. In module 11, we check the original problem for extremality. Module 12 checks whether the optimal solution belongs to the search area  in .
a Module 13 displays the calculated data and parameters (in the form of tables and graphs).
As a result of the calculations and design, the following parameters of thermal converters of the moisture content of liquid materials were obtained: