HRADILEK Zdenek 1, GAVLAS Josef 1, KRAL Vladimir 1,
SAJDAK Czeslaw 2, KUREK Alicja 2 & PRZYLUCKI Roman 2
1 VSB – Technical University of Ostrava, FEI, Dep. Electroenergetics, 17.listopadu 15, 70833 Ostrava-Poruba, Czech Republic, Zdenek.Hradilek@vsb.cz
2 Silesian University of Technology, Faculty of Materials Science, Metallurgy and Transport, Krasinskiego 8, 40 019 Katowice, Poland, kureka@polsl.katowice.pl
Abstract: The paper presents in short few computer progammes elaborated in 1995-1999 by Electrical Engineering and Informatics Faculty of VSB Technical University of Ostrava, Czech Republic and Material Science,Metallurgy and Transport Faculty of Silesian University of Technology , Katowice, Poland. The programmes are used by both facultyes for scientific research purposes in the field of electroheating. They are also used as a material for didactics as well as in work simulation and design of electric furnaces and heaters.
Since 1995 Electrical Engineering and Informatics Faculty of VSB in Ostrava and Material Science, Metallurgy and Transport Faculty of Silesian University of Technology have conducted scientific - research work “Computer software aiding scientific research in electroheating”. A few computer programmes have been elaborated and used by both Faculties in their scientific research and didactics. The paper presents in short computer programmes that are the results of jointly conducted research.
Keywords: education, computer, programmes, electric, furnaces
The paper presents in short six computer programmes that are the results of jointly conducted research:
PIKT and PIKP programmes enable to calculate electrical, thermal and exploitation parameters for channel-type furnaces; PIKT for melting and PIKP for preheating ferrous alloys and non-ferrous alloys [1]. Well known, modified method of two-winding transformer was used to determine the electrical values. This method comprises constructional and operational similarities of channel-type furnace and single-phase transformer [2,3]. The design of the inductor, the main part of the channel-type furnace, comprises electrical calculations (electrical parameters of the system: winding - magnetic core - liquid metal) and thermal calculations (heat exchange with the environment). It takes place in two stages: initial and final (”Design” and ”Verification”). In the initial stage first the demanded furnace power, and then the basic parameters of the inductor are determined. The later ones are set by means of iteration. For the initial values of coil voltage, power factor and furnace efficiency the following are calculated:
Iterational process (the change of coil voltage) ends when the difference between required and calculated effective power in the furnace channel is smaller than the assumed value. It is important to check whether the characteristic parameters come within acceptable or recommended limits.
In the second part of initial stage the following steps are performed:
Final calculations are performed in the final stage (block ”Verification”).
The above methodology of designing channel - type furnaces is the base for the PIKP and PIKT programmes.
The basis options in the main menu are:
If the calculations are to be carried out on similar example to the previous one (or they are its modifications in the process of multi-variant analysis and the choice of the best solution) and the input data and calculation results for the variant have been loaded in data bases, they can be introduced by the selection of option ”Files”.
During the calculation stage, it is possible to get help from data base (option ”Data base”) which makes the choice of dimensions and parameters easier. The designer has the information about the refractory and heat-insulating materials, transformer sheets, conductors, transformers, capacitors etc. He can also compare the parameters of already designed furnace with data about furnaces made in different countries by well known companies.
Calculations performed in the block ”Design” can be treated as initial ones, but they can also finish the calculating part of the furnace design. The user, aware of the furnace parameters can, by choosing the option ”Verification”, make more precise calculations. After changing dimensions and parameters several times, it is possible to find the best solution for the designed device. The option ”Printouts” allows to present partial or complete reports of the performed calculations.
PIKP and PIKT programmes elaborated in couple of versions differ in the kind melted or preheated charge, the contents of data base and information in the option ”Help”. They have, however, the same structure, organisation and the manner of operation.
The programmes have special protections which check the correctness of loaded data. They enable to perform current records by printouts of data and partial results and printouts of set of calculations. IT is possible to stop work at any time and record the data with some results on the disc and then continue the process.
PIKP and PIKT are installation programmes. They appear in 8 versions suitable to design furnaces for melting and preheating metals and their alloys.
Programme NISC aids designing through - induction heaters for the cylindrical charges. Such devices are commonly used in the process of steel and non-ferrous metals plastic working.
The programme enables the calculation of stationary and continuous heaters. Stationary heating is used in cases when there is no demand for a high heating rate of the technological process or when the length of the charge is big. Should the heating rate be high, the charges are heated progressively, at constant or stroke move inside the inductor.
The programme uses traditional, analytical methods of determining the electrical parameters of induction heating systems: inductor - charge. They were described in papers [1-3]. When calculating the power of thermal losses by particular elements of the heater, the multilayer models of complex heat exchange in steady state are used.
The design of the heaters can take place in two modes:
The first mode should be chosen when the technological conditions of plastic working process determine the heating time or the heating rate. The second mode is chosen when designer knows the power output, output voltage and frequency of the source of supply.
The organisation and operation of NISC programme is very similar, in some elements even identical to PIKP and PIKT programmes. When the programme gets started, two line appear on the screen:
Block ”Design” contains basic functions of the programme, enabling the calculation of basic electrical, thermal and exploitation parameters of induction heaters:
Figure 1.
Necessary prompts, making the choice of heater dimensions or supply parameters easier, appear in window ”Help”. The can use numerous data base containing rating and parameters of all materials, elements, subsystems and devices constituting the induction heater. Such data base can be modified by the designer. The correctness of loaded data is controlled. Errors are monitored. As in case of PIKP and PIKT programmes, the designer can form data sets of the designed heaters. That makes the calculation of other constructional variants or the choice of the best solutions easier.
PIT programme [4-6] helps to determine electrical and operating parameters of induction furnaces with ceramic crucible. Fig. 2 shows its diagram. Calculations can be done for three types of furnaces:
Figure 2. Block diagram of PIT programme
Programme menu, access to which is when the programme is stared and after every stage of calculations, has the following options: Input data, Basic crucible and inductor dimension, Assumption of total thermal losses, Thermal losses through side surface, Thermal losses through furnace bottom, Thermal losses through the cover and bath surface, Total power of furnace thermal losses, Furnace electrical calculations, Choice of conductor and its dimensions, Calculation results of furnace parameters, Compensation, Furnace parameters after compensation, Cooling system, Magnetic cores-screen, Furnace parameters print- out, Crucible furnaces parameters, Calculations of a new furnace, Record of a designed furnace parameters, Read-out of a designed furnace parameters.
Like in NISC programme the designer is aided with help enabling to take proper decisions. He can also use different data base, with parameters of the materials for furnace and electric device constructions (source of supply, transformers, capacitors). Errors and incorrect dimensions and parameters are pointed out.
Input data and calculation results can be placed on a disc, forming the files of parameters for furnace construction variants. (Designed furnace parameter read-in). These files can be used when correcting the dimensions, supply parameters etc.; in case of calculating the other versions of the furnace or elaborating series of types. The work is then started with reading-in an appropriate calculation variant (Parameter read-out of the designed furnace).
NAG-REZ programme enables to determine the basic electrical and thermal parameters of the device for the direct resistance heating of charges with cylindrical and rectangular section. Charge temperature calculations are based on typical model of linear objects heating at constant power volumetric density. Heat exchange is done by convection and radiation. Four options are available after the programme is started: Files, Data, Calculation, Results. For certain data (Data), electrical parameters of the heater and changes in charge temperature during heating are calculated (Calculation). Results give access to calculation results. They can have the form of a text or a graphic form (Fig.3). Temperature is calculated in few points of the charge - on its surface and inside.
Figure 3. Exemplary temperature changes in time (charge of rectangular section-middle part )
Computer programme KRUH-DIA is presented in more details in works [4]. It enables to determine working area of steelmaking arc furnace and furnace work simulation on circle diagram for all voltage degrees of furnace transformer. The programme has the option of drawing of operating characteristics and changes of furnace electrical parameters in time function, obtained on the basis of circle diagram for a given on-load voltage. Calculation results give characteristics of total active power P used by the furnace, arc power P0, power of electric losses Pz, power coefficient cos φ and electrical efficiency η in the function of arc current intensity. Operating characteristics of the furnace (Fig.4) are done with the help of Lotus, Quatro, Excel programmes.
Figure 4. Examples of operating characteristic of arc furnace obtained by KRUH-DIA programme
OHREV1 programme [7] enables the simulation of charge heating in resistance stationary furnace. Calculations are done with the following assumptions: temperature in the furnace is constant, heat exchange takes place through radiation and convection, the surface of heat absorption by the charge is known (corrected surface, depends on the way of placing the charge), Biot criterion is Bi < 0.25 ("thin" charge).
Menu has the following options: Files, Data, Results, Information. Files option has data of previously done calculations, after the calculations data sets are formed. In Data option apart from charge parameters and its surface of heat exchange - values of temperature in furnace, initial and final charge temperature and iteration step are introduced (Fig.5). When they are accepted and the iteration process is started the time of charge heating is calculated (time of reaching the end temperature) and charge temperature in the following iteration steps is calculated as well. Calculation results can be seen (Results) in graphic or tabular form (Fig.6).
Figure 5. In Data option apart from charge parameters heating
Figure 6. Calculation results in graphics form
The programme helps to evaluate quickly the influence of charge placement, its thermal properties and conditions of heat exchange upon the course of heating process. It is applied in didactics. The more elaborated version is being prepared; it will be useful for aided design of resistance furnaces.
[1] Sajdak Cz., Samek E.: Nagrzewanie indukcyjne. Podstawy teoretyczne i zastosowanie. Wyd.Slask, Katowice 1987
[2] Langer E.. Teorie indukcniho a dielektrickeho tepla. CSAV, Praha 1964
[3]Nemkov S., Demidowicz V.B.. Teorija i rascziot ustrojstw indukcionnogo nagriewa. Energoatomizdat, Leningrad 1988
[4] Hradilek Z. et all. Computer software aiding scientific research in electric heating engineering. IV Seminarium ”Nowe technologie i materialy w metalurgii i inzynierii materialowej”, Katowice 1996, 35-40 (in Polish)
[5] Sajdak Cz., Kurek A.. Wspomaganie komputerowe projektowania indukcyjnych piecow tyglowych. Skrypt Politechniki Slaskiej nr 1972, Gliwice 1996 (in Polish)
[6] Sajdak Cz., Kurek A.. PIT program aiding crucible induction furnace design. ELEKTROENERGETIKA’1996, Kosice 1996, 219-224
[7] Hradilek Z. et all: Calculation of exploitation and electrical parameters of resistance and channel induction furnaces. VI Seminarium “Nowe technologie i materialy w metalurgii i inzynierii materia³owej”, Katowice 1998, 81-84 (in Polish)