The methodology of theoretical studies of heat exchange processes in boiler units based on the mathematical model of burning coal dust has been developed. For the first time, the continuous curve of the fractional composition of an ensemble of coal particles is presented. The mathematical model is consistent with the aeromechanical and thermal characteristics of the torch, obtained on the basis of calculated and experimental data. The concept of a torch continuum is introduced as a continuous medium in which the processes of combustion and heat exchange are investigated. The methods of dividing the combustion chamber into zones, the equations of stationary and non-stationary heat conduction, radiation and convective heat exchange are used. These methods have been tested on a number of high-temperature installations, including boilers with natural circulation, for example, E-220 at the CHP plant in Bishkek, Kyrgyz Republic in the Central Asian region. In the course of the experiments, coals with different thermal characteristics were burned. In a special computer program obtained a 3D image of burning coal dust. Analysis of the calculated and experimental data showed a discrepancy between them of 4-5%. Analysis of computer simulation data showed a discrepancy with the calculated data of 3-4%, and with experimental 5-6%. Thus, the dependence of the parameters of the heterogeneous flame on the mathematical description of the fractional composition of coal dust is substantiated and the characteristics of the combustion process, previously not taken into account in the theory of heat transfer, are revealed. The task was solved-theoretically confirmed new methodological approaches to the theory of heat transfer in the furnace of the boiler unit.
The existing theories of heat transfer in combustion chambers of boiler units fail to take into account a number of important factors that affect the reliability of results, and the methodological approaches to optimizing combustion processes can be revised in view of the spatial and temporal parameters of flame. Hence, the research aimed to improve the fundamental theoretical and methodological principles of studying heat transfer in coal dust combustion in the combustion chambers of industrial steam generators. The authors proposed to extend the theory of heat transfer with the mathematical description of particle size distribution of coal dust. In addition, the authors used the developed mathematical model of coal dust combustion based on a continuous curve of the particle size distribution in the ensemble. The mathematical model is consistent with the aeromechanical and thermal characteristics of flame. This work introduced a concept of flame continuum as a continuous medium, where the processes of combustion and heat transfer are studied. To achieve the research aim, in this paper, the methods of combustion chamber zoning, the equations of stationary and non-stationary heat conduction, radiation, and convective heat transfer, were used. These methods were tested on a number of high-temperature units.
The authors of the paper emphasize that when the Nyquist-Shannon sampling theorem is used in practice, there arise several problems, which can be explained only through the use of new methodologies and mathematical models. The review of the researchers' works, as well as the authors' own practical research in the course of processing the statistical sample, which is described by a wave-like sine-cosine function, leads to the conclusion that it is necessary to take into account optimization criteria for high-tech processes and innovative indicators of building functions for the statistical sample, for example, when signals are transmitted and sampled using neural networks at production facilities. In the practice of economic calculations, for example, when making a graphic presentation of trend lines based on the functions built subject to the sampling conditions by the Nyquist theorem, the authors propose to use new methods for approximating piece linear functions, which allow for achieving a smaller error as compared to standard calculation methods. The work resulted in the creation of a neural network regulation algorithm, which will be trained based on the collected data and adapted to a specific type of a boiler unit. Besides, it was established that the task of neural network algorithms in the program is to find the optimal value of the weight coefficient for each argument of the resulting function to obtain the maximum number of predictions of the flare level and the particle burn-up time, which are consistent with reality. The use of these methods for the first time made it possible to significantly reduce the error, which is confirmed not only by calculations, but also by experimental data.
We present the cationic impurity assisted band offset phenomena in NixCd1-xO (x= 0, 0.02, 0.05, 0.1, 0.2, 0.4, 0.8, 1) thin films and further discussed in the light of orbital hybridization modification. Compositional and structural studies revealed that cationic substitution of Cd 2+ by Ni 2+ ions leads to a monotonic shift in (220) diffraction peak, indicating the suppression of lattice distortion while evolution of local strain with increasing Ni concentration mainly associated to the mismatch in electro-negativity of Cd 2+ and Ni 2+ ion. In fact, Fermi level pinning towards conduction band minima takes place with increasing Ni concentration at the cost of electronically compensated oxygen vacancies, resulting modification in the distribution of carrier concentration which eventually affects the band edge effective mass of conduction band electrons and further endorses band gap renormalization. Besides that, the appearance of longitudinal optical (LO) mode at 477 cm -1 as manifested by Raman spectroscopy also indicate the active involvement of electron-phonon scattering whereas modification in local coordination environment particularly anti-crossing interaction in conjunction with presence of satellite features and shake-up states with Ni doping is confirmed by X-ray absorption near-edge and X-ray photoelectron spectroscopy studies. These results manifest the gradual reduction of orbital hybridization with Ni incorporation, leading to decrement in the band edge effective mass of electron. Finally, molecular dynamics simulation reflects 13% reduction in lattice parameter for NiO thin film as compared to undoped one while projected density of states calculation further supports the experimental observation of reduced orbital hybridization with increasing Ni concentration.Inter university accelerator centre) between the localized d states rather than between band like states like usual semiconductors [20]. So the term "optical gap" instead of "band gap" will be better to be casted off.In the present report, we have synthesized the NixCd1-xO (NDO) thin films for the whole composition range and a detailed study has been carried out on their structural, optical and chemical properties. In particular, we demonstrate the doping induced local strain, electron-electron, electron-ionized impurity interaction and strong electron phonon coupling leads to renormalization of band gap in NDO thin films.The dramatic dependence of the optical gap, moreover, with composition also has a strong correlation with phonon scattering such as optical phonon deformation potential, charged impurity scattering and also phonon stiffening as evidenced by Raman spectroscopy. Moreover, we consider the p-d hybridization between O p and Ni/Cd d orbitals in order to determine the CBM and VBM energy levels, suggesting that p-d hybridization becomes less effective with increasing Ni doping and subsequently affects band gap renormalization by reducing the effective mass of electron at conduction band edge. Complementary Xray absorption near-edge sp...
In the paper, high temperature induced phase transformation (PT) in chemically grown CdO thin films has been demonstrated whereas their corresponding electronic origin is further investigated by density functional theory. In particular, cubic rocksalt to hexagonal wurtzite PT in 900 ℃ annealed CdO thin films is confirmed by X-ray diffraction (XRD), consistent with High Resolution Transmission Electron Microscopy (TEM). Such high temperature treatment also leads to significant enhancement in optical band gap from 2.2 to 3.2 eV as manifested by UV-Visible spectroscopy. Moreover, atomic force microscopy and scanning electron microscopy clearly evidence the structural evolution via formation of nano-sheet network in wurtzite phased CdO films. Furthermore, X-ray Absorption spectra at oxygen kedge revealed a notable shift in inflection point of absorption edge while X-ray Photoelectron spectroscopy of Cd 3d and O 1s suggested the gradual reduction in CdO2 phase with increasing annealing temperature. In addition, different complementary techniques including Rutherford Backscattering, Raman Spectroscopy have also been exploited to understand the aforementioned PT and their structural correlation. Finally, molecular dynamics simulation along with density functional theory calculations suggest that symmetry modification at Brillouin zone boundary provides a succinct signature for such PT in CdO thin film.
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