Modeling Epitaxial Layer Growth from Gas Phase for Analysis of Influence of Changing Technological Process with Variation in Growth Zone Heating

In this paper, we analyze the nonstationary heat transfer during growth of epitaxial layers in epitaxy reactors from the gas phase. Based on this analysis, we formulate several recommendations on organization of heating of the growth zone for increasing homogeneity of epitaxial layers. We introduce an analytical approach for analysis of heat transfer during the growth of epitaxial layers from the gas phase. The approach gives a possibility to simultaneously take into account the nonlinearity of heat transfer, as well as changes of their parameters both in space and time.

Mathematical modeling of coupled heat transfer on cooled gas turbine blades

The paper presents a physico-mathematical model for determining the heat transfer parameters between viscous gasdynamic flotations and cooled gas turbine blades made using the technology of composite permeable membranes (CPM). The mathematical model includes equations of dynamic and thermal boundary layers taking into account injection, three-dimensional transient heat conduction in CPM cooled frames, complex hydraulic flow and cooling inside the channels of a cooled blade with air taken from the power plant compressor. A complex problem was solved to determine the thermal state of microrocket engines, where a method was proposed for immersing a multiply-connected domain in a region of the simplest form. A new economical, absolutely stable method is proposed for numerically solving of spatial nonstationary heat transfer problems in multiply-connected domains. The results obtained showed greater cooling efficiency at lower cooling medium costs.

STUDY OF THE RATE OF SUBLIMATION OF DRY ICE IN THE COOLING PROCESS OF THE PULP

Рассмотрены процесс сублимации сухого льда и распределение температур внутри гранулы диоксида углерода при нестационарном режиме теплопередачи в пористом материале, в качестве которого использовали мятку подсолнечника температурой 19C и массой 30 г. Основой исследования был ряд экспериментов, позволяющих сформировать зависимости изменения массы гранул СО2 во времени с учетом влияния заданных внешних факторов на процесс сублимации. Для минимизации погрешностей при оценке времени сублимации в эксперименте отбирали пеллеты диоксида углерода длиной 20 мм и массой 2 г. Эксперимент проводили в двух вариантах, меняя воздействие окружающей среды на процесс сублимации: теплопередача посредством конвективного теплообмена в среде покоящегося воздуха и теплопередача в засыпке гранулы пористым материалом. Обработка результатов экспериментальных исследований проведена методами математического моделирования с использованием вычислительного пакета Mathcad. Показана возможность формирования достоверной модели с заменой параболического уравнения уравнением пробной функции, определяемой уравнением теплопроводности Фурье для одномерного тела, дальнейшее решение которого осуществлено полуаналитическим методом Галеркина. Доказано соответствие полученных регрессионных уравнений экспериментальным исследованиям. В результате исследования математической модели получены данные о динамике перемещения границы раздела фаз для пеллет цилиндрической формы. Результаты исследования могут быть использованы для расчетов режимов современного прессового оборудования. The process of sublimation of dry ice and the temperature distribution inside the carbon dioxide granules at a nonstationary heat transfer mode in a porous material, which was used as a sunflower mint at a temperature of 19C and a mass of 30 g, are considered. Experiments allowing to form dependences of changes in the mass of CO2 granules in time taking into account the influence of specified external factors on the sublimation process were the basis of the study. To minimize errors in the estimation of sublimation time, carbon dioxide pellets with a length of 20 mm and a mass of 2 g were selected in the experiment. The experiment was carried out in two versions, changing the effect of the environment on the sublimation process: heat transfer by means of convective heat transfer in a medium of resting air and heat transfer in the filling of the granule with a porous material. Processing of the results of experimental studies carried out by methods of mathematical modeling using a computational package Mathcad. The possibility of forming a reliable model with the replacement of the parabolic equation by the equation of the trial function determined by the Fourier heat equation for a onedimensional body, the further solution of which is carried out by the semianalytical Galerkin method, is shown. The correspondence of the obtained regression equations to experimental studies is proved. As a result of the study of the mathematical model, data on the dynamics of the phase boundary movement for cylindrical pellets are obtained. The results of the study can be used to calculate the modes of modern press equipment.

DETERMINATION OF THE COEFFICIENT OF HEAT TRANSFER DURING COOLING OF SILVER THERMO PROBES, TAKING INTO ACCOUNT THE EFFECTS OF TEMPERATURE-TIME DELAY

Existing methods for determining the characteristics of the nonstationary heat transfer process (temperature field, heat transfer coefficient, heat flux density, surface temperature) are considered and analyzed when cooling silver spherical and cylindrical thermo-probes. New analytical solutions are proposed using a special program IQLab, which increase the accuracy of calculations when testing the cooling capacity of various liquids. The results of the calculations are compared with the experimental data.

EVALUATION OF HEAT PROTECTION CHARACTERISTICS OF BUILDINGS WITH INTERMITTENT HEATING INSULATED WITH SANDLESS COARSE-POROUS EXPANDED CLAY CONCRETE

Mathematical modeling of process of nonstationary heat transfer through walling exploited in intermitt ent heating conditions is viewed. Analytical dependence is revealed for fi nding of maximum permissible thickness of heat insulation layer providing required heating time. Based on this procedure the results of calculation of outer walls diff erent variants are presented. Comparative analysis of heating time of walling insulated with sandless coarse-porous expanded clay concrete.

Equilibrium acoustic velocity in vapor-liquid mixture in layer of spherical particles

Theoretical and experimental study of acoustic velocity in vapor-liquid mixture that contained close-packed layer of spherical particles was performed with respect to nonstationary heat transfer between mixture and particles in compression half-wave. Theoretical model allows to explain the decay of equilibrium acoustic velocity compared to its adiabatic value in case of increasing of void fraction in the mixture. Calculated results are in agreement with experimental data, obtained in vertical channel with vapor-liquid filtration with close-packed layer of spherical particles of borosilicate glass, steel and lead.