Modeling heat and mass transfer processes during evaporation of a water film in a horizontal channel with a cocurrent flow of moist air

Modeling of heat and mass transfer processes in a horizontal channel during evaporative cooling of a moist air flow with regard to the finite thickness of the liquid film is considered. The mathematical model consists of a system of differential equations in the boundary layer approximation. The simulation results have been obtained in a wide range of initial parameters: temperature T 0 = 10÷50°C, humidity φ0=0÷100%, Reynolds number Re=100÷2000. Calculations were carried out at atmospheric pressure. Quantitative analysis of influence of initial parameters of flows on values of parameters of wet air flow at the outlet of the channel with and without taking into account the final thickness of the water film was carried out.

Numerical simulation of the formation of dry spots during film evaporation

This paper presents a developed methodology for calculating heat and mass transfer processes in a cylindrical evaporation cell. The mathematical model reproduces all significant features of the evaporation cell geometry. In this cell, a layer of liquid is formed on a substrate with a diameter of 51 mm, heated below. To simulate heat transfer during film evaporation on a heated substrate, a numerical technique based on the Volume of Fluid method was used. The developed model was used to study the process of dry spot formation during film evaporation. The calculated data are compared with the experiment on the profile of the free surface of the film during evaporation and rupture. In general, results of this testing demonstrated good agreement with experiment. As a result, it was shown that developed numerical method makes it possible to describe process of formation dry spots.

REPRESENTATION OF THE SPECIFIC SURFACE AREA OF A POROUS MEDIUM BY STATISTICAL CONTINUOUS MONOMIAL FUNCTIONS

Удельная поверхность пористых сред является важным геометрическим параметром в расчетах процессов пищевых систем и оборудования для их переработки. Расчетные формулы процессов тепло- и массообмена в настоящее время содержат осредненные значения геометрических параметров, получаемые в эксперименте. Использование формул удельной поверхности по осредненным характеристикам пористой среды существенно ограничивает точность и надежность расчетов. Получены непрерывные одночленные по всему диапазону размеров сообщающихся пор расчетные формулы удельной поверхности, основанные на функции распределения плотности вероятности размеров сообщающихся пор разных модельных конфигураций в полиразмерной дисперсной (несцепленной) и связной (сцепленной) пористых средах для двух видов исходных формул удельной поверхности, различных видов модельных поперечных сечений и длины пор. Проведен их сравнительный анализ. Установлено, что на расчет удельной поверхности влияет моделируемая длина пор. Вид поперечного сечения не влияет на расчет удельной поверхности. Полученные формулы позволяют вычислять удельную поверхность для ансамбля отдельных размерных групп пор и в целом для всей совокупности их размеров. Приведен пример расчета по полученным формулам. The specific surface area of porous media is an important parameter in the calculations of the processes of food systems and equipment. The calculated formulas of the heat and mass transfer processes currently contain the averaged values of the geometric parameters obtained in the experiment. The use of formulas the specific surface area based on the averaged characteristics of a porous medium significantly limits the accuracy and reliability of calculations. Continuous monomial calculated formulas for the specific surface and based on the function of the probability density of the size distribution open pores ware obtained. Their comparative analysis is carried out. It was found that the transverse shape is not reflected in the formulas for the specific surface area, but the simulated pore length does. The specific surface area formulas allow calculating the specific surface area for an ensemble of separate size groups of pores and, in general, for the entire set of their sizes. An example of calculation by the obtained formulas is given.

Operando magnetic resonance imaging for mapping of temperature and redox species in thermo-electrochemical cells

Low-grade waste heat is an abundant and underutilised energy source. In this context, thermo-electrochemical cells (i.e., systems able to harvest heat to generate electricity) are being intensively studied to deliver the promises of efficient and cost-effective energy harvesting and electricity generation. However, despite the advances in performance disclosed in recent years, understanding the internal processes occurring within these devices is challenging. In order to shed light on these mechanisms, here we report an operando magnetic resonance imaging approach that can provide quantitative spatial maps of the electrolyte temperature and redox ion concentrations in functioning thermo-electrochemical cells. Time-resolved images are obtained from liquid and gel electrolytes, allowing the observation of the effects of redox reactions and competing mass transfer processes such as thermophoresis and diffusion. We also correlate the physicochemical properties of the system with the device performance via simultaneous electrochemical measurements.

New energy, angle momentum and entropy balance approach to modelling climate and macroturbulent atmospheric dynamics, heat and mass transfer at macroscale. III. Low-frequency approximation and singularities in fields of meteoelements

An generalized low-frequency approximation of energy, angle momentum and entropy balance relationships to modelling climate and macro-turbulent atmospheric dynamics, heat and mass transfer at macroscale is introduced and allow significantly to simplify the main fundamental equations. A new equilibrium approach to modelling the global mechanisms of climatic and macroturbulent atmospheric low-frequency processes, including heat and mass transfer processes, teleconnection effects, etc., is based on the use of equilibrium relations for entropy, energy, angular momentum, spectral theory of atmospheric macroturbulence and moisture turnover in connection with the continuity of forms of atmospheric circulation (teleconnection, genesis of fronts). The physical features of singularities in the fields of meteorological elements and the balance of the angular momentum as well as a generalized Arakawa-Schubert model are introduced and discussed.

Conceptual issues of professional education of specialists in the "Environmental Protection Technologies"

Composing the programs for the education of specialists in the field of environmental protection requires clear ideas about the concepts, place of basic disciplines and the main issues of the future specialty. Peculiarities of methodological aspects of description of levels and assessment of quality of education in terminology of competences and learning outcomes are considered. They consist in the predominance of competencies, that have a physical meaning and ensure the filling of the "core" of the educational program with physical principles, methods and models. The study of polluting processes in natural objects requires knowledge of the physics of aerodisperse systems in connection with the solution of aerosol emissions into the atmosphere, knowledge of the physics of the dispersible silt-covered upcasts into the aquatic environment, knowledge and understanding of physical phenomena of heat and mass transfer processes in soil, as in the granular system, knowledge of the physics of external radiation, including sound, heat, electromagnetic, in particular, ionizing radiation, and their impact on the environment. Peculiarities of the educational system of training specialists in the field of environmental protection take into account the tasks of systemic radioecology, among which the tasks of radiation monitoring are especially important. The conceptual approach to the study of radioecology is proposed not as a whole, mixing the laws of physics, chemistry and, for example, biology, but by individual branches, and systematically.

Analysis the dynamics formation of a vapor supersonic jet under outflow from thin nozzle

The dynamics formation of a vapor jet with near-critical state parameters outflowing from a high-pressure vessel through a thin nozzle is studied. The numerical modeling of this process, by using a system of model equations for gas-vapor-liquid mixture, which include conservation laws of mass, momentum, and energy of phases in accordance with one-pressure, one-velocity and two-temperature approximations, was conducted, taking into account heat and mass transfer processes of evaporation and condensation under conditions of equilibrium state with modified reactingTwoPhaseEulerFoam solver of open package OpenFOAM. The process of barrel shock formation in supersonic boiling jet with shaping Mach disk is shown. It was found that the process of boiling fluid outflow is accompanied by formation of vortex zones near axis of symmetry and leads to generation of acoustic wave pulses series preceding the main jet flow, which are the source of pulsations, observed in experiments. The justification of applied numerical method reliability is shown by comparing the computational and analytical solutions for Sedov’s problem of a point explosion in gas-water mixture at the plane case.

Flow visualization around cylinder under surface discharge action in the still atmosphere

The paper presents the universal gas-discharge system for surface discharge generation on a cylinder body providing PIV experiments and shadow studies. The system enables the flow visualization around cylinder, discharge power consumption measurements and of temperature fields on the cylindrical surface recording. Under surface discharge action on cylindrical surface in the quiescent air, the flow accompanied by the formation of a near-wall vortex structure and a set of the radially-oriented jets is visualized. The observed jets leave the thermal boundary layer and are able to influence to the gas areas located far away. The presented results indicate the effectiveness of the surface discharges use to control gas-dynamic, thermo-physical and mass transfer processes in the vicinity of streamlined bodies such as cylinders.

Fractal Characterization of Heat and Mass Transfer Processes in Nanostructured Materials

The relationship between the fractal self-organization of structural-phase inhomogeneity in nanostructured materials and the processes of heat and mass transfer in them is considered. It is characterized by a non-Euclidean relationship between the rate of increase in the number of the considered elements of the medium and an increase in the scale of their consideration and is described by the transfer equations in fractional derivatives with respect to coordinate and time.