Journal of Engineering Thermophysics最新文献

Numerical simulation of a dispersed phase scattering in a turbulent droplet-laden flow in a cylindrical channel with a peripheral swirling has been performed with variations in the initial weight concentration of water droplets within the range M_L1 = 0−0.1 and the initial droplet diameter d₁ = 10–100 µm using Eulerian and Lagrangian descriptions. The gas phase is described by a system of three-dimensional URANS equations, taking into account the effect of particles on transport processes in the carrier phase. The turbulence of the gas phase is calculated using the elliptical Reynolds stress transfer model, taking into account the effect of the dispersed phase. The Eulerian and Lagrangian descriptions give qualitatively similar computation results for the mass concentration profiles of droplets over the entire studied range of their initial diameters and concentrations (the difference in the computation results does not exceed 20%) and the position of the local concentration maximum. Comparisons have been made with the data of LES computations and measurements of the swirling droplet-laden flow at the swirl number S = 0.7, for which the precession of the vortex core occurs.

This paper develops methods for diagnostics of the droplet phase in gas–droplet flows under conditions of fast droplet evaporation, including the functions of droplet distribution by size, direction, and velocity. Measurements were made for the spatial distribution of the droplet phase in a gas–droplet flow formed during a jet outflow of the wall liquid film with a cocurrent gas flow into a vacuum from a supersonic conical nozzle with the Mach number M = 2.75. The features of the behavior of the liquid film on the outlet edge of the nozzle, the ultimate cooling temperature of the liquid, and disintegration of the film into droplets with the formation of back flows are discussed.

It is well known that in a distillation column with uniform irrigation of the structured packing at the inlet, irrigation of the packing layers located below becomes uneven starting from a certain layer. This leads to a significant decrease in the heat and mass transfer intensity. To mitigate this phenomenon, it is necessary to redistribute the liquid and achieve uniform irrigation. This paper presents the results of experiments where packing or its elements with various characteristics were employed as redistributors.

In the present study, the specific heat capacity of solid magnesium–lithium alloys with composition of 5, 10, and 17 at % lithium in the temperature range of 185 to 755–780 K was measured for the first time. Measurements were performed by the method of differential scanning calorimetry using a DSC 404 F1 apparatus. The estimated uncertainty of the data obtained was 2–3%. The temperature dependences were developed and the table of recommended values on their basis were presented for use in various scientific and practical tasks. It has been established that the specific molar heat capacity data of the magnesium–lithium alloys containing 5–17 at % lithium practically coincide with each other over a wide temperature range and can be estimated within the measurement uncertainty limits using the heat capacity temperature dependence of solid magnesium. It is possible to estimate the heat capacity of the studied alloys (with an accuracy not exceeding the measurement uncertainty) up to the melting point of lithium (456 K) using the Neumann–Kopp rule; however, such an estimation can be carried out in a much narrower temperature range than the previous one.

This theoretical work employs biomedical engineering and fluid mechanics to examine blood flow dynamics in a thin, elongated artery subjected to a magnetic field and featuring porous walls. It explores the impact of linear, quadratic, and nonlinear radiations on blood flow. It also addresses the consequences of slip factors. By employing appropriate similarity transformations, the sets of partial differential equations governing the system are transformed into a set of ordinary differential equations. These are then solved utilizing the NDSolve technique in MATHEMATICA. This research offers a tangible explanation for simulating and analyzing distinct flow properties, like velocity, temperature, concentration, and microorganism motile density fields. The results demonstrate that quadratic thermal radiation produces elevated temperature levels inside blood flow compared to linear and nonlinear radiations. Bumped thermal slip establishes a lower temperature pattern in blood flow, indicating less heat exchange between the blood and the arterial wall. The Nusselt number rises in each instance with the associated rise in the unsteady parameter values. The findings corroborate the conclusions of prior studies.

Studying the patterns of changes in the concentration of components in droplets of binary solutions is critically important for optimization of processes in various industries, including chemistry, pharmaceuticals, and materials science; in designing various types of engines; and in evaporative cooling systems with complex compositions of reacting sprays. This article presents the results of an experimental study of the dynamics of volatile component escape from pendant droplets of aqueous solutions of ethanol, methanol, and acetone in an air flow. The concentration measurements were performed by the capacitance method. The method is based on the dependence of the probe capacitance on the solution permittivity, which is an additive value of the dielectric permittivities of the liquids constituting the solution, the change in the droplet volume during its evaporation taken into account. It is shown that, with an acceptable measurement error, the capacitance method can be used for determination of the concentration of components in a binary mixture droplet with diameter ranging from 1.5 to 3 mm. The experiments have shown that, at identical parameters of the flow around the droplet, the time of complete evaporation of the volatile component was determined by its initial content; the patterns of concentration change in aqueous solutions of acetone, methanol, and ethanol are the same, and, under equal external conditions, are described by a second-order curve. It has been shown that experimental data obtained at different air flow velocities can be generalized through the homochronicity criterion. For a more complete generalization of the experiments, it is necessary to present them in dependence on a complex that includes both the parameters of the ambient medium and the physical properties of liquids under study.

The dynamics of boiling-up of a jet of superheated water has been investigated by experiment at a discharge from a high-pressure chamber through a short oval nozzle. Changes in the shape, the opening angle and the length of the jet spray cone have been traced under changes in thermodynamic parameters (temperature T_s, pressure p_s), corresponding to the phase equilibrium line in a wide range T_s = 383–573 K, p_s = 0.1–8.6 MPa. A manifestation of the jet inversion has been revealed. The droplet size of a boiling-up jet has been determined by the microscopic method. The paper presents data on the particle sizes distribution in a flow in different boiling-up regimes.

The paper presents the results of an experimental study of boiling-up of a jet of superheated distilled water flowing through two short cylindrical nozzles. Data on the change in the shape and angle of the spray cone have been obtained. The length of a jet of metastable liquid has been studied. The droplet composition of boiling-up water has been analyzed by the microscopy method. It has been found that when a superheated liquid flows through two identical cylindrical nozzles, there is no complete opening of the flow.

Filmwise condensation of vapor is used in the vast majority of modern industrial condensers. This is a rather complex phenomenon, associated with the necessity of taking into account various interrelated factors, including the influence of the vapor velocity on the condensation process. This work is part of a series of review articles addressing the basics of hydrodynamics and heat transfer during vapor condensation on smooth and finned horizontal tubes. The main focus of the work is on the hydrodynamics and heat transfer during filmwise condensation of moving (including fast-moving) vapor. The purpose of this brief review is to present our own experimental results and those available in scientific literature that are of fundamental importance for understanding the process under study and will also be useful in designing of filmwise condensers.

Impinging round parallel jets are one of the simplest and mostefficient tools of heat and mass transfer enhancement and they areapplied in cooling electronic equipment, gas turbine blades,combustion chamber walls, etc. As a rule, these devices use asystem of jets. One of the simple ways to study the interaction ofa jet array is to study the interaction between two jets. However,even with this approach, there are a large number of parametersthat affect the process of jet interaction: the distance betweenthe jets, the ratio of diameters, the ratio of flow rates, etc.,and this greatly complicates the description of characteristics ofthe interaction of turbulent jets with each other and with thesurface. Moreover, in a jet array, each jet is surrounded by atleast two jets, so in this work we investigated heat transfer oftwo- and three-jet cooling and looked for differences betweenthem. In the experiments, the distances between the jets and fromthe nozzle to the surface were varied. Local heat transfercharacteristics were analyzed using infrared thermography. It wasfound that at distance s/D (=) 1.2, the distribution of local Nufor the three-jet interaction differs significantly from thetwo-jet interaction, however, at s/D (=) 1.8, there are almost novisible distinguishing characters.