Effect of heater size on heat transfer in a falling liquid film

Проведены расчеты полей скорости и температуры, а также положение границы раздела жидкость-газ при стекании тонкой пленки жидкости по плоской подложке, наклоненной к горизонту. На подложке расположен нагреватель квадратной формы, мощность которого фиксирована, а размеры варьировались в ходе расчетов:- одним из перспективных методов отвода высоких тепловых потоков от электронного оборудования являются технологии, использующие тонкие пленки жидкости, движущиеся по охлаждаемой поверхности. Целью работы было исследование зависимости динамики и теплообмена в пленки от размера нагревателя;- на основе разработанной трехмерной нестационарной модели движения проведены расчеты теплообмена в движущейся поенке. При этом учитывалось действие всех основных физческих факторов при их взаимодействии: диффузионный и конвективный теплопереносы, зависимость вязкости от температуры, термокапиллярный эффект, появление и эволюция поверхностных деформаций;- установлено, что размер нагревателя существенно влияет на поля температуры и поверхностные деформации, а также на значение температурных экстремумов. Выведена аналитическая формула для расчета наибольшего достигаемого на подложке превышения температуры её среднего значения;- результаты могут применяться при проектировании систем охлаждения электронного оборудования. On the basis of the developed three-dimensional non-stationary model of motion, calculations of heat transfer in a moving roll were carried out. In this case, the action of all the main physical factors during their interaction was taken into account: diffusion and convective heat transfer, the dependence of viscosity on temperature, the thermocapillary effect, the appearance and evolution of surface deformations.  it was found that the size of the heater significantly affects the temperature fields and surface deformations, as well as the value of temperature extremes. An analytical formula is derived for calculating the maximum temperature rise attainable on the substrate of its average value.

Heat transfer in a centrifugal vortex tube

The results of an experimental study of the heat flux in a model of a centrifugal vortex apparatus with a lower rotating disk are presented. An experiment considered three cases at a distance between the disks H=R/2 and H=R: “water”, “water-air”, and “water-oil”. Using the colorimetric method, the dependence of the heat flux on Reynolds is shown. The case “water-air” was chosen to evaluate the contribution to heat exchange from the thermocapillary effect (Marangoni) at high Re. For the case of two immiscible liquids of different densities (water-oil), the effect of “centrifugal levitation” is found.

Numerical studies of the advective flow of heptadecane in a horizontal layer with a longitudinal temperature gradient at the lower boundary

Numerical studies of the convective flow of heptadecane in a horizontal layer with a suddenly applied longitudinal temperature gradient at the lower high-thermal conductivity boundary have been carried out by the finite element method. A system of nonstationary dimensionless equations of free convection containing stream function, velocity vortex, and temperature as variables was solved. The calculations were carried out with a free upper boundary with and without taking into account the influence of the thermocapillary effect.

Studying the surfactant dynamics at non-isothermal liquid surface with thermography

The dynamics of liquid multiphase systems largely depends on the conditions on the interface. The behavior of a system with adsorbed surfactant layers at the interface boundaries may differ qualitatively from the behavior of a system with pure surface. The experimental study of such systems is difficult, since the presence of adsorbed layer can most often be judged only by indirect signs. Therefore, most of the research is carried out by numerical modeling. Unfortunately, the currently existing numerical studies of liquid multiphase systems with adsorbed surfactant layer are far from perfect due to numerous simplifications and approximations assumed in theoretical models. In this paper, we propose a new approach for visualization and studying the boundary between a clean surface and an adsorbed surfactant layer. It is based on the comparison of track images of the fluid motion in the volume and the registration of the temperature distribution at the interface boundary. This approach made it possible to unambiguously associate the characteristic regions on the temperature profile with the position of the so-called stagnation point. The proposed method for visualizing the stagnation point can be useful in a number of problems of interface hydrodynamics based on the thermocapillary effect.

Experimental Study on Coherent Structures by Particles Suspended in Half-Zone Thermocapillary Liquid Bridges: Review

Coherent structures by the particles suspended in the half-zone thermocapillary liquid bridges via experimental approaches are introduced. General knowledge on the particle accumulation structures (PAS) is described, and then the spatial–temporal behaviours of the particles forming the PAS are illustrated with the results of the two- and three-dimensional particle tracking. Variations of the coherent structures as functions of the intensity of the thermocapillary effect and the particle size are introduced by focusing on the PAS of the azimuthal wave number m=3. Correlation between the particle behaviour and the ordered flow structures known as the Kolmogorov–Arnold—Moser tori is discussed. Recent works on the PAS of m=1 are briefly introduced.

Inverse-thermocapillary evaporation in a thin liquid film of self-rewetting fluid

Purpose The present study aims to investigate the inverse-thermocapillary effect in an evaporating thin liquid film of self-rewetting fluid, which is a dilute aqueous solution (DAS) of long-chain alcohol. Design/methodology/approach A long-wave evolution model modified for self-rewetting fluids is used to study the inverse thermocapillary characteristics of an evaporating thin liquid film. The flow attributed to the inverse thermocapillary action is manifested through the streamline plots and the evaporative heat transfer characteristics are quantified and analyzed. Findings The thermocapillary flow induced by the negative surface tension gradient drives the liquid from a low-surface-tension (high temperature) region to a high-surface-tension (low temperature) region, retarding the liquid circulation and the evaporation strength. The positive surface tension gradients of self-rewetting fluids induce inverse-thermocapillary flow. The results of different working fluids, namely, water, heptanol and DAS of heptanol, are examined and compared. The thermocapillary characteristic of a working fluid is significantly affected by the sign of the surface tension gradient and the inverse effect is profound at a high excess temperature. The inverse thermocapillary effect significantly enhances evaporation rates. Originality/value The current investigation on the inverse thermocapillary effect in a self-rewetting evaporating thin film liquid has not been attempted previously. This study provides insights on the hydrodynamic and thermal characteristics of thermocapillary evaporation of self-rewetting liquid, which give rise to significant thermal enhancement of the microscale phase-change heat transfer devices.