Актуальные вопросы теплофизики и физической гидрогазодинамики

A new model for heating and evaporation of a droplet on a superhydrophobic surface will be described. The model uses the analytical solution to the spherically symmetric heat transfer equation with the source term which is implemented in the numerical code and used at each time step of the calculations. It was assumed that heat supplied by conduction and radiation from the substrate to the droplet is instantaneously and homogeneously distributed throughout the whole droplet volume. A new approach to the verification of the predictions of the earlier developed model of puffing/micro-explosion in multi-component composite droplets will be described. The results of the generalization latter model to consider the shifting of the water sub-droplet away from the centre of the fuel droplet will be presented.

Boiling and droplet condensation are major phase change phenomena. Performance enhancements in these phase change phenomena can be achieved with surface modification. One of the most promising approaches includes the use of biphilic surfaces, which have mixed wettability on the surface. Phase change on biphilic surfaces and optimization efforts for various biphilic surfaces in both boiling and dropwise condensation will be covered in this lecture.

Droplet dynamics on a heated surface plays an important role in applications ranging from spray cooling to solidification and pharmaceuticals. A liquid droplet placed on a heated substrate which is at a significantly higher temperature compared to the saturation temperature of the liquid hovers over a thin film of vapor. This film boiling regime of the droplet is termed as the Leidenfrost (LF) state and is detrimental to heat transfer due to the low thermal conductivity of the vapor. The transition boiling regime is characterized by intermittent contacts between the heated substrate and the liquid droplet and marks the transition between vigorous nucleate boiling and film boiling. Here, we show that in the transitional boiling regime, an unconstrained droplet exhibits trampolining where the droplet bounces to higher heights with each consecutive contact with the substrate. I will discuss the role of substrate morphology and permeability on the excess vapor gap established beneath the droplet during the film boiling regime. I will also discuss the different modes of bouncing and trampolining of a Leidenfrost droplet on a heated substrate and the influence of substrate temperature.

The vast majority of natural and technical flows are turbulent. While turbulence is beneficial for engineering applications where effective mixing and heat transfer are important, it also has dramatic negative effects. For example, turbulence causes the annoying whistling of wind turbines, the dramatic rumbling of jet engines, and it can trigger resonances and pressure fluctuations in gas and water turbines, which drastically reduces the efficiency and operability of electric power plants.
Thanks to immense advances in large-scale numerical simulation and high-performance computers, we are now able to simulate turbulent flows with high accuracy. However, such simulations alone neither reveal the mechanism that drives turbulence, nor do they tell us how to control turbulence in a beneficial way.
In this talk linearized mean field analysis of turbulent flows is introduced. This physics-based method uncovers the driving mechanisms that lead to the formation of turbulent structures and it offers an analytic framework for turbulent flow control. The core idea is to build a linearized operator from a set of governing equations and analyse this operator using stability and resolvent analysis. The method will be demonstrated for different technical applications within the field of aeroacoustics, thermoacoustics and instability control. The talk will conclude with an overview of future challenges and opportunities.

Closed-loop turbulence control has current and future engineering applications of truly epic proportions, including cars, trains, airplanes, jet noise, air conditioning, medical applications, wind turbines, combustors, and energy systems, i.e., well-known topics presented in this conference. Recently, Artificial Intelligence (AI) / Machine Learning (ML) has opened game-changing new avenues (Brunton & Noack 2015): the automated model-free discovery and exploitation of unknown nonlinear actuation mechanisms directly in the plant - included automated reduced-order modeling of the plant. In this talk, we review recent successes on these avenues towards broadband frequency turbulence control with distributed actuation/sensing.

The removal of surface-attached particles with cavitation bubbles is usually attributed to the jetting or shear stresses when bubbles collapse. In this Letter, we report an unexpected phenomenon that millimeter-sized spherical particles made of heavy metals (e.g., stainless steel), when initially resting on a fixed rigid substrate, are suddenly accelerated like projectiles through the production of nearby laser-induced cavitation bubbles of similar sizes. We identify two dominant regimes for the particle's sudden acceleration, namely, the unsteady liquid inertia dominated regime and the bubble contact dominated regime. We find the nondimensional maximum vertical displacement of the particle follows the fourth power and the square power scaling laws for respective regimes, which is consistent with the experimental results. Our findings can be applied to nonintrusive particle manipulation from solid substrates in a liquid.

Краткий обзор спектров атмосферной турбулентности и результатов лабораторных экспериментов по турбулентности в тонких слоях. Немного теории и обсуждение возможных связей между явлениями.

Spray cooling is a promising thermal management solution for high-heat-flux electronics. To facilitate the application of spray cooling in electronics cooling, we have improved the experimental system by designing a high heat flux heat source and an electronic device. A relatively high critical heat flux and better temperature uniformity have been achieved. A quantitative evaluation of parameters has been proposed to provide guidance for the performance enhancement of spray cooling system and to facilitate the high-heat-flux heat dissipation in electronic devices.

В рамках лекции будет рассказано о принципах работы на Новом Физтехе университета ИТМО: науке в России на мировом уровне, элитном физическом образовании и важности организационных вопросов в эффективном функционировании научно-образовательных подразделений.

Лаборатория новых магнитных материалов была создана в Балтийском федеральном университете им. И. Канта в 2013 году, в 2022 году это структурное подразделение - научно-образовательный центр, занимающийся не только наукой, но и образованием, просветительской и организационной деятельностью. Зачем? Рассмотрим механизмы запуска, развития, ловушки на пути становления и инструменты поддержки научного сообщества.

В докладе обсуждаются ключевые задачи и сложности, возникающие при работе молодежных научных лабораторий. Представлены возможные треки развития членов коллективов таких лабораторий. Выделена связь работы лабораторий с образовательными программами в вузах. Определены перспективные шаги для развития лабораторий с учетом совокупности внешних и внутренних факторов.