We present a scheme to extract information about plumes, a prominent coherent structure in turbulent thermal convection, from simultaneous local velocity and temperature measurements. Using this scheme, we study the temperature dependence of the plume velocity and understand the results using the equations of motion. We further obtain the average local heat flux in the vertical direction at the cell center. Our result shows that heat is not mainly transported through the central region but instead through the regions near the sidewalls of the convection cell. where v is the velocity field, p the pressure divided by density, T the temperature field, andẑ is the unit vector in the vertical direction. Furthermore, δT = T − T 0 where T 0 is the mean temperature of the bulk fluid, g is the acceleration due to gravity and α, ν, and κ are respectively the volume expansion coefficient, kinematic viscosity and thermal diffusivity of the fluid. The state of fluid motion is characterized by the geometry of the cell and two dimensionless parameters: the Rayleigh number, Ra = αg∆L 3 /(νκ), which measures how much the fluid is driven and the Prandtl number, Pr = ν/κ, which is the ratio of the diffusivities of momentum and heat of the fluid. Here ∆ is the maintained temperature difference between the bottom and the top, and L is the height of the cell. When Ra is sufficiently large, the convective motion becomes turbulent. In turbulent convection, local velocity and temperature measurements taken at a point within the convection cell display complex fluctuations in time. On the other hand, visualization of the flow reveals recurring coherent structures. One prominent coherent structure is a plume, which is a mushroom-like flow generated by buoyancy. Thus at least two strategies can be employed to study turbulent thermal convection or turbulent flows in general. One is to analyze and understand the fluctuations of the local measurements. The other is to characterize the coherent structures and study and understand their dynamics. These two approaches are not independent but provide complementary knowledge of turbulent flows. In particular, there is the natural question of whether and how information about the coherent structures can be extracted from the local measurements.For turbulent flows not driven by buoyancy, various methods including proper orthogonal decomposition, conditional sampling and wavelet analysis have been proposed to identify coherent vortical structures from local velocity measurements [2]. On the other hand, much less work has been done in identifying plumes or extracting information about plumes in turbulent thermal convection [3,4,5]. Belmonte and Libchaber[3] used the skewness of the temperature derivative as a signature of the plumes. Zhou and Xia[4] associated the difference in the skewness of the positive and negative parts of the temperature difference with the presence of plumes and identified the plumes whenever the temperature difference becomes larger than a chosen threshold [6]. In Ref.[5], plu...
Interfacial dynamics and heat transfer are encountered in a great number of industrial technologies; for example, engines, boilers, turbines, heat exchangers, condensers, fuel cells, microchip cooling systems, enhanced oil recovery technologies, etc. The research topics of interfacial dynamics and heat transfer have attracted continuous attention in multiple disciplines including thermal physics, fluid mechanics, and multiphase flows. To promote the development and optimization of those industrial technologies, understanding-from both fundamental and application viewpoints-of the fluid flows, heat and mass transfer, interfacial dynamics including interface deformation and morphology change, and their mutual couplings plays an extremely important role. However, there are still many challenges to fully understand these complex phenomena, since they often appear at multiscales, i.e., in macro-, meso-, micro-, and nano-scales. In addition, interfacial dynamics and heat transfer are usually involved with many other multiple physical and/or chemical processes simultaneously in industrial technologies, e.g., electrical field, magnetic field, acoustic field, chemical concentration field, chemical and electrochemical reactions, etc. It seems that interdisciplinary research using experimental, theoretical, and numerical approaches could be the right way to explore these complex phenomena and reveal their governing principles and mechanisms. This special issue of Interfacial Dynamics and Heat Transfer is a collection of research papers involved in the interdisciplinary research area of interfacial phenomena, heat and mass transfer, and related multidisciplinary applications, in which several advanced research methods including theoretical, numerical, and experimental approaches are used. In the initial call of this issue, five specific topics are included: (1) nano-and micro-structured surfaces for enhancement of phase change phenomena; (2) contact line phenomena, droplets, spray, film flows, dry spots formation, wettability effect; (3) boiling, nucleation, bubbles, entrainment, critical heat flux; (4) thermocapillary flows, instability, interfacial wave, evaporation, condensation; and (5) two-phase flows, and heat and mass transfer in microchannels and ministructures. All papers in this special issue have undergone a peer-review process to meet the high-quality requirements of the journal of Interfacial Phenomena and Heat Transfer. The Guest Editors would like to express our gratitude to all contributing authors and invited reviewers for their great efforts.
This paper presents a numerical work on the effect of wick construction on the isothermal performance of an annular heat pipe. Two type connection wick structures were designed, the axial direction connection wick structure and radial direction connection wick structure. A three-dimensional symmetrical model with liquid-vapor phase transition was built. The isothermal performance of the annular part at the front end of the heat pipe was good, the temperature of liquid pool part was about 5-6 K higher than the annular part, and the isothermal performance of axial direction connection wick structure is better than radial direction connection wick structure. The influence of the wick on the vapor flow will affect the vapor temperature distribution, the isothermal surface distribution is obviously the same as the form of the axial direction connection wick at the outlet of the liquid pool, and the isothermal surface will rotate with the axial direction connection wick structure.
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