Three-dimensional simulation of interfacial convection in CO_2–ethanol system by hybrid lattice Boltzmann method with experimental validation

By using a hybrid lattice-Boltzmann–finite-difference method(hybrid LBM–FDM method),three-dimensional simulations of solutal interfacial convection were conducted for the process of CO2absorption into ethanol.A self-renewal interface model is adopted as an interfacial perturbation model.The simulation results revealed some three-dimensional features of the induced interfacial convection,such as the development of diverging cellular flow and Rayleigh plume-like convection in liquid phase.The concentration distribution of the simulation result is validated and found to be in well agreement with the Schlieren visualization results qualitatively.Additionally,the mass transfer enhancements by interfacial convection were investigated via both simulation and experiment for the absorption process,and the mass transfer is shown to be enhanced by the interfacial convection by about two-fold comparing with that by diffusion.

Simulation of interfacial Marangoni convection in gas-liquid mass transfer by lattice Boltzmann method

Interfacial Marangoni convection has signifi-cant effect on gas-liquid and/or liquid-liquid mass transfer processes.In this paper,an approach based on lattice Boltzmann method is established and two perturbation models,fixed perturbation model and self-renewable interface model,are proposed for the simulation of interfacial Marangoni convection in gas-liquid mass transfer process.The simulation results show that the concentration contours are well consistent with the typical roll cell convection patterns obtained experimentally in previous studies.

Bionic Research on Fish Scales for Drag Reduction

To reduce friction drag with bionic method in a more feasible way, the surface microstructure of fish scales was analyzed attempting to reveal the biologic features responding to skin friction drag reduction. Then comparable bionic surface mimicking fish scales was fabricated through coating technology for drag reduction. The paint mixture was coated on a substrate through a self-developed spray-painting apparatus. The bionic surface with micron-scale caves formed spontaneously due to the interra- cial convection and deformation driven by interfacial tension gradient in the presence of solvent evaporation. Comparative experiments between bionic surface and smooth surface were performed in a water tunnel to evaluate the effect of bionic surface on drag reduction, and visible drag reduction efficiency was obtained. Numerical simulation results show that gas phase de- velops in solid-liquid interface of bionic surface with the effect of surface topography and partially replaces the solid-liquid shear force with gas-liquid shear force, hence reducing the skin friction drag effectively. Therefore, with remarkable drag re- duction performance and simple fabrication technology, the proposed drag reduction technique shows the promise for practical applications.

Theoretical and experimental advances on heat transfer and flow characteristics of metal foams

Open cell metal foam can be applied to greatly improve thermal performance of heat sink and heat exchanger,so that it has been widely used in the fields of thermal(or heat)control system of aerospace vehicle and energy utilization system and become a very important topic for research in the aerospace thermophysics field,and more and more attentions have been attracted.The optimal design of metal foam heat transfer devices is based on the understanding the flow and heat transfer characteristics in metal foam.This article reviews some recent progresses of theoretical and experimental researches on heat transfer enhancement and flow characteristics of metal foam.We found that the pore cell simplification models of metal foams generally fall into four categories,among which the most commonly used cell model is Kelivin model.Some exploratory works performed by the current authors are also introduced,such as the effect of boundary conditions on the heat transfer enhancement;the theoretical modelling of interfacial convective heat transfer taking into account heat conduction between foam ligaments;and the flow characteristics under relatively high velocity.The analytical results show that the flow characteristics of metal foam at relatively high speed are completely different from those at low speed,a further thorough study of the heat transfer and flow characteristics of metal foam is necessarily required.In this paper,two types of partial filling techniques are discussed.The heat transfer performance of partially filled tubes was evaluated by both the performance evaluation criteria and the performance evaluation plot of enhanced heat transfer techniques oriented for energy-saving.The results show that the filling type of metal foam have a significant impact on its heat transfer enhancement performance.Therefore,the filling method of metal foam should be further studied,in order to optimize the thermophysical properties of heat transfer devices.