Investigation of mass transfer model of CO_(2) absorption with Rayleigh convection using multi-relaxation time lattice Boltzmann method

CO_(2) absorption into absorbents is a widely used method to reduce carbon emissions,in which the concentration gradient near the gas-liquid interface may induce Rayleigh convection(RC).Once RC occurs,the mass transfer rate will be significantly enhanced.Therefore,it is necessary to explore the mass transfer enhancement mechanism further and develop a penetration/surface divergence hybrid mass transfer model.In this study,we conduct research on the process of CO_(2) absorption into ethanol with RC.Firstly,we use a multi-relaxation time lattice Boltzmann method to simulate the absorption process and obtain the flow and concentration fields.And we also verify the reliability of the numerical simulation results by comparing with the experimental results.Then,we analyze the characteristics of non-uniform flow and concentration fields in RC.Moreover,we divide the near-interface region into diffusion-dominated and convection-dominated mass transfer zones by checking whether the horizontal average velocity is greater than 1.0×10^(-4) m·s^(-1).Furthermore,based on the differences in mass transfer mechanisms of the aforementioned two zones,we propose a penetration/surface divergence hybrid model to predict the instantaneous mass transfer coefficient.The prediction results demonstrate that the hybrid model can precisely predict the instantaneous mass transfer coefficient of the entire CO_(2) absorption process.Our proposed hybrid model provides a promising way to deal with the complex mass transfer problems with non-uniform flow and concentration fields.

Flow structures of turbulent Rayleigh-Benard convection in annular cells with aspect ratio one and larger

We present an experimental study of flow structures in turbulent Rayleigh-Bénard convection in annular cells of aspect ratiosΓ=1,2 and 4,and radius ratio 0.5.The convecting fluid is water with Prandtl number Pr=4.3 and 5.3.Rayleigh number Ra ranges 4.8×10^(7)≤Ra≤4.5×10^(10).The dipole state(two-roll flow structure)forΓ=1 and the quadrupole state(fourroll flow structure)forΓ=2 and 4 are found by multi-temperature-probe measurement.Nusselt number Nu is described by a power-law scaling Nu=0.11Ra^(0.31),which is insensitive to the change of flow structures.However,the Reynolds number Re is influenced by increasing aspect ratios,where Re is found to scale with Ra andΓas Re~Ra^(0.46)Γ^(-0.52).The normalized amplitudes of two flow structures as a function of Ra exist difference.Based on relative weights of the first four modes using the Fourier analysis,we find that the first mode dominates inΓ=1 cell,but the second mode contains the most energy inΓ=2 and 4 cells.With increasingΓ,the flow structures exhibit different characteristics.

Global Well-posedness for the 2D Micropolar Rayleigh–Bénard Convection Problem without Velocity Dissipation

In this article,we study the Cauchy problem to the micropolar Rayleigh–Bénard convection problem without velocity dissipation in two dimension.We first prove the local well-posedness of a smooth solution,and then establish a blow up criterion in terms of the gradient of scalar temperature field.At last,we obtain the global well-posedness to the system.

Convective stability analysis of a micropolar fluid layer by variational method

This paper studies Rayleigh-B’enard convection of micropolar fluid layer heated from below with realistic boundary conditions.A specific approach for stability analysis of a convective problem based on variational principle is applied to characterize the Rayleigh number for quite general nature of bounding surfaces.The analysis consists of replacing the set of field equations by a variational principle and the expressions for Rayleigh number are then obtained by using trial function satisfying the essential boundary conditions.Further,the values of the Rayleigh number for particular cases of large and small values of the microrotation coefficient have been obtained.The effects of wave number and micropolar parameter on the Rayleigh numbers for onset of stationary instability for each possible combination of the bounding surfaces are discussed and illustrated graphically.The present analysis establishes that the nature of bounding surfaces combination and microrotation have significant effect on the onset of convection.