CO2 sequestration in porous media: experimental data and LB simulations

This study investigates conjugate natural convection in a 2D enclosure with multiple solid blocks, incorporating volumetric thermal radiation. The enclosure features a sinusoidal temperature profile on one side and cooling on the other, with N periodically arranged, thermally conductive blocks. The enclosure has a sinusoidal temperature profile on one side and cooling on the other, with N thermally conductive blocks. The non-orthogonal multi-relaxation time lattice Boltzmann method (NMRT-LBM) is used, employing D2Q9 and D2Q5 schemes for velocity and temperature, respectively. Radiative transfer is modeled using a D2Q8 BGK LBM scheme. The influence of various parameters on heat transfer is explored, including thermal properties, radiation effects (Planck number, emissivity, extinction coefficient), and geometrical factors (solid-to-fluid volume fraction, number of blocks). The accuracy of our model is validated against benchmark problems. Results show that solid fraction and block number significantly impact heat transfer. Wall emissivity enhances heat transfer at low Planck numbers. Conversely, reducing solid fraction, Planck number, and extinction coefficient all improve heat transfer. Interestingly, subdividing the initial block can reduce heat transfer, especially for a large number of blocks and low Planck numbers. These findings highlight the potential of NMRT-LBM as a valuable tool for simulating complex heat transfer phenomena involving thermal radiation, with applications in building design optimization for energy efficiency.

This study introduces a numerical tool that utilizes the non-orthogonal multi-relaxation time lattice Boltzmann method (MRT-LBM) to simulate the coupled thermal and mass diffusion occurring within porous media exposed to naturally convecting moist air flow.The D2Q9 velocity distribution function and separate D2Q5 schemes for temperature and concentration capture double-diffusive convection. The validity of model is established through comparison with a differentially heated porous cavity under varying conditions. Our numerical investigations delve into the influence of key parameters—porosity (ε), Lewis number (Le), Rayleigh number (Ra), buoyancy ratio (Br), and Darcy number (Da)—on flow, temperature, and solute distributions. The resulting isotherms, iso-concentrations, streamlines, Nusselt numbers, and Sherwood numbers reveal an important impact on flow structures and thermal-mass transport mechanisms. Notably, an increased Darcy number enhances both heat and mass transfer. This validated model provides a comprehensive understanding of porous media behavior, potentially informing future building comfort strategies related to thermal management and species transport.

To improve thermal efficiency of such concentrating solar power system (CSP), thermal heat losses from the receiver must be minimized. In this manuscript, convective and radiative heat losses from solar cavity receiver are numerically assessed by using Lattice Boltzmann Method (LBM). Combined natural convection-surface radiation heat transfer mode in open rectangular solar cavity receiver is presented. The two parallel walls are insulated while the wall facing the opening is subjected to a constant temperature with parabolic profile. The open boundary is assumed to be a black surface at ambient temperature while the other walls are diffuse, gray and opaque. LBM-BGK model with double distribution functions (D2Q9-D2Q4) is adopted here to predict dynamic and thermal fields. Effects of heating temperature, inclination angle, radiative proprieties and geometric aspect ratio on heat losses inside the cavity are analyzed and discussed.

It was found that an increasing of the inclination angle induces a large increasing on convective heat loss. Also, by increasing the heating temperature from 200°C to 600°C an amplification of 88% is observed for the total heat loss inside the cavity. On the other hand, the doubling of the aspect ratio of the cavity induces a reduction in thermal losses of about 10%.

“Cardiovascular disease is the world’s biggest killer, as well as the second biggest cause of death in the UK with over three million people suffering from atherosclerotic cardiovascular disease” (UK Government, 2020). Atherosclerosis, the narrowing of arteries due to a build-up of plaque, can be treated through medical interventions such as balloon angioplasty and stent implantation to dilate the stenosed vessel and to restore and maintain physiological blood flow. However, these procedures can result in adverse complications like stent thrombosis and in-stent restenosis. Factors such as stent morphology, stent spacing and stent implantation position alter the local haemodynamic environment, which is known to regulate stent thrombosis. The Lattice Boltzmann method is used to numerically model two-dimensional blood flow around a stent strut to explore how stent morphology affects the local haemodynamics. This method is a niche CFD approach with possible addition of mesoscopic physics, examination of real stent profiles and the coupling of an advection-diffusion equation to obtain relative residence time (RRT) values. Three different stent strut profiles (circular, square and trapezium) from the market are analysed in this work. As these struts had different strut heights, additional simulations that studied the same profiles but with equal strut height were required to highlight the effects of strut profile on local haemodynamics. Metrics of haemodynamics including wall shear stress (WSS), shear rate, RRT and re-circulation region length post strut were measured for each profile. These metrics were then used to assess the thrombogenicity of each stent strut design. The results showed that the circular profile was the least thrombotic profile, with the smallest: (i) max WSS, (ii) max shear rate, (iii) max RRT and (iv) re-circulation region post strut of the three struts. The trapezium shaped profile was the most thrombotic, with the largest of the previously mentioned metrics. Therefore, the simulation results from different stent profiles with equal strut height show that the more streamlined a stent strut is, the less likely stent thrombosis is to occur.

References

UK Government. (2020). UK Government tackles heart disease with new partnership [Press release]. Retrieved from https://www.gov.uk/government/news/uk-government-tackles-heart-disease-with-new-partnership#:~:text=Cardiovascular%20disease%20is%20the%20world%27s

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