This study investigates the use of X-ray microtomography (XMT) to reveal the structure of complex porous biological tissues and the fluid flow through them during wetting. It also evaluates fluid dynamical simulations based on XMT data to reproduce and analyse these flows, with a final aim of revealing fluid transport and void formation in such tissues. To fulfil the objectives, the wetting flow of a polymer liquid through an initially dry conditioned Norway spruce wood sample is visualised using XMT at the MAX IV synchrotron. The liquid flow front progression captured after 24 s and 48 s reveals uneven filling of longitudinal tracheids and flow between them via the tiny pits which connect tracheids. Most tracheids fill between 24 and 48 s, possibly due to removal of air inclusions. Large density gradients near cell walls suggest that the fluid followed and deposited along wall structures. Computational fluid dynamics simulations (CFD) of saturated flow through the tomography-based geometry indicate velocity profiles that resemble pipe flow in longitudinal tracheids and flow rate differences among them. The latter indicates that the geometry itself may cause the experimentally observed uneven flow. Streamlines show intra-tracheid flow development and clear flow direction change at the pits. Additionally, wetting simulations, using a constant contact angle, capture initial uneven filling between the tracheids on shorter time scales than could be capture by the experiments. These simulations furthermore show air entrapment during filling, consistent with experimental observations. Combining XMT with CFD enables detailed studies of flow in biological porous media. Faster X-ray scanning, incorporating dynamic contact angles and accounting for diffusion in simulations could further refine insights into fluid progression during capillary-driven flow into complex structures of porous biological tissues.

In this study, a three-dimensional hydrodynamic model is developed to investigate diurnal thermal dynamics induced by pumped hydropower storage operations. At this stage, the focus is on thermal mixing in a generic reservoir, with the aim of providing a methodology that can be adapted to various reservoir scenarios. Key issues include enhancing the understanding of how numerical grid resolution impacts modeling results and demonstrating a method for conducting mesh studies in standing water bodies influenced by flow fields, such as those generated by pumping. The model, being implemented in Delft3D FM, is designed to simulate the upper reservoir of a pumped hydropower plant under initial conditions of thermal stratification. A systematic mesh study was conducted by varying cell sizes in different directions to evaluate their influence on the modeling results. A Richardson analysis shows that the longitudinal resolution, along the main reservoir direction, has minimal impact, while the vertical and the lateral resolutions are critical to avoid thin layers in the mesh and prevent oscillations and numerical inaccuracies. The research demonstrates that pumped hydropower operations alter the thermal regime in the upper reservoir, leading to thinning and temperature fluctuations in the epilimnion, as well as weakening the thickness and strength of the thermocline. Additionally, these operations promote the formation of a large-scale recirculation zone. The adaptable model framework allows for changes in bathymetry, initial stratification conditions, and pumping scenarios, enabling new insights into general temperature dynamics and mixing patterns. 

Iron ore pellet production processes produce large amounts of CO2 emissions when burning fossil fuels. One example is the grate-kiln process, where normally a coal flame is used to indurate pellets. To mitigate the emissions, coal used in rotary kilns can be replaced with for example hydrogen. However, the fuel is mixed with secondary process air, and replacing a solid fuel with a gaseous one changes the mixing characteristics. This demands different means of injecting the fuel. A coaxial jet can be used to control the mixing of fuel and secondary air, as well as the flow field. The aim is to control the mixing of hydrogen and secondary air to achieve a hydrogen flame that is similar to the reference coal flame. This study numerically investigates different coaxial jet configurations. Steady-state simulations of a simplified model of the real kiln are performed using a Reynolds Stress turbulence model. Results show that decreasing the momentum flow ratio between the outer and inner jet, 𝑀jet, to a certain value delays the spread of the hydrogen jet and thus gives a longer jet. Further decreasing this ratio gives an even longer jet, but has the side effect of producing recirculation of hydrogen.

This review article provides a comprehensive overview of the fundamentals, modelling approaches, experimental studies, and challenges associated with hydrogen gas flow in pipelines. It elucidates key aspects of hydrogen gas flow, including density, compressibility factor, and other relevant properties crucial for understanding its behavior in pipelines. Equations of state are discussed in detail, highlighting their importance in accurately modeling hydrogen gas flow. In the subsequent sections, one-dimensional and three-dimensional modelling techniques for gas distribution networks and localized flow involving critical components are explored. Emphasis is placed on transient flow, friction losses, and leakage characteristics, shedding light on the complexities of hydrogen pipeline transportation. Experimental studies investigating hydrogen pipeline transportation dynamics are outlined, focusing on the impact of leakage on surrounding environments and safety parameters. The challenges and solutions associated with repurposing natural gas pipelines for hydrogen transport are discussed, along with the influence of pipeline material on hydrogen transportation. Identified research gaps underscore the need for further investigation into areas such as transient flow behavior, leakage mitigation strategies, and the development of advanced modelling techniques. Future perspectives address the growing demand for hydrogen as a clean energy carrier and the evolving landscape of hydrogen-based energy systems.

A reliable battery thermal management system plays a crucial role in the safe, efficient, and long-term operation of a high-performance lithium battery system. This study evaluates the temperature rise, pressure drop, capacity loss, and cyclical cost of an air-cooled battery system consisting of 90 cylindrical battery cells placed ina staggered arrangement in the module. The effect of spacing between the adjacent cells and inflow velocity is investigated for the battery system operating at high charge/discharge rates of 3C and 5C. The results demonstrate that the hybrid model, which consists of the battery life model integrated with the simplified modeling approach for the thermal evaluation of battery packs, provides a cost-effective tool for multi-objective analysis and optimization of air-cooled battery packages.The results reveal that the air-based cooling system has the potential to fulfill the safety standards in all studied cases, and employing battery modules with larger cell spacing at a constant inflow velocity may reduce the maximum temperature, pressure drop, and cyclical cost by up to 2.14%, 93.36%, and 35.69%, respectively, while extending the lifespan of the battery system by up to 55.45%. However, it is found that the air-based cooling system approaches its limit of thermal performance at high inflow velocities. A novel index (MCR index) is proposed in this paper to characterize the limitationsassociated with adjusting cell spacing for air-based battery cooling systems. It is observed that for systems with an MCR index beyond 600, the effect of cell spacingon thermal performance becomes negligible. This can be used as a useful guideline for optimizing air-based battery thermal management systems or integratingthem with other cooling methods.

Sheet Moulding Compound (SMC) based composites have a large potential in industrial contexts due to the possibility of achieving comparatively short manufacturing times. It is however necessary to be able to numerically predict both mechanical properties as well as manufacturability of parts.

In this paper a fully 3D, semi-empirical model based on fluid mechanics for the compression moulding of SMC is described and discussed, in which the fibres and the resin are modelled as a single, inseparable fluid with a viscosity that depends on volume fraction of fibres, shear strain rate and temperature. This model is applied to an advanced carbon-fibre SMC with a high fibre volume fraction (35%). Simulations are run on a model of a squeeze test rig, allowing comparison to experimental results from such a rig. The flow data generated by this model is then used as input for an Advani-Tucker type of model for the evolution of the fibre orientation during the pressing process. Numerical results are also obtained from the software 3DTimon. The resulting fibre orientation distributions are then compared to experimental results that are obtained from microscopy. The experimental measurement of the orientation tensors is performed using the Method of Ellipses. A new, automated, accurate and fast method for the ellipse fitting is developed using machine learning. For the studied case, comparison between the experimental results and numerical methods indicate that 3D Timon better captures the random orientation at the outer edges of the circular disc, while 3D CFD show larger agreement in terms of the out-of-plane component. One of the advantages of the new image technique is that less work is required to obtain microscope images with a quality good enough for the analysis.

In recent years, wall-bounded cross-flow heat exchangers have gained significant attention for battery cooling applications. Due to similarities in geometry, these systems are often evaluated based on the heat and flow knowledge of free cross-flow heat exchangers. To determine the reliability of this assumption, this study performs a numerical comparison of the thermo-fluid behavior of wall-bounded and free cross-flow heat exchangers. Both heat exchangers have similar dimensions, with transverse and longitudinal pitch ratios of 2.074 and 1.037, respectively, and are investigated at a Reynolds number of 40000 using the Unsteady Reynolds-Averaged Navier–Stokes (URANS) method. It is observed that the  transition model provides the most accurate predictions of the flow field when compared to available experimental data. The results suggest that for wall-bounded heat exchangers with an aspect ratio of 2 or larger, the flow behavior in the central flow region resembles that of a free heat exchanger, but with varying magnitudes due to the increase in velocity in the core region to counterbalance the reduction near the walls. The area-averaged mean Nusselt number from 2D and 3D models for free heat exchangers shows no significant difference compared to wall-bounded heat exchangers. However, there are considerable differences in the local Nusselt number distributions in the angular and spanwise directions. Overall, it is determined that certain conditions must be satisfied to ensure that applying the thermo-fluid characteristics of a free cross-flow heat exchanger to wall-bounded cross-flow heat exchangers in battery thermal management systems is accurate.

Purpose

The purpose of this paper is to present a fast and bare bones implementation of a numerical method for quickly simulating turbulent thermal flows on GPUs. The work also validates earlier research showing that the lattice Boltzmann method (LBM) method is suitable for complex thermal flows.

Design/methodology/approach

A dual lattice hydrodynamic (D3Q27) thermal (D3Q7) multiple-relaxation time LBM model capable of thermal DNS calculations is implemented in CUDA.FindingsThe model has the same computational performance compared to earlier publications of similar LBM solvers. The solver is validated against three benchmark cases for turbulent thermal flow with available data and is shown to be in excellent agreement.

Originality/value

The combination of a D3Q27 and D3Q7 stencil for a multiple relaxation time -LBM has, to the authors’ knowledge, not been used for simulations of thermal flows. The code is made available in a public repository under a free license.

Recent studies have revealed that effective thermal management systems are necessary to maintain the performance, lifespan, and safety of lithium battery systems. A unique and novel modeling approach is presented in this work with the aim of estimating the thermal performance of air-based cooling systems for large-scale lithium battery packages. The overall model consists of sub-models, including an analytical model for battery cells and a numerical heat and flow model for the battery module, which are validated against experimental data and empirical correlations, respectively. The chosen approach implies that the sub-models can operate independently, allowing accurate transient simulations with reduced processing time. The model is employed to evaluate the effect of cell spacing on the thermal performance of an air-cooled battery system designed for a hybrid electric vehicle. The results demonstrate that the maximum temperature within the cells positively correlates with transverse and longitudinal pitch ratios; however, the maximum temperature difference in the module has a negative correlation with these pitch ratios. In contrast, temperature uniformity shows non-monotonic behavior, making it an applicable criterion to balance between temperature rise and thermal gradients. Moreover, considerable temperature non-uniformity is noted in the early rows, which becomes less significant as pitch ratios decrease.