A nonlinear multi-scale model for blood circulation in a realistic vascular system

In the last decade, numerical models have become an increasingly important tool in biological and medical science. Numerical simulations contribute to a deeper understanding of physiology and are a powerful tool for better diagnostics and treatment. In this paper, a nonlinear multi-scale model framework is developed for blood flow distribution in the full vascular system of an organ. We couple a quasi one-dimensional vascular graph model to represent blood flow in larger vessels and a porous media model to describe flow in smaller vessels and capillary bed. The vascular model is based on Poiseuille’s Law, with pressure correction by elasticity and pressure drop estimation at vessels' junctions. The porous capillary bed is modelled as a two-compartment domain (artery and venous) using Darcy’s Law. The fluid exchange between the artery and venous capillary bed compartments is defined as blood perfusion. The numerical experiments show that the proposed model for blood circulation: (i) is closely dependent on the structure and parameters of both the larger vessels and of the capillary bed, and (ii) provides a realistic blood circulation in the organ. The advantage of the proposed model is that it is complex enough to reliably capture the main underlying physiological function, yet highly flexible as it offers the possibility of incorporating various local effects. Furthermore, the numerical implementation of the model is straightforward and allows for simulations on a regular desktop computer.

CFD Simulation of CO2 and Methane Adsorption at Various Temperature for MOF-5 using Dual-site and Single-site Langmuir Model

The annual increase in energy demand has led to an increase in greenhouse gas emissions, in particular CO2 emissions from the power generation industry. Carbon Capture and Utilization are technologies applied to capture CO2 gases and transform the gases into a different energy source. The adsorption technology to capture CO2 gases was chosen due to the minimum energy consumption and low costs required for an industrial application for sustainability. Metal-Organic Framework (MOF) has a reasonably high CO2 adsorption capability. It has been applied as an adsorbent for capturing and storing CO2. In this study, a comparison of CFD simulation with experimental CO2 and methane adsorption values in solid adsorbent beds containing MOF-5 at various temperatures was presented. The simulation was performed using 2D and 3D models from 0℃ at STP to 130℃ for CO2 and methane gas molecules. In addition, the isothermal and kinetic adsorption model was added to the simulations. This includes Single- and Dual-Site Langmuir adsorption isotherm and Linear Driving Force. The porous media model was then activated to imitate packed bed adsorbent and measured the pressure drop from the simulation. The results showed that the CO2 adsorption values of MOF-5 decrease as the adsorbent temperature increases. There was a decline of 0.002 mmol/g of adsorbed CO2 molecules per 10-kelvin difference. The CO2 adsorption value was 0.53 mmol/g at STP and 1.15 mmol/g for CH4 at STP. Both CO2 and CH4 adsorption were used to suggest optimal CO2 adsorption for the Pressure Swing Adsorption cycle.

CFD Simulation of Dry Pressure Drop in a Cross-Flow Rotating Packed Bed

The cross-flow rotating packed bed (RPB) has attracted wide attention in recent years because of its advantages of large gas capacity, low pressure drop and lack of flooding limitation. However, the complex structure of the packing makes it difficult to obtain the gas flow characteristics in the cross-flow RPB by experiments. In this study, the dry pressure drop in the cross-flow RPB was investigated by computational fluid dynamics (CFD). The packing was modeled by the porous media model and the rotation of the packing was simulated by the sliding mesh model. The simulation results obtained by three turbulence models were compared with experimental results, and the RNG k-ε model was found to best describe the turbulence behaviors in the cross-flow RPB. Then, the effects of gas flow rate and rotating speed on dry pressure drop in different parts of the cross-flow RPB were analyzed. The results of this study can provide important insights into the design and scale-up of cross-flow RPB.

Numerical Prediction of Homogeneity of Gas Flow through Perforated Plates

Vanes and baffles are often used as flow distributors where uniform flow is required in the apparatus of large cross-section surface areas. As an alternative, perforated plates with a range of open area ratios are applied to produce required gas flow homogeneity. Usually, the plates with various open area ratios are combined into large panels, of which total surface area can reach hundreds of square meters for large-sized industrial apparatus. Numerical modelling of the flow through such panels can be thought of as overly complex, time-consuming, and inefficient due to numerous small open area ratios in the plates and large differences in dimensions between open area ratios and free-stream areas. For this reason, numerical models of gas flow are limited to single plates only with constant open area ratios. A new indirect modelling approach of gas flow through the perforated plates panel with structural elements and various open area ratios with application of the porous media model is proposed. A perforated plate was experimentally investigated in terms of pressure drop and velocity distribution. The data obtained were used for the validation of the numerical results, which differed from the experimental results by less than 5%. In the next step, numerical analyses were performed for plates with open area ratios in the range of 30 to 70% for gas velocities of 5 and 10 m/s. A general correlation for pressure drop as a function of open area ratio was proposed. Finally, systematic numerical studies of the flow through both perforated and porous plates including structural elements were performed. The internal resistance of the porous core was calculated by means of a developed correlation. A good agreement between results with an error lower than 15% was observed.

Numerical Investigation on the Urban Heat Island Effect by Using a Porous Media Model

The urban heat island (UHI) effect resulted from urbanization as well as industrialization has become a major environmental problem. UHI effect aggravates global warming and endangers human health. Thus, mitigating the UHI effect has become a primary task to address these challenges. This paper verifies the feasibility of a three-dimensional turbulent porous media model. Using this model, the authors simulate the urban canopy wind-heat environment. The temperature and flow field over a city with a concentric circular structure are presented. The impact of three factors (i.e., anthropogenic heat, ambient crosswind speed, and porosity in the central area) on turbulent flow and heat transfer in the central business district of a simplified city model with a concentric circular structure were analyzed. It is found that the three-dimensional turbulent porous media model is suitable for estimating the UHI effect. The UHI effect could be mitigated by reducing the artificial heat and improving the porosity of the central city area.

Effect of Gas-Liquid Contact Intensification on Heat and Mass Transfer in Deflector and Rod Bank Desulfurization Spray Tower

The deflector and the rod bank are commonly used to optimize flue gas distribution in the original spray tower (OST) of a wet flue gas desulfurization system (WFGD). In this paper, the internal optimization mechanism of the deflector desulfurization spray tower (DST) and the rod bank desulfurization spray tower (RBST) are studied. Based on the Euler–Lagrange method, the standard k-ε turbulence model, an SO2 absorption model and a porous media model, the numerical simulation of the desulfurization spray tower is carried out with the verification of the model rationality. The results show that there are gas-liquid contact intensification effects in DST and RBST. Compared with OST, gas-liquid contact intensification enhances the heat and mass transfer effects of DST and RBST. The temperature difference between inlet and outlet of flue gas increased by 3.3 K and the desulfurization efficiency of DST increased by 1.8%; the pressure drop decreased by 37 Pa. In RBST, the temperature difference between the flue gas inlet and outlet increased by 5.3 K and the desulfurization efficiency increased by 3.6%; the pressure drop increased by 33 Pa.

Modification of rotary air preheater toward achieving extended life-span utilizing porous media approach: A case study

The main goal of this study is to achieve the extended operating life of the rotary regenerative air pre-heater (Ljungström) of Bandar Abbas power plant by modifying operational parameters by decreasing the corrosion. To achieve this goal, a three-dimensional CFD simulation of the Ljungström is carried out, utilizing the thermal non-equilibrium porous media model. Temperatures are validated against measured data from the power plant with a maximum relative error of 5.54% on the Celsius scale, and mass flow rates are validated with a maximum relative error of −5.25%. The effect of the Ljungström key parameters including the rotational speed, cold layer material, inlet air/flue gas temperature, and mass flow rate, are analyzed in presence of leakages and neglecting it, using porous media approach. The leakage effect is investigated considering radial and axial/peripheral clearances. Finally, a simulation is performed by applying feasible improved parameters extracted from the above analyses considering the effect of all parameters together in presence of leakages, which shows a 6.14% improvement in the Ljungström effectiveness, reducing the total leakage to about one-third of the actual model and eliminating any corrosion.

The Airflow Field Characteristics of UAV Flight in a Greenhouse

The downwash airflow field of UAVs is insufficient under the dual influence of greenhouse structure and crop occlusion, and the distribution characteristics of the flight flow field of UAVs in greenhouses are unclear. In order to promote the application of UAVs in greenhouses, the flow field characteristics of UAVs in a greenhouse were studied herein. In a greenhouse containing tomato plants, a porous media model was used to simulate the obstacle effect of crops on the airflow. The multi-reference system model method was selected to solve the flow field of the UAV. Studies have shown that the airflow field generated by UAV flight in a greenhouse is mainly affected by the greenhouse structure. With the increase in UAV flight height, the ground effect of the downwash flow field weakened, and the flow field spread downward and around. The area affected by the flow field of the crops became larger, while the development of the crop convection field was less affected. The simulation was verified by experiments, and linear regression analysis was carried out between the experimental value and the simulation value. The experimental results were found to be in good agreement with the simulation results.