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Summary: We investigate the transmission of aerosol particles in an airplane cabin with a joint approach using experiments and simulation. Experiments were conducted in a realistic aircraft cabin with heated dummies acting as passengers. A Sheffield head with an aerosol generator was used to emulate an infected passenger and particle numbers were measured at different locations throughout the cabin to quantify the exposure of other passengers. The same setting was simulated with a computational fluid dynamics model consisting of a Lagrange continuous phase for capturing the air flow, coupled with a Lagrange suspended discrete phase to represent the aerosols. Virtual measurements were derived from the simulation and compared with the experiments. Our main results are: the experimental setup provides good measurements well suited for model validation, the simulation does correctly reproduce the fundamental mechanisms of aerosol dispersion and simulations can help to improve the understanding of aerosol transmission for example by visualizing particle distributions. Furthermore, with findings from the simulation it was possible to crucially improve the experimental setup, proving that feedback between the numerical and the hardware world is indeed beneficial. [ABSTRACT FROM AUTHOR]

Diazo compounds are gathering interest for their potential in promoting greener synthesis routes. We investigate, at a lab‐scale, the continuous synthesis of diazo acetonitrile (DAN) using a micro‐structured flow reactor and a flow reaction calorimeter. Data concerning DAN formation in the former, and relative to reaction heat and gas flow rate in the latter, are collected. We present a physical and a grey‐box model, both of which are calibrated to our data. Compared to the physical model, the grey‐box approach allows to better incorporate the complex chemical reaction pathways of DAN. [ABSTRACT FROM AUTHOR]

A novel reactor concept for ammonia decomposition utilizing tail gas from a purification unit as heat supply is presented. The designed micro‐structured reactor integrates both endothermic ammonia decomposition and exothermic tail gas combustion. The reactor and corresponding process are simulated using a mathematical multi‐scale model, which combines the results of multiple detailed computational fluid dynamics simulations into a fast surrogate model. The latter is coupled with a process simulation software via a so‐called container to simulate the entire process. The efficiency of the presented reactor concept is determined and benefits over alternative approaches are highlighted. [ABSTRACT FROM AUTHOR]

Shape optimization of flow fields for electrochemical cells is performed. Simulation models of the flow field are introduced with and without the porous transport layer. The latter model is less detailed and used for shape optimization whereas the former one is used to validate the obtained results. Three objective functions are proposed based on the uniformity of the flow and residence time as well as the wall shear stress. After considering the respective optimization problems separately, techniques from multi‐criteria optimization are used to treat the conflicting objective functions systematically. The results highlight the potential of this approach for generating novel flow field designs for electrochemical cells. [ABSTRACT FROM AUTHOR]

In this paper, we consider the topology optimization for a bipolar plate of a hydrogen electrolysis cell. We present a model for the bipolar plate using the Stokes equation with an additional drag term, which models the influence of fluid and solid regions. Furthermore, we derive a criterion for a uniform flow distribution in the bipolar plate. To obtain shapes that are well‐manufacturable, we introduce a novel smoothing technique for the fluid velocity. Finally, we present some numerical results and investigate the influence of the smoothing on the obtained shapes. [ABSTRACT FROM AUTHOR]

Objectives: We want to investigate whether temperature measurements obtained from MR thermometry are accurate and reliable enough to aid the development and validation of simulation models for Laser-induced interstitial thermotherapy (LITT). Methods: Laser-induced interstitial thermotherapy (LITT) is applied to ex-vivo porcine livers. An artificial blood vessel is used to study the cooling effect of large blood vessels in proximity to the ablation zone. The experimental setting is simulated using a model based on partial differential equations (PDEs) for temperature, radiation, and tissue damage. The simulated temperature distributions are compared to temperature data obtained from MR thermometry. Results: The overall agreement between measurement and simulation is good for two of our four test cases, while for the remaining cases drift problems with the thermometry data have been an issue. At higher temperatures local deviations between simulation and measurement occur in close proximity to the laser applicator and the vessel. This suggests that certain aspects of the model may need some refinement. Conclusion: Thermometry data is well-suited for aiding the development of simulations models since it shows where refinements are necessary and enables the validation of such models. [ABSTRACT FROM AUTHOR]

We model a microchannel cooling system and consider the optimization of its shape by means of shape calculus. A three‐dimensional model covering all relevant physical effects and three reduced models are introduced. The latter are derived via a homogenization of the geometry in 3D and a transformation of the three‐dimensional models to two dimensions. A shape optimization problem based on the tracking of heat absorption by the cooler and the uniform distribution of the flow through the microchannels is formulated and adapted to all models. We present the corresponding shape derivatives and adjoint systems, which we derived with a material derivative free adjoint approach. To demonstrate the feasibility of the reduced models, the optimization problems are solved numerically with a gradient descent method. A comparison of the results shows that the reduced models perform similarly to the original one while using significantly less computational resources. [ABSTRACT FROM AUTHOR]

We consider the optimal shape design of polymer distributors for the industrial spinning process, where long residence times are known to have a negative impact on the quality of the fibers. To this end we introduce a cost function based on the material age and the pressure energy required for the fluid transport. We obtain the shape derivative of the cost function without using the material derivative of the state based on a recent differentiability result for the Lagrangian formulation of shape optimization problems. Numerical experiments for a three-dimensional distributor verify the feasibility of our approach. [ABSTRACT FROM AUTHOR]

We consider the optimal shape design of polymer distributors used for industrial fiber spinning. In this laminar flow problem the residence time, the volume‐averaged age distribution of the fluid particles, has to be controlled to avoid material degradation. The residence time is modelled by an advection‐diffusion‐reaction equation with the fluid velocity being the transport field. This approach is more suitable for PDE‐constrained shape optimization than the Lagrangian particle‐tracking approach, where the observable is a finite set of trajectories. In order to develop an efficient shape optimization algorithm we derive the shape gradient of a tracking‐type cost functional by introducing the adjoint state. [ABSTRACT FROM AUTHOR]

The transport of gas‐solid suspensions in bended pipes can lead to erosion of the walls due to particle impact. In this context the numerical prediction of the erosion rate is usually based on an Eulerian flow description in combination with Lagrangian particle tracking, which however does not lend itself straightforwardly to the continuous adjoint approach of shape optimization. In order to find a pipe design, which is less prone to erosion, we therefore use a one‐way coupled Eulerian particle model. Upon formally computing the shape derivative of the resulting PDE‐constrained shape optimization problem, we minimize the erosion rate for a three‐dimensional tube bend under laminar flow conditions using a gradient descent method. [ABSTRACT FROM AUTHOR]

We introduce a new approach to solve shape optimization problems with state constraints. The problem is reformulated on a fixed reference domain using conformal pull-back. The shape dependence is then hidden in the conformal parameter. The problem is discretized using FEM and solved as an NLP. Finally the optimal shape can be reconstructed from the optimal conformal parameter. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Objectives: To evaluate tissue expansion during cryoablation, the displacement of markers in ex vivo kidney tissue was determined using computed tomographic (CT) imaging., Methods: CT-guided cryoablation was performed in nine porcine kidneys over a 10 min period. Markers and fiber optic temperature probes were positioned perpendicular to the cryoprobe shaft in an axial orientation. The temperature measurement was performed simultaneously with the acquisitions of the CT images in 5 s intervals. The distance change of the markers to the cryoprobe was determined in each CT image and equated to the measured temperature at the marker., Results: The greatest increase in the distance between the markers and the cryoprobe was observed in the initial phase of cryoablation. The maximum displacement of the markers was determined to be 0.31±0.2 mm and 2.8±0.02 %, respectively., Conclusions: The mean expansion of ex vivo kidney tissue during cryoablation with a single cryoprobe is 0.31±0.2 mm. The results can be used for identification of basic parameters for optimization of therapy planning., (© 2023 Walter de Gruyter GmbH, Berlin/Boston.)

The purpose of this study was to develop a thermometry software tool for temperature monitoring during laser-induced interstitial thermotherapy (LITT). C++ programming language and several libraries including DICOM Toolkit, Grassroots DICOM library, Insight Segmentation and Registration Toolkit, Visualization Toolkit and Quasar Toolkit were used. The software's graphical user interface creates windows displaying the temperature map and the coagulation extent in the tissue, determined by the magnetic resonance imaging (MRI) thermometry with the echo planar imaging sequence and a numerical simulation based on the radiation and heat transfer in biological tissues, respectively. The software was evaluated applying the MRI-guided LITT to ex vivo pig liver and simultaneously measuring the temperature through a fiber-optic thermometer as reference. Using the software, the temperature distribution determined by the MRI method was compared with the coagulation extent simulation. An agreement was shown between the MRI temperature map and the simulated coagulation extent. Furthermore, the MRI-based and simulated temperatures agreed with the measured one - a correlation coefficient of 0.9993 and 0.9996 was obtained, respectively. The precision of the MRI temperature amounted to 2.4°C. In conclusion, the software tool developed in the present study can be applied for monitoring and controlling the LITT procedure in ex vivo tissues.