Numerical investigation of interfacial mass transfer in two phase flows using the VOF method

A mass transfer model is developed using the volume-of-fluid (VOF) method with a piecewise linear interface calculation (PLIC) scheme in ANSYS FLUENT for a free-rising bubble. The mass flow rate is defined via the interface by Fick\u27s law and added into the species equation as a source term in the liquid phase using the user-defined functions (UDFs) in ANSYS FLUENT. The interfacial concentration field for the mass flow rate is discretized by two numerical methods. One of them is based on the calculation of the discretization length between the centroid of the liquid volume and the interface using the liquid void fraction and interface normal vectors at the interface cells, while in the second method the discretization length is approximated using only the liquid void fraction at the interface cells. The influence of mesh size, schemes, and different Schmidt numbers on the mass transfer mechanism is numerically investigated for a free-rising bubble. Comparison of the developed mass transfer model with the theoretical results shows reasonable and consistent results with a smaller time-step size and with cell size

Design and experimental setup of a new concept of an aerosol-on-demand print head

Aerosol jet printing is an alternative to inkjet printing, the currently most established fabrication technique for printed electronics, with the benefits of small feature sizes, more homogeneous thickness of the printed layers, and the possibility to print on 3D structures. Printers are available on the market, in which the aerosol is generated outside of the print heads, with the disadvantage that only continuous operation is possible due to the long distance between atomization unit and print head. We report on the development and validation of a new integrated principle, with the atomization of the ink directly inside the print head. This enables a compact design, printing in all spatial directions and jet-on-demand operation. Based on fluid dynamic simulations, an optimized integrated print head design was developed, and fabricated. First tests have been performed in a preliminary laboratory test setup. The successful focusing of the aerosol to approximately 1/7 of the spread of the non-focused aerosol spray was validated in experiments, thus confirming the operating principle of the new aerosol-on-demand print head

3D-printed structured catalysts for CO2 methanation reaction: Advancing of gyroid-based geometries

This work investigates the CO2 methanation rate of structured catalysts by tuning the geometry of 3D-printed metal Fluid Guiding Elements (FGEs) structures based on periodically variable pseudo-gyroid geometries. The enhanced performance showed by the structured catalytic systems is mostly associated with the capability of the FGEs substrate geometries for efficient heat usages. Thus, variations on the channels diameter resulted in ca. 25% greater CO2 conversions values at intermediate temperature ranges. The highest void fraction evidenced in the best performing catalyst (3D-1) favored the radial heat transfer and resulted in significantly enhanced catalytic activity, achieving close to equilibrium (75%) conversions at 400 \ub0C and 120 mL/min. For the 3D-1 catalyst, a mathematical model based on an experimental design was developed thus enabling the estimation of its behavior as a function of temperature, spatial velocity, hydrogen to carbon dioxide (H2/CO2) ratio, and inlet CO2 concentration. Its optimal operating conditions were established under 3 different scenarios: 1) no restrictions, 2) minimum H2:CO2 ratios, and 3) minimum temperatures and H2/CO2 ratio. For instance, for the lattest scenario, the best CO2 methanation conditions require operating at 431 \ub0C, 200 mL/min, H2/CO2 = 3 M ratio, and inlet CO2 concentration = 10 %