Paweł Ziółkowski

This paper presents an experimental and numerical investigation of phase change transpiration cooling through a high-porosity oxide ceramic matrix composite (CMC) structure exposed to hot gas flow. A custom-built test chamber with quartz observation windows was constructed to study transpiration phenomena using circular porous CMC plates (54mm diameter, 5mm thick) at various water pressures and hot-gas temperatures. Hot gas wasgenerated by hydrogen combustion in air with an adiabatic flame temperature of approximately 1300◦C (λ = 2) and outlet temperatures up to 1050◦C. Cold permeability tests established a baseline flow rate of 4.3mL/min at 5bar, corresponding to 36.5g/s/m2. With the cooling loop open at lower pressure, added heat removal in the loop promoted liquid-film formation despite the lower mass flow through the plate. Closing the water outlet increased the differential pressure from 3bar to 5bar, raised the transpiration flow rate from 3mL/min to 25mL/min, and led to full evaporative transpiration. A three-dimensional CFD model with approximately five million cells was developed in ANSYS Fluent 2025 R1 using the k-ω SST turbulence model with P1 radiation and species transport. The model predicted near-wall temperatures of 800◦C to 900◦C against the measured ≈850◦C, and an outlet temperatureof 927◦C versus 950◦C measured—agreement within 5%. The combined results provide operational guidelines for differential water pressure to ensure proper transpiration cooling, informing the full-scale combustor design for carbon capture applications.

This study evaluates energy conversion and heat transfer in a germicidal chamber employing gold nanorods (AuNRs) irradiated with an infrared laser (808 nm, 0.8 W) to generate heat via localized surface plasmon resonance. The investigation focused on the preliminary selection of chamber materials and the geometry of the bottom surface supporting the AuNRs as the heat source in a photothermoablation application. A one-way multiphysics and multiscale approach was applied, integrating nanoscale heating phenomena with a macroscale fluid and heat flow. The validated 2D numerical model shows satisfactory agreement with experimental data and is suitable for further design analyses. Computational Fluid Dynamics (CFD) simulations were conducted to determine temperature and entropy distributions, mean and maximum temperatures, and Nusselt numbers, allowing the assessment of the energy conversion process under different configurations and AuNR dimensions. The results indicate that a configuration with a gradually descending stepped structure enhances interactions between nanoparticles and the fluid, increasing the internal energy and producing elevated temperatures. Under optimal conditions, a temperature rise of approximately 75 °C was achieved. These findings demonstrate that integrating material selection, surface geometry, and nanoparticle absorbance optimization can significantly improve the efficiency of bacterial inactivation in germicidal chambers. This study provides a framework for future investigations on fully three-dimensional multiscale and multiphysical modeling, as well as a targeted AuNR design to maximize the thermal performance.

In recent years, investigation of new or combined therapeutic modalities for cancer treatment lead to relevant scientific advances. Among these innovative therapeutic modalities photothermal therapy (PTT) attracts attention as an alternative or complementary possibility to current anti-cancer treatments as it allows for the selective ablation of cancer cells. In the present study, PTT is investigated by using gold nanoparticles (AuNPs) as photothermal transducers. AuNPs are injected into human skin and used for PTT-assisted tumor ablation. The effectiveness of the PTT is evaluated as a function of AuNPs morphology, dimensions and the wavelength of the laser source. Five different laser sources with wavelengths ranging from 465 to 980 nm are used. The experimental findings point out that 808 and 980 nm are the optimal laser wavelengths for the PTT of human skin. Especially gold nanorods stabilized by poly(ethylene glycol) layer are identified as effective photothermal transducers. The experimental results are fully corroborated by numerical calculations. The outcomes emphasize the potential and the relevance of synthetically tailoring AuNPs particularly in optimizing their optical properties and assessing the effects of AuNP aggregation for specific applications.

In the wake of the COVID-19 pandemics, the demand for innovative and effective methods of bacterial inactivation has become a critical area of research, providing the impetus for this study. The purpose of this research is to analyze the AuNPs-mediated photothermal inactivation of E. coli. Gold nanoparticles irradiated by laser represent a promising technique for combating bacterial infection that combines high-tech and scientific progress. The intermediate aim of the work was to present the calibration of the model with respect to the gold nanorods experiment. The purpose of this work is to study the effect of initial concentration of E. coli bacteria, the design of the chamber and the laser power on heat transfer and inactivation of E. coli bacteria. Using the CFD simulation, the work combines three main concepts. 1. The conversion of laser light to heat has been described by a combination of three distinctive approximations: a- Discrete particle integration to take into account every nanoparticle within the system, b- Rayleigh-Drude approximation to determine the scattering and extinction coefficients and c- Lambert–Beer–Bourger law to describe the decrease in laser intensity across the AuNPs. 2. The contribution of the presence of E. coli bacteria to the thermal and fluid-dynamic fields in the microdevice was modeled by single-phase approach by determining the effective thermophysical properties of the water-bacteria mixture. 3. An approach based on a temperature threshold attained at which bacteria will be inactivated, has been used to predict bacterial response to temperature increases. The comparison of the thermal fields and temporal temperature changes obtained by the CFD simulation with those obtained experimentally confirms the accuracy of the light-heat conversion model derived from the aforementioned approximations. The results show a linear relationship between maximum temperature and variation in laser power over the range studied, which is in line with previous experimental results. It was also found that the temperature inside the microchamber can exceed 55 °C only when a laser power higher than 0.8 W is used, so bacterial inactivation begins. The experimental data allows to determinate the concentration of nanoparticles. This parameter is introduced into the mathematical model obtaining the same number of AuNPs. However, this assumption introduces a certain simplification, as in the mathematical model the distribution of nanoparticles is uniform. This work is directly connected to the use of gold nanoparticles for energy conversion, as well as the field of bacterial inactivation in microfluidic systems such as lab-on-a-chip. Presented mathematical and numerical models can be extended to the entire spectrum of wavelengths with particular use of white light in the inactivation of bacteria. This work represents a significant advancement in the field, as to the best of the authors’ knowledge, it is the first to employ a single-phase computational fluid dynamics (CFD) approach specifically combined with the thermal inactivation of bacteria. Moreover, this research pioneers the use of a numerical simulation to analyze the temperature threshold of photothermal inactivation of E. coli mediated by gold nanorods (AuNRs). The integration of these methodologies offers a new perspective on optimizing bacterial inactivation techniques, making this study a valuable contribution to both computational modeling and biomedical applications.