Manfredo Guilizzoni

Improving the thermal performance of compact heat exchangers is a key challenge in the development of energy-efficient systems. This work investigates the use of topology optimization to generate novel surface geometries that enhance thermal efficiency specifically in narrow rectangular channels. A physics-based topology optimization software, ToffeeX, has been employed to explore turbulator designs within defined spatial and material constraints. The optimization process has focused on maximizing heat transfer, with particular attention on the effect of solid volumetric fraction. Simulations have been carried out using the CFD tools of the optimization software to evaluate the thermal behavior of the proposed configurations. Among the tested designs, a solid volumetric fraction of 8% has led to the most effective solution, achieving a 25% increase in outlet fluid temperature compared to a conventional ribbed reference configuration. Validation using CFD simulations with another package, OpenFOAM, has confirmed these results, showing consistent trends across methodologies. These findings highlight the potential of combining topology optimization with numerical simulation to develop advanced geometries for heat transfer enhancement. The proposed approach supports the development of more efficient and compact heat exchangers, paving the way for future experimental studies and broader industrial applications.

Conventional heat pipes (CHPs) with capillary wicks are fundamental in various engineering applications due to their exceptional heat transfer efficiency and minimal temperature gradients. Despite the recent advancements in heat pipe modeling, existing reviews predominantly emphasize loop or pulsating heat pipes, neglecting the extensive application and design challenges associated with CHPs. This review aims to address this lack by providing a comprehensive analysis of existing modeling techniques for CHPs, with a specific focus on their methodological innovations, validation strategies, and limitations, in order to outline a structured classification of models and provide useful suggestions for future research. The main findings of this work reveal a predominance of numerical lumped parameter models, which balance simplicity and computational efficiency, but often oversimplify complex phenomena. In fact, although numerical 2D and 3D models could offer greater accuracy at higher computational costs, they often share similar limitations with lumped parameter models. Additionally, some crucial aspects, including gravitational effects, real gas behavior in vapor modeling, activation effects, and operating limits, remain underexplored. Therefore, future research should address these gaps, to enhance the applicability of CHPs across different fields and operating conditions. In particular, an integrated approach is recommended, combining physics-based models with data-driven techniques, and supported by a robust and systematic experimental validation strategy, to ensure the reliability and generality of the developed models. Such modeling efforts are expected to guide the development of more effective and reliable heat pipe designs.

Fluids is pleased to present a Special Issue named “Fluids and Surfaces”, a curated collection of ten research articles focused on capillary phenomena and the interaction between fluids and surfaces

Evaporative cooling systems have emerged as low-energy consumption alternatives to traditional vapor compression systems for building air conditioning. This study explored the feasibility of utilizing polymeric foamed materials produced through additive manufacturing as wetting materials in evaporative cooling systems. Specifically, two different commercial polylactic acid filaments, each containing a percentage of a chemical blowing agent, were studied. Experiments were designed to evaluate the influence of critical process parameters (line width, flow rate, speed, and layer height) on the performance of the resulting foamed materials in terms of evaporative cooling by conducting water absorption, capillarity, porosity, and wettability tests. Considering that high water absorption, capillarity, and porosity, coupled with an intermediate contact angle, are advantageous for evaporative cooling effectiveness, a low flow rate was found to be the most important parameter to improve these properties’ values. The results showed that the appropriate combination of polymer and process parameters allowed the production of foamed polymer-based materials processed by additive manufacturing technology with optimal performance.

Indirect evaporative cooling systems have attracted much interest in recent years as they guarantee good cooling effectiveness, with lower energy demand with respect to traditional systems, thus helping to address the issue of climate change. Many studies have shown that an increase in the wettability of recuperator plates results in an improvement in the system performance. However, if the water injected into the system comes from the city water supply, it will contain calcium carbonate residuals, which will form limescale layers on the plates, thus possibly changing their wetting behavior. Therefore, the wettability of three surfaces (an aluminum uncoated surface, AL, a standard epoxy coating, STD, and a hydrophilic lacquer, HPHI) was analyzed in the presence of limescale formations, and compared with that obtained in a previous study for corresponding clean surfaces. The results showed that the HPHI contact angle was reduced in the presence of limescale (median: 50°), that for STD was slightly increased (median: 81°), and that for AL was again reduced (median: 75°). Consequently, HPHI was confirmed to be the most wettable surface in both clean and limescale conditions. Finally, an analysis was undertaken evaluating the spreading factor and the reversible work of adhesion, which were in good agreement with the qualitative visual observations of the plates covered with limescale.