Investigating the boiling behavior of nanofluids remains a topic of considerable research interest. The existing theoretical framework often underscores Brownian motion and thermophoresis among the predominant mechanisms that influence nanoparticles' movement within nanofluids. However, most current numerical models addressing nanofluid boiling either neglect these mechanisms or incorporate them inadequately. A comprehensive review of the literature reveals two primary gaps. The larger set of numerical studies on nanofluids boiling does not account for any governing equation for nanoparticle concentration, neglecting the primary mechanisms of nanoparticle movement. The smaller set includes such an equation but limits its application to the vapor domain, thereby overlooking the liquid nanofluid phase. Moreover, in the context of film boiling involving nanofluids, an insulating vapor film forms between the nanofluid and the heated surface. This vapor film is dynamic, experiencing evaporation at its outer boundary, leading to an increase in nanoparticle concentration at the vapor-liquid interface—another aspect always neglected in existing numerical models. To address these research gaps, this study introduces a specialized governing equation employing the Continuous-Species-Transfer method within the framework of Computational Multi-Fluid Dynamics. Importantly, it also incorporates governing equations for thermophoresis and Brownian motion to account for the motion of nanoparticles. The method's efficacy is further corroborated by solving a two-dimensional axisymmetric film boiling problem on a vertical cylinder, with results aligning well with analytical studies that consider Brownian motion and thermophoretic behavior. Overall, the study fills a critical gap in the literature by providing a comprehensive tool for examining complex interfacial behaviors in nanofluid film boiling.

@en

Many governments around the world have taken action to utilise carbon capture (CC) technologies to reduce CO2 emissions. This technology is particularly important to reduce unavoidable emissions from industries like cement plants, oil refineries, etc. The available literature in the public domain explores this theme from two distinct perspectives. The first category of papers focuses only on modelling the CC plants by investigating the details of the processes to separate CO2 from other gas components without considering the industrial applications and synergies between sectors. On the other hand, the second category investigates the required infrastructure that must be put in place to allow a suitable integration without considering the specific particularities of each carbon capture technology. This review gives a comprehensive guideline for the implementation of CC technologies for any given application while also considering the coupling between different energy sectors such as heating, power generation, etc. It also identifies the research gaps within this field, based on the existing literature. Moreover, it delves into various aspects and characteristics of these technologies, while comparing their energy penalties with the minimum work required for CO2 separation. Additionally, this review investigates the main industrial sectors with CC potential, the necessary transportation infrastructure from the point sources to the end users, and the needs and characteristics of storage facilities, as well as the utilisation of CO2 as a feedstock. Finally, an overview of the computation tools for CC processes and guidelines for their utilisation is given. The guidelines presented in this paper are the first attempt to provide a comprehensive overview of the technologies, and their requirements, needed to achieve the cross-sector coupling of CC plants for a wide range of applications. It is strongly believed that these guidelines will benefit all stakeholders in the value chain while enabling an accelerated deployment of these technologies.@en

This study investigates the impact of nanoparticle diameter on film boiling in Al ₂O ₃ water-based nanofluids along a vertical cylinder, focusing on nanoparticle sizes of 5 nm, 10 nm, 30 nm, and 50 nm. Using a Continuous-Species-Transfer method within a Computational Multi-Fluid Dynamics framework, the behavior of nanoparticles in both liquid and vapor states is simulated, considering Brownian motion and thermophoretic effects. A 2D axisymmetric analysis reveals how nanoparticle sizes influence temperature gradients, nanoparticle concentration patterns, thermophysical properties, and the Nusselt number to assess heat transfer efficiency. Findings indicate that during film boiling, smaller nanoparticles exhibit higher concentrations on the heated wall over time. Additionally, nanofluids with smaller particles demonstrate higher thermal conductivity and viscosity near the heated wall, along with lower surface tension. Interestingly, nanofluids with 30 nm and 50 nm nanoparticles perform closely, indicating a size threshold beyond which further reductions do not significantly enhance boiling heat transfer. In contrast, nanofluids containing 5 nm and 10 nm nanoparticles exhibit markedly superior thermal removal efficiency, underscoring the critical role of nanoparticle size in optimizing film boiling performance.

@en

This research explores how nanoparticle shapes affect the thermal behavior of nanofluid film boiling along a vertical cylinder, utilizing a Continuous-Species-Transfer method embedded in a Computational Multi-Fluid Dynamics framework. By modeling the behavior of nanoparticles in both liquid and vapor phases, with considerations for Brownian motion and thermophoresis, a comprehensive 2D axisymmetric analysis is conducted. The analysis focuses on the effects of various Al ₂O ₃ nanoparticle shapes – spheres, bricks, blades, cylinders, and platelets – on boiling heat transfer performance. Results demonstrate that while nanoparticle shape has a minimal impact on deposition dynamics, it significantly affects kinematic viscosity, particularly for platelet-shaped nanoparticles. Blade-shaped nanoparticles stand out for their substantial enhancement of thermal transport, as demonstrated by pronounced temperature gradients and elevated thermal conductivity. Furthermore, these nanoparticles contribute to a notable improvement in the Nusselt Number, suggesting enhanced efficiency in boiling heat transfer. This improvement is particularly significant at higher nanoparticle concentrations, where the effects are more pronounced, though not strictly linear when compared to the effects at lower concentrations. Future work will explore different nanoparticle materials, boiling scenarios, and experimental validation.

@en

This study investigates the impact of nanoparticle types on the thermal dynamics of film boiling in water-based nanofluids, specifically focusing on nanofluids containing Al ₂O ₃ and Cu nanoparticles along a vertical cylinder. The investigation employs the Continuous-Species-Transfer approach and also considers the effects of Brownian motion and thermophoresis. A 2D axisymmetric analysis is performed, evaluating the influence of nanoparticle type—Al ₂O ₃ and Cu—on the boiling heat transfer efficacy. Through the examination of volume fraction, temperature distributions, nanoparticle concentration, and thermophysical characteristics, the study also examines the Nusselt number. Results show the nanoparticle enrichment at the vapor–liquid interface and the degree of this nanoparticle enrichment influences nanoparticle concentration at the cylinder wall, with higher enrichment at the interface inversely related to wall concentration. While Al ₂O ₃ nanoparticles show higher concentration at the wall, Cu nanoparticles are more effective in enhancing Nusselt number, particularly in nanofluids with higher nanoparticle concentrations.

@en

Simulations of thermally driven phase change phenomena of nanofluids are still in their infancy. Locating the gas–liquid interface location as precisely as possible is one of the primary problems in simulating such flows. The VOF method is the most applied interface description method in commercial and open-source CFD software to simulate nanofluids’ thermal phase change. Using the VOF method directs to inaccurate curvature calculation, which drives artificial flows (numerical non-physical velocities), especially in the vicinity of the gas–liquid interface. To recover accuracy in simulation results by VOF, a solver coupling VOF with the level-set interface description method can be used, in which the VOF is employed to capture the interface since it is a mass conserving method and the level-set is employed to calculate the curvature and physical quantities near the interface. We implemented the aforementioned coupled level-set and VOF (CLSVOF) method within the open-source OpenFOAM ^Ⓡ framework and conducted a comparative analysis between CLSVOF and VOF (the default interface capturing method) to demonstrate the CLSVOF method’s advantages and disadvantages in various phase change scenarios. Using experimental mathematical correlations from the literature, we consider the effect of nanoparticles on the base fluid. Results shows that the new inferred technique provides more precise curvature calculation and greater agreement between simulated and analytical/benchmark solutions, but at the expense of processing time.

@en

A benchmark study is conducted using isoAdvection as the interface description method. In different studies for the simulation of the thermal phase change of nanofluids, the Volume of Fluid (VOF) method is a contemporary standard to locate the interface position. One of the main drawbacks of VOF is the smearing of the interface, leading to the generation of spurious flows. To solve this problem, the VOF method can be supplemented with a recently introduced geometric method called isoAdvection. We study four benchmark cases that show how isoAdvection affects the simulation results and expose its relative strengths and weaknesses in different scenarios. Comparisons are made with VOF employing the Multidimensional Universal Limiter for Explicit Solution (MULES) limiter and analytical data and experimental correlations. The impact of nanoparticles on the base fluid are considered using empirical equations from the literature. The benchmark cases are 1D and 2D boiling and condensation problems. Their results show that isoAdvection (with isoAlpha reconstruct scheme) delivers a faster solution than MULES while maintaining nearly the same accuracy and convergence rate in the majority of thermal phase change scenarios.

@en

For reliability and thermal management of power devices, the most frequently used technique is to employ heatsinks. In this work, a new configuration of offset strip fin heatsink based on using the concept of curvy fins and U-turn is proposed with the aim of improving the heat transfer performance. With this aim, a three-dimensional model of heatsink with Silicon Insulated-Gate Bipolar Transistors (IGBTs) and diodes, solder, Direct Bonded Copper (DBC) substrate, baseplate and thermal grease is developed. Richardson's extrapolation is used for increasing the accuracy of the numerical simulations and to validate the simulations. To study the effectiveness of the new offset design, results are compared with conventional offset strip fin heatsink. Results show that in aspects of design of heatsinks (including heat transfer coefficient, maximum chip temperature and thermal resistance), the new introduced model has advantages compared to the conventional offset strip fin design. These enhancements are caused by the combination of the longer coolant passage in the heatsink associated with generation of disturbance and recirculation areas along the curvy fins, creation of centrifugal forces in the U-turn, and periodic breaking up boundary layers. Also, it is shown that due to narrower passage and back-and-forth route, the new introduced design can handle the hot spots better than conventional design.

@en

The formation of bubbles and their departure from a superheated horizontal surface is simulated in this paper. The bubble nucleation occurs from a cylindrical cavity. The simulation will be done by a new OpenFOAM-based two phase solver. The two-dimensional Taylor wave problem, which is a well-known benchmark for boiling phenomena, is used to validate the model and simulation. The boiling starts from a cavity and the growth and departure of the created bubbles are simulated. The bubble dynamic, temperature, and pressure distributions have been analyzed, demonstrating the capability of the new developed OpenFOAM-based two phase solver to predict boiling phenomena.

@en

This paper presents a state-of-the-art review on heat sinks configurations used in flow boiling to cool electronic components. Two phase cooling methods and in this case using them in channels have disadvantages including complexities in flow field and instabities. The major role of designs of flow boiling heat sinks is to mitigate or delay these instabilities to reach stable and high performance cooling from heat transfer and pressure drop point of views. First, these instabilities in heat sinks with two phase coolants and phenomena leading to them are briefed. Then studies on presenting modifications and new designs of flow boiling heat sinks are reviewed. Description for five instabilities, three modifications and five heat sink configuration are addressed. It shows the highest cooling performance belongs to manifold microchannel and the piranha pin fin microstructure heat sinks.

@en