bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of liquid height to bubble size ratio on the boiling crisis in pool boiling
Authors: Alvarez Rodrigo Cavalcanti , Bucci Matteo 
Published: June 2024

Abstract
We conducted experiments to analyze water boiling under 10 K subcooling and atmospheric conditions in a horizontal pool boiling test setup, focusing on the effect of liquid height above the heating surface. Our main interest was the transition in boiling crisis mechanisms at liquid heights comparable to bubble size. For pool heights above 4.0 mm, we observed a relatively constant critical heat flux (CHF) of approximately 1.21 MW/m^2. Conversely, CHF significantly dropped to around 0.19 MW/m^2 for liquid heights below 2.5 mm. For depths between 2.5 – 4.0 mm the measured CHF values varied within these limits. Our pool boiling facility featured a stainless-steel chamber filled with deionized water heated by external circulating oil. A ceramic cartridge supported a transparent heater at the cell’s center-bottom, which utilized an indium tin oxide layer on a sapphire substrate for heat dissipation. We monitored bubbles’ footprint dynamics during boiling using infrared and high-speed video cameras. Preliminary high-speed data analysis revealed different hydrodynamic mechanisms corresponding to the obtained CHFs. For heights above 4.0 mm, the formation of an irreversible dry patch is triggered by bubble interactions. Conversely, at heights below 2.5 mm, one of the bubbles nucleating shortly after the onset of boiling failed to detach from the surface shortly. Instead, it grew in size and eventually spread over the entire surface, prematurely triggering a boiling crisis. We attributed this behavior to a lack of buoyancy forces to detach the bubble from the surface as it grew above the liquid level. Pool heights between 2.5 – 4.0 mm showed both behaviors. Further investigations will focus on exploring the transition in boiling mechanisms shifting from buoyancy- to surface-tension-dominated processes by varying bubble dimensions through the introduction of surfactants. Ultimately, we aim to analyze fundamental boiling parameters and heat flux to characterize how boiling dynamics, boiling crisis and CHF value vary with the bubble-to-liquid height ratio.
Experimental investigation of electrically enhanced boiling of FC 72 using high-resolution phase-detection diagnostics
Authors: Graffiedi Marco , Garivalis Alekos Ioannis , Marco Paolo Di , Bucci Matteo 
Published: June 2024

Abstract
This work features the boiling of FC72 on a transparent sapphire substrate. Tests are performed using a thin ITO film (indium tin oxide) coated on the sapphire substrate as the heat source, a fast speed video camera to capture the boiling process using a technique to track the phase (liquid or vapor) in contact with the heating surface, an InfraRed video camera to capture the average temperature on the surface, and a metallic grid to impose an electric field perpendicular to the boiling surface. The maximum average electric field tested in this work is 3.3kV/mm, which led to a 18% increase of the critical heat flux. This study analyses in detail the phase distribution data showing that (1) there is no evidence of microlayer formation, and suggesting that (2) the triple contact line evaporation accounts for approximately 20% of the total heat flux, while (3) the quenching stage accounts for approximately 80%. Finally, phase distribution images are processed to characterize the size of vapor patches, showing that a boiling crisis occurs when the distribution of the vapor patches becomes scale-free, and corroborating the hypothesis that the boiling crisis can be modelled as a bubble interaction instability using a percolation model.
Hydrodynamic characteristics of the microlayer under vapour bubbles on solid surfaces
Authors: Zhang Xiaolong , Mellas Ismail El , Magnini Mirco 
Published: June 2024

Abstract
This study investigates the hydrodynamic behaviour of the microlayer, a thin liquid film of a few micrometres thickness that forms beneath vapour bubbles during boiling under specific conditions. This microlayer serves as a rapid heat transfer medium through evaporation due to its low thermal resistance, making it a compelling subject for enhanced heat transfer research. We employ the geometric Volume-Of-Fluid (VOF) method for numerical simulations, allowing us to accurately replicate the growth of a vapour bubble on solid surfaces. The computational approach offers a level of detail and resolution that can compensate for certain aspects of microlayer behaviour absent in experimental methods. Our simulations reveal the complete spatial distribution of the microlayer and the profiles of the bubble interface near the meniscus front (the part of the interface near the solid). We compare the results with experimental data and conduct simulations with various bubble growth laws to explore how the microlayer responds to different growth scenarios. These findings lay the foundation for incorporating the microlayer’s contribution to overall boiling heat transfer in future models, potentially unlocking new avenues for enhanced heat transfer applications.
Convective boiling heat transfer enhancement via femtosecond laser textured inclined microfeatures
Authors: Mertens F , Nagarajan B , Castagne S , Steelant J , Vetrano MR 
Published: June 2024

Abstract
Designing efficient cooling devices is crucial in a multitude of applications. Although cooling technologies have existed for decades, there is a lack of efficient heat dissipation methods, especially for space applications where thermal management devices must dissipate heat in reduced gravity and where convective boiling heat transfer is frequently employed. In this framework, we evaluate the change in bubble production for different types of surface textures produced on 200 µm thick 316L SS foils using a femtosecond laser. The investigated textures include microscale grooves and conical holes with tilted (= 45°) geometry. In addition, we also evaluate the effect of laser-induced periodic surface structures (LIPSS), which are sub-micron scale features fabricated by fs laser processing. The fluid used is PP1, a replacement of 3M™ FC-72 in heat transfer applications.
Vapor bubble on a single nucleation site : Temperature and heat flux measurements
Authors: Kharkwal Himanshi , Zamoum Mohammed , Barthés Magali , Lanzetta François , Combeau Hervé , Tadrist Lounès 
Published: June 2024

Abstract
This work aimed at gaining a detailed understanding of heat transfer when boiling occurs on a heated substrate. More specifically, this work focuses on thermal transfers occurring at wall-fluid interfaces at the transition between natural convection and nucleate boiling regimes in pool boiling experiments. To avoid parasitic effects, the vapor bubble is created at a single artificial nucleation site. The boiling cell is instrumented with sensors for temperature measurement, pressure control, and parietal heat flux measurement. The fluid tested is Fluorinert FC-72. For providing a boiling surface and measuring heat flux, a boiling-meter consisting of a heating resistance, heat flux sensors and two thermocouples is used. This boiling-meter enables heat flux generation, the measurement of both temperature and heat flux, and can be rotated through 360°, enabling the influence of inclination to be studied. The boiling-meter is indented at its center to create a single vapor bubble. Thermal measurements are obtained and studied for different inclination angles between 0° and 180° at the saturation conditions. The results showed the nucleation site’s recurrent pattern of being active and inactive for whatever is the boiling surface inclination. Preliminary results are presented and discussed.
Numerical modeling and simulation of near-contact-line evaporation kinetics
Authors: Graur I. , Rednikov A. , Ronshin F. , Tadrist L. 
Published: June 2024

Abstract
A mathematical model of the liquid-vapor interface based on the Onsager reciprocity relations and the kinetic theory of gases is proposed. In the framework of this model, the heat and mass fluxes through an interface are related to the pressure and temperature jumps across it. The developed model is applied to the wedge-type geometry to simulate near-contact-line behaviors, where the kinetic effects are of paramount importance in view of flux singularities. The results of implementation of this model to the case of FC-72 evaporation are shown in comparison to a very widely used Schrage-type relation.
Improved linear notch mechanics for lightweight design using MFS
Authors: Fujisaki W 
Published: June 2024

Abstract
This paper is a study of a new prediction method for accurately evaluating the brittle fracture strength of notched materials with multiple holes using the methods of fundamental solutions(MFS). Conventional linear notch mechanics (LNM) was proposed in 1980’s to clarify the distinction between the fracture and non-fracture zones using a master-curve. It is effective for evaluating the fracture strength of notched materials with a single hole. When multiple holes are adjacent to each other, the conventional LNM is less accurate in predicting the fracture strength. To eliminate the shortcomings, I proposed the improved linear notch mechanics (ILNM), which uses the stress gradient χ at the bottom of the notch instead of a notch radius ρ. For lightweight design, the applicability of ILNM and its effectiveness are verified for notched materials with multiple holes by some experiments and some calculations.
Functional gradation of material coefficients and size –effects in heat conduction: Numerical simulations
Authors: Sladek V , Sladek J 
Published: June 2024

Abstract
It is well known that the classical theory of heat conduction is scale invariant. On the other hand, it is experimentally evident that size-dependent effects are observable in small samples of micro/nano-scale dimensions. Incorporation of higher-order gradients of primary field variables into constitutive relationships yields a qualitative explanation of size-effects. Form the mathematical point of view, the governing equations are given by the partial differential equations (PDE) with higher-order derivatives in higher-grade continuum theories. As compared with classical theory of continua, the other complication of governing equations occurs in case of continuous media with functional gradation of material coefficients, when the problem is described by the PDE with variable coefficients. The traditional weak formulations are considered in global sense, hence the whole analysed domain/boundary is to be discretized into finite size elements. On the other hand, the strong formulations bring better computational efficiency because of elimination of integrations, but the price which should be paid is the need to approximate higher order derivatives of field variables. One of the most criticized shortcoming of the finite element (FE) approximation is its limited continuity on element intersections. The C0 continuity is insufficient for calculation of gradients of field variables on element intersections as well as for numerical solution of problems with governing equations of higher than 2nd order partial differential equations (PDE). Recently widely spread and elaborated mesh-free approximations utilize the higher order continuous shape functions. Another advantage is elimination of discretization of the analysed domain into finite elements, since only the nodes are scattered on the domain and its boundary. Both the strong and weak formulations are applicable in combination with mesh-free approximations. The Moving Finite Element Approximation (MFEA) and its utilization in mesh-free formulations for heat conduction problems is presented in this paper.
Comparison between RBF and FDM for solving nonlinear time-dependent PDEs using Newton’s Method
Authors: Murphy S , Ogunleye O , Rubasinghe K , Yao G 
Published: June 2024

Abstract
In this paper, the improved localized method of approximated particular solutions (ILMAPS) using polyharmonic splines with constant polynomial basis is used to approximate solutions of nonlinear time-dependent PDEs. The discretization process is done through a simple implicit time stepping and a collocation technique on a set of points in local domains of influence. Resulted system of nonlinear algebraic equations is solved by Newton’s method. Numerical experiments suggest that the proposed method yields superior accuracy than other RBFs as well as FDM for solving nonlinear PDEs.
Lessons from accelerating an RBF-FD phase-field model of dendritic growth on GPUs
Authors: Mavrič Boštjan , Dobravec Tadej , Šarler Božidar 
Published: June 2024

Abstract
Phase-field modeling of dendritic growth presents the state of the art in the field of solidification modeling and are usually implemented using finite difference models combined with explicit time marching and accelerated by using GPUs. They are a prime candidate for such acceleration, since they require many arithmetic operations on relatively low ammount of data. We present an attempt at porting an existing RBF-FD code optimized for CPU execution to use GPU acceleration while keeping the resulting implementation portable between architectures. We discuss the acceleration achieved, scaling and implementation issues and critically discuss current landscape of GPGPU offerings.
Elasto-plastic simulation of hot shape rolling of steel by a meshless method
Authors: Hanoglu Umut , Vertnik Robert , Šarler Božidar 
Published: June 2024

Abstract
This paper describes the development of meshless simulation of thermomechanics of steel in a continuous hot rolling process using a novel meshless solution procedure. During the process, steel billets at high temperatures are transferred through multiple roll passes, each with a specific groove shape and roll gap. The major outcome of this simulation system is to design the rolling schedule and confirm whether the final shape is inside the acceptable range. For this purpose, a perpendicular 2D slice model approach is used to obtain fast and reasonably accurate simulation results. A return mapping algorithm solves the elasto-plastic material model with linear hardening to obtain displacements, strains and stresses. They are calculated by the local radial basis function collocation method (LRBFCM), which uses the local interpolation of the strong form of partial differential equations. The predefined slice positions are entered into the rolling system, and for each position, the slice contact line and amount of reduction are predicted and used as boundary conditions. Thermal and mechanical models are run sequentially, which is repeated until the final slice position reaches the exit from the last roll. The simulation system was validated with multiple rolling schedules provided by the industrial partner and was successfully used in the steel production plant afterwards. The meshless LRBFCM successfully solves a complex elasto-plastic large deformation problem of hot rolling for the first time.
A new test section made via additive manufacturing to perform local heat flux measurements
Authors: Cattelan G , Azzolin M , Bortolin S , Bonesso M , Pepato A , Del Col D 
Published: June 2024

Abstract
Recent advancements in the field of additive manufacturing have enabled the realization of products that were previously almost unattainable. In the field of heat transfer, the production of heat exchangers through additive manufacturing is promising because it allows for the creation of more compact heat exchangers that can be tailored to specific requirements with optimized and complex geometries. However, also heat transfer devices that must be specifically realized for heat transfer research purposes can benefit from the characteristics of the additive manufacturing technology. This paper presents an innovative test section created through additive manufacturing technology with the aim to investigate two-phase heat transfer of refrigerants inside a 2.9 mm internal diameter channel. Water is used as a secondary fluid to reject/extract the heat. As a first step, a CFD analysis was performed to design a special geometry for the test section allowing a local measurement of the heat transfer coefficient along the channel. The test section was realized with the DMLS (Direct Metal Laser Sintering) technology using the AlSi10Mg alloy. Despite the benefits introduced by this manufacturing process, DMLS technology can lead to anisotropy in the thermal conductivity of the test section material. Thus, cylindrical samples were produced by DMLS with different building orientations to perform specific measurements of the thermal conductivity by using the Hot Disk technique. Preliminary local heat transfer coefficients were measured with refrigerant R1234ze(E) during condensation at 40 °C saturation temperature and mass flux 150 - 200 kg m−2 s−1. Experimental heat transfer results are compared against predictions obtained from a correlation available in the literature.
Numerical simulation-based design of optimized surfaces for condensation heat transfer
Authors: Berto A , Gabellone M J , Mattiuzzo N , Bortolin S , Del Col D 
Published: June 2024

Abstract
Heat transfer enhancement is a well-established research topic due to its industrial relevance. The advent of 3D printing, also known as additive manufacturing, has opened up the pathway for the design of compact heat exchangers with innovative shapes, complex geometries and smaller size. In particular, additive manufacturing technologies speed up the transition from CAD models to physical prototypes and thus numerical simulation tools for two-phase heat transfer are expected in the future to play a key role for the design of heat exchangers. With regard to filmwise condensation, numerical methods capable to account for all the main forces involved (such as gravity, surface tension, vapor shear stress) must be considered for the optimization of the condensing surfaces. The present study is focused on the preliminary design of innovative shapes for enhancing the condensation heat transfer in a grooved wick heat pipe. Most of the condensation heat transfer studies available in the literature deal with vapor condensing inside tubes or over cylindrical/plain surfaces, while the condensation process occurring inside heat pipes has been less investigated. The grooved wick surfaces must be designed with the aim to promote the drainage of the condensate and minimize the thickness of the liquid film forming over the wick structures. In the present work, the behaviour of different surfaces is studied during condensation of refrigerants by performing Volume of Fluid (VOF) 2D numerical simulations with Ansys®Fluent. The numerical results allow to determine the liquid film thickness and the heat flux distribution along the grooves.
Forced air flow through a rectangular channel with 3D turbulence enhancers: visualization of flow structures by laser sheet scattering
Authors: Vitali L , Corti M , Gramazio P , Fustinoni D , Niro A 
Published: June 2024

Abstract
In recent times, the design of heat transfer devices is strongly evolving due to both the diffusion of additive manufacturing techniques, that use a wide variety of materials, and Computational Fluid Dynamics (CFD) -based shape optimization techniques. Considering high-aspect ratio rectangular channels, that represent the geometry of heat transfer devices used, among other applications, for batteries cooling systems and compact automotive heat exchangers, the first step of a project towards the design of optimized turbulence enhancers is the validation of the CFD methodology. In particular, since it is important to have a fast-running 3D simulation with physical meaning, several techniques of increasing complexity and computational requirements and times are currently under scrutiny, and their validation is mainly carried out by experiments that measure both local and global heat transfer enhancement. In this context, flow visualization is a powerful tool to get insights of the physical mechanisms that generate convective heat transfer enhancement. In this paper, the setup of a laser sheet scattering method to visualize turbulent structures in a Plexiglas, 1:10 aspect-ratio, rectangular channel ribbed on one of the main surfaces is presented, and results on two different cutting planes are presented for 90° and V-down squared ribs for Re = 500.
Morphological optimization of butterfly-shaped inserts for heat transfer enhancement in tubular heat exchangers: a numerical study
Authors: Pagliarini L , Bozzoli F , Cattani L , Rainieri S 
Published: June 2024

Abstract
Single-phase heat transfer enhancement in heat exchangers represents a crucial issue for effective thermal treatment in many industrial applications, especially when highly viscous fluids or gases are processed. Increase of heat transfer capabilities might be obtained by passive techniques, such as tube corrugations or static inserts promoting boundary layers disruption at the fluid-wall interface. Different inserts have been proposed for tubular heat exchangers over the past decades, including twisted tapes, wired coils, conical rings and butterfly-shaped geometries. However, the literature lacks optimal geometries definitions. The aim of the present work is to achieve a morphological optimization of a butterfly insert through an adjoint approach to maximize heat transfer over pressure losses in heat exchangers tubes. In the present investigation, conjugate conduction-convection heat transfer in the computational domain is solved through a steady RANS approach. Turbulence is treated by means of the Realizable k-ε model with enhanced wall function. The model is successfully validated against experimental data. The optimization results suggest a reduction of the opening angle of the butterfly inserts of about 22°. The reported remarks can be used as guidelines for fabrication of optimized designs in tubular heat exchangers applications.
Non-invasive thermal measurements during newborn’s therapeutic hypothermia and processing of their results
Authors: Tumidajski J , Wagstyl D , Bandoła D , Bojdoł M , Ostrowski Z , Rojczyk M , Walas W , Halaba Z , Nowak A J 
Published: June 2024

Abstract
This paper focuses on the heat transfer processes occurring during the treatment of neonates suffering from hypoxic-ischemic. This is a type of brain dysfunction (brain injury) that happens (mainly during delivery) when the brain experiences a decrease in blood flow (because of abnormal blood circulation) and in consequence, a decrease in oxygen. It frequently results in an increase in brain temperature to the danger level and hypoxia in some other organs. Treatment requires a specialized cooling device to decrease the temperature of the neonate’s body and particularly the brain temperature. One of the cooling methods is so-called “selective brain cooling”, which consists of direct cooling of the head by a cooling cap. In this work results of non-invasive measurements for 11 patients suffering from hypoxic-ischemic encephalopathy and treated at the University Clinical Hospital in Opole, Poland. Collected data were processed in a novel way to formulate a whole series of cumulative energy balances for all patients. It is found that cumulative balancing allows one to determine the metabolic heat rate and results in a more stable history of the therapy than balancing step by step.