bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Assessment of local temperature elevation at the surface of tissue exposed to radiation of milimeter waves using simplified analytical approach
Authors: Poljak Dragan , Saric Josipa
Published: June 2024

Dominant effect of human exposure to electromagnetic fields in GHz frequency range corresponding to operation of 5G mobile communications systems is tissue heating i.e. local temperature elevation at the body surface, i.e. skin, ear and eyes. For the frequencies below transition frequency of 6GHz specific absorption rate (SAR) is used to quantify the volume heating. On the other hand, the surface heating above 6GHz is quantified via absorbed power density (Sab
). Once these quantities are determined by means of internal field dosimetry procedures it is possible to determine the local surface temperature increase by solving the bio-heat transfer equation. The present paper deals with the calculation of tissue surface heating due to exposure to millimeter waves. Internal dosimetry is based on the planar tissue model exposed to dipole antenna radiation. Electromagnetic model is based on the analytical solution of Pocklington integro-differential equation while the assessment of tissue surface heating in planar tissue model has been carried by analytically solving a simplified variant of the bio-heat transfer equation. Some illustrative results for power density and temperature elevations will be presented for different antenna parameters.
A needle-form 3-omega sensor for thermal characterization of cryopreserved biological tissues
Authors: Alliston Spencer P , Dames Christopher E
Published: June 2024

Thermal properties of cryopreserved tissues are critically important to the biopreservation community, which continues to seek more effective ways to store biological samples for improved outcomes in organ transplants as well as to facilitate the preservation of a record of biodiversity. Here, we present a reusable thermal needle-type 3-omega method designed for in situ characterization of such tissues, as well as other soft materials. The 3-omega method is a classic thermal materials characterization technique, which has been integrated into a modified microfabricated neural probe. This enables the measurement to be robust to environmental and experimental factors in cryopreservation. We demonstrate the viability of such a sensor to measure thermal conductivity for amorphous and crystalline solid samples of biological tissues, as demonstrated on 3mm thick chicken liver. These measurements can also be used for differentiation of solid samples, which is of particular interest for studies involving the kinetic limits of amorphous solidification (vitrification). In this, we demonstrate the value of a packaged thermal sensor to advancing the thermal understanding of cryopreserved biological systems and other solid-liquid phase change systems.
Thermal management system for cell-biology experimental setup studying calcium signalling in microgravity
Authors: Hochuli A , Wuest S L , Stamatiou A , Fenk B , Estermann P , Schiffmann D , Ammann S , Palacios A , Zumbühl C , Kummer R , Böhmer M
Published: June 2024

A novel hardware featuring specific LED arrays shall be developed to investigate free calcium in biological cells exposed to microgravity conditions. The temperature-sensitive samples require a precise and reliable temperature control system that can operate without electricity. In this paper, we assess the effectiveness of a passive temperature control system based on phase change material. Two extreme operation scenarios are investigated simulatively with the software COMSOL 6.1 for correct dimensioning and material selection. The simulation results of the first operation scenario show that the required temperature range for mammalian cells can be maintained during a power interruption of two hours. The simulation results of the second operation scenario show that excess heat generated by the LED arrays is effectively evacuated with a phase change material-based thermal management system. The physics software modules “heat transfer in solids and fluids” and “surface-to-surface radiation” were required to simulate illuminating LEDs adequately.
Multi-phase-field lattice Boltzmann simulations of semi-solid simple shear deformation in thin film
Authors: Yamanaka N , Sakane S , Takaki T
Published: June 2024

Semi-solid deformation during casting often results in significant solidification defects, such as segregation bands. Consequently, the development of a numerical simulation tool is crucial for accurately replicating semi-solid deformation. In our previous study, we applied a multi-phase-field lattice Boltzmann (MPF-LB) model to semi-solid deformation, facilitating seamless simulation from polycrystalline solidification to semi-solid deformation in a two-dimensional (2D) problem. This study extends the 2D MPF-LB model to a three-dimensional (3D) problem and develops a simulation method for semi-solid simple shear deformation in thin films. To enhance the efficiency of the 3D semi-solid simulation, we implemented parallel computations using multiple graphics processing units. Through a discussion of the relationships among the stress–strain curve, grain rearrangement behavior, and fluid flow, we confirmed that the developed 3D MPF-LB model successfully reproduced the characteristic phenomena of semi-solid deformation, and has high potential to investigate the nuanced mechanisms of semi-solid deformation.
Effects of the asymmetric and oscillating turbulent melt flow on the heat transfer and solidification inside the thin slab continuous casting (TSC) mold under the applied electromagnetic brake (EMBr)
Authors: Vakhrushev A , Karimi-Sibaki E , Wu M , Tang Y , Hackl G , Watzinger J , Bohacek J , Kharicha A
Published: June 2024

The thin slab casting (TSC) is a breakthrough near-net-shape technique for flat products accompanied by rapid casting and solidification rates. The TSC quality hinges on the turbulence, super-heat flow and growth of the solidified shell. The electromagnetic brake (EMBr) is commonly applied to control the fresh melt flow after feeding through a submerged entry nozzle (SEN). Numerical modelling is a perfect tool to investigate the multiphase phenomena in the continuous casting (CC). The presented study considers the heat transfer through the solid shell and water-cooled copper mold including the averaged thermal resistance of the slag skin and the air gap coupled with the turbulent flow and magnetohydrodynamics (MHD) model using an in-house code developed inside the open-source computational fluid dynamics (CFD) package OpenFOAM®. The model is applied to investigate different undesired asymmetric melt flow issues: (i) with the misaligned or (ii) partially blocked SEN; (iii) caused by the mean flow fluctuations with the natural frequencies; (iv) related to the oscillations of the fresh melt jets for the specific SEN designs and casting regimes. The variation of the flow pattern and superheat distribution is studied and presented for different scenarios both with and without applied EMBr.
Effect of Marangoni flow during the solidification of a Fe-0.82wt.%C steel alloy
Authors: Sari Ibrahim , Andreas Ludwig Menghuai Wu , Kharicha Abdellah
Published: June 2024

A two-phase Mixture model is proposed to simulate the liquid-solid phase transition of a Fe-0.82wt%C steel alloy under the effect of Marangoni flow. This model simplifies computations by solving a single momentum and enthalpy equation for the mixture phase using a three-dimensional finite volume method. The simulation involves solidifying a rectangular ingot (100 × 10 × 100 mm3) from the cold bottom surface towards the hot-free surface at the top. To facilitate heat exchange with the surrounding environment, a high heat transfer coefficient of h = 600 W/m2/K was applied on the bottom surface to establish an upward solidification direction. However, a lower heat transfer coefficient of 20 W/m2/K was applied on the top free surface, which was considered flat. This study aims to examine the effect of Marangoni flow generated by surface tension on flow and segregation patterns. The results show that the Marangoni flow emerges at the free surface and penetrates into the liquid depth, leading to the formation of hexagonal patterns along the liquid thickness. Upon full solidification, macro-segregation also exhibits hexagonal structures, mirroring the stationary hexagonal shapes generated by Marangoni flow.
A new hybrid local radial basis function collocation method for 2.5D thermo-mechanical modelling of continuous casting of steel
Authors: Vuga Gašper , Dobravec Tadej , Mavrič Boštjan , Šarler Božidar
Published: June 2024

This study presents a new strong-form meshless method to solve the thermo-mechanical problem of the solidification process in the continuous casting of steel. A two-dimensional slice that travels in the casting direction is modelled in the Lagrangian system. The newly developed mechanical model is one-way coupled to the thermal model, where the heat flux due to the mould, sprays, rolls and radiation are imposed to solve heat transfer in the strand. The resulting temperature and metallostatic pressure govern the Norton-Hoff visco-plastic model used for computing shrinkage of the solid shell and induced residual stresses. The results are used to estimate critical areas susceptible to hot-tearing formation. The mechanical model uses a generalised plane strain assumption that includes linear strains perpendicular to the slice and enables the computation of the straightening of the strand. The thermo-mechanical model is spatially discretised with a local radial basis function collocation method (LRBFCM). The mechanical part includes a new hybrid method that combines LRBFCM with finite differences for increased stability. The presented work shows how the developed model is used to assess the impact of casting velocity on the solid shell shrinkage and the probability of hot-tearing occurrence in the continuous casting of square billets.
Fast thermodynamic simulation of electrical control cabinets via thermal resistor networks
Authors: Haag D , Stergiaropoulos K
Published: June 2024

A fine-grid Computational Fluid Dynamics (CFD) simulation without thermo-electric coupling provides an accurate prediction of temperatures inside low-voltage control cabinets. But due to its high computational demand and complexity, the approach is not eligible for a widespread use in pre-production design. This study presents a lightweight and robust model based on the thermal-electrical analogy and Kirchhoff’s current law. The thermal resistor network is created for each control cabinet individually. An isothermal coarse-grid CFD simulation is used to approximate flow resistances. Convective resistances are calculated with Nusselt number correlations. The approach was tested on 120 randomly generated 2D control cabinet configurations. Component temperature errors were evaluated based on a normal distribution approximation. For moderate temperature rises up to 20 K the model had a mean error of 0.38 K and a standard error of 1.51 K compared to the reference fine-grid CFD model and was up to 12.8 times faster.
Optimization of Switching Algorithms for a Thermal Switch-PCM-Switch Stack in a Building Wall for Energy Savings
Authors: Chen Sarah M , Kaur Sumanjeet , Dames Christopher E
Published: June 2024

Thermally switchable building envelopes can provide energy savings compared to their traditional static counterparts. For example, in the summertime cooling season the envelope can switch into a thermally conductive state at night to exploit the free cooling of the nighttime air, while switching back into a highly insulating state during the warm daytime. Further benefits can be realized by incorporating phase change materials (PCMs) into the same building envelope between two thermal switches, because the PCM can store that nighttime cooling for later use during the day. Here we use analytical and numerical modelling to investigate the advantages of a switch-PCM-switch building envelope and specifically look to optimize the switching algorithms for the two switches. We frame the problem using dimensionless groups in order to identify the key parameter groupings that determine the response. We then build a lightweight lumped element model with runtime speeds of <0.5 seconds per scenario, which enables a brute force search of over 300,000 potential switching algorithms to identify the one with the highest total and net energy savings. We compare the results of the brute force approach with an algorithm that was proposed previously based on physical intuition [1]. We then conduct a similar brute force investigation of switching algorithms optimizing for average daily cost of energy, focusing on scenarios where time-of-day energy pricing is important. Using the resulting optimal switching algorithms, we present cost and energy savings for several real cities based on their realistic temperature data and time-of-day pricing.
Thermal management of high-powered short-duration electronics aided by a phase change material thermal energy storage
Authors: Martheleur D , Groulx D
Published: June 2024

Quantifying the performance of phase change materials (PCMs) for thermal energy storage in high-power short-duration electronics applications requires performing tests that push the material to its limit. This involves designing experiments to test solid-liquid PCMs in near real-world thermal load conditions to test its performance. Conventional cooling methods are sized to manage the maximum loading the cooling system will be subjected to in its operation, even if this loading occurs for a short period of time. This design ethos is inefficient and results in heavy and expensive equipment being used in an application where it will be underutilized most of its useful life. In this work, a PCM thermal energy storage (TES) device was built using a plate-and-frame heat exchanger and investigated to determine the suitability of this system to manage the temperature of high-power electronics with a low duty cycle. These experiments showed how a PCM-TES can be used in conjunction with conventional temperature management equipment to create a reliable cooling solution while allowing the conventional cooling components to be decreased in size and capacity. This work shows that, for a given application, a cooling system can be more efficiently designed with the use of a PCM-TES and opens the door to additional research on this topic.
Limitations of the enthalpy-porosity method for numerical simulation of close-contact melting on inclined surfaces
Authors: Van Riet V , Shockner T , Beyne W , Ziskind G , De Paepe M , Degroote J
Published: June 2024

One of the main challenges for latent thermal energy storage (LTES) systems is low heat transfer rates due to the low thermal conductivity of most phase change materials (PCM). Close-contact melting (CCM) can accelerate melting times in LTES systems but the current numerical techniques for solid liquid phase change have difficulties with accurately predicting this process. In this study, close-contact melting of PCM on an inclined surface is simulated using the enthalpy-porosity method in ANSYS Fluent. All PCM properties, including density, are temperature-dependent. In this way, phenomena such as natural convection, volume change and buoyancy between the solid and liquid are taken into account. The volume change is compensated by a gaseous expansion volume. Both 2D and 3D simulations are used to show discrepancy between state-of-the-art enthalpy porosity modelling and experimentally observed phenomena in the case of CCM. The mushy zone constant, which is set to 105 to allow motion of the solid bulk, causes the solid phase to deform as a highly viscous fluid instead of moving as a rigid body. The velocity differences inside the solid are more than 50 % of its sinking velocity. As a result, the movement of the solid resembles creep behaviour and the obtained CCM patterns are not physically accurate. Furthermore, the density difference between the solid and liquid phases causes an avalanching effect in the mushy zone, which artificially strengthens convection. In conclusion, the enthalpy porosity method exhibits significant limitations in accurately capturing close-contact melting phenomena.
Experimental validation of a design model for latent thermal energy storage extended with sensible heat
Authors: Beyne Wim , Degroote Joris , De Paepe Michel
Published: June 2024

Latent thermal energy storage can be a key technology for a green energy transition by matching fluctuating heat demand and supply. In order to implement a storage system, it needs to be designed which requires estimating the outlet temperature of a system for a given geometry and time history of the heat transfer fluid’s mass flow rate and inlet temperature. Currently, design methods are either overly simplistic, focusing solely on e.g. the phase change time or requiring the solution of partial differential equations which can be computationally expensive. The present paper proposes a novel approach where a latent thermal energy storage system is decomposed into a heat transfer fluid vessel, a sensible storage system and a storage system with only latent heat. Computationally inexpensive models are available for all three of these sub heat exchangers. A heat exchanger model is obtained by connecting the sub heat exchangers in parallel. This novel approach is used to model an industrial scale shell and tube latent thermal energy storage heat exchanger. The predicted outlet temperature is compared to the measured outlet temperature and the design model obtains good agreement.
1D modelling of a latent heat thermal energy storage prototype using boiling water as heat transfer fluid
Authors: Col Amandine Da , Bentivoglio Fabrice , Stutz Benoit
Published: June 2024

This paper presents a numerical model to simulate the thermohydraulic behaviour of a shell-and-tubes Latent Heat Thermal Energy Storage (LHTES) during discharging period, involving a boiling heat transfer fluid (HTF). It is based on a 1D homogeneous approach for the HTF (water) and a 1.5D approach for the phase-change material (sodium nitrate) allowing calculation times significantly shorter than those of CFD. This approach has been validated with experimental data in a previous study for a LHTES with a monophasic HTF. The two highlights of this paper are as follows: On the one hand, computational fluid dynamics has been used to develop equivalent homogeneous materials for PCM side, integrating the thermal properties of the phase-change material and the helical and longitudinal fins present in the LHTES. On the other hand, the model uses the asymptotic correlation of Steiner and Taborek to describe boiling heat transfers and usual correlations for single phase heat transfers. The paper focuses on the validation of the model against experimental data from the InPower project. The prototype is a 340 kWh storage that has been tested under different conditions. The model reproduces the total energy retrieved during a system discharge with relative error of 8.5% and an absolute mean error of 8.23 kW on outlet power. The main weakness of the model is the homogeneous model for the HTF that generates error in water level and local temperatures.
Melting of a phase change material in a rectangular cavity in the presence of metallic fins
Authors: Naldi C , Martino G , Dongellini M , Biserni C , Morini G L , Lorente S
Published: June 2024

The melting of the phase change material (PCM) octadecane, confined in a rectangular cavity heated from the bottom, is numerically studied. Simulations are performed through finite element software in order to analyze the impact of metal fins within the enclosure on the melting time. The results are analyzed in terms of the time-dependent position of the melting front, time-dependent average liquid fraction, and time needed for the PCM melting. The obtained outcomes highlight how, with a low number of metallic fins, the initial melting regime dominated by conduction at a certain time gives way to a convective melting regime characterized by Rayleigh–Bénard cells, in full agreement with the results of the theoretical analysis. On the contrary, with a high number of metallic fins, conduction is the only mechanism that governs heat transfer and the rapid melting slows down when the phase change front reaches the top of the fins. More specifically, the addition of the fins within the cavity yields a reduction in the time needed for the complete PCM melting up to 90% in the analyzed cases. The reported results provide new insights regarding the heat transfer mechanisms involved in PCMs melting within bottom-heated enclosures.
Study of the phase change processes of encapsulated phase change material for solar thermal energy storage in domestic hot water production
Authors: Bianqui C , Viedma A , Egea A , García A
Published: June 2024

This study aims to examine the melting processes of encapsulated PCM in a cylindrical-shaped capsule, made of stainless steel. It has a diameter of 60 mm and a height of 20 mm. The chosen PCM is the paraffin RT35HC, which has a melting point around 35 ºC. Experiments are conducted in a water-filled thermal bath, placing the capsule vertically and heating the water using a thermostat. Temperature field analysis of the PCM is performed using thermocouples, and simultaneously, the inside of the encapsulated material is observed through a transparent wall. It has been proven that the sensors are capable of detecting the gradual evolution of the liquid phase of the PCM and its accumulation at the top of the capsule due to its lower density.
Experimental thermal analysis of an innovative heat sink coupled to a nanoemulsion
Authors: Righetti G , Burgos J , Hernández L , Mondragón R , Barison S , Agresti F , Biasetto L , Mancin S
Published: June 2024

This work presents some new experimental measurements collected on a very innovative system proposed for electronic cooling. This setup combines a classical heat sink with a latent thermal storage. The storage material is a phase change nanoemulsion made of water and 5 wt% of a commercial RT40HC paraffin wax with 1-octadecanol as nucleating agent (weight fraction 1:10 with respect to PCM), while the heat sink is made of copper via 3D printing. The integration between the two components does not interfere with the external air convective heat transfer, as the emulsion is embedded inside the heat sink, which has an internal cavity. The tests analyse the temperature of the component and the emulsion in different locations during the charging and discharging phases at several heat fluxes.
Ventilation system with heat recovery and PCM thermal energy storage for “free” cooling in buildings
Authors: Jocić A , Lenassi P , Osterman E , Stritih U
Published: June 2024

For the conventional cooling of buildings, we are using electrical energy from the network, which increases annually due to the increase in comfort. Alternatives are being sought to reduce electricity consumption. Phase change materials (PCMs) in ventilation systems can provide us with the accumulation of night-time coolness in the summer months, resulting in a reduction in the consumption of electricity for cooling. Heat storages that take advantage of the phase change are used for short-term storage of thermal energy, as in this case, they have the greatest potential. In the introduction to the paper, a review of heat storage devices and their use is made which shows their connection with the Energy Performance Building Directive (EPBD) and the Energy Efficiency Directive (EED). Based on the measured results of the measurements in the Laboratory for Heating, Sanitary and Solar Technology and Air-conditioning (LHSA), a comparison with the model that calculates the storage of heat and cold in a phase change material (PCM - Phase Change Material) developed by a group of researchers from BUT Brno was made. With the TRNYSY software tool and the model simulations of the ventilation gains in the summer season were made and compared with the gains when using the heat exchanger (recuperator) and the PCM heat accumulator for the selected room.
Strategic planning of open pit mining operations using the Micromine Beyond Optimiser
Authors: Anisimov Oleh , Bariatska Nataliia , Cherniaiev Oleksii
Published: June 2024

Modern software products allow to determine the quantity and quality of ore at any point of the deposit and, accordingly, to identify the optimal pit shell using specialized algorithms. Such algorithms make it possible to create the final open pit shell even with a broken bottom for several neighboring ore bodies. Currently, optimization solutions in the mining industry require the determination of the maximum present value of profit or the minimum stated costs. It allows to make strategic planning decisions. Strategic planning of open-pit mining operations in the development of mineral deposits in Ukraine can be implemented using the Micromine Beyond Pit Optimizer. The authors considered the parameters that affect the boundaries of the pit field and the optimization criteria.
Design of elements of specialized technological equipment for finishing processing of parts
Authors: Romanchenko Oleksiy , Lohunov Oleksandr
Published: June 2024

This article is devoted to solving the current problem of use of the polyester materials application for the synthesis of specialized technological finishing equipment elements that usually used by enterprises for the repair and maintenance of mining equipment. The article discusses the possibility of the polyester materials application when creating equipment elements. The equipment’s parts are created by using additive technologies, in which the creation of the part occurs by sequential application of material layers. The use of polyester materials makes it possible to reduce labor intensity, increase the economic efficiency of production and ensure compliance with environmental standards both during the production process and during subsequent processing. Based on the modeling results, an analysis of the strength characteristics of the specialized technological equipment reservoirs made of steel 3 (ISO – E 235-C, Fe 360-C) and polyethylene terephthalate (PET plastic) was carried out. The possibility of application of the PET plastic as an analogue material for the reservoir manufacture with the ensuring of the necessary strength characteristics has been established.