bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interfacial waviness during condensation heat transfer
Authors: Berto A , Lavieille P , Azzolin M , Bortolin S , Miscevic M , Del Col D 
Published: December 2021

Abstract
Heat transfer coefficients and liquid film thickness have been measured during convective condensation inside a 3.4 mm internal diameter channel. Condensation tests have been run with refrigerant R245fa during vertical downflow at mass velocity equal to 50 kg m-2 s-1 and 100 kg m-2 s-1. The test section is composed of two heat exchangers for the measurement of the heat transfer coefficient connected by means of a glass tube designed for the visualization of the two-phase flow patterns and for the measurement of the liquid film thickness. The liquid film thickness is determined by coupling a shadowgraph technique and chromatic confocal measurements. The measured values of heat transfer coefficient and liquid film thickness are reported and analysed together to investigate the effect of waves on the condensation heat transfer mechanisms.
Numerical assessment of a gas-fired condensing boiler model for residential buildings application
Authors: Simic K , T’Jollyn I , Faes W , Borrajo Bastero J , Laverge J , De Paepe M 
Published: December 2021

Abstract
According to the official statistical reports, gas-fired boiler units still remain to be one of the main equipment types for meeting the space heating and daily hot water demand of the residential dwellings across the European Union. Due to the prevalence of the natural gas grid and performance stability, gas-fired boilers are considered to remain as one of the standard energy sources. On the other hand, even though gas-fired water heating technology is a well-known concept, existing numerical models found in the literature are often case-specific with poor reusability mostly reflected in fitted efficiencies. Algorithms behind these models usually require the input of large amount of hardly attainable design characteristics of the units. In this paper, a modelling method for acquiring the performance of a heating gas-fired condensing boiler unit will be shown. The model is based on the limited input data available in the official characteristics of the units issued by the relevant manufacturers. The simulations are programmed by using the programming language Modelica and the software tool Dymola. The model is based on the fixed natural gas intake which combusts into a stable mixture of the combustion gases that further heat the circulating water. During the heat transfer process inside the condensing boilers there is a possibility for condensate formation out of the water vapour of the combustion gases which increases the efficiency of the unit. The formation of condensate, however, is depending on the return water temperature of the unit which has to be lower than the dew point temperature of the combustion gasses. The goal of this research is to determine how accurate can performance indicators of gas-fired boilers be attained with the use of a limited amount of available input data together with clearly defined assumptions that follow the modelling methodology.
Node generation in complex 3D domains for heat conduction problems solved by RBF-FD meshless method
Authors: Zamolo Riccardo , Nobile Enrico 
Published: December 2021

Abstract
A novel algorithm is presented and employed for the fast generation of meshless node distributions over arbitrary 3D domains defined by using the stereolithography (STL) file format. The algorithm is based on the node-repel approach where nodes move according to the mutual repulsion of the neighboring nodes. The iterative node-repel approach is coupled with an octree-based technique for the efficient projection of the nodes on the external surface in order to constrain the node distribution inside the domain. Several tests are carried out on three different mechanical components of practical engineering interest and characterized by complexity of their geometry. The generated node distributions are then employed to solve a steady-state heat conduction test problem by using the Radial Basis Function-generated Finite Differences (RBF-FD) meshless method. Excellent results are obtained in terms of both quality of the generated node distributions and accuracy of the numerical solutions.
Modelling turbulent heat transfer in rough channels using phenomenological theory
Authors: Peeters J W R 
Published: December 2021

Abstract
Rough walls are often encountered in industrial heat transfer equipment. Even though it is well known that a rough wall affects velocity fields and thermal fields differently (and therefore also skin friction factors and Stanton or Nusselt numbers), predicting the effect of rough walls on turbulent heat transfer remains difficult. A relation between the scalar spectrum and the Stanton number is derived for channels with both smooth and rough walls. It is shown that the new relation agrees reasonably well with recent DNS experiments for wall roughness sizes of k
+
< 150 and when Pr = 0.7 − 1.0. Under these conditions, a thermal analogue of Moody’s diagram can be created using the newly developed relation.
Heat transfer in shallow caves: influence of turbulent convection
Authors: Qaddah B , Soucasse L , Doumenc F , Mergui S , Rivière P , Soufiani A 
Published: December 2021

Abstract
The enhancement of the conservation conditions of cave paintings requires a detailed understanding of heat transfer in such cavities. This article presents a numerical investigation of turbulent free convection in a parallelepipedic cavity. Non-homogeneous wall temperatures are prescribed from a large-scale model taking into account external temperature fluctuations damped by heat diffusion in the rock massif above the cavity. Large Eddy Simulation is performed to solve the turbulent flow fields for a given wall temperature field corresponding to a Rayleigh number of 8.5 x 109. The outcomes of the model are analysed in terms of statistical mean. Results show complex large scale flow patterns with regions of high turbulent intensity. The Q-criterion is used to identify turbulent structures for an instantaneous flow field. Then we analyse the spatial distribution of the conductive heat flux at the walls to locate the regions with intense convection. We show that the conductive flux smaller than the wall-to-wall radiative flux in the major part of the cavity, and close to its value at some spots.
Jet impingement cooling using fluidic oscillators: an experimental study
Authors: Saliba Georges , Raimbault Vincent , Colin Stéphane , Batikh Ahmad , Orieux Stéphane , Gilblas Rémi , Baldas Lucien 
Published: December 2021

Abstract
A growing portion of the thermal load on board airplanes is due to densely packed electronic systems. This increased thermal load along with constraints on weight and volume have made simple and reliable cooling solutions an urgent need in the aerospace industry. There is a wealth of cooling solutions available in order to meet these demands, the simplest and most adaptable of which is probably jet impingement cooling. In this study, fluidic oscillators capable of producing pulsating jets were used to cool a heated surface and were then compared to equivalent steady jets. Although pulsating jets can be produced using a number of devices, fluidic oscillators offer the advantage of not having any moving parts. These oscillators are sustained by a self-induced internal flow instability and can function at different scales. Although the major part of this work is based on prototypes that produce jets with sub-millimetric widths, designs at one tenth that scale, i.e. with an exit slot width of 50 µm, are also presented. Reynolds numbers ranging from ReD = 3500 to 5250 and jet-to-plate spacing from 1D to 10D were studied (where D is the initial width of the jet). The Nusselt number distribution is found for each case and a comparison is made between the performance of equivalent steady and pulsating jets based on the average Nusselt number.
Dynamic LES of the magnetohydrodynamic flow in a square duct with the varied wall conductance parameters
Authors: Blishchik A , Kenjereš S 
Published: December 2021

Abstract
The current study is focused on the magnetohydrodynamics and demonstrates how electrical conductivity of the wall can affect the turbulent flow in the square duct. Different variations of the boundary walls have been considered including arbitrary conductive walls. The Large Eddy Simulations method with the dynamic Smagorinsky sub-grid scale model have been used for the turbulent structures resolving. Results show the significant impact of the wall conductance parameters for both Hartmann and side walls.
Hydrogen diffusion under the effect of stress and temperature gradients
Authors: Zhang Zhichao , Ayas Can , Popovich Vera , Peeters Jurriaan 
Published: December 2021

Abstract
In this paper, a finite element (FE) model is developed to investigate lattice hydrogen diffusion in a solid metal under the influence of stress and temperature gradients. This model is applied to a plate with a circular hole which is subjected to temperature and hydrogen concentration gradients. It is demonstrated that temperature gradients significantly influence hydrogen diffusion and hence susceptibility to hydrogen embrittlement when utilizing hydrogen for gas turbines.
Algorithms for thermal diffusivity measurement of heterogeneous 1D materials based on Infrared Microscopy Enhanced Angstrom Method
Authors: Guo Wei , Chen Anqi , Wu Yanyan , Zhu Yuan , Zeng Shaobo 
Published: December 2021

Abstract
An infrared microscopy enhanced Angstrom method has been develpoed to measure the thermal diffusivity. Infrared microscopy technique can acquire temperatures of multiple points at one shot. Two algorithms for calculating thermal diffusivity were proposed and compared in practice. One is based on global temperature data and the other is based on local temperature data. The according calculated thermal diffusivities are denoted as

α

n

G

and

α

n

L

. Three 1D materials of different heterogeneity (Cu wire, Ni-Cu wire and PVA-CNT fiber) were measured on the experimental platform. The calculated

α

n

G

and

α

n

L

values show that for homogeneous material such as Cu, these two algorithms give similar results, while for heterogeneous ones (Ni-Cu and PVA-CNT), they come to be discrepant. The data fluctuation analysis of

f

n

L

zooms in the discrepancy and verifies that

α

n

L

is more sensitive to local property change and more competent in revealing heterogeneous properties.
A 2D Numerical Simulation of Binary Alloy Solidification: Effect of Mesh Resolution on Formation of Channel Segregates
Authors: Kumar Alok , Singh Anup , Kumar Arvind 
Published: December 2021

AbstractMesh refinement is crucial for capturing the complex phenomena that governs the formation of channel segregates during binary alloy solidification. In this article, the influence of mesh size on the formation of channel segregates during the solidification of Sn-5wt%Pb alloy is numerically investigated. A solver is developed in OpenFOAM for solving the coupled transport equations of mass, momentum, energy and species. Subsequently, the simulations are performed for different mesh sizes to predict the flow field, temperature, species and solid fraction distribution including the morphology of channel segregates. From this study, it is observed that the mesh size significantly affects the morphology and the strength of channel segregates. For very fine mesh size, having sufficient number of grid point along their width, the formed channels are more continuous and the flow inside channels is resolved.
Optimal design of subcooled triangular microchannel heat sink exchangers with variable heat loads for high performance cooling
Authors: Ariyo David Olugbenga , Bello-Ochende Tunde 
Published: December 2021

Abstract
Deionized water at a temperature of 25 °C was used as the cooling fluid and aluminium as the heat sink material in the geometric optimization and parameter modelling of subcooled flow boiling in horizontal equilateral triangular microchannel heat sinks. The thermal resistances of the microchannels were minimized subject to fixed volume constraints of the heat sinks and microchannels. A computational fluid dynamics (CFD) ANSYS code used for both the simulations and the optimizations was validated by the available experimental data in the literature and the agreement was good. Fixed heat fluxes between 100 and 500 W/cm2 and velocities between 0.1 and 7.0 m/s were used in the study. Despite the relatively high heat fluxes in this study, the base temperatures of the optimal microchannel heat sinks were within the acceptable operating range for modern electronics. The pumping power requirements for the optimal microchannels are low, indicating that they can be used in the cooling of electronic devices.
Forced convection heat transfer characteristics of Al2O3 nanofluids in a minichannel - an experimental study
Authors: Roque D , Ajeeb W , Murshed S M S , Pereira J M C 
Published: December 2021

Abstract
In this study, an experimental investigation on the convective heat transfer characteristics of Al2O3 nanofluids flowing through an horizontal minichannel under the laminar and turbulent flow and constant heat flux conditions is performed. Several sample nanofluids were prepared using two base fluids (water and the mixture 80/20 DW/EG vol.%) and several low concentrations of Al2O3 nanoparticles ranging from 0.01 to 0.1 vol%. An existing experimental setup was modified for this study. The measurements were taken for the base fluid and nanofluids at each flow and heating conditions. The results are analyzed in terms of Nu and friction factor (f) in comparison with those of the base fluid. The results demonstrate that the used low concentrations of Al2O3 nanoparticles are not enough to yield any noticeable enhancement in heat transfer of the nanofluid samples. The deviations between the results of the nanofluids and the base fluid are small and within the uncertainty range of the experimental setup.
Velocity measurements of individual droplets in liquid-liquid Taylor flows in circular capillaries
Authors: Shojaee Zadeh Seyyed Saeed , Walsh Patrick , Egan Vanessa 
Published: December 2021

Abstract
This study is focused on the effect of droplet length on droplet velocity in liquid-liquid Taylor flows for microfluidic applications. An experimental set up was designed to measure droplet velocity over a wide range of droplet lengths and flow velocities while also varying viscosity ratio. Five different fluid combinations were examined by employing AR20, FC40, HFE7500 and water. Results indicate the complexity of predicting droplet velocity in such flow regimes and also show a strong influence of viscosity ratio and Bond number.
Modelling plant transpiration and leaf climate using CFD
Authors: Plas Wito , De Paepe Michel 
Published: December 2021

Abstract
Research into vertical farms or plant factories is steadily increasing over the years, as the demand for sustainable food production and a shift to more environmental friendly food production is occurring. Modelling plant climate in these confined spaces is therefore essential to guarantee optimal growing conditions. Modelling of plant climate has already been done in greenhouses, but at length scales much bigger than individual leaves. In this study, one single plant will be modelled, using computational fluid dynamics and by incorporating additional source terms in the relevant transport equations. Plants are modelled using the big leaf approach, where a plant is modelled as one artificial leaf. Water vapour flux in plants is controlled by two resistances in series, the aerodynamic resistance, which is a function of the boundary layer around the leaves and the stomatal resistance, which is the resistance against water vapour transport in leaves. Two different plants are studied, impatiens pot plant and basil plants. Values of stomatal resistance for these crops are obtained from literature or were measured. Evapotranspiration was compared with the Penman-Monteith equation.
A parametric analysis of thermodynamic losses in an anode of a solid oxide fuel cell
Authors: Prokop Tomasz , Brus Grzegorz , Kimijima Shinji , Szmyd Janusz 
Published: December 2021

Abstract
In this paper, generation of thermodynamic losses in the micro-channels of a Solid Oxide Fuel Cell electrode is discussed. Diffusive-convective equation is implemented to compute local concentrations of reagents. The model accounts for both the Fick’s, and the Knudsen’s diffusion. For a number of cases the total losses are decomposed to isolate the contributions of the diffusion, the current conduction, and the chemical reaction irreversibilities.
Thermodynamic modeling and controlling of a combined Free Piston Stirling Engine System (FPSE) with a Permanent Magnet Linear Synchronous Machine (PMLSM)
Authors: Majidniya M , Boileau T , Remy B , Zandi M 
Published: December 2021

Abstract
Converting thermal energy to electricity is one of the most common energy conversions in the field of electricity production. This transformation of energy is essential for both renewable and non-renewable heat sources. One of the main parameters of such a system that is responsible for this conversion is its efficiency. To have an efficient transformation, many improvements have been made to the old methods, and also new techniques were developed. One of these new methods that will be discussed here is a combined system of a Free Piston Stirling Engine (FPSE) with a Permanent Magnet Linear Synchronous Machine (PMLSM). The two purposes of presenting such a system are that firstly, the theoretical efficiency of a Stirling engine is high. Secondly, by eliminating crank-shaft from this system compared to the standard Stirling engine system, some of the losses will be removed. To study this system, a thermodynamic model of a RE-1000 FPSE was presented and validated. Then it was coupled with a PMLSM, and the combined system was controlled. The total efficiency of this system in steady-state is 14.4%.
Performance evaluation of thermoelectric generators under cyclic heating
Authors: Williams N P , Roumen L , McCauley G , O’Shaughnessy S M 
Published: December 2021

Abstract
The effect of thermal cycling on thermoelectric generator (TEG) performance is investigated for six nominally identical samples subjected to the same heating cycle profile. All TEGs experienced performance degradation, with maximum power outputs between 28 % and 49 % of pre-cycling values and a post-cycling decrease in the dimensionless figure of merit ZT of 21 % to 49 %. Sudden significant power reductions and subsequent internal resistance increases were observed for all samples, indicative of internal damage to the structure of the TEGs arising from material interface separation and micro-crack formation.
Lumped parameter modelling of two-phase ejectors: numerical implications of the equilibrium assumptions
Authors: Besagni Giorgio 
Published: December 2021

Abstract
The use of carbon dioxide as refrigerant is attracting a growing attention and is a cutting-edge research topic. In spite of its many advantages, carbon dioxide has a major shortcoming, viz., low critical temperature. Owing to the low critical temperature, carbon dioxide cycles encompass both the sub-critical and the trans-critical operation conditions; the trans-critical operating conditions are characterized by high thermodynamic losses, requiring particular attention in the integrated component/system design criteria. In this perspective, in recent years, ejector technology has been widely recognized as a promising technical solution to support the deployment of carbon dioxide cycles, by reducing throttling losses. Unfortunately, the large variation in system operations as well as the changes in sub-critical and trans-critical operating conditions makes the numerical simulation of carbon dioxide ejector-based system a cutting-edge challenge. This paper contributes to the present day discussion on the validation of lumped parameter models for carbon dioxide ejectors. A model taken from the literature has been tested against literature data and the equilibrium assumptions, underlying the modelling approach have been tested.
Computational fluid dynamic modelling of supersonic ejectors: comparison between 2D and 3D modelling
Authors: Besagni Giorgio , Croci Lorenzo , Cristiani Nicolò , Inzoli Fabio , Guédon Gaël Raymond 
Published: December 2021

Abstract
It is known that the global performances of ejector-based systems (viz., at the “global-scale”) depend on the local flow properties within the ejector (viz., at the “local-scale”). For this reason, reliable computational fluid-dynamics (CFD) approaches, to obtain a precise and an a-priori knowledge of the local flow phenomena, are of fundamental importance to support the deployment of innovative ejector-based systems. This communication contributes to the existing discussion by presenting a numerical study of the turbulent compressible flow in a supersonic ejector. In particular, this communication focuses on a precise knowledge gap: the comparison between 2D and 3D modelling approaches as well as density-based and pressure-based solvers. The different approaches have been compared and validated against literature data consisting in entrainment ratio and wall static pressure measurements. In conclusion, this paper is intended to provide guidelines for researchers dealing with the numerical simulation of ejectors.
Nanofluid suspensions as heat carrier fluids in single U-tube borehole heat exchangers
Authors: Jahanbin A , Semprini G , Pulvirenti B 
Published: December 2021

Abstract
The borehole heat exchanger (BHE) is a critical component to improve energy efficiency and decreasing environmental impact of ground-source heat pump systems. The lower thermal resistance of the BHE results in the better thermal performance and/or in the lower required borehole length. In the present study, effects of employing a nanofluid suspension as a heat carrier fluid on the borehole thermal resistance are examined. A 3D transient finite element code is adopted to evaluate thermal comportment of nanofluids with various concentrations in single U-tube borehole heat exchangers and to compare their performance with the conventional circuit fluid. The results show, in presence of nanoparticles, the borehole thermal resistance is reduced to some extent and the BHE renders a better thermal performance. It is also revealed that employing nanoparticle fractions between 0.5% and 2 % are advantageous in order to have an optimal decrement percentage of the thermal resistance.
Experimental analysis of the thermal comfort provided by an electrical heater and a heat pump
Authors: García-Cascales J R , Illán-Gómez F , Velasco F J S , Vera-García F , Dengra Vera A , García F 
Published: December 2021

Abstract
After considering heating sector, one realises that there is no clear and consensual way to quantify or qualify the thermal comfort of the different technologies available to satisfy the heating demand of a home. This contribution tries to call attention to this by means of an experimental study of the thermal comfort provided by two very different technologies, an electrical heater and a heat pump. To do so, a test matrix is developed by considering [2]. Some experiments are carried out in a climate chamber constructed following [1]. The variables registered are used to determine the comfort variables defined in [3] for each technology. After both technologies are compared and some conclusions are drawn.