Anastasios Nikolaos Georgoulas

• Dr.
• Lecturer at University of Brighton

This paper presents a feasibility study on a fully passive cooling system for electric vehicles using Loop Heat Pipes (LHP) to transfer the batteries excess heat to the underbody of the vehicle. Multiple LHPs are in contact with a battery module, on the evaporator side, while their condensers are embedded in the underbody of the vehicle, cooled via...

To explore the complicated physics of boiling heat transfer, researchers are increasingly using numerical simulation methods like the Volume of Fluid (VOF) and the Diffuse Interface (DI) approaches. The VOF method, popular for macro-scale simulations (μm to mm), effectively tracks the bubble growth and detachment. On the other hand, the DI method,...

In Battery Thermal Management System (BTMS), Loop Heat Pipes (LHPs) may act as thermal vectors connecting the bottom of the battery pack with the remote chiller of the EV’s HVAC system, whilst graphite sheets allow to achieve satisfactory temperature homogenization of the cell surface, containing the added system weight and thermally isolating one...

In this work, we present a dynamical theory of boiling based on fluctuating hydrodynamics and the diffuse interface approach. The model is able to describe boiling from the stochastic nucleation up to the macroscopic bubble dynamics. It covers, with a modest computational cost, the mesoscale area from nano to micrometers, where most of the controve...

Flow boiling within conventional, mini and micro-scale channels is encountered in a wide range of engineering applications such as nuclear reactors, steam engines and cooling of electronic devices. Due to the high complexity and importance of the boiling process, several numerical and experimental investigations have been conducted for the better u...

Building from previous successful results from the Authors, a Loop Heat Pipe (LHP) based Battery Thermal Management System (BTMS) is investigated over a range of different ambient temperatures (from 20°C to 50°C), using a state-of-the-art environmental chamber. LHPs act as thermal vector from the bottom of the battery pack to a remote chiller, whil...

Boiling has the peculiarity of being involved both in frontier technological applications, such as nano cooling, and in everyday life activities, such as food cooking. For that reason, everyone is very familiar with this kind of phase transition. Associated with the empirical knowledge of the process, despite tens of years of scientific exploration...

The authors previously proposed and successfully studied the feasibility of an innovative Battery Thermal Management System (BTMS) relying on Loop Heat Pipes (LHPs) and graphite sheets. LHPs act as thermal vector connecting the bottom of the battery pack and a remote chiller, whilst the graphite sheets allow to achieve satisfactory temperature homo...

Electric Vehicles (EVs) are at the centre of the recent industrial sustainable revolution and are identified as a potential route to reduce GHG emissions and tackling global warming. In the development of EVs, battery thermal management is a crucial aspect in ensuring high performance, market competitiveness and environmental sustainability. It is...

Microchannel heat sinks are pointed to have a great potential in cooling systems. This paper presents a systematic study to develop a microchannel heat sink to be used in cooling applications. Particular emphasis is given to PV panels cooling. A systematic experimental approach is used to optimize the heat sink geometry. Then the potential advantag...

Flow boiling within microchannel heat sinks constitute a promising solution for the cooling of high-performance electronic devices, dissipating high values of heat flux. Yet still, due to the complexity of flow boiling in small scales, the effect of important parameters is not clearly defined. In the present study a numerical investigation on the e...

Experimentalists are limited in the amount of information they can derive from drop impact experiments on porous surfaces because of the short timescales involved and the normally opaque nature of porous materials. Numerical simulations can supplement experiments and provide researchers with previously unattainable information such as velocity and...

Aiming to improve on fast charge timings, all-electric range and to reduce costs and complexity, a Battery Thermal Management System (BTMS) with Loop Heat Pipes (LHPs) and graphite sheets is proposed. The LHP placed at the bottom of a prismatic cell module will transfer heat from the cells to a chiller, already part of the HVAC system of the vehicl...

The present investigation aims to devise a thermal management system (TMS) for electric vehicles able to improve on limitations like charging time and all-electric range, together with the safety and environmental impact of the chosen thermal medium. A research gap is identified, as focus is often on addressing system thermal performance without co...

In the present paper, a fundamental analysis on the effect of the channel aspect ratio on the bubble dynamics and heat transfer characteristics for the early transient stages of the bubble growth within confined microchannels of rectangular cross-section, under saturated flow boiling conditions, is conducted, utilising high resolution, 3D, transien...

Phase change heat transfer within microchannels is considered one of the most promising cooling methods for the efficient cooling of high-performance electronic devices. However, there are still fundamental parameters, such as the effect of channel hydraulic diameter Dh, whose effects on fluid flow and heat transfer characteristics are not clearly...

An innovative Battery Thermal Management System for a 3-cell Electric Vehicle module is proposed, involving Loop Heat Pipes and graphite sheets, with the particular aim of fast charging and reacting to automotive requirements. The design feasibility is verified through a Lumped Parameter Model, which has been validated comparing the data from an ex...

In the present paper the effect of solid surface thermophysical properties under saturated flow boiling conditions within a considered microchannel is numerically investigated. The simulations are performed by utilising a custom, enhanced VOF-based solver that has been developed in OpenFOAM CFD Toolbox and accounts for conjugate heat transfer betwe...

The process of flow boiling within micro-passages plays a very important role in many industrial applications. However, there is still a lack of understanding of the effect of an important controlling parameter: surface wettability. In this paper, an advanced numerical investigation on the effect of wettability characteristics on single and multipl...

Aiming to improve on key Electric Vehicles issues, such as maximum temperature during fast charging, parasitic power and cost reduction, an innovative thermal management system for a 3-cell battery module, including a flat plate Loop Heat Pipe and graphite sheet inserts, is presented. The proposed Loop Heat Pipe, located at the bottom of the module...

In the present paper, an enhanced Volume of Fluid model is applied for the conduction of parametric numerical simulations, to investigate break-up phenomena of accelerating, elongated, vapour bubbles, within circular mini-channels. The effect of fundamental controlling parameters in the resulting break-up characteristics is investigated. Four diffe...

Anumerical investigation on the effectof wettability characteristicson a single bubble growth duringsaturated flow boiling conditions within a microchannel,is conducted in the present paper.The numerical simulations are conducted with the open-source toolbox OpenFOAM, utilising auser-enhanced Volume OF Fluid (VOF)solver.The proposed solver enhancem...

The key concept in wound dressing design and development is the fact that keeping a wound moist accelerates healing. Therefore, the selection of the appropriate wound dressing type is vital. The absorption of wound exudate by wound dressings can be considered as a microfluidic phenomenon that can be investigated either by performing high resolution...

Liquid penetration analysis in porous media is of great importance in a wide range of applications such as ink jet printing technology, painting and textile design. This article presents an investigation of droplet impingement onto metallic meshes, aiming to provide insights by identifying and quantifying impact characteristics that are difficult t...

An enhanced Volume Of Fluid (VOF) based numerical simulation framework that accounts for conjugate heat transfer between a solid region and a two-phase flow region with phase-change due to evaporation and/or condensation, is applied in order to investigate the effect of global flow oscillation frequency and amplitude on the liquid film evaporation...

An enhanced Volume Of Fluid (VOF) based numerical simulation framework that accounts for conjugate heat transfer between a solid region and a two-phase flow region with phase-change due to evaporation and/or condensation, is applied in order to investigate the effect of global flow oscillation frequency and amplitude in generated instabilities in t...

When dealing with numerical simulations of boiling phenomena, the spontaneous appearance of vapor bubbles is one of the most critical feature to be addressed. Capturing bubble formation during the dynamics, instead of patching vapor regions as initial conditions, is crucial for the correct evaluation of nucleation rates and nucleation site density,...

The prediction of flow pattern transitions is extremely important to understand the coupling of thermal and fluid dynamic phenomena in two phase systems and it contributes to the optimum design of heat exchangers. Two phase flow regimes have been extensively studied under controlled mass flow rate and velocity. On the other hand, less effort has be...

When a droplet impacts a pore with sufficiently high velocity the droplet breakups into liquid patterns both above the surface and inside the pore. In the present work, Computational Fluid Dynamics (CFD) simulations are carried out, considering the results obtained by an experimental analysis of droplets impacting on a single narrow gap, to study t...

This poster presents a droplet of water after impacting on a metallic mesh. The model is using an enhanced VOF-based numerical code where a smoothing approach that filters out spurious current velocities as well as Kistler's dynamic contact angle treatment to accurately account for surface wettability effects have been implemented within the genera...

In the present paper, an enhanced Volume Of Fluid (VOF) based numerical simulation framework is applied for the conduction of parametric numerical experiments, aiming to investigate break-up phenomena of elongated vapour slugs, within circular mini-channels. The effect of fundamental controlling parameters, in the resulting break-up characteristics...

The thermo-fluid dynamic behaviour of a Single Loop Pulsating Heat Pipe (SLPHP) has been characterized during the 66 th ESA Parabolic. The SLPHP, with a 2 mm inner diameter, has been tested in bottom heated mode, varying the working fluid (FC-72 and ethanol), the heat power input (from 1W to 24W) and the gravity level (0.01g, 1g and 1.8g). Two tran...

Flow boiling in micro-channels constitutes an effective cooling method which has been proven experimentally to be able to remove significantly high heat fluxes, while keeping the component of interest at an appropriate operating temperature. Plenty of experimental works exist in literature so far, but appropriate models to predict flow boiling heat...

Loop Heat Pipes (LHP) and other two-phase passive thermal devices, such as Heat Pipe Loops (HPL), represent a very attractive solution for the energy management of systems with a distributed presence of heating and cooling zones that request fast start-up, reliability, low cost and lightness. Even if the usual application for these devices is in th...

A numerical framework for modelling micro-scale multiphase flows with sharp interfaces has been developed. The suggested methodology is targeting the efficient and yet rigorous simulation of complex interface motion at capillary dominated flows (low capillary number). Such flows are encountered in various configurations ranging from micro-devices t...

Droplet impact on porous media has a broad range of applications such as material processing, drug delivery and ink injection etc. The simulation studies of such processes are rather limited. To represent the spreading and absorption process of the droplet on porous materials, robust numerical schemes capable of accurately representing wettability...

The present study addresses a detailed experimental and numerical investigation on the impact of water dropletson smooth heated surfaces. High-speed infrared thermography is combined with high-speed imaging to couple the heat transfer and fluid dynamic processes occurring at droplet impact. Droplet spreading (e.g. spreading ratio) and detailed surf...

The “Direct Numerical Simulations” (DNS) of droplet impact processes is of great interest and importance for a variety of industrial applications, where laboratory experiments might be difficult, costly and time-consuming. Furthermore, in most cases after validated against experimental data, they can be utilised to further explain the experimental...

A one dimensional lumped parameter model has been developed within the general framework of the open source software Octave, in order to describe the physical behaviour of a Loop Heat Pipe. By means of the electro-thermal-hydraulic analogy, this model gives the values of temperature and pressure for every part of the device, in response to varying...

In the present investigation an enhanced Volume Of Fluid (VOF) based numerical simulation framework is applied for the conduction of parametric numerical simulations, aiming to investigate observed break-up phenomena of vapour slugs, within circular mini-channel branches of a hybrid thermosyphon / pulsating heat pipe device, during microgravity exp...

This study presents the numerical reproduction of the entire surface temperature field resulting from a water droplet spreading on a heated surface, which is compared with experimental data. High-speed infrared thermography of the back side of the surface and high-speed images of the side view of the impinging droplet were used to infer on the soli...

Poster Presented in DIPSI Workshop 2017

The inescapable human desire to move further in space exploration is leading towards higher spacecraft power levels and electronics miniaturization. This trend not only affects power systems but also thermal control ones in terms of higher amount of heat to be dissipated and higher heat fluxes. PHP, a two phase passive device working in the confine...

The present numerical investigation identifies quantitative effects of fundamental controlling parameters on the detachment characteristics of isolated bubbles in cases of pool boiling in the nucleate boiling regime. For this purpose, an improved Volume of Fluid (VOF) approach, developed previously in the general framework of OpenFOAM Computational...

The coastal zone is a transitory zone between land and sea. Due to its importance to man, not only for its high food production but also for recreation, sea transportation and industrial activities, coastal zone receives high environmental pressure from him. This paper deals with degradation phenomena of the coastal zone in the west section of the...

The ability to accurately predict the dynamics of a droplets impinging on solid and porous surfaces remains of interest due to a number of important applications including material processing, ink printing, drug delivery, fuel injection etc.. In the current work we present the numerical investigation of four cases of such droplets (one based on imp...

This paper discusses the implementation of an explicit density-based solver, that utilises the central-upwind schemes for the simulation of cavitating bubble dynamic flows. It is highlighted that, in conjunction with the Monotonic Upstream-Centered Scheme for Conservation Laws (MUSCL) scheme they are of second order in spatial accuracy; essentially...

Micro-droplet formation and mobilization is an emerging area of research due to its wide-ranging usage within microfluidics application relevant to tight porous media (Andrew et al., 2015). Physical understanding of this process at the pore scale is helpful in exploring macroscopic phenomena in oil and gas recovery and also forms the basisofmany po...

This paper discusses the implementation of an explicit density-based solver, based on the central-upwind schemes originally suggested by Kurganov, for the simulation of cavitating bubble dynamic flows. Explicit density based solvers are suited for highly dynamic, violent flows, involving large density ratios, as is rather common in cavitating flows...

Nestos is one of the most important transboundary rivers flowing through Bulgaria and Greece. In the Greek part of the river, two reservoirs, the Thisavros Reservoir and the Platanovrysi Reservoir, have already been constructed and started operating in 1997 and 1999, respectively. In the first part of the chapter, the reservoir sedimentation effect...

Boiling heat transfer has been a subject of extensive investigation during the last decades. Since the subprocesses in nucleate boiling, involve quite complex physics, the development of comprehensive correlations and/or models has not been possible so far. However, more recently, numerical simulations of the boiling process have proven to be capab...

Flow Boiling heat transfer within micro-channels has been a subject of extensive investigation during the last decades. Due to the underlined complexity, the development of comprehensive correlations and/or models for flow boiling has not been possible so far. However, more recently, numerical simulations have been proven being capable of reliably...

The present investigation, identifies the exact quantitative effects of fundamental parameters, on the detachment characteristics of isolated bubbles, emanating quasi-statically from submerged orifices into isothermal liquid pools. For this purpose, a Volume of Fluid (VOF) based interface capturing approach is further improved, for the conduction o...

The heat transfer mechanism of Nucleate Boiling (NB) is widely used in technological applications. However, there is an incomplete understanding of the fundamental physics of bubble dynamics, at small scales as well as at non-trivial geometrical configurations. In order to investigate bubble dynamics an adiabatic approach is often used, where gas/v...

A steel plate is one of the critical components of a scroll expander system that can experience cavitation micro-pitting while in service. The content of the present paper consists of two distinct but interrelated parts. The first part aims to highlight that the use of computational fluid dynamics (CFD) simulations can constitute a potential tool f...

Coastal erosion that is generated by the reduction of the annual sediment yield at river outlets, due to the construction of reservoirs, constitutes one of the main environmental problems in many parts of the world. Nestos is one of the most important boundary rivers, flowing through Bulgaria and Greece, characterized by its great biodiversity. In...

An experimental study to evaluate cavitation bubble dynamics is conducted. The aim is to predict the magnitude and statistical distribution of hydrodynamic impact pressure generated from the implosion of various individual acoustic cavitation bubbles near to a rigid boundary, considering geometrical features of the pitted area. A steel sample was s...

This study investigates the long-term capacity of the North Aegean coastal systems to transport and store conservative pollutants that originate from the Black Sea. Emphasis is placed on modeling the dispersion and accumulation of a passive tracer that represents a Black Sea pollutant (BSP) substance that continuously discharges from the Dardanelle...