Elaine M Cardoso

São Paulo State University | Unesp · Department of Mechanical Engineering

Nanocoating techniques have been used to increase the heat transfer coefficient by changing the surface morphology, which could potentially increase the heat transfer in pool boiling systems. The present study aims to determine the influence of nanocoated surfaces and the gap size on the heat transfer coefficient and the critical heat flux during t...

The search for new techniques to increase boiling heat transfer has been driven by more efficient and compact heat exchangers, especially in microelectronics and equipment with high thermal loads. Two-phase cooling systems are a promising thermal management technology for high-heat dissipation. In this context, the present study investigated the pe...

The aim of this study is to investigate the influences of different parameters on the boiling phenomenon. In this paper, a new correlation to predict the pool boiling heat transfer coefficient is presented. The developed correlation was based on a database of experimental results, taking into account the effect of surface/liquid combination by cons...

This study presents experimental results for the heat transfer coefficient during pool boiling of DI water and Al2O3-water based nanofluid at saturation conditions. Based on these data, an analysis of the heat transfer enhancement due to the nanofluids was performed. The experiments were performed for Al2O3-water based nanofluid with different volu...

This paper deals with the numerical investigation of split hemispherical fins mounted staggered over a base plate. The thermal and flow analyses have been carried out to evaluate the Nusselt number (Nu), pressure drop Δ P , and hydrothermal performance factor (HTPF) with air as a medium and Reynolds number ( Re = / 3000 to 15000). The cylindrical f...

In this research, three W-shaped ribs are taken to analyze their influence on the heat transfer rate in the internal cooling of a gas turbine blade at constant e/Dh (0.037) and heat flux. The ribs are located on rectangular channels in a square duct, and the experiments are conducted for low Reynolds numbers (12,000–20,000). The influence of Reynol...

This study experimentally investigated the flow boiling pressure drop and flow patterns of R-600a in a horizontal multiport extruded tube with 1.47 mm ID. The experiments were carried out with mass flux between 35 and 165 kgm−2s−1 and heat flux ranging from 4.5 to 18.5 kWm−2 at a saturation temperature of 24 °C. Flow patterns and void fraction dist...

The current study developed an analytical model to predict the PV module's operating temperature based on an experimental database, which considers cell temperature, local meteorological data (irradiance, ambient temperature, wind velocity, and humidity), voltage, and current generated by the photovoltaic system associated with the purely resistive...

This investigation is devoted to analyzing hydrodynamic behavior and mass transfer performance in water electrolysis processes in an alkaline solution (30%wt KOH) under different current densities, using vertical stainless steel 304 electrodes (20 mm X 60 mm) with a separation of 20 mm between them in an electrolyzer made of glass (80 mm X 80 mm X...

Due to microscale effects, the segmented microchannels or micro pin fins heat sinks came out as a high thermal management solution. In this context, the present work analyzes the influence of different heights of micro pin fins with an aligned array and investigates their influence on pressure drop and heat transfer behavior. The HFE-7100 is used a...

A geração de energia elétrica utilizando placas fotovoltaicas vem crescendo acentuadamente durante os últimos anos, principalmente, por se tratar de uma fonte de energia renovável, com impacto ambiental mínimo, comparado a outras fontes não-renováveis, mostrando-se uma alternativa viável diante da escassez de chuvas que, periodicamente, afeta a ger...

Flow patterns are found in many processes involving multiphase flows in the industry. This experimental investigation focuses on the behavior of the vorticity fields found in the liquid-vapor interface during flow boiling of R-600a with heat flux varying from 5 to 20 kW/m^2 and fixed mass flux of 890 kg/(m^2s) at a saturation temperature of 17 ºC....

The studies carried out in the area of cell preservation have been of significant importance in recent years. This process, known as cryopreservation, has been used for decades and aims to preserve various cellular materials at cryogenic temperatures. Different methods allow cryopreservation, where the best known are the slow freezing and vitrifica...

Engineered surfaces are increasingly used to cool electronic devices with dielectric fluids in two-phase change. A common type of such surfaces is the open-cell metal foam. In this work, our goal was two-fold, to assess the influence of the thickness of the foam and which models of foam-finned efficiency can be most suitably used to predict their t...

The installed solar energy capacity increased in Brazil up to 169% from 2018 to 2019. Although photovoltaic systems do not require deep maintenance, the efficiency of photovoltaic modules is decreased from 0.40 to 0.50% for each °C gained in the operating temperature. Thus, depending on the environmental conditions, a cooling system is necessary to...

It is notable the advancement in the high-power electronics development and the miniaturization of devices, requiring higher levels of energy dissipation. This work evaluates a micro-finned heat sink's thermal and hydrodynamic behavior, using convective flow boiling of the HFE-7100. Square micro-pin fins with 160 μm in height were manufactured on a...

This work used numerical techniques to calculate the extended surface efficiency and analyze the impact of the foam's thickness on its efficiency. Heat conduction was simulated in open-cell copper foam with three different thicknesses, 3 mm, 2 mm, and 1 mm, under convection boundary conditions obtained from pool boiling experiments with two dielect...

This work analyzes different working fluids (DI-water and Al2O3-water based nanofluid) flowing in a copper microchannel heat sink consisting of 20 parallel rectangular channels of 29.23 mm in length, 1.2 mm in width, and 1.2 mm in height for each microchannel and investigates their influence on the velocity flow field, pressure drop, and heat trans...

This paper presents an experimental work on pool boiling using HFE-7100 at saturated conditions, under atmospheric pressure, and copper and nickel foams as the heating surface with four different thicknesses varying between 0.5 mm and 3 mm, followed by an analysis of the effect of foam fin-efficiency based on Ghosh model. All foams showed a better...

The evolution of the processes for modifying/manufacturing surfaces has facilitated the advancement in pool boiling research with surfaces capable of increasing the heat transfer coefficient (HTC) and the critical heat flux (CHF) through micro/nanostructures heating surfaces. The hybrid processes, which associate the removal or addition of material...

We looking for an M.Sc. student who will focus on developing modified surfaces (micro-textured and with the addition of metal foams) as a technique for boiling heat transfer intensification. It is demanded that the M.Sc. student will collaborate with other M.Sc./Ph.D. students within the research group at UNESP/Ilha Solteira and our partners. This...

This work analyzes different materials (aluminum and copper) and geometries of heat sinks, by changing the number of channels, and investigates their influence on the velocity flow field, pressure drop, and heat transfer. The CFD software ANSYS FLUENT® was applied. The water is used as the working fluid. A uniform velocity and temperature (293.15 K...

The continuous search for techniques that optimize the heat transfer process, including phase-change processes, makes it necessary to understand the vapor bubble dynamics in the boiling process. The present work aims to study the bubble growth and departure process from an artificial cavity in the saturated nucleate boiling regime using HFE-7100 as...

Direct-Immersion Cooling nucleate boiling with dielectric fluids is a suitable solution for the industry of electronics because they allow the components to be immersed without short-circuiting damage and have a low saturation temperature, which keeps the system below the critical temperature. The use of techniques to extend or modify the heating s...

Porous structures, as metal foams, can enhance the heat transfer performance. For a safe industrial application , a predictive model for both heat transfer coefficient and maximum heat flux is required. But, there is no correlation for dielectric fluids on metal foams available in the literature. This work aims to develop a correlation based on dim...

Flow patterns are found in many processes involving multiphase flows in the industry. This experimental investigation focus on the behavior of the vorticity fields found in the liquid-vapor interface during flow boiling of R-600a with heat flux varying from 5 to 20 kW/m2 and fixed mass flux of 890 kg/(m2s) at a saturation temperature of 17 ºC. Test...

The studies carried out in the area of cell preservation have been of major importance in recent years. This process, known as cryopreservation, has been used for decades and aims to preserve various cellular materials at cryogenic temperatures. There are different methods that allow cryopreservation, where the best known are the slow freezing and...

Boiling heat transfer has been a trending research area for the last several decades due to its excellent heat removal capacity and direct applications in the distillation and pharmaceutical industries. The present investigation focuses on the augmentation of efficiency for the boiling requiring applications, as highlighted earlier. The experimenta...

In the present work, an attempt was made to experimentally quantify the boiling heat transfer coefficient (BHTC) of graphene oxide-water nano-suspension (NS) inflow boiling heat transfer regime. The NS was prepared at weight fractions of 0.025, 0.05, and 0.1% using the two-step method and further stabilized for 17 days (at wt% = 0.1). Results showe...

Microchannel based heat sinks have proven to be an effective technique for cooling high energy density devices such as microprocessors. Two-phase systems provide high heat transfer coefficients for low mass fluxes values and a uniform surface temperature distribution. The present study experimentally evaluates the performance of a microchannel-base...

Flow patterns are found in many processes involving multiphase flows in the industry. This study experimentally investigated the behavior of the velocity field in the liquid-vapor interface during flow boiling of isobutane at a saturation temperature of 17 °C with heat flux varying from 5 to 20 kW/m² and fixed mass flux of 890 kg/(m²s). Tests were...

The growing demand for techniques that optimize the heat transfer process, especially those involving phase change, makes it necessary to understand the dynamics of the vapor bubble in the boiling process. Thus, this study aims to analyze the bubble dynamics for pool boiling of HFE-7100 (at saturated conditions) on a plain copper surface. Experimen...

One promising way to enhance the heat transfer coefficient (HTC) and the critical heat flux (CHF) is modifying the heating surface morphology by using machining techniques, coating, and chemical processes. Microstructured surfaces, i.e., surfaces with the presence of micropillars on the surface, provide small perturbations in the liquid, affecting...

Pool boiling is a low-cost technique for cooling electronic devices; HFE-7100 is a dielectric fluid with advantageous properties for such application but its high wettability can cause temperature overshoot in the system. Hence, the use of porous heating surfaces improves the heat transfer performance, eliminating the temperature overshoot due to t...

An experimental apparatus and a computational routine were developed and implemented in order to obtain the sessile drop images and the contact angle measurement for different fluids and surface conditions. Moreover, experimental results of heat transfer coefficients during pool boiling of deionized water (DI water), Al2O3-DI water and Fe2O3-DI wat...

One promising way to enhance the heat transfer coefficient (HTC) and the critical heat flux (CHF) is modifying the heating surface morphology by using machining techniques, coating, and chemical processes. Micro-structured surfaces, i.e., surfaces with the presence of micro-pillars on the surface, provide small perturbations in the liquid, affectin...

Pool boiling is a suitable technique for direct immersion cooling in electronic devices coupled with dielectric fluids. However, these fluids have relatively poor thermophysical properties in contrast to water, and extremely small contact angle that causes temperature overshooting at the boiling incipience. So, the use of surface enhancement techni...

The advance of new technologies, associated with the minimization of manufacturing and installation costs, presents a great challenge for the refrigeration area since the heat generation has increased in recent years. Several studies have shown the influence of surface topography on the heat transfer performance, a strategic subject for the develop...

The objective of this work is to develop a methodology for the numerical analysis of a turbulent compressible reactive transient flow of a homogeneous premixed mixture within a convergent-divergent nozzle, applicable to rocket engines. The equations of continuity, momentum, energy and conservation of chemical species are discretized by applying the...

The need for more efficient and compact heat exchangers, especially in microelectronics, and products with high thermal load has been motivating the research on new technics for increasing the boiling heat transfer. The heated surface can be modified by using micro-fins that enlarge the effective area for heat transfer. In this context, this work a...

Pool boiling is a low-cost technique for cooling electronic devices; HFE-7100 is a dielectric fluid with advantageous properties for such application however, it can cause a temperature overshoot in the system. Hence, the use of porous heating surface improves the heat transfer performance, eliminating the temperature overshoot due to their interco...

O objetivo deste trabalho é desenvolver uma metodologia para análise analı́tica- numérica de um escoamento transiente reativo compressı́vel tubulento de mistura homogênea pré-misturada em um bocal convergente-divergente, empregado em motores a foguete. As equações de continuidade, momentum, energia e conservação de espécies quı́micas são modeladas...

One of the most challenging topics in thermal sciences is the simulation of turbulent combustion flows. However this type of flow occurs everywhere, from reciprocating internal combustion engines to rocket engines in the aerospace industry. As part of a larger research project, the main objective of this study is to present a synthesis of a large n...

Due to the high number and the variety of the physical mechanisms, the vapor bubble dynamic in pool boiling systems is not fully understood. Various models have been developed during the last decades to analyze the vapor bubble dynamic and its effects on boiling heat transfer. The present work aims to analyze the dynamic growth of a single vapor bu...

The present work analyzes the influence on the boiling heat transfer and the surface-fluid interaction (surface roughness and wettability) by adopting nanocoated heating surfaces, and gap size configurations (confined and unconfined conditions). The tests were performed using DI-water as the working fluid, at atmospheric pressure and saturation tem...

The need for more efficient and compact heat exchangers, especially in microelectronics, and products with high thermal load has been motivating the research on new technics for increasing the boiling heat transfer. The heated surface can be modified by using micro-fins that enlarge the effective area for heat transfer. In this context, we analyze...

In this work, we present the results of an analytical, numerical, and experimental analysis on the performance of a heat sink system designed as a parallel arrangement of microchannels for cooling a high-concentration photovoltaic (HCPV) cell. The analysis considered the worst-case scenario where no electricity is generated, and the solar incidence...

This study focuses on the effect of the nanostructured heating surface on the heat transfer coefficient (HTC) considering the nanofluid concentration used for coating surfaces and the heating surface morphology. Copper blocks with roughness values of Ra = 0.05 μm (smooth surface) and Ra = 0.23 μm (rough surface) were used as heating surfaces, and d...

RESUMO: Nas últimas décadas, a necessidade de produzir trocadores de calores mais eficientes e compactos, especialmente na indústria microeletrônica, tem motivado o estudo de novas técnicas para aumentar a transferência de calor por ebulição. A superfície de aquecimento pode ser modificada por meio da presença de protuberâncias (micro aletas, micro...

Um dos desafios mais importantes dos últimos anos apontados pela comunidade científica é a procura por fontes de energia renováveis com o intuito de diminuir a emissão dos gases do efeito estufa devido à utilização dos combustíveis fósseis. O aproveitamento da energia solar é uma das alternativas com maior potencial em suas duas formas de exploraçã...

The pool boiling phenomena can be largely affected by the fluid/surface interaction caused by changes in the surface roughness or in the properties of the working fluid by adding nanoparticles to the base fluid [1, 2]. This work focuses on the effect of surface roughness and nanofluid concentration on the surface wettability and the temperature pro...

This article presents experimental results for the confined and unconfined nucleate boiling of saturated HFE7100 (C 4 F 9 OCH 3) at atmospheric pressure and using nanostructured copper discs as heating surfaces. The nanos-tructures studied consisted of nanoparticles of maghemite (Fe 2 O 3) on the heating surface, comprised of a copper disc. Differe...

Nanocoating techniques have been used to increase the heat transfer coefficient by changing the surface morphology, which could potentially increase the heat transfer in case of pool boiling systems. The present work aims to study the effect of nanostructured surfaces and the gap size during the nucleate boiling of DI-water, at atmospheric pressure...

A better understanding of the mechanisms governing the nucleate boiling is required in order to intensify its use in thermal systems. Although intensive research on pool boiling processes has been undertaken for decades, the physical phenomena are still not sufficiently understood. Most of analytical studies in this area are based on empirical corr...

The pool boiling phenomena can be large affected by fluid/surface interaction caused by changes in the surface roughness or in the properties of the working fluid by adding nanoparticles to the base fluid. This work focuses on the effect of surface roughness and nanofluid concentration on the surface wettability and the wall-temperature distributio...

Solar energy could be used as a thermal energy source using solar collectors or as an electric energy source using photovoltaic cell systems. However, photovoltaic cells have some limitations regard higher temperatures and non-homogeneous temperature distributions carrying these systems to shortening its useful life and also decreasing its electric...

In this work, an analysis is proposed to simulate the growth of a single bubble on a horizontal surface in which the temperature is changing in time. Considering a hemispherical bubble, the Navier-Stokes equations, in spherical coordinates, are the mathematical model to the problem and they are solved numerically by a finite difference method. Due...

The sensitivity of contact angle to local changes in the surface morphology during nanofluid pool boiling process is critical to enhancement of the surface wettability. In this study an experimental setup and measuring scheme to predict the contact angle of a sessile droplet on a heating surface with a view to characterize the surface wettability i...

This work presents experimental results for deionized water and Al 2 O 3-DI water based nanofluid tested during pool boiling in order to investigate the effect of boiling time, nanofluid concentration, and the applied heat flux. Two nanofluid concentrations: 0.0007 and 0.007 vol.% were tested. The boiling tests were performed by applying fixed heat...

This study presents experimental results for the heat transfer coefficient during pool boiling of DI water and Al2O3-water based nanofluid at saturation conditions. Based on these data, an analysis of the heat transfer enhancement due to the nanofluids was performed. The experiments were performed for Al2O3-water based nanofluid with different volu...

This work aims to analyze the heat transfer performance during pool boiling of DI water on copper surfaces coated with maghemite nanoparticles. The nanocoated surfaces were produced by maghemite nanoparticle deposition, for different mass concentrations (0.029 and 0.29 g/l, corresponding to low and high nanofluid concentration, respectively), via b...

The fluid/surface interaction has an important influence on pool boiling phenomena and can be large affected by changing the surface roughness or the working fluid properties. This paper mainly focuses on the effect of surface roughness and nanofluid concentration on the wettability and also, on the heat transfer coefficient (HTC). In order to anal...

Os coletores fotovoltaicos/térmicos vêm ganhando destaque por sua capacidade de fornecer energia elétrica e térmica simultaneamente, e assim, melhorar a eficiência global da energia solar. Para tanto, o arrefecimento da célula fotovoltaica é necessário e a utilização de nanofluidos pode ser uma boa alternativa aos fluidos convencionais, melhorando...

In the last years, nanofluids have been extensively investigated because of their significant effect on the critical heat flux and pool boiling characteristics, due to nanoscale structures deposited on the heating surface. Researchers generally agree with the idea of a critical heat flux (CHF) enhancement, despite existing differences among the exp...

Nanofluid pool boiling can modify the morphology of the heating surface and the physical properties of the base fluids, interfering directly on the vapor bubbles dynamics and on heat transfer. In this study, the effect of surface roughness and nanoparticle concentration on the contact angle was analyzed. The tests were carried out on copper surface...

It is well known since the pioneering studies of Fritz [1935], that surface characteristics affect the boiling process. Since then, several surface modification methods were proposed focusing on the heat transfer enhancement. Most recently, with the advance of the nanotechnology, nanoscale structured surfaces are under extensive investigation in or...

The differences in the heat transfer coefficient (HTC) and critical heat flux (CHF) behaviors between nanostructured and smooth surfaces are attributed to modifications on the surface wettability and capillarity effects through the porous matrix generated by the nanostructure layer. Both act in order of improving rewetting effects, explaining the C...