Effects of Aligned Magneticfield and Radiation on the Flow of Ferrofluids Over a Flat Plate with Non-uniform Heat Source/sink

In this study we analyzed the influence of radiation and aligned magneticfield on the flow of ferrofluids over a flat plate in presence of non-uniform heat source/sink and slip velocity. We considered Fe3O4 magnetic nano particles embedded within the two types of base fluids namely water and kerosene. The governing partial differential equations are transformed into nonlinear ordinary differential equations by using similarity transformation and solved numerically using bvp5c Matlab package. The effects of dimensionless quantities on the flow and temperature profiles along with the friction factor and Nusselt number is discussed and presented through graphs and tables. It is found that present results have an excellent agreement with the existed studies under some special assumptions. Results indicate that a raise in the aligned angle enhances the skin friction coefficient and heat transfer rate

Conference Proceedings: 1st International Conference on Nanofluids (ICNf2019), 2nd European Symposium on Nanofluids (ESNf2019)

Conference proceedings of the 1st International Conference on Nanofluids (ICNf2019) and 2nd European Symposium on Nanofluids (ESNf2019), 26-28 June 2019 in Castelló (Spain), organized by Nanouptake Action (CA15119) and Universitat Jaume

Experimental research and development on the natural convection of suspensions of nanoparticles

Suspensions of nanoparticles, widely known as nanofluids, are considered as advanced heat transfer media for thermal management and conversion systems. Research on their convective thermal transport is of paramount importance for their applications in such systems such as heat exchangers and solar collectors. This paper presents experimental research on the natural convection heat transfer performances of nanofluids in di erent geometries from thermal management and conversion perspectives. Experimental results and available experiment-derived correlations for the natural thermal convection of nanofluids are critically analyzed. Other features such as nanofluid preparation, stability evaluation and thermophysical properties of nanofluids that are important for this thermal transfer feature are also briefly reviewed and discussed. Additionally, techniques (active and passive) employed for enhancing the thermo-convection of nanofluids in di erent geometries are highlighted and discussed. Hybrid nanofluids are featured in this work as the newest class of nanofluids, with particular focuses on the thermophysical properties and natural convection heat transfer performance in enclosures. It is demonstrated that there has been a lack of accurate stability evaluation given the inconsistencies of available results on these properties and features of nanofluids. Although nanofluids exhibit enhanced thermophysical properties such as viscosity and thermal conductivity, convective heat transfer coe cients were observed to deteriorate in some cases when nanofluids were used, especially for nanoparticle concentrations of more than 0.1 vol.%. However, there are inconsistencies in the literature results, and the underlying mechanisms are also not yet well-understood despite their great importance for practical applications.The Fundação para a Ciência e Tecnologia (FCT), Portugalhttp://www.mdpi.com/journal/nanomaterialsam2021Mechanical and Aeronautical Engineerin

Steady and unsteady aligned magnetohydrodynamics free convection flows of magnetic and non magnetic nanofluids along a wedge, vertical and inclined plates

Nanofluids are a new type of heat transfer fluid engineered by uniform and stable suspension of nanometer sized particles into liquids. The heat transfer in nanofluids is important especially in the context of chemical engineering, aerospace engineering and industrial manufacturing processes. The reason is that, nanofluids were found to transfer heat more efficiently than the conventional fluids. Therefore, nanofluids research could lead to a major breakthrough in developing next generation coolants for numerous engineering applications. Due to this reason, several flow problems related to heat transfer over vertical flat plate, inclined plate and wedge were studied in this thesis. The main purpose of this study was to investigate the characteristics of two dimensional flow and surface heat transfer for two cases which are steady and unsteady convection flows. Nanofluids with two different base fluids (water and kerosene) containing magnetic and non magnetic nanoparticles were considered. The effect of magnetohydrodynamics (MHD) on the flow and heat transfer was also studied. The study starts with the formulation of the mathematical models that governed the fluid flow and heat transfer. Next, the governing nonlinear equations in the form of partial differential equations were reduced into ordinary differential equations using appropriate similarity transformation. The resulting systems of ordinary differential equations were then solved numerically using Keller box method. The numerical values of the skin friction coefficient, the local Nusselt number which represents the heat transfer rate at the surface as well as the velocity and temperature profiles were obtained for various values of the magnetic field inclination angle, magnetic interaction, plate inclination angle, nanoparticles volume fraction, wedge angle, moving wedge, unsteadiness, Grashof number and thermal buoyancy. All results obtained, were displayed graphically in addition to tabular form. The comparisons of results with previous studies were made to validate the results. For both steady and unsteady problems, it is found that magnetic field inclination angle can be used as controlling factor for certain situation because it enhances the skin friction and heat transfer rate. The plate inclination angle parameter and nanoparticles volume fraction parameter have tendency to increase momentum and thermal boundary layers thickness. For unsteady problems, it is observed that the unsteadiness parameter has significant effect on the nanofluids motion and heat transfer characteristic

Thermally-actuated, phase change flow control for microfluidic systems

An easy to implement, thermally-actuated, noninvasive method for flow control in microfluidic devices is described. This technique takes advantage of the phase change of the working liquid itself—the freezing and melting of a portion of a liquid slug—to noninvasively close and open flow passages (referred to as a phase change valve). The valve was designed for use in a miniature diagnostic system for detecting pathogens in oral fluids at the point of care. The paper describes the modeling, construction, and characteristics of the valve. The experimental results favorably agree with theoretical predictions. In addition, the paper demonstrates the use of the phase change valves for flow control, sample metering and distribution into multiple analysis paths, sealing of a polymerase chain reaction (PCR) chamber, and sample introduction into and withdrawal from a closed loop. The phase change valve is electronically addressable, does not require any moving parts, introduces only minimal dead volume, is leakage and contamination free, and is biocompatible

Selected papers of the "1st International Conference on Nanofluids (ICNf)"

This Special Issue of Energies has emerged as a result of the 1st International Conference on Nanofluids (https://icnf2019.com/), which was organized under the auspices of Nanouptake COST Action (Overcoming Barriers to Nanofluids Market Uptake, http://www.nanouptake.eu/) in Castelló (Spain), in June 2019. The foci of ICNf2019 were the production and the characterisation of nanofluids for different areas of applications in the energy fields, namely heat transfer, storage of thermal energy, boiling, and solar systems, as well as industrial applications and health and safety issues. The first conference edition on this topic gathered more than 200 participants from 45 different countries. More than 125 contributions were presented in the nine sections of the congress. Some selected authors were invited to send extended versions of their work to the Energies ICNf2019 Special Issue. After a careful review process, nine articles from six different countries were selected for compilation in this Special Issue: a total of seven full research papers and two reviews. These papers cover a broad range of fundamental and applied research aspects on nanofluid science and development, and reflect the current investigations, knowledge, and challenges encountered in the use of nanofluids for energy applications

Investigation into stability and thermal-fluid behaviour of hybrid nanofluids as heat transfer fluids

Thesis (PhD (Mechanics))--University of Pretoria, 2021.The need to improve the poor thermal conductivity of conventional fluids to produce adequate heat transfer fluid cannot be over-emphasized, knowing fully well that heat transfer is key in any engineering process line. Hence, the birth of nanofluids, which is the formulation of a composite of suspended nanoparticles in a basefluid. Nanofluids have found wide applications ranging from heat exchangers, electronic cooling, automotive industry, medical, military, solar energy, manufacturing industry, to mention but a few. But the limitations of nanofluids led to the entrance of a new working fluid named binary nanofluid and ternary nanofluid. This study experimented with the trio influence of temperature (T), percent weight ratios (PWRs), nanoparticles size (NS) on the thermophysical behaviour of MgO–ZnO/Deionised water binary nanofluids (BNFs). 20 nm nano-size of ZnO nanoparticles were hybridised with MgO nanoparticles of nano-sizes 20 nm and 100 nm, and dispersed in deionised water to prepare 0.1 vol% binary nanofluids for percent weight ratios of MgO:ZnO (20:80, 40:60, 60:40 and 80:20). The viscosity (μ), electrical conductivity (σ), pH, and thermal conductivity (κ) of the binary nanofluids were experimentally evaluated for temperature 20 to 50 °C. Morphology was checked, and stability was monitored. The impact of temperature, PWRs, and nano-size on the pH, μ, σ, and κ of the binary nanofluid were ordered as PWR >NS >T, NS> PWR>T, T>NS >PWR, and T >NS >PWR, respectively. Using the obtained experimental dataset, correlations were proposed for the thermal property of each binary nanofluid as a function of temperature. Also, investigating the trio impact of PWR, temperature and � on the thermophysical characteristics of MgO-ZnO/DIW BNFs, to help close up the scarce literature gap. 20 nm nanoparticle sizes of MgO and ZnO were hybridized together and dissolved in deionized water to formulate 0.1 vol% and 0.05 vol.% binary nanofluids (NFs) for PWR of 20:80, 40:60, 60:40, 80:20 (MgO:ZnO). The κ for all BNFs was enhanced under the impact of rising temperature, with maximum κ enhancement of 5.60% and 22.07% relative to the deionised water (DIW) achieved for 0.05 vol% and 0.10 vol%, separately. The σ was enhanced slightly under the influence of increasing temperature, with maximum enhancement of 21.82% and 30.91% achieved for 0.050 vol% and 0.10 vol%, respectively. In addition, viscosity under temperature increase exhibited a decreasing pattern for all nanohybrids and basefluid. Furthermore, to better harness the benefit of the BNFs for thermal application, thermoelectrical conductivity (TEC) was evaluated with BNFs of 0.05 vol% observed to have higher TEC values than 0.10 vol% BNFs. The BNFs were found suitable as thermal fluids. A novel manner of furthering thermo-convection behaviour of thermal applications is the use of BNFs as heat transfer fluids. This study experimented the natural convection behaviour of MgO-ZnO NPs suspended in basefluid for � = 0.050 vol.% and 0.10 vol% at percent weight ratios of 20:80, 40:60, 60:40, 80:20 (MgO:ZnO) inside a square enclosure. Factors like Rayleigh number, Nusselt number (Nuav), coefficient of convective heat transfer (hav), and heat transfer rate (Qav) for various temperatures (20°C to 50°C) were examined. PWRs and temperature gradient of BNPs inside the binary nanofluids was observed to augment Nuav, hav, and Qav. Also, highest improvement of 72.60% (Nuav), 76.01% (hav), and 72.20% (Qav) was achieved. Employing BNFs in square enclosure yielded fine improvement for natural convection behaviour. Artificial intelligence (AI) methods, like artificial neural network (ANN) and surface fitting method were deployed to model the thermal conductivity of BNFs. For the ANN model, a learning algorithm was developed to determine the optimum neuron number. The ANN having 19 neurons in the inner layer got the optimized performance. A surface fitting method was also used on the experimental data, and the generated surface shows the behaviour of the BNFs. The outcome affirmed that the designed ANN model is best for predicting the thermal conductivity of MgO-ZnO/DIW binary nanofluids for different temperatures, nanoparticle sizes, PWRs and volume concentration over the surface fitting method.University of Pretoria Postgraduate Bursary for Doctoral Students.Olabisi Onabanjo University, Ago-Iwoye, Nigeria.Tertiary Education Trust Fund (TETFund), Abuja, Nigeria.Mechanical and Aeronautical EngineeringPhD (Mechanics)Unrestricte

Alliages base Cobalt en surfusion sous champ magnétique intense (propriétés magnétiques et comportement à la solidification)

Ce travail est dédié à l'étude de l'effet des champs magnétiques sur les propriétés magnétiques et le comportement à la solidification d'alliages à base de Cobalt en surfusion sous champ magnétique intense. Les alliages à base Co sont d'excellents candidats pour obtenir une surfusion en dessous ou proche du point de Curie sous champ intense en raison du faible écart entre ce point de Curie et la température du liquidus. Dans cette étude, un dispositif haute température de surfusion intégrant une mesure magnétique a été construit dans un aimant supraconducteur, et est utilisé pour la mesure in situ de l'aimantation de liquides surfondus et pour l'étude du sur-refroidissement et de l'évolution de la microstructure de solidification en champ intense. Le cobalt liquide en surfusion est fortement magnétique sous champ, et son aimantation est même supérieure à celle du solide au chauffage à la même température. L'aimantation de l'alliage proche eutectique Co-B en surfusion dépend de la température de surchauffe, tandis que le Co-Sn en surfusion est toujours paramagnétique. La surfusion moyenne et l'étendue de la recalescence de différents métaux et alliages est affectée par un champ externe. En champ magnétique uniforme, la surfusion du Cuivre est amplifiée, tandis que la surfusion du Cobalt et de Co-Sn reste identique. Cependant, l'étendue de la recalescence du Cobalt et de Co-Sn est réduite, et l'effet est d'autant plus important pour des teneurs supérieures en Cobalt. Le champ magnétique promeut la précipitation de la phase dendritique a-Co et la formation d'eutectique anormal dans la microstructure des alliages Co-Sn surfondus. Les processus d'évolution de la microstructure sont affectés par le champ magnétique, et dépendent de l'intensité du champ et de la surfusion. Ce travail offre de nouveaux horizons dans l'étude des propriétés magnétiques d'alliages métalliques en forte surfusion et dans l'étude de la solidification hors équilibre sous champ magnétique intense.This work is devoted to the investigation of the magnetic field effect on the magnetic properties and solidification behavior of undercooled Co based alloys in high magnetic field. Co based alloys are promising candidates to be undercooled below or approaching their Curie point in strong magnetic field due to their small temperature difference between liquid line and Curie point. In this dissertation, a high temperature undercooling facility with magnetization measurement system is built in a superconducting magnet, and is used for in situ measurement of the magnetization of the undercooled melts and study the undercoolability and solidification microstructure evolution in magnetic field. The deep undercooled Co melt is strongly magnetized in magnetic fields, and its magnetization is even larger than the magnetization of heated solid at the same temperature. The magnetization of undercooled Co-B near eutectic alloy is related with overheating temperature while the undercooled Co-Sn melt is always in paramagnetic state. Mean undercooling and recalescence extent of different metals and alloys are affected by external field. In uniform magnetic field, the undercooling of Cu is enhanced while the undercoolings of Co and Co-Sn keep constant. However, the recalescence extents of Co and Co-Sn alloys are reduced, and with the increasing Co content, the effect becomes larger. Magnetic field promotes the precipitation of aCo dendrite phase and the formation of anomalous eutectics in solidified microstructure of undercooled Co-Sn alloys. The microstructure evolution processes are affected by magnetic field depending on the field intensity and undercooling. This work opens a new way to investigate the magnetic properties of deeply undercooled metallic melts and non-equilibrium solidification in strong magnetic fields.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Heat transfer in cavities: configurative systematic review

No abstract available