scholarly journals Rayleigh–Bénard instability in nanofluids: a comprehensive review

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Jyoti Ahuja ◽  
Jyoti Sharma
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Base Fluid ◽  
Random Motion ◽  
Future Research ◽  
Comprehensive Review ◽  
Heat Transfer Efficiency ◽  
Low Volume ◽  
The Impact ◽  
Rayleigh Benard

AbstractThe extraordinary enhancement in heat transfer efficiency of nanofluids at extremely low volume fractions has attracted a lot of attention in identifying the governing mechanisms. The nanoscale effects, Brownian motion (random motion of particles inside the base fluid) and thermophoresis (diffusion of particles due to temperature gradient) are found to be important slip mechanisms in nanofluids. Based on these findings, a set of partial differential equations for conservation laws for nanofluids was formed. Since then, a large number of mathematical studies on convective heat transfer in nanofluids became feasible. The present paper summarizes the studies pertaining to instability of a horizontal nanofluid layer under the impact of various parameters such as rotation, magnetic field, Hall currents and LTNE effects in both porous and non-porous medium. Initially, investigations were made using the model considering fixed initial and boundary conditions on the layer, gradually the model was revised in the light of more practical boundary conditions and recently it has been modified to get new and more interesting results. The exhaustive analysis of instability problems is presented in the paper and prospects for future research are also identified.

scholarly journals Approximate Analytical Analysis of Unsteady MHD Mixed Flow of Non-Newtonian Hybrid Nanofluid over a Stretching Surface

Fluids ◽  
2021 ◽  
Vol 6 (4) ◽  
pp. 138
Author(s):  
Ali Rehman ◽  
Zabidin Salleh
Keyword(s):  
Heat Transfer ◽  
Differential Equations ◽  
Base Fluid ◽  
Research Work ◽  
Hybrid Nanofluid ◽  
Stretching Surface ◽  
Optimal Homotopy Analysis Method ◽  
Analytical Analysis ◽  
Transfer Ratio ◽  
The Impact

This paper analyses the two-dimensional unsteady and incompressible flow of a non-Newtonian hybrid nanofluid over a stretching surface. The nanofluid formulated in the present study is TiO2 + Ag + blood, and TiO2 + blood, where in this combination TiO2 + blood is the base fluid and TiO2 + Ag + blood represents the hybrid nanofluid. The aim of the present research work is to improve the heat transfer ratio because the heat transfer ratio of the hybrid nanofluid is higher than that of the base fluid. The novelty of the recent work is the approximate analytical analysis of the magnetohydrodynamics mixed non-Newtonian hybrid nanofluid over a stretching surface. This type of combination, where TiO2+blood is the base fluid and TiO2 + Ag + blood is the hybrid nanofluid, is studied for the first time in the literature. The fundamental partial differential equations are transformed to a set of nonlinear ordinary differential equations with the guide of some appropriate similarity transformations. The analytical approximate method, namely the optimal homotopy analysis method (OHAM), is used for the approximate analytical solution. The convergence of the OHAM for particular problems is also discussed. The impact of the magnetic parameter, dynamic viscosity parameter, stretching surface parameter and Prandtl number is interpreted through graphs. The skin friction coefficient and Nusselt number are explained in table form. The present work is found to be in very good agreement with those published earlier.

scholarly journals Mixed insulating and conducting thermal boundary conditions in Rayleigh–Bénard convection

2017 ◽  
Vol 835 ◽  
pp. 491-511 ◽  
Author(s):  
Dennis Bakhuis ◽  
Rodolfo Ostilla-Mónico ◽  
Erwin P. van der Poel ◽  
Roberto Verzicco ◽  
Detlef Lohse
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Heat Transport ◽  
Bottom Plate ◽  
Bulk Temperature ◽  
Stripe Pattern ◽  
Bénard Convection ◽  
Benard Convection ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

A series of direct numerical simulations of Rayleigh–Bénard convection, the flow in a fluid layer heated from below and cooled from above, were conducted to investigate the effect of mixed insulating and conducting boundary conditions on convective flows. Rayleigh numbers between $Ra=10^{7}$ and $Ra=10^{9}$ were considered, for Prandtl numbers $\mathit{Pr}=1$ and $\mathit{Pr}=10$. The bottom plate was divided into patterns of conducting and insulating stripes. The size ratio between these stripes was fixed to unity and the total number of stripes was varied. Global quantities, such as the heat transport and average bulk temperature, and local quantities, such as the temperature just below the insulating boundary wall, were investigated. For the case with the top boundary divided into two halves, one conducting and one insulating, the heat transfer was found to be approximately two-thirds of that for the fully conducting case. Increasing the pattern frequency increased the heat transfer, which asymptotically approached the fully conducting case, even if only half of the surface is conducting. Fourier analysis of the temperature field revealed that the imprinted pattern of the plates is diffused in the thermal boundary layers, and cannot be detected in the bulk. With conducting–insulating patterns on both plates, the trends previously described were similar; however, the half-and-half division led to a heat transfer of about a half of that for the fully conducting case instead of two-thirds. The effect of the ratio of conducting and insulating areas was also analysed, and it was found that, even for systems with a top plate with only 25 % conducting surface, heat transport of 60 % of the fully conducting case can be seen. Changing the one-dimensional stripe pattern to a two-dimensional chequerboard tessellation does not result in a significantly different response of the system.

Uncertainty Propagation Through a Simulation of Industrial High Pressure Die Casting

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Jiahong Fu ◽  
John Coleman ◽  
Gregory Poole ◽  
Matthew John M. Krane ◽  
Amy Marconnet
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Boundary Conditions ◽  
Die Casting ◽  
Uncertainty Propagation ◽  
Model Parameters ◽  
High Pressure Die Casting ◽  
Output Uncertainty ◽  
Pressure Die Casting ◽  
The Impact

Abstract While numerical models are often used in industry to evaluate the transport phenomena in solidification processes, the uncertainty in the results propagated from uncertain input parameters is rarely considered. In this work, in order to investigate the effects of input uncertainty on the outputs of high pressure die casting (HPDC) simulations, the Center for Prediction of Reliability, Integrity, and Survivability of Microsystems (PRISM) uncertainty quantification (PUQ) framework was applied. Three uncertainty propagation trials investigate the impact of uncertainty in metal material properties, thermal boundary conditions, and a modeling parameter on outputs of interest, such as fraction liquid at different times in the process cycle and shrinkage porosity volume, in an industrial A380 aluminum alloy HPDC process. This quantification of the output uncertainty establishes the reliability of the simulation results and can inform process design choices, such as the determination of the part ejection time. The results are most sensitive to the uncertainty in the interfacial heat transfer (for both outputs of interest) and the feeding effectivity (FE) (a model parameter controlling porosity formation determination), while the other heat transfer boundary conditions, model parameters, and all the properties play a secondary role in output uncertainty.

scholarly journals Impact of convection on thermographic analysis of silver based thermal joints

2020 ◽  
Vol 32 (4) ◽  
pp. 241-246
Author(s):  
Krzysztof Jakub Stojek ◽  
Jan Felba ◽  
Johann Nicolics ◽  
Dominik Wołczyński
Keyword(s):  
Heat Transfer ◽  
Thermal Analysis ◽  
Energy Loss ◽  
Thermal Resistance ◽  
Analysis Method ◽  
Content Type ◽  
Heat Transfer Efficiency ◽  
Lowered Pressure ◽  
Thermographic Analysis ◽  
The Impact

Purpose This paper aims to develop thermal analysis method of thermal joints characterization. The impact on convection on thermal resistance analysis with use thermography for silver-based thermal joints were investigated for non-metallized and metalized semiconductor surfaces. Heat transfer efficiency depends on thermal conductivity; radiation was used to perform thermographic analysis; the convection is energy loss, so its removing might improve measurements accuracy. Design/methodology/approach Investigation of thermal joints analysis method was focused on determination of convection impact on thermal resistance thermographic analysis method. Measuring samples placed in vacuum chamber with lowered pressure requires transparent window for infrared radiation that is used for thermographic analysis. Impact of infrared window and convection on temperature measurements and thermal resistance were referred. Findings The results showed that the silicon window allowed to perform thermal analysis through, and the convection was heat transfer mode which create 15% energy loss. Originality/value It is possible to measure thermal resistance for silver-based thermal joints with convection eliminated to improve measurements accuracy.

scholarly journals Maxwell Nanofluid Flow over an Infinite Vertical Plate with Ramped and Isothermal Wall Temperature and Concentration

2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Naveed Khan ◽  
Farhad Ali ◽  
Muhammad Arif ◽  
Zubair Ahmad ◽  
Aamina Aamina ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Molybdenum Disulfide ◽  
Wall Temperature ◽  
Base Fluid ◽  
Vertical Plate ◽  
Maxwell Fluid ◽  
Engine Oil ◽  
Isothermal Wall ◽  
The Impact ◽  
Infinite Vertical Plate

The aim of this study is to investigate how heat and mass transfer impacts the unsteady incompressible flow of Maxwell fluid. An infinite vertical plate with ramped and isothermal wall temperature and concentration boundary conditions is considered with the Maxwell fluid. Furthermore, in this study, engine oil has been taken as a base fluid due to its enormous applications in modern science and technologies. To see the importance of nanofluids, we have suspended molybdenum disulfide in engine oil base fluid to enhance its heat transfer rate. To investigate the flow regime, the system of equations was derived in the form of partial differential equations. The exact solutions to the complex system are obtained using the Laplace transform technique. Graphically, the impact of different embedded parameters on velocity, temperature, and concentration distributions has been shown. Through using the graphical analysis, we were interested in comparing the velocity, temperature, and concentration profiles for ramped and isothermal wall temperature and concentration. The magnitude of velocity, temperature, and concentration distributions is greater for an isothermal wall and less for a ramped wall, according to our observations. We observed that adding molybdenum disulfide nanoparticles to the engine oil increased the heat transfer up to 12.899%. Finally, the corresponding skin friction, Nusselt number, and Sherwood number have been calculated and presented in a tabular form.

scholarly journals Cybersecurity of Microgrid: State-of-the-Art Review and Possible Directions of Future Research

2021 ◽  
Vol 11 (21) ◽  
pp. 9812
Author(s):  
Norziana Jamil ◽  
Qais Saif Qassim ◽  
Farah Aqilah Bohani ◽  
Muhamad Mansor ◽  
Vigna Kumaran Ramachandaramurthy
Keyword(s):  
Critical Infrastructure ◽  
State Of The Art ◽  
Advanced Technology ◽  
Future Research ◽  
Electrical System ◽  
Comprehensive Review ◽  
Electrical Systems ◽  
Wide Range ◽  
Future Work ◽  
The Impact

The infrastructure of and processes involved in a microgrid electrical system require advanced technology to facilitate connection among its various components in order to provide the intelligence and automation that can benefit users. As a consequence, the microgrid has vulnerabilities that can expose it to a wide range of attacks. If they are not adequately addressed, these vulnerabilities may have a destructive impact on a country’s critical infrastructure and economy. While the impact of exploiting vulnerabilities in them is understood, research on the cybersecurity of microgrids is inadequate. This paper provides a comprehensive review of microgrid cybersecurity. In particular, it (1) reviews the state-of-the-art microgrid electrical systems, communication protocols, standards, and vulnerabilities while highlighting prevalent solutions to cybersecurity-related issues in them; (2) provides recommendations to enhance the security of these systems by segregating layers of the microgrid, and (3) identifies the gap in research in the area, and suggests directions for future work to enhance the cybersecurity of microgrids.

scholarly journals A literature review on park-and-rides

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Antora Mohsena Haque ◽  
Candace Brakewood ◽  
Shahrbanoo Rezaei ◽  
Anahita Khojandi
Keyword(s):  
Systematic Review ◽  
Best Practices ◽  
Future Research ◽  
Network Equilibrium ◽  
Comprehensive Review ◽  
Demand Models ◽  
Transit Services ◽  
Transit Agencies ◽  
The Impact ◽  
American Cities

American cities have been implementing park-and-rides (PNRs) since the 1930s; however, there has been a recent resurgence of literature examining this type of transit station. This paper aims to provide a comprehensive review of the current literature on PNRs and directions for future research. PNR studies published in the last ten years were reviewed and text mining was applied to extract key themes. Six themes were identified. The two most common areas of research were network equilibrium and optimization (12 of 37 studies) and demand models (8 of 37 studies). This was followed by guidelines and best practices as well as comparative studies (6 of 37 studies each). Parking utilization had the fewest number of recent studies (3 of 37 studies). This review revealed that the majority of PNR studies were conducted in geographic areas with extensive transit services, most studies have focused on rail-based PNRs, and the most widely used method was multinomial logit. Some areas for future research include studying remote PNRs, examining bus-based PNRs, and assessing the impact of emerging modes on PNR utilization. This systematic review could assist planners and transit agencies in further improving sustainable PNR networks in their cities.

Research on Inner Cooling Apparatus Sets in the Mold of 700mm×700mm Bloom

2011 ◽  
Vol 328-330 ◽  
pp. 1623-1626
Author(s):  
Ming Hua Bai ◽  
Jing Jing Liu ◽  
Jun Li Ge ◽  
Zhi Qiang Liu ◽  
Zhi Ming Zhang
Keyword(s):  
Heat Transfer ◽  
Casting Speed ◽  
Empirical Formula ◽  
Liquid Core ◽  
Feasibility Analysis ◽  
Equiaxed Crystal ◽  
Heat Transfer Efficiency ◽  
Improve Heat Transfer ◽  
Segregation Level ◽  
The Impact

Based on the problems emerged from market, 700mm×700mm super-large billet has been advanced. This paper calculated the casting speed and the depth of liquid core according to empirical formula for 700mm×700mm super-large billet, based on calculate and feasibility analysis acquired the appropriate casting speed is 0.2 m/min. A new mold has been advance based on mold thermoanalysis that is complex mold. Theoretically analyzed the function of setting inner cooling and deflected SEN, indicate that complex mold can improve heat transfer efficiency and equiaxed crystal ratio, reducing center segregation; level rotary flow can uniform molten steel ingredient and growth of shell, reduce the impact depth, achieve the effect of E-EMS; calculation show that reduce the depth of liquid core by applying complex mold, finally, reduce infrastructure fee of caster.

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