scholarly journals Natural Convection Enhancement in the Annuli Between Two Homocentric Cylinders by Using Ethylene Glycol / Water Based Titania Nanofluid

2021 ◽  
Vol 80 (2) ◽  
pp. 56-73
Author(s):  
Fateh Mebarek-Oudina ◽  
Ahmed Kadhim Hussein ◽  
Obai Younis ◽  
Sara Rostami ◽  
Rasoul Nikbakhti
Keyword(s):  
Natural Convection ◽  
Ethylene Glycol ◽  
Radial Distance ◽  
Volume Ratio ◽  
Temperature Profiles ◽  
Volumetric Fraction ◽  
Cold Temperatures ◽  
Maximum Value ◽  
Water Based ◽  
Volume Method

The natural convection heat tranfer in annulate region confined between two homocentric cylinders were numerically studied in the present work. The annulus was filled by ethylene glycol / water based Titania nanofluid. Both internal and external cylinders are presereved at an isothermal hot and cold temperatures respectively, whereas, the upper and lower walls are adiabatic. The numerical solution is obtained by applying the finite volume method along with the SIMPLER, and TDMA algorithms. In the current study, the solid volumetric fraction is varied as (0 % ? ? ? 3 %), the volume ratios of EG to water are varied as (0:100 %, 40 : 60 %, 100:0 %), while both the Rayleigh number and radii ratio are considered fixed at (Ra = 104 and ? = 2). The obtained results indicated that, the average Nusselt number increases as the solid volumetric fraction and the volume ratio of ethylene glycol in the base fluid increase. Moreover, the velocity profiles reach their maximum value in the half region adjacent the internal hot wall when TiO2 – water nanofluid is used. Also, the temperature profiles decrease along the radial distance for all considered values of volume ratios of EG to water.

Numerical Study of Natural Convection in Vertical Cylindrical Annular Enclosure Filled with Cu-Water Nanofluid under Magnetic Fields

2019 ◽  
Vol 392 ◽  
pp. 123-137 ◽  
Author(s):  
Mohamed A. Medebber ◽  
Abderrahmane Aissa ◽  
Mohamed El Amine Slimani ◽  
Noureddine Retiel
Keyword(s):  
Natural Convection ◽  
Magnetic Fields ◽  
Volume Fraction ◽  
Numerical Study ◽  
Physical Parameters ◽  
Cold Temperatures ◽  
Simpler Algorithm ◽  
Wide Range ◽  
Nanoparticles Volume Fraction ◽  
Volume Method

The two dimensional study of natural convection in vertical cylindrical annular enclosure filled with Cu-water nanofluid under magnetic fields is numerically analyzed. The vertical walls are maintained at different uniform hot and cold temperatures, THand TC, respectively. The top and bottom walls of the enclosure are thermally insulated. The governing equations are solved numerically by using a finite volume method. The coupling between the continuity and momentum equations is effected using the SIMPLER algorithm. Numerical analysis has been carried out for a wide range of Rayleigh number (103≤Ra≤106), Hartmann number (1 ≤Ha≤100) and nanoparticles volume fraction (0 ≤φ≤0.08). The influence of theses physical parameters on the streamlines, isotherms and average Nusselt has been numerically investigated.

A model for thermal conductivity of carbon nanotubes with ethylene glycol/water based nanofluids

2017 ◽  
Vol 59 (02) ◽  
pp. 10-13
Author(s):  
Trong Tam Nguyen ◽  
◽  
Hung Thang Bui ◽  
Ngoc Minh Phan ◽  
◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Ethylene Glycol ◽  
Water Based

scholarly journals Tribological performance of various metal-doped carbon dots as water-based lubricant additives and their potential application as additives of poly(ethylene glycol)

Friction ◽  
2021 ◽  
Author(s):  
Weiwei Tang ◽  
Xuejun Zhu ◽  
Yufeng Li
Keyword(s):  
Ethylene Glycol ◽  
Tribological Properties ◽  
Carbon Dots ◽  
Lubricant Additives ◽  
Poly Ethylene Glycol ◽  
Wear Properties ◽  
Water Based ◽  
Friction Reducing ◽  
Poly Ethylene ◽  
Metal Doped

AbstractAdvances in nano-lubricant additives are vital to the pursuit of energy efficiency and sustainable development. Carbon dots (CDs) have been widely investigated in the domain of lubricant additives owing to their extraordinary tribological properties, in particular, their friction-reducing and anti-wear properties. Metal-doped CDs are a new type of CDs, and their friction-reducing and anti-wear properties are attracting increasing attention. Therefore, a series of CDs doped with various divalent metal ions have been successfully synthesized via one-pot pyrolysis. The tribological properties of the synthesized CDs as water-based lubricant additives are in the following order: Zn-CDs > Cu-CDs ≫ Mg-CDs > Fe-CDs > U-CDs. Specifically, adding 1.0 wt% of Zn-CDs into water-based lubricant results in 62.5% friction and 81.8% wear reduction. Meanwhile, the load-carrying capacity of the water-based lubricant increases from 120 N to at least 500 N. Zn-CDs as an additive have long service life. Additionally, anion-tuned Zn-CDs fabricated via anion exchange exhibit promise as lubricant additives for poly(ethylene glycol). Based on the results of wear scar surface analyses, it is discovered that tribochemical films, primarily composed of iron oxides, nitrides, metal carbonates, zinc oxides, zinc carbonates, organic compounds, and embedded carbon cores, formed on the rubbing surfaces with a thickness of approximately 270 nm when Zn-CDs are used as additives. This film combined with the “ball-bearing” and third-particle effects of Zn-CDs contributed to excellent lubrication performance.

Entropy generation optimization for MHD natural convection of a nanofluid in porous media-filled enclosure with active parts and viscous dissipation

2017 ◽  
Vol 27 (2) ◽  
pp. 379-399 ◽  
Author(s):  
M.A. Mansour ◽  
Sameh Elsayed Ahmed ◽  
Ali J. Chamkha
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Viscous Dissipation ◽  
Entropy Generation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Convection Flow ◽  
Negative Effects ◽  
Content Type ◽  
Volume Method

Purpose This paper aims to investigate the entropy generation due to magnetohydrodynamic natural convection flow and heat transfer in a porous enclosure filled with Cu-water nanofluid in the presence of viscous dissipation effect. The left and right walls of the cavity are thermally insulated. There are heated and cold parts, and these are placed on the bottom and top wall, respectively, whereas the remaining parts are thermally insulated. Design/methodology/approach The finite volume method is used to solve the dimensionless partial differential equations governing the problem. A comparison with previously published woks is presented and is found to be in an excellent agreement. Findings The minimization of entropy generation and local heat transfer according to different values of the governing parameters are presented in details. It is found that the presence of magnetic field has negative effects on the local entropy generation because of heat transfer and the local total entropy generation. Also, the increase in the heated part length leads to a decrease in the local Nusselt number. Originality/value This problem is original, as it has not been considered previously.

Natural Convection From Protruding Heat Sources in a Channel

2003 ◽  
Author(s):  
Tunc Icoz ◽  
Qinghua Wang ◽  
Yogesh Jaluria
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Natural Convection ◽  
Rayleigh Scattering ◽  
Convection Heat Transfer ◽  
Separation Distance ◽  
Natural Convection Heat Transfer ◽  
Temperature Profiles ◽  
Heat Sources ◽  
Convection Heat

Natural convection has important implications in many applications like cooling of electronic equipment due to its low cost and easy maintenance. In the present study, two-dimensional natural convection heat transfer to air from multiple identical protruding heat sources, which simulate electronic components, located in a horizontal channel has been studied numerically. The fluid flow and temperature profiles, above the heating elements placed between an adiabatic lower plate and an isothermal upper plate, are obtained using numerical simulation. The effects of source temperatures, channel dimensions, openings, boundary conditions, and source locations on the heat transfer from and flow above the protruding sources are investigated. Different configurations of channel dimensions and separation distances of heat sources are considered and their effects on natural convection heat transfer characteristics are studied. The results show that the channel dimensions have a significant effect on fluid flow. However, their effects on heat transfer are found to be small. The separation distance is found to be an important parameter affecting the heat transfer rate. The numerical results of temperature profiles are compared with the experimental measurements performed using Filtered Rayleigh Scattering (FRS) technique in an earlier study, indicating good agreement. It is observed that adiabatic upper plate assumption leads to better temperature predictions than isothermal plate assumption.

Solvent-mediated crystalline phases of NixSy anchored on rGO sheets as electrocatalysts for hydrogen evolution application

2019 ◽  
Vol 12 (01) ◽  
pp. 1850089
Author(s):  
Hou Lin Yu ◽  
Wenliang Shi ◽  
Shuaishuai Li ◽  
Junma Zhang ◽  
Xiaobo Zhang ◽  
...  
Keyword(s):  
Ethylene Glycol ◽  
Hydrogen Evolution ◽  
Hydrothermal Process ◽  
Volume Ratio ◽  
Decisive Role ◽  
Catalytic Performance ◽  
Deionized Water ◽  
Alkaline Media ◽  
One Pot ◽  
Alkaline Environments

A facile, one-pot solvent-mediated hydrothermal process was adopted to prepare nickel sulfide nanoparticles decorated on reduced graphene oxide (NixSy/rGO) as electrocatalysts for hydrogen evolution reaction (HER). The designed solvent (ethylene glycol and deionized water) played a decisive role in controlling both crystalline phase and morphology of NixSy/rGO composites, leading to pure [Formula: see text]-NiS nanoparticles uniformly distributed on rGO sheets under suitable volume ratio of ethylene glycol and deionized water (2:1). The optimized [Formula: see text]-NiS/rGO showed prominent HER catalytic performance with a rather small Tafel slope of 93[Formula: see text]mV/decade and prominent current density of 10[Formula: see text]mA/cm2 at the overpotential of 177[Formula: see text]mV in alkaline environments when compared to pristine [Formula: see text]-NiS and NiS2/rGO catalysts. The excellent catalytic performance and long-term durability even after 8000 cycles confirmed the potential of [Formula: see text]-NiS/rGO composites as efficient electrocatalysts for HER in the alkaline media.

Effect of Periodic Imposed Heat Flux on Three-Dimensional Natural Convection in a Partially Heated Cubical Enclosure

2016 ◽  
Vol 831 ◽  
pp. 83-91
Author(s):  
Lahoucine Belarche ◽  
Btissam Abourida
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Control Volume ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Maximum Temperature ◽  
Cubical Enclosure ◽  
Simplec Algorithm ◽  
Volume Method

The three-dimensional numerical study of natural convection in a cubical enclosure, discretely heated, was carried out in this study. Two heating square sections, similar to the integrated electronic components, are placed on the vertical wall of the enclosure. The imposed heating fluxes vary sinusoidally with time, in phase and in opposition of phase. The temperature of the opposite vertical wall is maintained at a cold uniform temperature and the other walls are adiabatic. The governing equations are solved using Control volume method by SIMPLEC algorithm. The sections dimension ε = D / H and the Rayleigh number Ra were fixed respectively at 0,35 and 106. The average heat transfer and the maximum temperature on the active portions will be examined for a given set of the governing parameters, namely the amplitude of the variable temperatures a and their period τp. The obtained results show significant changes in terms of heat transfer, by proper choice of the heating mode and the governing parameters.

scholarly journals Nestling Growth and Thermoregulatory Development in Subalpine Dusky Flycatchers

The Auk ◽  
2001 ◽  
Vol 118 (1) ◽  
pp. 116-136 ◽  
Author(s):  
Maria Elena Pereyra ◽  
Martin L. Morton
Keyword(s):  
Sierra Nevada ◽  
Volume Ratio ◽  
Cold Temperatures ◽  
Neotropical Migrant ◽  
Nestling Growth ◽  
Ambient Temperatures ◽  
Thermal Environments ◽  
Dusky Flycatcher ◽  
Rates Of Growth ◽  
Empidonax Oberholseri

Abstract The Dusky Flycatcher (Empidonax oberholseri), a small, open-nesting Neotropical migrant, is a relatively common summer inhabitant of subalpine environments in the western and southwestern United States. Nestling growth and development of thermoregulation were studied in a population at Tioga Pass (3,000 m) in the eastern Sierra Nevada of California. Despite the selective advantages that might be expected from accelerating rates of growth and thermoregulatory development, in an environment where the season was relatively short and cold temperatures and inclement weather were common, there was little evidence of adaptive modification in either of those parameters; growth rates were comparable to those of other tyrant flycatchers. Feather eruption began around day 5, brushing in dorsal and ventral tracts began two days later, and brushing of the flight feathers around day 9. Asymptotic body masses were attained around day 12, but nestlings did not fledge for another 4 to 5 days. The physiological development of endothermy was closely correlated with increases in body mass and accompanying decreases in surface-area-to-volume ratio and age, but was not significantly correlated with changes in plumage development, when mass and age were statistically controlled. On exposure to ambient temperatures between −3 and 5°C for 10 min (roughly twice as long as the average female bout of inattentiveness), individual nestlings were unable to prevent deep hypothermia until after day 7. Homeothermy, at 80% of adult levels, was not attained until after day 12, although broods of nestlings maintained relatively stable body temperatures as early as day 5. Whereas clutch sizes in this population generally ranged from two to four eggs, the most stable thermal environments were provided by broods of three or four chicks. Although broods of nestlings were generally able to maintain temperatures within 5°C of adult levels, temperature profiles during storms indicated a remarkable capacity for nestlings to tolerate temperatures in the nest as low as 15°C for periods as long as 4 h without apparent ill effect.

scholarly journals Temporal Evolution of Cooling by Natural Convection in an Enclosed Magma Chamber

Processes ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 108
Author(s):  
Carlos Enrique Zambra ◽  
Luciano Gonzalez-Olivares ◽  
Johan González ◽  
Benjamin Clausen
Keyword(s):  
Natural Convection ◽  
Magma Chamber ◽  
Temporal Evolution ◽  
Basaltic Magma ◽  
Boussinesq Equations ◽  
Rhyolitic Magma ◽  
The Times ◽  
Volume Method ◽  
The Mathematical Model ◽  
Liquid Magma

This research numerically studies the transient cooling of partially liquid magma by natural convection in an enclosed magma chamber. The mathematical model is based on the conservation laws for momentum, energy and mass for a non-Newtonian and incompressible fluid that may be modeled by the power law and the Oberbeck–Boussinesq equations (for basaltic magma) and solved with the finite volume method (FVM). The results of the programmed algorithm are compared with those in the literature for a non-Newtonian fluid with high apparent viscosity (10–200 Pa s) and Prandtl (Pr = 4 × 104) and Rayleigh (Ra = 1 × 106) numbers yielding a low relative error of 0.11. The times for cooling the center of the chamber from 1498 to 1448 K are 40 ky (kilo years), 37 and 28 ky for rectangular, hybrid and quasi-elliptical shapes, respectively. Results show that for the cases studied, natural convection moved the magma but had no influence on the isotherms; therefore the main mechanism of cooling is conduction. When a basaltic magma intrudes a chamber with rhyolitic magma in our model, natural convection is not sufficient to effectively mix the two magmas to produce an intermediate SiO2 composition.

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