scholarly journals Recent Progress on Stability and Thermo-Physical Properties of Mono and Hybrid towards Green Nanofluids

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 176
Author(s):  
S.N.M. Zainon ◽  
W.H. Azmi
Keyword(s):  
Physical Properties ◽  
Visual Observation ◽  
Particle Volume ◽  
Factors Affecting ◽  
Practical Applications ◽  
Long Term Stability ◽  
Thermal Fluids ◽  
Vis Spectroscopy ◽  
The Stability ◽  
Thermo Physical Properties

Many studies have shown the remarkable enhancement of thermo-physical properties with the addition of a small quantity of nanoparticles into conventional fluids. However, the long-term stability of the nanofluids, which plays a significant role in enhancing these properties, is hard to achieve, thus limiting the performance of the heat transfer fluids in practical applications. The present paper attempts to highlight various approaches used by researchers in improving and evaluating the stability of thermal fluids and thoroughly explores various factors that contribute to the enhancement of the thermo-physical properties of mono, hybrid, and green nanofluids. There are various methods to maintain the stability of nanofluids, but this paper particularly focuses on the sonication process, pH modification, and the use of surfactant. In addition, the common techniques to evaluate the stability of nanofluids are undertaken by using visual observation, TEM, FESEM, XRD, zeta potential analysis, and UV-Vis spectroscopy. Prior investigations revealed that the type of nanoparticle, particle volume concentration, size and shape of particles, temperature, and base fluids highly influence the thermo-physical properties of nanofluids. In conclusion, this paper summarized the findings and strategies to enhance the stability and factors affecting the thermal conductivity and dynamic viscosity of mono and hybrid of nanofluids towards green nanofluids.

A Review of Preparation and Tribological Applications of Pickering Emulsion

2021 ◽  
pp. 1-27
Author(s):  
Yichen Bao ◽  
Kai Liu ◽  
Quan Zheng ◽  
Lulu Yao ◽  
Yufu Xu
Keyword(s):  
Pickering Emulsion ◽  
Solid Particles ◽  
Preparation Methods ◽  
Factors Affecting ◽  
Long Term Stability ◽  
New Strategy ◽  
New Type ◽  
The Stability ◽  
Near Future

Abstract Pickering emulsion is a new type of stable emulsion made by ultra-fine solid particles instead of traditional surfactants as stabilizers, which has received widespread attention in recent years. The preparation methods of stator-rotor homogenization, high-pressure homogenization, and ultrasonic emulsification were compared with others in this work. The main factors affecting the stability of Pickering emulsion are the surface humidity of the solid particles, the polarity of the oil phase, and the oil-water ratio. These factors could affect the nature of the solid particles, the preparation process of Pickering emulsion and the external environment. Consequently, the long-term stability of Pickering emulsion is still a challenge. The tribological investigations of Pickering emulsion were summarized, and the multifunctional Pickering emulsion shows superior prospects for tribological applications. Moreover, the latest development of Pickering emulsion offers a new strategy for smart lubrication in the near future.

Experimental Investigation for the Thermo-physical Properties and Stability of CeO2, ZrO2, and Al2O3 Mixed with Ethylene Glycol and Distilled Water

2019 ◽  
Vol 70 (11) ◽  
pp. 3908-3912
Author(s):  
Altayyeb Alfaryjat ◽  
Mariana Florentina Stefanescu ◽  
Alexandru Dobrovicescu
Keyword(s):  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Ethylene Glycol ◽  
Physical Properties ◽  
Visual Observation ◽  
Distilled Water ◽  
Step Method ◽  
Nanoparticles Concentration ◽  
Thermo Physical Properties

In this work, the effects of nanoparticles concentration on the density, thermal conductivity, and viscosity of Al2O3, CeO2 and ZrO2 suspended in 20% of ethylene glycol (EG) and 80% of distilled water (DW) is experimentally investigated. By using two step method, the nanofluid samples are provided at different concentrations, including 0.5%, 1% and 2 %. Visual observation of the nanofluid samples showed that CeO2-EG/DW and ZrO2-EG/DW have higher stability for one week more that Al2O3-EG/DW. The results indicate that the density, viscosity and thermal conductivity of the nanofluids increased with increasing the nanoparticles concentration. The highest enhancement of the thermal conductivity was found to be 9.6% for 2% concentration of CeO2-EG/DW at 25�C. Al2O3-EG/DW shows the lowest density and viscosity between all types of the nanofluids.

Experimental and Numerical Modeling for Powder Rolling

2012 ◽  
Vol 159 ◽  
pp. 115-121
Author(s):  
Zhen Xing Zheng
Keyword(s):  
Numerical Simulation ◽  
Visual Analysis ◽  
Rolling Force ◽  
Geometrical Nonlinearity ◽  
Rolling Process ◽  
Powder Rolling ◽  
Factors Affecting ◽  
Practical Applications ◽  
Process Factors ◽  
The Stability

There are multiple nonlinearities during the course of powder rolling and there is a difficulty for constructing its mechanical model and keeping the stability during the numerical calculation process. In addition, mechanical parameters determined by means of numerical simulation of rolling process are great significance both in theory and practical applications for the optimization of the process parameters and the design and manufacture of rolling equipment. Considering Material and Geometrical Nonlinearity during powder rolling, a constitutive model aiming to the powder rolling is constructed based on the Updated Lagrange (U.L.) formulation by which the basic theory of numerical simulation is deduced. The reasons are analyzed based on the experiments of powder rolling which led to the error during the numerical simulation and the effect of the different factors on powder rolling are analyzed. It is shown that the result of simulation is less than that of experiment and the whole result is dependable. The effect of various process factors is analyzed by the simulation of the rolling process and based on visual analysis of the simulation result, the primary and secondary factors affecting the relative density and the rolling force are obtained.

scholarly journals Effect of Mixing Temperature, Ultrasonication Duration and Nanoparticles/Surfactant Concentration on the Dispersion Performance of Al2O3 Nanolubricants

2020 ◽  
Author(s):  
Haijun Liu ◽  
Xianjun Hou ◽  
Xiaoxue Li ◽  
Hua Jiang ◽  
Zekun Tian ◽  
...  
Keyword(s):  
Oleic Acid ◽  
Visual Observation ◽  
Dispersion Stability ◽  
Thermal Method ◽  
Al2o3 Nanoparticles ◽  
Oleic Acid Concentration ◽  
Vis Spectroscopy ◽  
Ultrasonic Time ◽  
The Stability ◽  
Stability Time

Abstract The main goal of this study is to improve the dispersion stability of Al2O3 nanoparticles in polyalphaolefin oil to overcome the sedimentation problem of nanoparticles using the addition of oleic acid as a surfactant. This work investigates the effect of the settling time, temperature, ultrasonic duration and nanoparticles/surfactant (oleic acid) concentration on the dispersion stability of Al2O3 nanoparticles in oil-based solutions. Herein, the visual observation, UV–Vis spectroscopy, dynamic light scattering (DLS) analysis, and transmission electron microscopy (TEM) images were used to evaluate the dispersion stability of the Al2O3 nanoparticles. The results reveal that the thermal method during the synthesis of nanofluids using 50 °C temperature improves the dispersion of nanoparticles. The results also exhibited that increasing the ultrasonic amplitude and prolonging the ultrasonic time during the synthesis of nanofluids influences the dispersion stability. The results showed that the nanolubricant with 0.8 wt.% oleic acid provides better dispersion behavior. Furthermore, the nanolubricants containing 0.005wt% and 0.01wt% Al2O3 nanoparticles demonstrated outstanding dispersion performance, and the stability time reached more than 160 days.

scholarly journals A Novel Experimental Study on the Rheological Properties and Thermal Conductivity of Halloysite Nanofluids

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1834
Author(s):  
Thong Le Ba ◽  
Ahmed Qani Alkurdi ◽  
István Endre Lukács ◽  
János Molnár ◽  
Somchai Wongwises ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Halloysite Nanotubes ◽  
Visual Observation ◽  
X Ray ◽  
Conductivity Enhancement ◽  
Practical Applications ◽  
Zeta Potentials ◽  
Ft Ir ◽  
The Stability ◽  
Ft Ir Spectroscopy

Nanofluids obtained from halloysite and de-ionized water (DI) were prepared by using surfactants and changing pH for heat-transfer applications. The halloysite nanotubes (HNTs) nanofluids were studied for several volume fractions (0.5, 1.0, and 1.5 vol%) and temperatures (20, 30, 40, 50, and 60 °C). The properties of HNTs were studied with a scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDX), Fourier-transform infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRD), Raman spectroscopy and thermogravimetry/differential thermal analysis (TG/DTA). The stability of the nanofluids was proven by zeta potentials measurements and visual observation. With surfactants, the HNT nanofluids had the highest thermal conductivity increment of 18.30% for 1.5 vol% concentration in comparison with the base fluid. The thermal conductivity enhancement of nanofluids containing surfactant was slightly higher than nanofluids with pH = 12. The prepared nanofluids were Newtonian. The viscosity enhancements of the nanofluid were 11% and 12.8% at 30 °C for 0.5% volume concentration with surfactants and at pH = 12, respectively. Empirical correlations of viscosity and thermal conductivity for these nanofluids were proposed for practical applications.

Effect of the Thermostatic Expansion Valve Characteristics on the Stability of a Refrigeration System

2003 ◽  
Author(s):  
Veerendra Mulay ◽  
Dereje Agonafer ◽  
Roger Schmidt
Keyword(s):  
Low Temperature ◽  
Thermal Resistance ◽  
Physical Properties ◽  
Time Constant ◽  
System Performance ◽  
System Stability ◽  
Refrigeration System ◽  
Expansion Valve ◽  
The Stability ◽  
Thermo Physical Properties

The combination of increased power dissipation and increased packaging density has led to substantial increases in chip and module heat flux in high-end computers. The challenge has been to limit the rise in chip temperature. In the past virtually all-commercial computers were designed to operate at temperatures above the ambient. However researchers have identified the advantages of operating electronics at low temperatures. The primary purpose of low temperature cooling using vapor compression system are faster switching times of semiconductor devices, increased circuit speed due to lower electrical resistance of interconnecting materials, and a reduction in thermally induced failures of devices and components. Achievable performance improvements range from 1 to 3% for every 10°C lower transistor temperature, depending on the doping characteristics of the chip. The current research focuses on IBM’s mainframe, which uses a conventional refrigeration system to maintain chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperatures. Although performance has been the key driver in the use of this technology, the second major reason for designing a system with low temperature cooling is the improvement achieved in reliability to counteract detrimental effects, which rise as technology is pushed to the extremes. A mathematical model is developed to determine the time constant for expansion valve sensor blub. This time constant varies with variation in thermo-physical properties of sensor element that is bulb size and blub liquid. An experimental bench is built to study the effect of variation of evaporator outlet superheat on system performance. The heat load is varied from no load to full load (1KW) to find out the system response at various loads. Experimental investigation is also done to see how the changes in thermo-physical properties of the liquid in sensor bulb of expansion valve affect the overall system performance. Different types of thermostatic expansion valves are tested to investigate that bulb size; bulb constant and bulb location have significant effect on the behavior of the system. Thermal resistance between the bulb and evaporator return line can considerably affect the system stability and by increasing the thermal resistance, the stability can be further increased.

The manipulation of the physical properties of some typical zinc-blende semiconductors by the electric field

2019 ◽  
Vol 33 (09) ◽  
pp. 1950110
Author(s):  
Yan-Li Li ◽  
Hao-Yu Dong ◽  
San-Lue Hu ◽  
Jia-Ning Li ◽  
Meng-Qi Liu ◽  
...  
Keyword(s):  
Electric Field ◽  
Physical Properties ◽  
Density Functional ◽  
Stark Effect ◽  
Band Gaps ◽  
Functional Theory ◽  
Practical Applications ◽  
Nanoelectronic Devices ◽  
Zinc Blende ◽  
The Stability

In this research, we regulate the band gaps of some typical zinc-blende semiconductors by applying an external electric field. The variation of the geometric structures and the band gaps of AlP, AlAs, AlSb, GaP, GaAs, ZnO, ZnSe and ZnTe have been studied. We also calculated the stability, density of states, band structures and the charge distribution by the first-principles method based on density functional theory. Moreover, the giant Stark effect coefficients have also been analyzed in detail. From our results, we find that the magnitude and the direction of the electric field has a significant regulation effect on the band gaps and the electronic structures of AlP, AlAs, AlSb, GaP, GaAs, ZnO, ZnSe and ZnTe, which induces a phase transition from semiconductor to metal beyond a certain electric field. Therefore, we can regulate the physical properties of this type of semiconductors by tuning the magnitude and the direction of the electric field. This is very important for practical applications in nanoelectronic devices.

scholarly journals Experimental Investigation for the Thermo-physical Properties and Stability of CeO2, ZrO2, and Al2O3 Mixed with Ethylene Glycol and Distilled Water

2019 ◽  
Vol 70 (11) ◽  
pp. 3908-3912
Author(s):  
Altayyeb Alfaryjat ◽  
Mariana Florentina Stefanescu ◽  
Alexandru Dobrovicescu
Keyword(s):  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Ethylene Glycol ◽  
Physical Properties ◽  
Visual Observation ◽  
Distilled Water ◽  
Step Method ◽  
Nanoparticles Concentration ◽  
Thermo Physical Properties

In this work, the effects of nanoparticles concentration on the density, thermal conductivity, and viscosity of Al2O3, CeO2 and ZrO2 suspended in 20% of ethylene glycol (EG) and 80% of distilled water (DW) is experimentally investigated. By using two step method, the nanofluid samples are provided at different concentrations, including 0.5%, 1% and 2 %. Visual observation of the nanofluid samples showed that CeO2-EG/DW and ZrO2-EG/DW have higher stability for one week more that Al2O3-EG/DW. The results indicate that the density, viscosity and thermal conductivity of the nanofluids increased with increasing the nanoparticles concentration. The highest enhancement of the thermal conductivity was found to be 9.6% for 2% concentration of CeO2-EG/DW at 25�C. Al2O3-EG/DW shows the lowest density and viscosity between all types of the nanofluids.

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