scholarly journals Analysis of Maxwell bioconvective nanofluids with surface suction and slip conditions in the presence of solar radiations

2021 ◽  
Author(s):  
Naseer M. Khan ◽  
Naeem Ullah ◽  
Jahan Zeb Khan ◽  
Dania Qaiser ◽  
M. Riaz Khan
Keyword(s):  
Thermal Conductivity ◽  
Brownian Motion ◽  
Base Fluid ◽  
Future Generations ◽  
Industrial Processes ◽  
Mixing Effect ◽  
The Past ◽  
Fundamental Information ◽  
Nanoparticle Suspensions ◽  
The Subject

Abstract Several researchers have studied nanofluids over the past several decades and tried to identify potential agents that are added to nanofluids (nanoparticle suspensions) with tremendous thermal conductivity. In such suspensions, the Brownian motion of nanoparticles is the only means expected to be associated with the improved thermal conductivity of nanofluids, and the sections that may add to this are the subject of main conversation and discussion. In the current evaluation, the effect of Brownian motion has been investigated by injecting nanoparticles into the base fluid, and the existing fundamental information is available at creation. Propagation results show that this mixing effect can significantly increase the thermal conductivity of nanofluids. One of the interesting features of this model is that the temperature can be increased by the energy of sunlight, which is required for some industrial processes. The stretching property of the sheet is more conducive to the temperature rise. This model contains features that have not been previously studied, which is driving demand for this model in a variety of industries, now and in future generations.

Dual Role of Nanoparticles in the Thermal Conductivity Enhancement of Nanoparticle Suspensions

2005 ◽  
Author(s):  
Calvin H. Li ◽  
G. P. Peterson
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Theoretical Models ◽  
Conductivity Enhancement ◽  
Nanoparticle Suspensions ◽  
The Difference ◽  
Physical Phenomena ◽  
Good Agreement

Experimental evidence exists that the addition of a small quantity of nanoparticles to a base fluid, can have a significant impact on the effective thermal conductivity of the resulting suspension. The causes for this are currently thought to be due to a combination of two distinct mechanisms. The first is due to the change in the thermophysical properties of the suspension, resulting from the difference in the thermal conductivity of the fluid and the particles, and the second is thought to be due to the transport of thermal energy by the particles, due to the Brownian motion of the particles. In order to better understand these phenomena, a theoretical model has been developed that examines the effect of the Brownian motion. In this model, the well-known approach first presented by Maxwell, is combined with a new expression that incorporates the effect of the Brownian motion and describes the physical phenomena that occurs because of it. The results indicate that the enhanced thermal conductivity may not in fact be due to the transport of energy by the particles, but rather, due to the stirring motion caused by the movement of the nanoparticles which enhances the heat transfer within the fluid. The resulting model shows good agreement when compared with the existing experimental data and perhaps more importantly helps to explain the trends observed from a fundamental physical perspective. In addition, it provides a possible explanation for the differences that have been observed between the previously obtained experimental data, the predictions obtained from Maxwell’s equation and the theoretical models developed by other investigators.

Latent Heat of Fusion and Melting Temperature of Molten Salt Based Carbon Nanotube Suspensions Used as Phase Change Materials

2015 ◽  
Author(s):  
Pau Gimenez-Gavarrell ◽  
Vincent D. Romanin ◽  
Sonia Fereres
Keyword(s):  
Thermal Conductivity ◽  
Energy Storage ◽  
Melting Temperature ◽  
Latent Heat ◽  
Base Fluid ◽  
Phase Change Materials ◽  
Heat Of Fusion ◽  
Latent Heat Of Fusion ◽  
Base Materials ◽  
Nanoparticle Suspensions

Thermal Energy Storage (TES) can improve the efficient and economical use of available resources associated with renewable energies. The choice of Phase Change Materials (PCM) for TES applications is particularly attractive, since PCMs provide high energy storage densities, low costs, and allow energy storage at constant temperatures during the melting/solidification process. However, most commonly used PCMs have low thermal conductivity values, typically less than 1 W/mK. This leads to insufficient heat exchange rates in many applications, where power is as important as the amount of energy stored. Previous studies have shown that adding nanoparticles to molten salts can enhance the thermal conductivity and heat capacity, thus improving performance in TES systems. This study analyzes how adding nanoparticles to ionic liquids/solids affects the latent heat of fusion and melting temperature, critical characteristics of many thermal management systems. An important aspect of nanoparticle suspension preparation is the synthesis method, both from the point of view of scalability and effect on thermophysical properties. Several nanoparticle suspensions are synthesized with carbon nanotubes (CNT) and salt or ionic liquid base materials, using different synthesis methods and sonication times. The melting point and latent heat of fusion are measured for the base materials and nanoparticle suspensions using a Differential Scanning Calorimeter (DSC). The change in latent heat and melting temperature of the nanofluid with respect to the base fluid is shown to be present but not substantial. Possible explanations for the modification of thermal properties with respect to the base fluid are discussed.

Temperature and Viscosity Effects on the Thermal Conductivity of Ferro-Nanofluid

2009 ◽  
Author(s):  
Chin-Ting Yang ◽  
Shao-Hua Cheng
Keyword(s):  
Thermal Conductivity ◽  
Brownian Motion ◽  
Diesel Fuel ◽  
Base Fluid ◽  
Volume Fraction ◽  
Volume Ratio ◽  
Polydimethyl Siloxane ◽  
Viscosity Effects ◽  
Lower Viscosity ◽  
Lower Temperature

The aim of this study is to understand the temperature and viscosity effects on the thermal conductivity of ferro-nanofluid. The base-fluid of ferro-nanofluid is made of polydimethyl-siloxane (PDMS) and diesel fuel which have similar thermal property but different viscosity. The viscosity of base-fluid is controlled by changing the volume ratio of both fluids. The measured results show that the thermal conductivity is smaller when the base fluid is highly viscous, and the thermal conductivity approaches to the value predicted by the Maxwell equation. It should be that the Brownian motion effect on highly viscous fluid is not as important as on lower viscosity fluid. Usually rising temperature will decrease viscosity of base fluid. In our study, rising temperature to 58°C can reduce the viscosity of 90%diesel fuel+10%PDMS to pure diesel fuel base fluid at 23 °C. At the same viscosity condition, rising temperature will decrease the thermal conductivity of ferro-nanofluid. The reason is that the thermal conductivity of base-fluid decrease dramatically. Comparing thermal conductivity of 2% volume fraction ferro-nanofluid to base-fluid at 23°C and 58°C respectively, the value increases 8.3% at 23 °C but increases 18.8% when the temperature is 58°C. This means the Brownian motion is more active at higher temperature than lower temperature.

Parametric Analysis of Effective Thermal Conductivity Models for Nanofluids

2012 ◽  
Author(s):  
Mohsen Sharifpur ◽  
Tshimanga Ntumba ◽  
Josua P. Meyer
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Brownian Motion ◽  
Effective Thermal Conductivity ◽  
Parametric Analysis ◽  
Base Fluid ◽  
Volume Fraction ◽  
Hybrid Models ◽  
The Impact ◽  
Conductivity Models

There is a lack of reported research on comprehensive hybrid models for the effective thermal conductivity of nanofluids that takes into consideration all major mechanisms and parameters. The major mechanisms are the nanolayer, Brownian motion and clustering. The recognized important parameters can be the volume fraction of the nanoparticles, temperature, particle size, thermal conductivity of the nanolayer, thermal conductivity of the base fluid, PH of the nanofluid, and the thermal conductivity of the nanoparticle. Therefore, in this work, a parametric analysis of effective thermal conductivity models for nanofluids was done. The impact of the measurable parameters, like volume fraction of the nanoparticles, temperature and the particle size for the more sited models, were analyzed by using alumina-water nanofluid. The result of this investigation identifies the lack of a hybrid equation for the effective thermal conductivity of nanofluids and, consequently, more research is required in this field.

scholarly journals CFD Study on Wall/Nanoparticle Interaction in Nanofluids Convective Heat Transfer

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Mohammad Reza Tarybakhsh ◽  
Ali Akbar Lotfi Neyestanak ◽  
Hamed Tarybakhsh
Keyword(s):  
Heat Transfer ◽  
Brownian Motion ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Base Fluid ◽  
Convection Heat Transfer ◽  
Constant Wall Temperature ◽  
Forced Convective Heat Transfer ◽  
The Subject ◽  
Considerable Discussion

The Brownian motion of the nanoparticles in nanofluid is one of the potential contributors to enhance effective thermal conductivity and the mechanisms that might contribute to this enhancement are the subject of considerable discussion and debate. In this paper, the mixing effect of the base fluid in the immediate vicinity of the nanoparticles caused by the Brownian motion was analyzed, modeled, and compared with existing experimental data available in the literature. CFD was developed to study the effect of wall/nanoparticle interaction on forced convective heat transfer in a tube under constant wall temperature condition. The results showed that the motion of the particle near the wall which can decrease boundary layer and the hydrodynamics effects associated with the Brownian motion have a significant effect on the convection heat transfer of nanofluid.

scholarly journals Limits for thermal conductivity of nanofluids

2010 ◽  
Vol 14 (1) ◽  
pp. 65-71 ◽  
Author(s):  
Chandrasekar Murugesan ◽  
Suresh Sivan
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Particle Shape ◽  
Large Degree ◽  
The Past ◽  
Upper Limit ◽  
Upper Limits ◽  
Transfer Mechanisms

Nanofluids have offered challenges to thermal engineers and attracted many researchers over the past decade to determine the reasons for anomalous enhancement of thermal conductivity in them. Experiments on measurement of nanofluid thermal conductivity have ended in a large degree of randomness and scatter in their values. Hence in this paper, lower and upper limits for thermal conductivity of nanofluids are developed. The upper limit is estimated by coupling heat transfer mechanisms like particle shape, Brownian motion and nanolayer while the lower limit is based on Maxwell's equation. Experimental data from a range of independent published sources is used for validation of the developed limits.

scholarly journals Effects of Brownian motion on freezing of PCM containing nanoparticles

2016 ◽  
Vol 20 (5) ◽  
pp. 1533-1541 ◽  
Author(s):  
Jamalabadi Abdollahzadeh ◽  
Jae Park
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Phase Change ◽  
Phase Change Material ◽  
Base Fluid ◽  
Phase Change Materials ◽  
Medium Temperature ◽  
Slowing Down ◽  
Change Material

Enhancement of thermal and heat transfer capabilities of phase change materials with addition of nanoparticles is reported. The mixed nanofluid of phase change material and nanoparticles presents a high thermal conductivity and low heat capacity and latent heat, in comparison with the base fluid. In order to present the thermophysical effects of nanoparticles, a solidification of nanofluid in a rectangular enclosure with natural convection induced by different wall temperatures is considered. The results show that the balance between the solidification acceleration by nanoparticles and slowing-down by phase change material gives rise to control the medium temperature. It indicates that this kind of mixture has great potential in various applications which requires temperature regulation. Also, the Brownian motion of nanoparticles enhances the convective heat transfer much more than the conductive transfer.

Contradictory Evidence for the Role of Temperature and Particle Size in Nanofluid Thermal Conductivity

2011 ◽  
Vol 1347 ◽  
Author(s):  
Rebecca J. Christianson ◽  
Jessica Townsend
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Cooling Capacity ◽  
Conductivity Enhancement ◽  
The Past ◽  
Nanoparticle Suspensions ◽  
Significant Step ◽  
Tremendous Amount ◽  
Contradictory Evidence

ABSTRACTThe prospects for increased cooling capacity from the use of nanofluid coolants has created a tremendous amount of interest. However, in the years since the initial thermal conductivity measurements of nanoparticle suspensions were reported, there has been much inconsistency in data published in the literature. The International Nanofluids Benchmarking Exercise was a significant step towards creating a reliable set of data on the thermal conductivity enhancement of stable nanofluids, however there remain many unanswered questions. Most significant, perhaps, is the contradictory results on the effects of particle size and temperature. In the past year alone it is possible to find published reports on nominally identical samples claiming precisely opposing trends in thermal conductivity with decreasing particle size at room temperature. Some studies also claim an increasing enhancement at higher temperatures, sometimes linking this to small particle sizes. In this work we review the literature claims for particle size and temperature results, the theories used to support those claims, as well as presenting new data with the aim of resolving the dispute and identifying the origins of the evidence for contradictory claims.

An Experimental Investigation on Thermal Conductivity and Viscosity of Graphene doped CNTs /TiO2 Nanofluid

2020 ◽  
Vol 17 (3) ◽  
Author(s):  
A.M. Zetty Akhtar ◽  
M.M. Rahman ◽  
K. Kadirgama ◽  
M.A. Maleque
Keyword(s):  
Thermal Conductivity ◽  
Zeta Potential ◽  
Base Fluid ◽  
Minimum Quantity Lubrication ◽  
Cutting Fluid ◽  
Cutting Zone ◽  
Observation Method ◽  
The Stability ◽  
The Relationship ◽  
Zeta Potential Analysis

This paper presents the findings of the stability, thermal conductivity and viscosity of CNTs (doped with 10 wt% graphene)- TiO2 hybrid nanofluids under various concentrations. While the usage of cutting fluid in machining operation is necessary for removing the heat generated at the cutting zone, the excessive use of it could lead to environmental and health issue to the operators. Therefore, the minimum quantity lubrication (MQL) to replace the conventional flooding was introduced. The MQL method minimises the usage of cutting fluid as a step to achieve a cleaner environment and sustainable machining. However, the low thermal conductivity of the base fluid in the MQL system caused the insufficient removal of heat generated in the cutting zone. Addition of nanoparticles to the base fluid was then introduced to enhance the performance of cutting fluids. The ethylene glycol used as the base fluid, titanium dioxide (TiO2) and carbon nanotubes (CNTs) nanoparticle mixed to produce nanofluids with concentrations of 0.02 to 0.1 wt.% with an interval of 0.02 wt%. The mixing ratio of TiO2: CNTs was 90:10 and ratio of SDBS (surfactant): CNTs was 10:1. The stability of nanofluid checked using observation method and zeta potential analysis. The thermal conductivity and viscosity of suspension were measured at a temperature range between 30˚C to 70˚C (with increment of 10˚C) to determine the relationship between concentration and temperature on nanofluid’s thermal physical properties. Based on the results obtained, zeta potential value for nanofluid range from -50 to -70 mV indicates a good stability of the suspension. Thermal conductivity of nanofluid increases as an increase of temperature and enhancement ratio is within the range of 1.51 to 4.53 compared to the base fluid. Meanwhile, the viscosity of nanofluid shows decrements with an increase of the temperature remarks significant advantage in pumping power. The developed nanofluid in this study found to be stable with enhanced thermal conductivity and decrease in viscosity, which at once make it possible to be use as nanolubricant in machining operation.

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