Low Volume Concentration Research Articles

Particle stresses in dilute, polydisperse, two-way coupled turbulent flows.

Direct numerical simulations are performed of turbulent planar Couette flow which are seeded with two-way coupled particles at low volume concentration. Based on an understanding of the development of particle stress (horizontal momentum carried vertically on average by the particle phase) in monodisperse systems at various particle Stokes numbers, several bidisperse and continuously polydisperse systems are simulated which are chosen to understand how flows containing blends of particle Stokes numbers can be effectively modeled in the dilute regime. Under noninteracting conditions, the particle stresses from particles with different inertia and different feedback stresses are shown to be linearly additive, providing a convenient method for effectively representing dispersed phase stress in polydisperse systems. While this is true, it is demonstrated that a single effective particle size is in general not sufficient at representing the entire mixture.

Excitonic optical nonlinearity of dielectric nanocomposites in weak optical fields

The paper presents a model of optical nonlinearity in a dielectric nanoсomposite for wavelengths ranging from 200 to 800 nm and intensities of up to 1000 W/cm2. Results of the numerical modeling of the optical response in a nanocomposite consisting of dielectric nanoparticles Al2O3 with low volume concentration (of the order of 0.3 %) embedded in a transparent dielectric liquid matrix are presented. It is found that with the volume concentration remaining unchanged, the value of nonlinear response in unit volume increases with decreasing nanoparticles size. The spectrum of the nonlinear extra term of the refractive index is shown to be affected by various parameters, such as the size and anisotropy of nanoparticles. It is notable that for 45-nm Al2O3 nanoparticles with 0.3 % volume concentration the value of the nonlinear optical response reaches 1.5·10–4 cm2/W near the resonant absorption band.

Biasing a ferronematic - a new way to detect weak magnetic field.

The magnetic properties of a ferronematic, i.e., a nematic liquid crystal doped with magnetic nanoparticles in low volume concentration are studied, with the focus on the ac magnetic susceptibility. A weak dc bias magnetic field (a few Oe) applied to the ferronematic in its isotropic phase increases the ac magnetic susceptibility considerably. Passage of the isotropic-to-nematic phase transition resets this enhancement irreversibly (unless the dc bias field is applied again in the isotropic phase).

Experimental Research on Heat Transfer Characteristics of CuO Nanofluid in Adiabatic Condition

The laminar convective heat transfer behavior of CuO nanoparticle dispersions in glycol with the average particle sizes (about 70 nm) was investigated experimentally in a flow loop with constant heat flux. To enhance heat exchange under high temperature condition and get the more accurate data, we try to improve the traditional experimental apparatus which is used to test nanofluid heat transfer characteristics. In the experiment five different nanoparticle concentrations (0.25%, 0.50%, 0.80%, 1.20%, and 1.50%) were investigated in a flow loop with constant heat flux. The experimental results show that the heat transfer coefficient of nanofluid becomes higher than that of pure fluid at the same Reynolds number and increased with the increasing of the mass fraction of CuO nanoparticles. Results also indicate that at very low volume concentrations nanofluid has no major impact on heat transfer parameters and the pressure of nanofluids increased by the mass fraction increase.

Evaluation of Cell Types and Morphologies in Sickle Cell Disease with an Imaging Flow Cytometer

Sickle cell disease (SCD) is a hemoglobinopathy characterized by vaso-occlusive episodes and hemolysis. Hemoglobin S is prone to polymerize at low oxygen tension, causing the red cell to become sickle shaped, more rigid and sticky. Evaluation of blood cell morphology, counts and activation are important components of the patient evaluation. This is usually accomplished by evaluation of the blood film, performing a complete blood count (CBC), and with the use of flow cytometry. A typical blood film from an SCD patient shows anisocytosis, poikilocytosis, polychromasia, nucleated erythrocytes, sickled cells, and irregular contracted cells.The methods of blood cell evaluation all have disadvantages. Preparation of the blood film is laborious and its evaluation is highly subjective and requires extensive experience. Some CBC counters (e.g., Siemens - ADVIA 2120) are able to detect dense cells (increased hemoglobin content-high MCHC cells) by their volume and hemoglobin concentration after the red blood cells (RBC) are swelled to spheres with a hypotonic solution. Dense cells resist becoming spheres and are detected by their low volume and high hemoglobin concentration. However, the number of dense cells might be underestimated because reversibly sickled cells are capable of undergoing the sphering and will not be detected. In addition, the hypotonic solution can lyse the cells. Finally, RBC counters cannot detect cells on the basis of specific cell markers, which can be used to define cell types and cell morphology and activation status (platelets).Conventional flow cytometry can detect cell markers, but yields little information on morphology and cannot detect dense cells.Here, we used the ImagestreamX Flow Cytometer (Amnis) to analyze SCD blood. In addition to providing information available with conventional cytometers, this instrument provides an image of each cell analyzed, thus allowing for detailed morphological assessment of a large population of cells. We analyzed 5 patients. All were outpatients not suffering from acute complications. Blood was collected by venipuncture into citrate anticoagulant, stained with antibodies or other reagents, and then fixed in 4% paraformaldehyde. We evaluated the blood for cell numbers and morphology, reticulocytes, dense cells, platelet-monocyte aggregates, phosphatidylserine exposure, and platelet activation status. The blood from all of the SCD patients displayed characteristics not found in control blood. We could clearly distinguish RBC morphologies corresponding to sickle cells, dense cell and reticulocytes. Reticulocytes, identified by CD71 positivity, often displayed a "puckered" morphology, as previously seen in electron micrographs. We calculated the percentage of RBCs that were sickled based on the shape ratio of > 2 (length along the long axis/maximum thickness along the short axis). The sickle cell percentage was 1.4±0.5% (normal 0%) out of total RBC population. We also evaluated dense cell morphology after separating the cells on a percoll density gradient. The cells appeared flattened and "deflated", clearly indicating their loss of intracellular fluid. We also analyzed platelet activation status based on staining for P-selectin, the activated form of integrin aIIbb3 (PAC-1 antibody), and phosphatidylserine exposure. Platelets staining positively for these markers also demonstrated morphological evidence of activation: shape change and filopodia extension. Platelet-monocyte aggregates were higher in all of the patients than in controls (0.036% vs 0%) and were easily distinguished from coincident events by morphology. The number of platelets associated with individual monocytes varied from 1 to 3. Other heterotypic cell aggregates were rare.In summary, imaging flow cytometry provides a powerful tool for the analysis of blood in SCD. The technique allows cell population analysis like conventional cytometry, while yielding detailed morphological information on many parameters of relevance in the disease. Further, the morphological assessment avoids many of the potential artifacts arising from blood film preparation and allows an unbiased assessment of the results. DisclosuresKonkle:Baxalta: Consultancy, Research Funding; Biogen: Consultancy, Research Funding; CSL Behring: Consultancy, Other: IDMC chair; Pfizer: Other: IDMC member; Octapharma: Research Funding; Novo Nordisk: Consultancy.

Measurement of thermal conductivity of graphene–water nanofluid at below and above ambient temperatures

The present paper deals with the design, development and the measurement of thermal conductivity of graphene–water nanofluid using a transient hot wire technique at temperatures below and above ambient conditions ranging from 10°C to 50°C. The equipment is designed to measure the thermal conductivity using a single platinum wire of diameter 50μm and 100mm length. The platinum micro-wire acts both as a temperature sensor and heating element. Low volume concentrations (0.05, 0.1 and 0.15%) of graphene, having the size less than 100nm, dispersed in 100ml of water with SDBS (sodium dodecyl benzene sulfonate) as surfactant, for prolonged stability, is used in the present study. The results showed an enhancement in the thermal conductivity of 37.2% for 0.15% volume concentration of graphene at 50°C when compared with that of the water at the same temperature. An interesting observation from this study is that the average thermal conductivity enhancement percentage with the increase in volume concentration (say from 0.05% to 0.15%) is found to be 3.3% higher when compared with that of the average enhancement with the increase in temperature from 10°C to 50°C.

Tailoring Engineered Cementitious Composites with local ingredients

Engineered Cementitious Composites (ECC) is a kind of High Performance Fiber Reinforced Cementitious Composites (HPFRCC) with a low fiber volume content of 2%. The unique properties of tensile strain hardening behavior and tight multiple cracks ensure that ECC can meet the stringent requirements of resiliency and durability of concrete infrastructures. While there are strong initiatives for the adoption of ECC in China, wider applications will require localization of material ingredients. In this paper, ECCs with local ingredients, including domestic PVA fibers, fly ash and crumb rubber, were developed under the guidance of micromechanics model for ECC. The fiber/matrix interface parameters and matrix parameters from single fiber pullout test and fracture toughness test respectively, were obtained for the tailoring of domestic ECC. The experimental results indicated that cost-effective ductile ECCs can be designed successfully using local material ingredients. These composites show an ultimate tensile strength of 4–5MPa and tensile strain capacity of 3–6%.

Effect of nanofiller shape on effective thermal conductivity of fluoropolymer composites

Filler particle shape and size influence interconnectivity within a polymer matrix and both play a significant role in controlling the effective thermal conductivity of a composite. This study examines the effect of nanofiller particle shape in a polytetrafluoroethylene (PTFE) matrix on thermal energy transport. Experimental measurements using a laser flash analysis method are performed on PTFE with three different shaped carbon fillers: nano-diamond spheres, carbon nanotubes (CNT) and graphene flakes. Filler concentration ranged from 0 to 30%. The experimental results are coupled with a particle connectivity model to understand the relationship between energy transport and filler connectivity. Results show filler particles with more micron scale dimensions form better interconnected networks at lower volume concentrations than fillers with fewer micron scale dimensions. Filler connectivity influences effective conductivity: specifically, nano-diamond spheres showed negligible interconnectivity and result in negligible change in thermal conductivity. The CNT, with one-micron scale dimension (i.e., length) and flakes, with two-micron scale dimensions (i.e., length and height), both exhibited linear increases in interconnectivity and effective thermal conductivity. Graphene interconnectivity in PTFE is six times that of CNT and thermal conductivity is 0.5 W/mK, two times that of CNT, respectively. These results provide new insights on how to optimize nanoparticle structure to enhance thermal energy transport.

An Innovative Ultrasound Signal Processing Technique to Selectively Detect Nanosized Contrast Agents in Echographic Images

The aim of this paper was to optimize the employment of a novel algorithm for acquisition and processing of medical ultrasound (US) signals to facilitate its clinical translation. The implemented procedure is dedicated to selective enhancement of nanoparticle (NP) contrast agents in echographic images and is based on the differences in US signal backscatter between NP-containing targets and more homogeneous objects. Previous preliminary studies verified the feasibility of this approach on silica nanospheres (SiNSs) dispersed at a constant volume concentration (0.7%) in agarose gel samples. The present extended these evaluations, addressing two issues of direct clinical interest: 1) safety: SiNSs were coated with a biocompatible layer made of polyethylene glycol (PEG) and the adopted NP volume concentration was reduced to 0.2%, which is in the nontoxic range and 2) reproducibility: a different phantom configuration was used, to verify the independence of algorithm performance from a specific target region shape. The obtained results demonstrated that the proposed method can be effectively applied to enhance the presence of PEG-coated SiNSs in the diameter range 160-660 nm at a low and biocompatible volume concentration: the combined employment of a phantom with a different geometry and a lower concentration of PEG-coated NPs, in fact, caused only slight variations in the suppression patterns of noncontrast echoes, without affecting the final diagnostic effectiveness of the investigated contrast detection scheme. This approach also provides specific advantages with respect to the available measurement techniques dedicated to the enhancement of targeted US contrast agents for molecular imaging purposes.

Rheological study of mudflows at Lianyungang in China

An experimental study of the rheological properties of mudflows at Lianyungang in China was carried out by the RS6000 rheometer, including steady and dynamic measurements. Five samples with the range of mud volume concentration from 0.058 to 0.179 were investigated. Based on the experimental data, a Dual-Herschel–Bulkley model was developed to analyze the flow curve and interpolate the static and dynamic yield stresses. The results show that in the steady measurement, the consolidation time and the system temperature show some effects on the rheogram and the yield stress for the sample with low sediment volume concentration, and the effects are strengthened gradually with the sediment volume concentration increasing. Under a shear stress sweep, two linear visco-elastic regions, showing the viscous and the elastic behaviors respectively, were discovered. Complex viscosity, elastic modulus and loss modulus in the elastic region are several orders of magnitude larger than those in the viscous region. Furthermore, the analysis of experimental data show that both steady and dynamic rheological properties can be expressed as appropriate exponential functions of the sediment volume concentration.

Pressure drop and convective heat transfer of Al2O3/water and MWCNT/water nanofluids in a chevron plate heat exchanger

Heat transfer and pressure drop characteristics of Al2O3/water and MWCNT/water nanofluids flowing in a chevron-type plate heat exchanger were experimentally investigated and compared with those of water. Results showed that heat transfer seemed to be improved by using nanofluids at constant Reynolds number. However, little heat transfer enhancement was observed based on a constant flow velocity. The heat transfer deterioration of MWCNT/water nanofluids was more intensive than Al2O3/water nanofluids due to the relatively large viscosity increase of MWCNT/water nanofluids. A new heat transfer correlation was proposed based on the experimental data of water and it predicts the experimental data of nanofluids accurately when the measured nanofluid properties (thermal conductivity and viscosity) were adopted for calculation. Besides, the pressure drop of nanofluid was reasonably higher than that of water and seemed to increase with increasing particle volume concentrations due to the increase in viscosity. However, there was not much difference between the pressure drop of nanofluids and that of water at low particle volume concentrations. A correlation for predicting the friction factor was obtained and it fitted the experimental data very well.

Heat Transfer Enhancement of Low Volume Concentration of Carbon Nanotube-Fe3O4/Water Hybrid Nanofluids in a Tube With Twisted Tape Inserts Under Turbulent Flow

In this paper, it is estimated the heat transfer coefficient and friction factor for fully developed turbulent flow of carbon nanotube (CNT)-Fe3O4/water hybrid nanofluids flow through a tube with twisted tape inserts at constant heat flux conditions. The nanocomposite of CNT-Fe3O4 was prepared by in situ method; which contains dispersion of carboxylated-CNTs in distilled water followed by mixing of ferrous chloride and ferric chloride in the molar ratio of 2:1. Sodium hydroxide was used as reducing agent to form CNT-Fe3O4 nanocomposite. The detailed surface morphology and magnetic properties were performed by X-ray diffraction and scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The stable hybrid nanofluids were prepared by dispersing nanocomposite in distilled water, and the heat transfer and friction factor experiments were conducted for particle volume concentrations of 0.1% and 0.3%. The results indicate that a maximum of 31.10% enhancement in Nusselt number with a penalty of 1.18-times increase of pumping power was observed for particle concentration of 0.3% at a Reynolds number of 22,000 as compared to base fluid data. The Nusselt number is further enhanced to 42.51% for 0.3% nanofluid flow through a tube with twisted tape of H/D = 5 at a Reynolds number of 22,000 compared to base fluid data. The empirical correlations were proposed for the estimation of Nusselt number and friction factor to match well with the experimental data.

Effect of polyaniline salts on the mechanical and corrosion properties of organic protective coatings

Abstract The aim of this work was to assess the effect of polyaniline salts (PANI-HA) with various dopant types on the mechanical and corrosion properties of organic protective coatings dependent on the pigment volume concentration. The doping acids used included phosphoric acid (H 3 PO 4 ), sulphuric acid (H 2 SO 4 ), hydrochloric acid (HCl), p-toluenesulphonic acid (PTSA), and 5-sulphosalicylic acid (CAS). The polyaniline salt types were described by their physico-chemical parameters. An epoxy ester resin was used as the binder for the organic coatings. The organic protective coatings included the various PANI-HA types. The prepared organic coatings were subjected to mechanical testing, corrosion tests and linear polarisation technique. Organic coatings achieved during mechanical tests comparable results regardless of the type of PANI dopant or PVC (pigment volume concentration) with the exception of organic coatings fulfilling the condition PVC = CPVC (critical pigment volume concentration) which exhibited decrease of mechanical resistance. The results of accelerated corrosion tests and techniques of linear polarisation testify that in particular the PVC parameter affects the resulting corrosion resistance. During those tests, the organic coatings exhibited improved corrosion resistance, particularly at low pigment volume concentrations (PVC = 0.1–5%) irrespective of the pigment used.

Pretreatment and desalination of flowback water from the hydraulic fracturing

A process based on pre-treatment and membrane desalination was studied for the treatment of the flowback water from drilling for shale gas in Lubocino in Poland. The effectiveness of pre-treatment technology, which contained NaOH alkalization, KMnO4 oxidation, filtration, sorption, and fine filtration, was studied. Also the usefulness of nanofiltration (NF) and reverse osmosis (RO) membranes for flowback desalination was tested. The study was carried out in the semi-pilot scale. The applied pre-treatment technology made possible to obtain a product that can be placed on the NF and RO elements (turbidity = 0.882 NTU, silt density index = 3.1). The 4040-SR100-N2 NF element was ineffective for flowback water purification, and the retention of contaminants was low (5.1% conductivity, 18.2% total hardness, 9.2% TOC). The AG4040FM RO element was characterized by higher retention (conductivity 93.9%, total hardness 98.3%, TOC 78.1%), but low volume concentration ratio (VCR) (VCR = 1.6) with more than 50% decrease in the permeate flux obtained. The AD-90 RO element was characterized by the highest retention (conductivity 99.3%, total hardness 99.8%, TOC 91.1%), and VCR was 4 by minimal decrease of permeate flux. Proposed pre-treatment technology combined with desalination on AD-90 RO element allows to obtain flowback water reusage. The return of flowback water to the environment requires the application of advanced oxidation to decrease the level of organic contamination.

Key Future Directions For Research On Turbidity Currents and Their Deposits

Turbidity currents, and other types of submarine sediment densityflow, redistribute more sediment acrossthe surface of the Earth than any other sediment flow process, yet their sediment concentration has never been measured directly in the deep ocean. The depositsof these flows are of societal importance asimperfect records of past earthquakes and tsunamogenic landslides and as the reservoir rocks for many deep-water petroleum accumulations. Key future research directions on these flows and their deposits were identified at an informal workshop in September 2013. This contribution summarizes conclusions from that workshop, and engages the wider community in this debate. International efforts are needed for an initiative to monitor and understand a series of test sites where flows occur frequently, which needs coordination to optimize sharing of equipment and interpretation of data. Direct monitoring observations should be combined with cores and seismic data to link flow and deposit character, whilst experimental and numerical models play a key role in understandingfield observations. Such an initiative may be timely and feasible, due to recent technological advances in monitoring sensors, moorings, and autonomous data recovery. This is illustrated here by recently collected data from the Squamish River delta, Monterey Canyon, Congo Canyon, and offshore SE Taiwan. A series of other key topics are then highlighted. Theoretical considerations suggest that supercritical flows may often occur on gradients of greater than , 0.6u. Trains of up-slope-migrating bedforms have recently been mapped in a wide range of marine and freshwater settings. They may result from repeated hydraulic jumps in supercritical flows, and dense (greater than approximately 10% volume) near-bed layers may need to be invoked to explain transport of heavy (25 to 1,000 kg) blocks. Future work needs to understand how sediment is transported in these bedforms, the internal structure and preservation potential of their deposits, and their use in facies prediction. Turbulence damping may be widespread and commonplace in submarine sediment density flows, particularly as flows decelerate, because it can occur at low ( , 0.1%) volume concentrations. This could have important implications for flow evolution and deposit geometries. Better quantitative constraints are needed on what controls flow capacity and competence, together with improved constraints on bed erosion and sediment resuspension. Recent advances in understanding dilute or mainly saline flows in submarine channels should be extended to explore how flow behavior changes as sediment concentrations increase. The petroleum industry requires predictive models of longer-term channel system behavior and resulting deposit architecture, and for these purposes it is important to distinguish between geomorphic and stratigraphic surfaces

Heat transfer performance of silver/water nanofluid in a solar flat-plate collector

An experimental study is carried out to investigate the heat transfer characteristics of silver/water nanofluid in a solar flatplate collector. The solar radiation heat flux varies between 800 W/m2and 1000W/m2, and the particle concentration varies between 0.01%, 0.03%, and 0.04%. The fluid Reynolds number varies from 5000 to 25000. The influence of radiation heat flux, mass flow rate of nanofluid, inlet temperature into the solar collector, and volume concentration of the particle on the convective heat transfer coefficient and the collector efficiency are studied. Both parameters increase with increase in the particle volume concentration and flow rate. The maximum percentage increase obtained in the convective heat transfer coefficient is 18.4% for the 0.04% volume concentration at a Reynolds number of 25000. An increase in the performance of nanofluid is also witnessed when compared to the base fluid, which has a strong dependency on volume concentration and mass flow rate. MgO. The nanofluid achieved a 3°C temperature difference during the daytime peak solar radiation compared with the base fluids. With a concentration of 0.2% ZnO, a temperature difference of 2.55°C for daytime and 1°C for nighttime was reached, and this was determined to be the most attractive option for solar energy utilization. Yousefi et al. [15] witnessed a 28% performance improvement in a flat-plate collector when it was operated with water-Al2O nanofluids. Tyagi [16] theoretically compared the conventional flat-plate collector with a direct absorption solar collector (DAC) and observed the former to be 10% more efficient. Otanicar [17] studied the conomic and environmental influences of using nanofluids to enhance solar collector efficiency with conventional solar collectors. Dongxiao et al. [18] presented excellent photothermal properties of carbon-black aqueous nanofluids at highvolume fractions. Further work on nanofluids’ application to direct solar absorption has been carried out by Lijuan Mu [19] using a custom-made direct solar absorber. The radiative properties of several nanofluids are tested for the highest temperature difference across the heat exchangers. Based on the above-mentioned review of the literature, it has been clearly observed that most of the previous studies on solar flat-plate collectors were conducted using metal oxide nanoparticles in relatively high concentrations. These high concentrations of metal oxide nanoparticles cause a higher pressure drop that then requires a higher pumping power. Since a limited number of studies exists in the literature with respect to pure metal nanoparticles, it is recommended to study the heat transfer characteristics of pure metal nanoparticles with relatively low concentrations (<1%) by volume and high thermal conductivity compared with metal oxides. Therefore, in the present study, the efficiency of a solar flat-plate collector is studied with a low particle volume concentration of less than 0.04% silver-water nanofluid. These experiments are conducted for a solar radiation flux ranging from 800 W/m2 to 1000 W/m2, and the Reynolds number varying from 5000 to 25000. The effect of radiative heat flux, mass flow rate, inlet temperature, and volume concentration on the convective heat transfer coefficient and the collector efficiency are studied. The tailormade setup for a collector area is 2.4m2 and the collector plate is made of nine parallel copper strips

Structural Changes in Ferronematic Liquid Crystals Studied by Surface Acoustic Waves

The response in attenuation of surface acoustic wave (SAW) of frequency 30MHz propagating along ferronematic liquid crystals (6CHBT) to both electric and low magnetic field (up to 0.25 T) has been studied experimentally. Two low volume concentrations (Φ1=1×10-5 and Φ2=1×10-4) of spherical magnetic nanoparticles were added to liquid crystal during its isotropic phase. In contrast to undoped 6CHTB the distinctive SAW attenuation responses induced by both electric and magnetic fields in ferronematic liquid crystals below Fréedericksz transition have been observed suggesting structural changes and the orientational coupling between the magnetic moment of magnetic particles and the director of the liquid crystal. The geometrical re-ranking of magnetic nanoparticles was registered for some orientations of magnetic field, too. Observed results confirmed the significant influence of the presence of magnetic nanoparticles on the structural properties of 6CHTB.

Measurements and correlations of frictional pressure drop of TiO2/R123 flow boiling inside a horizontal smooth tube

Nanorefrigerant is one kind of nanofluids. It is the mixture of nanoparticles with refrigerants. It has better heat transfer performance than traditional refrigerants. Recently, some researches have been done about nanorefrigerants. Most of them are related to thermal conductivity of these fluids. Viscosity also deserves as much consideration as thermal conductivity. Pumping power and pressure drop depend on viscosity. In this paper, the volumetric and temperature effects over viscosity of TiO2/R123 nanorefrigerants have been studied. Numerical conditions include temperature from 300 to 325K, nanoparticle concentrations from 0.5% up to 2%, mass fluxes from 150 to 200kgm−2s−1, inlet vapor qualities from 0.2 to 0.7 and diameter of tube from 6 to 10mm. The effect of pressure drop with the increase of viscosity has also been investigated. Based on the analysis it is found that viscosity of nanorefrigerant increased accordingly with the increase of nanoparticle volume concentrations and decreases with the increment of temperature. Furthermore, pressure drop augmented significantly with the intensification of volume concentrations and vapor quality. Therefore, low volume concentrations of nanorefrigerant are suggested for better performance of a refrigeration system.

Rheological behaviour and the hysteresis phenomenon of Al2O3 nanofluids

The effects of temperature and low-volume concentration on the dynamic viscosity of the Al2O3/water and Al2O3/ethylene glycol/water nanofluids are investigated. Nanofluids were prepared and characterised. Data were collected for temperatures ranging from 25 to 80°C. The presence of aggregated Al2O3 nanoparticles in the fluid, with average diameter of 109 nm which is ∼8 times the primary diameter (13 nm) of Al2O3 nanoparticles was witnessed. Furthermore, only at temperature below 40°C water-based alumina nanofluid at 0·05% v/v showed Newtonian behaviour. On the other hand, Al2O3/ethylene glycol/water mixture exhibited Newtonian behaviour. Results clearly showed the presence of a critical temperature, beyond which the particle suspension properties were noticed to be radically changed, which results in activating the hysteresis phenomenon. The hysteresis phenomenon on viscosity measurement, which is believed to be the first observed for ethylene glycol/water-based nanofluids, has raised serious concerns regarding the use of nanofluids for heat transfer enhancement.

Pressure Drop and Heat Transfer of Nanofluid in Turbulent Pipe Flow Considering Particle Coagulation and Breakage

Numerical simulations of Al2O3/water nanofluid in turbulent pipe flow are performed with considering the particle convection, diffusion, coagulation, and breakage. The distributions of particle volume concentration, the friction factor, and heat transfer characteristics are obtained. The results show that the initial uniform distributions of particle volume concentration become nonuniform, and increase from the pipe wall to the center. The nonuniformity becomes significant along the flow direction from the entrance and attains a steady state gradually. Friction factors increase with the increase of particle volume concentrations and particle diameter, and with the decrease of Reynolds number. The friction factors increase remarkably at lower volume concentration, while slightly at higher volume concentration. The presence of nanoparticles provides higher heat transfer than pure water. The Nusselt number of nanofluids increases with increasing Reynolds number, particle volume concentration, and particle diameter. The rate increase in Nusselt number at lower particle volume concentration is more than that at higher concentration. For a fixed particle volume concentration, the friction factor is smaller while the Nusselt number is larger for the case with uniform distribution of particle volume concentration than that with nonuniform distribution. In order to effectively enhance the heat transfer using nanofluid and simultaneously save energy, it is necessary to make the particle distribution more uniform. Finally, the expressions of friction factor and Nusselt number as a function of particle volume concentration, particle diameter and Reynolds number are derived based on the numerical data.