Increase In Volume Concentration Research Articles

Thermophysical Properties of Al<sub>2</sub>O<sub>3</sub>-Water Nanofluids

Aqueous nanofluids composed of alumina nanoparticles with different sizes at a concentration from 0.1vol% to 0.5vol% were prepared by a two-step method. The suspension and dispersion characteristics were experimentally examined by zeta potential, average size and absorption spectrum. The thermophysical properties such as the viscosity, surface tension, thermal conductivity, saturation vapor pressure and latent heat of vaporization were measured. The influences of the particle size, particle volume concentration and temperature on the thermophysical property were investigated. It was found that the viscosity and thermal conductivity increased with decreasing nanoparticle size. In contrast, the surface tension, saturation vapor pressure and latent heat of vaporization decrease with decreasing nanoparticle size. The viscosity, thermal conductivity and saturation vapor pressure have an increasing tendency with increasing volume concentration. However, surface tension and latent heat of vaporization showed a reverse tendency. Furthermore, the temperature also showed had obvious influence on the nanofluids viscosity, thermal conductivity and surface tension.

Thermophysical Performances of Al<sub>2</sub>O<sub>3</sub>-Water Nanofluids and Its Heat Transfer Enhancement in Heat Pipe

Al2O3-water nanofluids with volume concentration of 0.1%~0.5% were prepared by a two-step method, the thermophysical parameters such as thermal conductivity, viscosity and surface tension were measured, The results showed that the thermal conductivity of Al2O3-water nanofluids increased with increasing temperature and volume concentration, while the viscosity decreased with increasing temperature but increased with increasing volume concentration, in contrast to the thermal conductivity, the surface tension significantly decreased with increasing temperature and volume concentration. Furthermore, Al2O3-water nanofluids with 0.5% volume concentration were added into heat pipe. The experimental measurements showed that the Al2O3-water nanofluids have improved the heat transfer performance of heat pipe and the heat transfer coefficient of the heat pipe with Al2O3-water nanofluids enhanced by 85.7% when compared with the heat pipe with deionized water.

Lattice Boltzmann simulation of natural convection heat transfer of Al 2O 3/water nanofluids in a square enclosure

In the present study, mathematical modeling is performed to simulate natural convection of Al 2O 3/water nanofluids in a vertical square enclosure using the lattice Boltzmann method (LBM). Results indicate that the average Nusselt number increases with the increase of Rayleigh number and particle volume concentration. The average Nusselt number with the use of nanofluid is higher than the use of water under the same Rayleigh number. However, the heat transfer rate of the nanofluid takes on a lower value than water at a fixed temperature difference across the enclosure mainly due to the significant enhancement of dynamic viscosity. Furthermore, great deviations of computed Nusselt numbers using different models associated with the physical properties of a nanofluid are revealed. The present results are well validated with the works available in the literature and consequently LBM is robust and promising for practical applications.

Lattice Boltzmann simulation of heat transfer and fluid flow in a microchannel with nanofluids

Mathematical modeling is performed to simulate forced convection flow of 47 nm- Al2O3/water nanofluids in a microchannel using the lattice Boltzmann method (LBM). Single channel flow and conjugate heat transfer problem are taken into consideration and the heat transfer rate using a nanofluid is examined. Simulations are conducted at low Reynolds numbers (2 ≤ Re ≤ 16). The computed average Nusselt number, which is associated with the thermal conductivity of nanofluid, is in the range of \( 0.6 \le \overline{Nu} \le 13 \). Results indicate that the average Nusselt number increases with the increase of Reynolds number and particle volume concentration. The fluid temperature distribution is more uniform with the use of nanofluid than that of pure water. Furthermore, great deviations of computed Nusselt numbers using different models associated with the physical properties of a nanofluid are revealed. The results of LBM agree well with the classical CFD method for predictions of flow and heat transfer in a single channel and a microchannel heat sink concerning the conjugate heat transfer problem, and consequently LBM is robust and promising for practical applications.

Numerical study of flow and heat transfer characteristics of alumina-water nanofluids in a microchannel using the lattice Boltzmann method

In the present study, mathematical modeling is performed to simulate force d convection flow of Al 2O 3/water nanofluids in a microchannel using the lattice Boltzmann method (LBM). Simulations are conducted at low Reynolds numbers (Re ≦ 16). Results indicate that the average Nusselt number increases with the increase of Reynolds number and particle volume concentration. The fluid temperature distribution is more uniform with the use of nanofluid than that of pure water. Furthermore, great deviations of computed Nusselt numbers using different models associated with the physical properties of a nanofluid are revealed. The results of LBM agree well with the classical CFD method for predictions of flow and heat transfer in a single channel and a microchannel heat sink concerning the conjugate heat transfer problem, and consequently LBM is robust and promising for practical applications.

Eulerian–Eulerian two-phase numerical simulation of nanofluid laminar forced convection in a microchannel

In this paper, laminar forced convection heat transfer of a copper–water nanofluid inside an isothermally heated microchannel is studied numerically. An Eulerian two-fluid model is considered to simulate the nanofluid flow inside the microchannel and the governing mass, momentum and energy equations for both phases are solved using the finite volume method. For the first time, the detailed study of the relative velocity and temperature of the phases are presented and it has been observed that the relative velocity and temperature between the phases is very small and negligible and the nanoparticle concentration distribution is uniform. However, the two-phase modeling results show higher heat transfer enhancement in comparison to the homogeneous single-phase model. Also, the heat transfer enhancement increases with increase in Reynolds number and nanoparticle volume concentration as well as with decrease in the nanoparticle diameter, while the pressure drop increases only slightly.

Experimental study of mixed convection with water–Al 2O 3 nanofluid in inclined tube with uniform wall heat flux

An experimental investigation was carried out to study mixed convection of Al 2O 3–water nanofluid inside an inclined copper tube submitted to a uniform wall heat flux at its outer surface. The effects of nanoparticles concentration and power supply on the development of the thermal field are studied and discussed under laminar flow condition. Results show that the experimental heat transfer coefficient decreases slightly with an increase of particle volume concentration from 0 to 4%. Two new correlations are proposed to calculate the Nusselt number in the fully developed region for horizontal and vertical tubes, for Rayleigh number from 5 × 10 5 to 9.6 × 10 5, Reynolds number from 350 to 900 and particle volume concentrations up to 4%.

Comparison Of Muscle Hypertrophy During Follicular And Luteal Phases Following 6-days Blood-Flow Restricted Resistance Training

If anabolic/catabolic effects exist for female hormones, training-induced muscle hypertrophy might differ between follicular (low estrogen and progesterone) and luteal (elevated estrogen and progesterone) phases of the menstrual cycle. We reported previously that rapid significant increases in muscle mass occur following a short period (6 days, twice daily) of low-intensity resistance training combined with blood flow reduction (BFR). PURPOSE: To investigate the comparison of muscular hypertrophic responses between follicular and luteal phases of the menstrual cycle following low-intensity BFR resistance training. METHODS: Eight previously untrained, eumenorrheic women (age, 22-37 yrs; body weight, 52.9±4.8 kg; BMI, 21.3±1.6 kg/m2) performed unilateral low-intensity (30% of one-repetition maximal, 1-RM) dumbbell curl training (4 sets, 75 total contractions) combined with BFR once a day for 6 days. The opposite arm served as an untrained control throughout the training period. This 6-day training program was conducted during both menstrual cycle phases: early follicular (FP) and mid-luteal (LP). MRI-measured upper arm muscle volume and isometric elbow flexion strength were measured in both arms on before and two days after the final training bout. RESULTS: Serum concentrations of estrogen and progesterone were 57±40 pg/ml and 0.8±0.8 ng/ml, respectively, for FP and 198±113 pg/ml and 15.0±13.5 ng/ml for LP. Significantly (P<0.05) greater muscle hypertrophy was observed in the LP (biceps muscle volume; 5.7%) compared to the FP (3.7%). A significant positive correlation was observed between the training-induced increase in muscle volume and serum concentration of estrogen (r=0.66, P<0.05), but not with progesterone (r=0.27). There was no change in muscle volume in the control arm for both cycle phases. Increases in isometric elbow flexion strength were higher in the LP than that of the FP. Relative strength (isometric strength per unit muscle cross-sectional area) was similar between pre- and post-training in both phases. CONCLUSIONS: Our results suggest that female hormones may either exert an anabolic effect and/or a decreased catabolic effect during muscle hypertrophy and strength gains, although the independent effects of estrogen and progesterone were not evident.

Experimental studies on extraction of cobalt ions from dilute aqueous solutions by using complexation-ultrafiltration process

The extraction of cobalt ions from dilute aqueous solutions was investigated by ultrafiltration with the help of poly(acrylic acid) sodium salt (PAASS). Polysulfone and polyethersulfone hollow fiber ultrafiltration membranes were employed in this process. The kinetics of complexation reaction was studied for PAASS with Co2+. Results showed that, under a large excess of PAASS, it takes 65, 55 and 40 min at pH 5, 6 and 7, respectively, to get the equilibrium of complexation. The reaction kinetics can be described by a pseudo-first-order equation. Then, the effects of various parameters on the extraction of Co2+ were examined in detail. Results indicated that loading ratio, pH value and low-molecular competitive complexing agent affect significantly cobalt rejection coefficient R. Furthermore, a concentration experiment was carried out at pH 7. With increasing volume concentration factor, membrane flux declines slowly, and R value is always about 1. The concentrated retentate was used further for a decomplexation experiment. The decomplexation ratio of cobalt-PAASS complex reaches as high as 90.1%. After the decomplexation step, a diafiltration experiment was performed at pH 2.5. Cobalt ions can be extracted satisfactorily from the retentate, and a purified PAASS is obtained.

Influence of temperature and properties variation on nanofluids in building heating

Theoretical investigations on the application of nanofluids in the hydronic heating system of buildings have been presented in this paper. Realistic fluid velocities and temperatures employed in heat exchange equipment were used to compare the convective heat transfer coefficient and the pumping power requirement of nanofluids of various particle volume concentrations. The base fluid used in the analyses as a basis for comparison was a solution comprised of 60% ethylene glycol and 40% water (by weight). The thermophysical and heat transfer performance of the base fluid have been compared with copper oxide nanoparticles dispersed in the same base fluid with volumetric particle concentration ranging up to 4%. First, the variations of thermophysical properties such as viscosity, thermal conductivity, specific heat and density have been evaluated for different concentrations. Using these properties, several plots have been developed for quantitatively determining the enhancement of convective heat transfer coefficient as a function of flow velocity, Reynolds number and the nanoparticle volumetric concentration. For constant Reynolds number for flow in tubes, the Nusselt number and convective heat transfer coefficient increases as nanoparticle volume concentration increases. As the properties of nanofluids and the base fluid are temperature dependent, we have performed calculations for two fluid temperatures (323 K and 360 K). The results show that a higher convective heat transfer coefficient is achieved at higher temperatures for a nanofluid of equal concentration circulating at equal velocity. Frictional pressure loss and pumping power increases relative to the base fluid with particle volume concentration, but decreases with mean fluid temperature.

Potentiated effect of systemic administration of oxytocin on hypertonic NaCl intake in food-deprived male rats

Subcutaneous administration of oxytocin (OT) increases water intake and sodium/urine excretion in food-deprived male rats. This study analyzes the effect of OT administration (at 0830 and 1430h) on the consumption of water and hypertonic NaCl (1.5%). In the first experiment, injections of OT increased the intake of hypertonic NaCl (but not of water) in food-deprived rats but not in ad lib-fed animals during the second 12 h (2030 to 0830) of the treatment day. The net concentration of the fluid consumed by OT/deprived animals was close to isotonic. In the second experiment, the initial effect of OT administration was an increase in urine volume and urinary sodium excretion and concentration by food-deprived animals during the first 12 h (0830 to 2030). These findings suggest that in food-deprived animals, systemic administration of OT induces NaCl intake as a consequence of previous urine loss and urinary sodium excretion.

Temperature dependent thermal conductivity enhancement of copper oxide nanoparticles dispersed in propylene glycol-water base fluid

Nanofluids are new generation heat transfer fluids and are preferred over conventional fluids for heat transfer applications. Nanofluids are characterised by their enhanced thermal conductivities, high energy density and better heat transfer capabilities than the base fluids without nanoparticles. Glycol based fluids exhibit an anti-freezing characteristics at sub zero temperatures and hence widely used in heat exchangers in cold regions. In the present experimental work, CuO nanoparticles of size less than 50 nm are suspended in the base fluid of propylene glycol-water (60:40 by volume) mixture, in the range of 0.025, 0.1, 0.4, 0.8 and 1.2% volume fraction and CuO nanofluids were prepared. The effective thermal conductivity of nanofluids for different particle volume concentration is measured at different temperatures of nanofluids. The experimental results obtained show that thermal conductivity of nanofluids increases with increase in temperature and particle volume concentration of nanofluids. The conductivity data obtained in present investigation are compared with conductivity models and correlations available in the literature.

On the Specific Heat Capacity of CuO Nanofluid

This paper reviews briefly the definition of heat capacity and clarifies the defined specific heat capacity and volumetric heat capacity. The specific heat capacity and volumetric heat capacity, with our measured experimental data for CuO nanofluids, are discussed as an illustrating example. The result indicates that the specific heat capacity of CuO nanofluid decreases gradually with increasing volume concentration of nanoparticles. The measurement and the prediction from the thermal equilibrium model exhibit good agreement. The other simple mixing model fails to predict the specific heat capacity of CuO nanofluid. The nanoparticle size effect and solid-liquid interface effect on the specific heat capacity of nanofluid are discussed.

Slip flow of coal water slurries in pipelines

Experiments were carried out on a pilot scale slurry transport apparatus to investigate slip flow behavior of coal water slurries (CWSs) in pipes with various diameters (25, 32, 40 and 50 mm). The effects of volume concentration, particle size and slurry temperature on wall slip behavior (wall slip velocity, critical wall shear stress and slippage contribution) were investigated. A numerical technique based on Tikhonov regularization was applied to determine the wall slip behavior. As the slurry temperature or the particle size increased, the critical wall shear stress was observed to decrease and the wall slip velocity was observed to increase significantly, while when the solid concentration was very close to the maximum packing fraction, a slight increase in volume concentration would lead to a rapid decrease in wall slip velocity and a sharp increase in critical wall shear stress. The temperature influence on critical wall shear stress and yield stress increased as volume concentration increased. At low wall shear stress, the slippage contribution was mainly dependent on the difference between yield stress and critical shear stress. While at high wall shear stress, it was dependent on both of the shear viscosity of the bulk slurries and the wall slip velocity.

Reverse osmosis of the retentate from the nanofiltration of secondary effluents

Wastewater reclamation and reuse are being widely implemented due to the lack of fresh water. When salinity is a limiting parameter to obtain the required water quality for agricultural uses, a desalination step is necessary to achieve it. Therefore, techniques such as nanofiltration (NF) or reverse osmosis (RO) can play an important role and have to be deeply studied in order to implement an economically feasible tertiary treatment. In this work, NF of a secondary effluent from a municipal wastewater treatment plant has been evaluated for increasing feed concentration in order to reach a final conversion of approximately 75%. Experiments were carried out with a laboratory plant containing a spiral wound membrane (DURASLICK-2540, General Electric) with an active area of 2.2m 2. Tests were performed increasing volume concentration factors (VCFs) up to almost 4 and replicated three times to confirm the results statistically. After NF experiments an RO step of the retentate was carried out in order to concentrate the final brine. In NF experiments, for the highest VCF values, fluxes recommended for the membrane maker (17 Lm −2 h −1) were produced at a transmembrane pressure (TMP) of 3.2 bar. The TMP hardly increased with the VCF. NF membranes yielded a conductivity retention index around 42%, reaching nearly 99% for sulphate ions and only 23% for chloride ions.

Formation mechanism of cavitating spalls

The dynamics of formation of cavitation zones in a liquid upon reflection of a shock pulse from the free surface is studied numerically in a one-dimensional formulation using the Iordanskii-Kogarko-van Wijngaarden two-phase model. It is shown that the formation of a system of cavitation zones (clusters) with a dynamically increasing volume concentration of the gas phase near the free surface is due to oscillations of the structure of the rarefaction wave profile. The fast relaxation of tensile stresses in the cavitation zone ends in the formation of a quasistationary mass-velocity field, which provides for almost unbounded growth of cavitation bubbles in subsurface clusters and explains the occurrence of the spall layers observed in experiments.

Study of the behaviour of a reverse osmosis membrane for wastewater reclamation — influence of wastewater concentration

Water scarcity is becoming a serious problem in the Mediterranean countries. To minimize negative effects, wastewater reclamation can be one of the possible solutions. Reverse osmosis (RO) is the process that ensures the highest water quality. Thus, the required quality goal can be reached adjusting the wastewater portion to be treated and the portion directed to the blending tank. In this work, a study with a low-pressure RO pilot plant was conducted in the laboratory. A spiral wound composite polyamide membrane ( ESPA1-2540, Hydranautics) with an active area of 2.59 m 2 was tested for increasing volume concentration factors (VFC). Thus, the membrane elements behaviour within a pressure vessel in a full-scale plant was simulated. The experiments were run three times to confirm statistically the results. These ones showed an almost constant permeate flux (17L m −2 h −1) while keeping the transmembrane pressure constant at 6.8 bar with a VCF of 2.5. Concerning the salt retention, it was observed a slightly reduction on increasing the VFC. However, the permeate conductivity was lower than 80 µS/cm in all cases.

Observation of ambient aerosol particle growth due to in‐cloud processes within boundary layers

Aerosol microphysical and optical properties were measured on board the CIRPAS Twin Otter aircraft during 16 flights at the Southern Great Plain (SGP) site in northern central Oklahoma as part of the Aerosol Intensive Operation period in May 2003. Within well‐mixed boundary layers on four cloudy days, vertical profiles measured on board the Twin Otter show that dry aerosol size, volume concentration, and scattering coefficients all increased with increasing altitude, whereas the total number concentration remained essentially constant. A one‐dimensional model, which uses simultaneous meteorological measurements as inputs, shows that the observed increase in aerosol volume concentration with increasing altitude is consistent with in‐cloud sulfate production at the top of the boundary layer. The sulfate production rate was sufficiently fast to overcome the homogenization resulting from turbulent mixing. In contrast, on cloud‐free days, measurements on a second aircraft show nearly uniform aerosol volume concentrations within well‐mixed boundary layers. The observed vertical gradients in aerosol volume concentration suggest that even within well‐mixed boundary layers, surface measurements may not be representative of aerosols properties (e.g., loading and scattering coefficients, etc.) at elevated altitudes, especially when SO2 concentration and cloud coverage are high.

Effect of Ammonia on Secondary Organic Aerosol Formation from α-Pinene Ozonolysis in Dry and Humid Conditions

This study examines the influence of ammonia (NH3) on secondary organic aerosol (SOA) formation from the alpha-pinene/ozone oxidation system for dry and humid conditions. Aerosol yield differed depending on which OH scavenger was used, with the highest yield noted for CO, followed by cyclohexane and 2-butanol. Number and volume concentrations were quickly increased within the reactor by 15 and 8%, respectively, when NH3 was added after the reaction ceased. The increase in number concentration indicated the formation of new particles resulting from gas-to-particle conversion. Moreover, average particle size increased from 242 to 248 nm. The resulting aerosol growth was attributed to ammonium salts formed by the reaction between organic acids and NH3. When NH3 was added to aerosolized cis-pinonic acid in the environmental reactor, a dramatic increase in both number and volume concentrations of cis-pinonic acid was observed. This provides further evidence that NH3 can interact with gas-phase organic acids forming condensable salts and thereby enhancing SOA formation. Initially present NH3 significantly enhanced aerosol yield in alpha-pinene-ozone reactions, regardless of the presence of water vapor. The role of NH3 on SOA formation in the dry and humid conditions is discussed in terms of a theoretical modeling study.

Effects of ototopic steroid and NSAIDS in clearing middle ear effusion in an animal model

A model of otitis media with effusion (OME) has been developed in the Sprague-Dawley (SD) rat. This model was used to study the effects of an ototopic steroid and nonsteroidal anti-inflammatory drug (NSAID) on lipopolysaccharide (LPS)-induced OME. Twenty-six rats were randomized into 4 groups: saline solution, LPS, NSAID + LPS, and steroids + LPS. Test substance was injected into the middle ear at 0, 2, and 4 hours. The effusion was collected at 2, 4, and 6 hours. Statistical analysis of effusion volume and albumin concentration was performed. The LPS group demonstrated statistically significant increase in both effusion volume and albumin concentration compared with saline solution. Intergroup comparison revealed significantly less effusion volume in the steroid group and less albumin concentration in the NSAID group when compared with the LPS group. Transtympanic steroid reduced LPS induced middle ear effusion while NSAID reduced albumin concentration in the rat model. Our results lend support to the current use of anti-inflammatory ototopicals in the treatment of inflammatory middle ear disease.