Convective heat transfer enhancement of the Water-based magnetite nanofluids in the presence of a 3-D low-intensity magnetic field (original) (raw)
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Enhancement of thermal conductivity upon application of magnetic field to Fe3O4 nanofluids
Journal of Applied Physics, 2011
Enhancement of thermal conductivity of fluids upon addition of nanoparticles has been previously observed. In this study, Fe 3 O 4 magnetite particles were used and thermal conductivity enhancements both in water and in heptane with increasing volume fraction have been shown. Upon measuring thermal conductivity under externally applied magnetic field, it has been shown experimentally that thermal conductivity can be further increased even at low concentrations and low magnetic field strengths in both fluids. Theoretical calculations are presented to support the effect of magnetic field on the thermal conductivity enhancement. This enhancement is attributed to the thermomagnetic convection which due to a temperature gradient, results in a non-uniform magnetic body force resulting in more efficient thermal conductance.
Magnetic field induced enhancement in thermal conductivity of magnetite nanofluid
Journal of Applied Physics, 2010
Magnetite nanofluid is synthesized using continuous chemical process. Powder x-ray diffraction and transmission electron microscopy show single phase spinel structure with size of 9.83 and 9.9 nm, respectively. Thermal conductivity of magnetite nanofluid has been studied as a function of transverse magnetic field and temperature. We found almost 30% enhancements in thermal conductivity for 4.7% volume fraction under transverse magnetic field. This result is explained on the basis of formation of continuous three-dimensional zipperlike structure of magnetic nanoparticles inside magnetic fluid. The temperature dependent thermal conductivity shows no enhancement in the temperature region of 25-65 °C.
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This paper focuses on the convective heat transfer characteristics of Fe3O4-water magnetic nanofluids under laminar and turbulent conditions. After verifying the accuracy of the experimental apparatus, the effects of magnetic field strength, concentration, Reynolds number and temperature on the convective heat transfer coefficient have been studied. The convective heat transfer characteristics of nanofluids under laminar and turbulent flow conditions were studied in depth, and the influence of each factor on the heat transfer coefficient was analyzed by orthogonal experimental design method. Under the laminar flow conditions, the convective heat transfer of magnetic nanofluids performed best when the Reynolds number was 2000, the magnetic field strength was 600, the temperature was 30?C, and the concentration was 2%. The convective heat transfer coefficient, h, increased by 3.96% than the distilled water in the same conditions. In turbulent state, the convective heat transfer of mag...
Applied Sciences
This paper discusses the forced convective heat transfer characteristics of water–ethylene glycol (EG)-based Fe3O4 nanofluid and Fe3O4–MWCNT hybrid nanofluid under the effect of a magnetic field. The results indicated that the convective heat transfer coefficient of magnetic nanofluids increased with an increase in the strength of the magnetic field. When the magnetic field strength was varied from 0 to 750 G, the maximum convective heat transfer coefficients were observed for the 0.2 wt% Fe3O4 and 0.1 wt% Fe3O4–MWNCT nanofluids, and the improvements were approximately 2.78% and 3.23%, respectively. The average pressure drops for 0.2 wt% Fe3O4 and 0.2 wt% Fe3O4–MWNCT nanofluids increased by about 4.73% and 5.23%, respectively. Owing to the extensive aggregation of nanoparticles by the external magnetic field, the heat transfer coefficient of the 0.1 wt% Fe3O4–MWNCT hybrid nanofluid was 5% higher than that of the 0.2 wt% Fe3O4 nanofluid. Therefore, the convective heat transfer can be...
Journal of Applied Physics, 2014
Rate of heat generated by magnetic nanoparticles in a ferrofluid is affected by their magnetic properties, temperature, and viscosity of the carrier liquid. We have investigated temperature dependent magnetic hyperthermia in ferrofluids, consisting of dextran coated superparamagnetic Fe 3 O 4 nanoparticles, subjected to external magnetic fields of various frequencies (188-375 kHz) and amplitudes (140-235 Oe). Transmission electron microscopy measurements show that the nanoparticles are polydispersed with a mean diameter of 13.8 6 3.1 nm. The fitting of experimental dc magnetization data to a standard Langevin function incorporating particle size distribution yields a mean diameter of 10.6 6 1.2 nm, and a reduced saturation magnetization ($65 emu/g) compared to the bulk value of Fe 3 O 4 ($95 emu/g). This is due to the presence of a finite surface layer ($1 nm thickness) of non-aligned spins surrounding the ferromagnetically aligned Fe 3 O 4 core. We found the specific absorption rate, measured as power absorbed per gram of iron oxide nanoparticles, decreases monotonically with increasing temperature for all values of magnetic field and frequency. Using the size distribution of magnetic nanoparticles estimated from the magnetization measurements, we have fitted the specific absorption rate versus temperature data using a linear response theory and relaxation dissipation mechanisms to determine the value of magnetic anisotropy constant (28 6 2 kJ/m 3) of Fe 3 O 4 nanoparticles. V
Thermal performance analysis of tunable magnetite nanofluids for an energy system
Applied Thermal Engineering, 2017
This study is based on the effect of external magnetic field on heat transfer performance and pumping power of Fe3O4/DI-water nanofluid is experimentally investigated under both laminar and turbulent flow regimes. The magnetite ferrofluids with 0.25% and 0.50% of weight fractions are prepared by a chemical precipitating method using ammonium hydroxide reagent for maximising the stabilisation. The experiments were conducted at various mass flow rates with two different external magnets arrangements and input powers. The result shows that the enhancement in local heat coefficient was more pronounced by introducing more magnets on the tube of the test section, especially in the turbulent flow regime. The heat transfer coefficient improves with an increase in Reynolds number as well. In addition, the effect of the magnetic field was not significant on the increment of pressure loss. Therefore, the highest performance index and lowest exergy loss were found for external magnets configurations at 0.25 wt% of nanofluids. The rise in heat transfer is assumed to be an accumulation of nanoparticles near the ring magnets, which may lead to a local thermal conductivity improvement. This aggregation formation enhancing the momentum and energy transfer in the fluid flow.
Thermal Conductivity of Magnetic Nanofluids in External Magnetic Field
Enhancement of thermal conductivity of fluids upon addition of nanoparticles has been previously observed. In this study, Fe 3 O 4 magnetite particles were used and thermal conductivity enhancements both in water and in heptane with increasing volume fraction have been shown. Upon measuring thermal conductivity under externally applied magnetic field, it has been shown experimentally that thermal conductivity can be further increased even at low concentrations and low magnetic field strengths in both fluids. Theoretical calculations are presented to support the effect of magnetic field on the thermal conductivity enhancement. This enhancement is attributed to the thermomagnetic convection which due to a temperature gradient, results in a non-uniform magnetic body force resulting in more efficient thermal conductance.
Fabrication, characterization and measurement of thermal conductivity of Fe 3O 4 nanofluids
Journal of Magnetism and Magnetic Materials, 2010
Magnetite Fe 3 O 4 nanoparticles were synthesized by a co-precipitation method at different pH values. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electronic microscopy. Their magnetic properties were evaluated on a vibrating sample magnetometer. The results show that the shape of the particles is cubic and they are superparamagnetic at room temperature. Magnetic nanofluids were prepared by dispersing the Fe 3 O 4 nanoparticles in water as a base fluid in the presence of tetramethyl ammonium hydroxide as a dispersant. The thermal conductivity of the nanofluids was measured as a function of volume fraction and temperature. The results show that the thermal conductivity ratio of the nanofluids increases with increase in temperature and volume fraction. The highest enhancement of thermal conductivity was 11.5% in the nanofluid of 3 vol% of nanoparticles at 40 1C. The experimental results were also compared with the theoretical models.
ScienceDirect, 2016
In this paper, experimental determination of dynamic viscosity of water based magnetite nanofluid (Fe 3 O 4 /water) was performed. The viscosity was measured in the temperature range of 20-55 °C for various samples with solid volume fractions of 0.1%, 0.2%, 0.4%, 1%, 2% and 3%. The results showed that the viscosity considerably decreases with increasing temperature. Moreover, the viscosity enhances with an increase in the solid volume fraction, remarkably. The calculated viscosity ratios showed that the maximum viscosity enhancement was 129.7%. Using experimental data, a new correlation has been proposed to predict the viscosity of magnetite nanofluid (Fe 3 O 4 /water). A comparison between the experimental results and the correlation outputs showed that the proposed model has a suitable accuracy.