Effect of Magnetic Field Orientation on Nanofluid Free Convection in a Porous Cavity: A Heat Visualization Study

A range of experiments was conducted to measure the heat transfer characteristics of titanium oxide/deionized water nanofluid (NF) inside a steel-made Pyrex annular system. A set of experiments was designed and performed at inlet temperature (IT) of the NF (333 K-363 K), the applied heat flux (AHF) (4.98 kW/m 2 to 112 kW/m 2 ), 1988 < Re < 13,588 and dispersion concentration of wt.%=0.05 to wt.%=0.15) on the average heat transfer coefficient (HTC) and boiling section's average pressure drop (PD). It was demonstrated that the increase in the volume flow and the AHF can increase the HTC while increasing the weight concentration of the NF, initially increased the HTC such that the maximum enhancement in the HTC was 35.7% at wt.%=0.15 and Re=13500, however, over the time, the HTC of the NF decreased. The reduction in HTC was attributed to the formation of continual sedimentation on the boiling surface after 1000 minutes of the operation. The IT of the NF slightly increased the HTC, which was due to the enhancement in the thermal and physical properties such as thermal conductivity. The maximum enhancement in HTC due to increase of the IT from 333 K to 363 K was 4.2% at wt.%=0.15 and Re=13500. The bubble formation was also found to be a strong function of the applied HF such that with increasing the HF, the rate of the bubble formation increased, which was also the reason behind the augmentation in the HTC at larger AHFs. Also, the PD was augmented due to the increase in the velocity and flow and also weight concentration of NF. The highest value measured for PD was 9 kPa recorded at a weight fraction of 0.15 and Re=13500, which was 28% larger than that of measured for the base fluid. It was also found that a continual fouling layer of nanoparticles (NPs) was formed on the boiling surface, which induced a thermal resistance against the boiling heat transfer. The fouling formation reduced the HTC of the NF such that the maximum reduction in the HTC was 21.6% after 1000 minutes of the operation of the heater.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Flow Boiling Heat Transfer Characteristics of Titanium Oxide/Water Nanofluid (Tio2/Di Water) in an Annular Heat Exchanger

Nakhjavani

Zadeh

2020

“…Later on, Ogut [8] introduced second law of thermodynamics to analyze mixed convection in an inclined liddriven cavity in presence of magnetic field and pointed out the fluid flow and entropy generation decrease for increase in Hartmann number. After that, the heatline visualization technique was first time implemented by Zahmatkesh and Ardekani [9] to investigate the effect of magnetic field orientation on free convection flow of nanofluids in a square porous cavity. Their results demonstrated the heat transfer rate deteriorates for the increase in magnetic field strength.…”

Section: Introductionmentioning

confidence: 99%

“…Manca et al [14] numerically studied mixed convection in a channel with an open cavity and their results showed that maximum temperature values decrease with the increase in Reynolds and Richardson numbers and the highest thermal performance in terms of both maximum temperature and average Nusselt number achieved in the opposing forced flow mode. Later on, Manca et al [15] experimentally investigated this analysis [9] and found that Nusselt numbers increase when the ratio of the length to the height of cavity increase for a considered range of Richardson numbers. Rahman et al [16] numerically studied the development of magnetic field effect on mixed convective flow in a horizontal channel.…”

Section: Introductionmentioning

confidence: 99%

Finite Element Solution of Hydromagnetic Mixed Convection in a Nanofluid Filled Vented Grooved Channel

Ali

Alim

Ahmed

2021

The mixed convection flow in a differentially heated grooved channel filled with water based nanofluid under the influence of external magnetic field has been analyzed numerically in this study. Nanofluid's thermal conductivity model has been modified to develop a new physical problem and finite element method has been implemented to solve the dimensionless governing equations. Numerical simulations have been performed for different values of pertinent parameters. Fluid flow and temperature distributions have been exhibited in terms of streamlines and isotherms due to the variation of Richardson number, Hartmann number and concentration of nanoparticles in base fluid water. The results show that flow field and temperature distributions within the channel affected significantly with the effects of Richardson number, Hartmann number and concentration of nanoparticles. In addition, it is found that heat transfer rate increases and decreases respectively with the increase in strength of magnetic field which depends strongly on Richardson number. Moreover, heat transfer rate accelerates effectively for increasing volume fraction, Reynolds number and Richardson number. The present simulation has been validated by comparing the present results with other published works on the basis of special cases.

“…Very recently Bakar et al [24] studied the effect of magnetic field on fluid flow and heat transfer in a two-dimensional square cavity numerically. The streamlines and isotherm plots and the variation of Nusselt numbers on hot and cold walls were presented.Zahmatkesh and Ardekani [25] analyzed the effect of magnetic field orientation on free convection of several water-based nanofluids in a square porous cavity. Inspection of the results demonstrates that increase in the magnetic field strength deteriorates the heat transfer rate.…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation of Horizontal Magnetic Field Effect on the Flow Characteristics of Gallium Filled in a Vertical Annulus

Ahmadpour

Rezazadeh

Mirzaei

et al. 2021

In the present numerical study, the effect of an external horizontal magnetic field on the natural convection of an electrically conducting molten metal (gallium) inside a vertical cylindrical crucible has been investigated. The effect of the external magnetic field is evaluated on the flow pattern and also the temperature field of molten gallium in the mold with an aspect ratio of A=1.0 and a radii ratio of λ=3.0. A series of simulations are carried out for Hartmann numbers of 0, 22.5, 112, and 167 and Rayleigh numbers of 104, 105, and 106. The obtained results show that for a given Rayleigh number, increasing the Hartmann number suppresses convection flows in all directions with different intensities. Moreover, it was found that the employed horizontal magnetic field leads to vanishing the axisymmetric pattern of flow structures. This is due to the formation of Roberts and Hartmann layers near the walls parallel (0° and 180°) and normal (90° and 270°) to the magnetic field, respectively. Additionally, it is found that the presence of the magnetic field results in the reduction of convection heat transfer. This reduction is lower in the 90° and 270° directions due to the development of Roberts layers near the walls parallel to an external magnetic field. Finally, the numerical results have been validated against the published reliable data.