Md. Motawakkel Billah

Md. Motawakkel Billah 

Phone: 0181929444
Email: billah@ius.edu.bd

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Publications:

1. Hybrid-nanofluid mixed convection in square cavity subjected to oriented magnetic field and multiple rotating rough cylinders.

It has been published   by renowned publisher Elsevier.

Abstract:

In this study, mixed convective hybrid-nanofluid flow in a partially heated square cavity with two rotating rough cylinders in presence of an external magnetic field is numerically investigated. A pair of rotating rough cylinders is placed at different locations inside the cavity. The cavity is permeated by an external magnetic field at different inclination angles. Maxwell's thermal conductivity model is modified incorporating Brownian motion of hybrid nanoparticles. The conservation equations of the flow and thermal fields are simulated using finite element method. The effects of different influential parameters such as cylinders rotation velocity (0 ≤ ω ≤ 50), Hartmann number (0 ≤ Ha ≤50), hybrid nanoparticle volume fraction (0% ≤ φ ≤ 5%) and magnetic inclination angle (0° ≤ α ≤ 135°) on the flow and thermal fields are explored via streamlines, isotherms and bar charts of average Nusselt number. The simulated results ensure that mixed convective flow is accelerated with cylinders rotation speed but declines with higher magnetic field strength and hybrid-nanoparticle volume fraction. Heat transfer enhancement is recorded up to 261.29% at highest rotating speed of rough cylinders (ω: 0–50, φ = 1%, Ha = 10). Enhancement of heat transfer rate is found decreasing for increasing magnetic field strength. Lowest heat transfer rate is occurred at highest magnetic field impact (Ha = 50) which is 144.62% less than that of heat transfer in absence of magnetic field (Ha = 0). Optimum heat transfer is found for 5% hybrid nanoparticle volume fraction which is 101.2% more compared to base fluid water. The presence of triangular rough components accelerates the fluid flow and heat transfer rate significantly. In addition, 48.89% more heat transfer is obtained for rotating rough cylinders with triangular components compared to smooth cylinders. Moreover, maximum heat transfer is achieved at magnetic inclination angle of 90°. It is also observed that the flow and thermal fields strongly depend on the cylinders arrangements.

Link: https://www.sciencedirect.com/science/article/pii/S259012302300227X

1. Helium Plasma Jet Interaction with Different Target Materials and the Plasma Characteristics on the Irradiation Area. Accepted by

The European Physical Journal Applied Physics (EPJ AP)

Abstract:

The experimental study on the dynamic behavior of helium atmospheric pressure plasma jet exposed on the surface of different conductivity is reported in this article. Electrical, optical, and gas dynamics characteristics are monitored using a high voltage probe, current probe, and imaging technique. The turbulence-free plasma jet length is estimated from the image of the plasma jet and correlated with the calculating Electrohydrodynamic number (Ehd number). It has been shown that plasma species strongly modify the gas dynamics on the contact surface. The irradiation area on agar gel, metal, and Teflon is observed and the different flow regimes (free jet, stagnant region, and accelerating region) are identified. The irradiation area is significantly broadened for the polymer-like substrate and intensity is higher close to the stagnant region. The excited nitrogen and OH intensity is higher than the other observed chemical species on the target surface. The turbulence is higher near the outer radius of the irradiated surface, and it increases with operating voltage. The estimated electron excitation temperature for the free plasma jet is 0.84 eV whereas its values are 0.77 eV, 0.79 eV, 0.84 eV, and 1.07 eV when the plasma jet is in contact with Agar gel, water, Teflon, and metal, respectively. The chemistry of the water changes with the presence of the metal probe inside the water.

Link:

https://l.messenger.com/l.php?u=https%3A%2F%2Fwww.researchgate.net%2Fpublication%2F368839474_Helium_Plasma_Jet_Interaction_with_Different_Target_Materials_and_the_Plasma_Characteristics_on_the_Irradiation_Area%2Fstats&h=AT1v7DjUYBprAleSu2uH6KUEfrfUuUWO12PTanUicXrO6qqH3CsHP9VM5Yc3V0Tjad8HHX7AUGi_HXLZgum7QFqi1Br15Hv6ziXFB_PsGRImyOy35-hyB8MIp3YBgzj_s5DOyQ