Browsing by Author "Zahra, Nida"

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Applications of nanofluids in photovoltaic thermal systems: A review of recent advances
(2019-12-15)
Abbas, Naseem
;
Awan, Muhammad Bilal
;
Amer, Mohammed
;
Ammar, Syed Muhammad
;
Sajjad, Uzair
The aim of this study is to present a critical review of the impact of nanofluids on the performance enhancement of PV/T systems. The review has analyzed the effects of nanoparticle type, size, volume fraction and concentration ratio on the performance of PV/T systems. Furthermore, the type of base-fluid, flow channels, and flow types have also been studied comprehensively in relation to nanofluids characteristics and properties. Results have shown that the inclusion of nanofluid enhances the overall efficiency of the PV/T systems. It has been concluded that the organic fluids are better base fluids than water, and nanofluids with better thermal conductivity enhance the maximum efficiency once optimum size, volume fraction and correct concentration ratio of nanofluid are selected. Moreover, straight microchannel and the addition of Fe3O4, SiC and TiO2 nanofluids with low concentration ratio provides better efficiency and flexibility. The motive beyond that is the micro-channels turbulent flow occurs at low Reynolds number. Accordingly, maximum efficiency can be obtained at higher velocity laminar flows. Increasing the velocity to higher ranges of turbulent flow does not allow proper time for heat transfer and can cause clustering of nanoparticles. The observations of this review are proposed to PV/T systems and it is helpful for the thermal system design practitioners towards achieving high efficiency in any thermal system. (C) 2019 Elsevier B.V. All rights reserved.
Optimization of Cr Seed Layer Effect for Surface Roughness of As-Deposited Silver Film using Electron Beam Deposition Method
(2020-02-01)
Abbas, Naseem
;
Hussain, Muzamil
;
Zahra, Nida
;
Ahmad, Hassaan
;
Muhammad, Syed
The surface roughness is an important parameter in determining the physical properties and quality of thin films deposited by physical vapor deposition (PVD) method. The presence of an intermediate layer between metallic nanoparticles and substrate significantly promotes the adhesion and reduces the surface roughness. In this article, we have investigated the effect of Chromium (Cr) seed layer to optimize the surface roughness on the growth of as-deposited silver (Ag) film using borosilicate glass and silicon wafer substrates. For this purpose, Ag thin films were deposited with a Cr seed layer of different thickness on borosilicate glass and silicon wafer substrates using an electron beam (E-Beam) deposition method. The Cr thin film of different thickness ranging from 1 nm to 6 nm was thermally evaporated and pure Ag with the same thickness was evaporated at the same rate on previously coated substrates. The deposition of the nanostructured thin film was confirmed by UV-Vis and XRD characterizations. The difference in transmittance for uncoated and coated substrates ensured the deposition. The presence of pure Ag crystalline phase was confirmed by XRD pattern. Surface roughness was measured using Atomic Force Microscopy (AFM) and the conductance was measured using 4-probe conductivity method. The density of nanoparticles and smoothness were visualized from two dimensional (2D) and three dimensional (3D) surface height histograms of representative AFM images. The quantitative roughness was measured in terms of root mean square (RMS) roughness and mean roughness. The high dense and smoother thin films were found for similar to 2-4 nm Cr layer thickness in case of the glass substrate. The slight increase in roughness was observed for similar to 1-6 nm Cr layer thickness in case of the silicon substrate. The dependence of the conductivity of thin films on surface roughness is investigated to verify the effect of surface roughness on different applications of Ag thin film. The conductance results have been analyzed as; for a glass substrate, conductivity was maximum for thin films containing similar to 2 nm Cr seed layer thickness, while for silicon substrate the maximum conductivity was found for the thin film containing similar to 1 nm Cr seed layer.