期刊論文;;Articles

Permanent URI for this collectionhdl:11536/5

Browse

Now showing 1 - 6 of 6

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.
Condensing heat transfer coefficients of R134a in smooth and grooved multiport flat tubes of automotive heat exchanger: An experimental investigation
(2019-05-01)
Ammar, Syed Muhammad
;
Abbas, Naseem
;
Abbas, Saleem
;
Ali, Hafiz Muhammad
;
Hussain, Iftikhar
Condensation heat transfer coefficient of R134a was obtained in multi-port micro channel smooth and grooved flat tubes of automotive heat exchanger. The test consisted of two smooth and one grooved tube. The test range covered mass flux 490-1600 kg/m(2) s, heat flux 5.5-19 kW/m(2) and saturation temperature 51-68 degrees C. Results revealed that condensation heat transfer coefficient increased with an increment of mass flux, vapor quality and decreased with the increase of saturation temperature. The effect of heat flux on heat transfer coefficient was negligible. The grooved tube showed larger heat transfer coefficient than that of smooth tubes. A comparison of the present data of flat tube with existing correlations revealed that the heat transfer coefficient was not reasonably predicted, therefore new correlation was developed for heat transfer coefficient that predicted 86% data within +/- 30% with a mean error of 16%. (C) 2019 Elsevier Ltd. All rights reserved.
Cost effective cooling of photovoltaic modules to improve efficiency
(2019-09-01)
Sajjad, Uzair
;
Amer, Mohammed
;
Ali, Hafiz Muhammad
;
Dahiya, Anurag
;
Abbas, Naseem
This study presents the performance of solar photovoltaic modules provided with cooling in terms of its normalized power output, performance ratio, and module efficiency. The aim of the study is to improve the performance, efficiency, and development of an economical cooling system by installing photovoltaic modules on the duct of cooled air of air-conditioners being used in most of the houses, offices and other buildings. The performance was researched and compared for two photovoltaic modules, one being cooled and other without cooling. The module being cooled showed 7.2% and 6% higher electrical efficiency and performance ratio respectively compared to the module without cooling. The results obtained in this study comprehend the importance and feasibility of the research.
Experiments for suitability of plastic heat exchangers for dehumidification applications
(2019-07-25)
Amer, Mohammed
;
Chen, Miao-Ru
;
Sajjad, Uzair
;
Ali, Hafiz Muhammad
;
Abbas, Naseem
The present study conducted a series of experiments concerning the condensation of humid air used in a typical adsorption dehumidifier. The experiments were carried out with the standard ambient condition (27 degrees C dry bulb temperature and 21.2 degrees C wet bulb temperature) for the cold side. Yet the regeneration side (hot side) inlet temperature is 55 degrees C with RH% being 100%. Three novel plastic heat exchangers (plate plastic heat exchanger-PHX, bare tube plastic heat exchanger with asymmetry tube layout-BTHX, and round tube plastic heat exchanger with uniform tube layout-RTHX) were tested and compared experimentally. Test results, in terms of heat flux or heat transfer coefficient, show that the BTHX is superior to RTHX and PHX for offering additional condensate splashing mode. The splashing feature is especially beneficial for larger cold side flow rate since the plateau of heat transfer performance is moved toward larger cold side flow rate regime. The asymmetry tube geometry design (BTHX) shows even better heat transfer performance than the uniform tube bundle design (RTHX) for providing more space at the downstream of the tube bundle.
Fabrication and characterization of silver thin films using physical vapor deposition, and the investigation of annealing effects on their structures
(2019-11-01)
Abbas, Naseem
;
Shad, Muhammad Rizwan
;
Hussain, Muzamil
;
Mehdi, Syed Muhammad Zain
;
Sajjad, Uzair
Silver nanoparticles have attracted increasing interest due to their chemical stability, catalytic activity, localized surface plasma resonance, and high conductivity. In this article, silver thin films with a thickness of similar to 20 nm were fabricated on commercial glass (20mm x 20mm) substrate using physical vapor deposition technique, through the bombardment of the electron beam. To check the effect of annealing temperature, the fabricated substrates were annealed at the temperature range of 373.15 K to 1073.15 K with the difference of 100 K under a vacuum condition of similar to 0.99 bar at constant time of 20 min; in addition, a single sample that had undergone no annealing effect has also been provided as a reference substrate. We investigated the physical and morphology evaluation information of fabricated annealed silver thin films on the glass substrate using the Ultra-Violet and Visible (UV-vis) spectroscopy, x-ray diffraction (XRD) and the field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS). The results obtained from this study show that by increasing the annealing temperature of silver thin films, the flat silver thin films changed into rough silver thin films, by further increment change the silver thin films into silver nano-particles. At the annealed temperature of 1073.15 K, the 20 nm silver thin film was completely removed from the glass as well as bending occurred on the glass substrate. In the end, the absorbance spectra of each sample and the referenced sample were also measured.
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.