Browsing by Author "Amer, Mohammed"

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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.
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.
Experimental and Numerical Investigations on Jet Impingement Cooling for Electronic Modules
(2019-10-01)
Chu, Wen-Xiao
;
Huang, Kuan-Chang
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Amer, Mohammed
;
Wang, Chi-Chuan
;
機械工程學系
In this paper, the influence of outlet arrangement and plenum structure on impingement cooling is experimentally and numerically investigated in a typical 1-U confined server space. Three outlets include Z-type, bilateral, and U-type arrangements, and the plenum configurations contain partially inclined, fully inclined, and staged layouts. As a result, using the U-type outlet or staged plenum may prominently compromise the impingement cooling performance on the target plates with lower pumping power. With numerical investigation, it is found that, for the case with Z-type outlet, the flowrate of jet impingement increases alongside the streamwise direction. Besides, the impingement stagnation region on target plates with the minimum thermal resistance may shift toward the outlet. Meanwhile, the uniformity of jet impingement can be improved by 10.7% and 50.3% when the bilateral and U-type outlets are applied, respectively, and the jet impingement is changed to perpendicular direction due to the opposite cross flow from the coming flow direction. On the other hand, by applying the inclined plenum and staged plenum, the uniformity of jet impingement can be dramatically improved by 113.9% and 215.1%, respectively. However, the local jet impingement velocity distribution is still nonuniform. Hence, a novel design of impingement plate based on the concept of Coanda effect is proposed. The peak value of the thermal resistance on target plate can be reduced by 21.8% and 16.0% at the center region and the fore part of the jet array.
Experimental investigation on defrosting of a cold flat plate via ultrasonic vibration under natural convection
(2020-10-01)
Amer, Mohammed
;
Wang, Chi-Chuan
;
機械工程學系
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Department of Mechanical Engineering
The present experimental study examines the effect of ultrasonic vibration on the frost formation under a free convective environment. A stainless steel SS ANSI 316 flat surface is tested under 12-24 degrees C dry bulb temperature and 58-84% relative humidity. The experiments are conducted with direct contact and non-contact high-frequency ultrasonic source having continuous or intermittent vibrations. The ultrasonic transducer contains 28 +/- 0.5 kHz resonance frequency. It is found that increasing the relative humidity will increase the frost thickness and influences the frost property. Imposing ultrasonic vibration under high relative humidity and low ambient temperature increases the droplets' circularity with comparatively sparse distribution. Test results indicate that non-contact vibration has no effect on the frost formation. Intensive intermittent contact vibration is the most effective way to suppress frost growth. Compared to continuous contact vibration, either it is applied after each an hour or after every 30 min as an intensive continuous, intensive intermittent contact vibration shows a reduction in frost thickness as much as 24%. In addition, the ultrasonic vibration should be applied after the supersaturation stage since ultrasonic vibration enhances the supercooled process.
Experiments for suitability of plastic heat exchangers for dehumidification applications
(2019-07-25)
Amer, Mohammed
;
Chen, Miao-Ru
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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.
Nanofluid: Potential evaluation in automotive radiator
(2020-01-01)
Abbas, Farrukh
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Ali, Hafiz Muhammad
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Shah, Tayyab Raza
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Babar, Hamza
;
Janjua, Muhammad Mansoor
Characteristic potential of nanofluids compared to conventional fluids (i.e. water, ethylene glycol, and oils) reported by numerous researchers has extended the concept of their use in multifarious systems. Idiosyncratic thermal and hydrodynamic behavior of nanofluids makes them best candidate to be used in automotive thermal management This article provides comprehensive review of applied research conducted on the potential evaluation of nanofluids in automotive cooling systems. All the key parameters that chiefly influence the nanofluid's performance in a cooling system have been identified along with logical discussion in the current study. Nanofluid assisted thermal management of automotive has been proved to be lucrative, however, ephemeral sustainability of nanofluids poses the major challenge. Set back of thermally effective nanofluids is their trivial suspension period. To alleviate the complication of sustainability of high thermal conductive nanofluids, scientists developed a new class of nanofluids called hybrid nanofluids. Hybrid nanofluids contain two kinds of nanopartides - one having high thermal conductivity and the other having high sustainability - resulting in a comparatively stable and thermally effective nanofluid. Hybrid nanofluids have merely been tested in an automotive cooling system. This study has also discussed the potential of hybrid nanofluids if employed for automotive thermal management. (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
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Hussain, Muzamil
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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.
Performance improvement of photovoltaic modules via temperature homogeneity improvement
(2020-07-15)
Muneeshwaran, M.
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Sajjad, Uzair
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Ahmed, Tanveer
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Amer, Mohammed
;
Ali, Hafiz Muhammad
Though the PV module performance can be enhanced by cooling, the associated temperature nonuniformity across the PV panel can deteriorate its efficiency. In this study, a significant effort is conducted for an air-cooling system that can control the temperature uniformity across the PV panel. The cooling of a rooftop PV module is enabled by the air-conditioning unit installed on the building's roof. PV panel performance, with and without the cooling, is experimentally investigated for the uniform cold air duct. Experimental results showed that the cooled panel temperature is 6-12 degrees C lower than that of the uncooled one. However, even with the cooling, the temperature non-uniformity of 4-7 degrees C was noticed across the PV panel. To improve the temperature uniformity across the module, converging cold air ducts with different area ratios (AR) of 0.667 and 0.333 were designed and analyzed numerically. The effect of inlet air temperature (Tin-air = 18-23 degrees C) and inlet airflow velocity (U = 2-3 m/s) on panel temperature were also studied. The results suggested that the PV panel with CCD having an AR of 0.333 exhibited a temperature non-uniformity of 1.5-2.5 degrees C and demonstrated a 17-22% improvement in module efficiency under Tin-air = 18 degrees C and U = 3 m/s. (C) 2020 Elsevier Ltd. All rights reserved.
Review of defrosting methods
(2017-06-01)
Amer, Mohammed
;
Wang, Chi-Chuan
;
機械工程學系
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Department of Mechanical Engineering
This study reviewed the defrosting techniques applicable for the heating, ventilation, air-conditioning, and refrigeration industry, including passive, active, and system techniques. The passive methods normally use treated surfaces by changing the surface morphology through micro-grooved, anti-frost coating, hydrophilic, hydrophilic, or superhydropholic coating. For passive defrosting techniques, the microgrooved surfaces can improve the drainage of the frost melt effectively. It is generally agreed that the superhydropholic coating can delay the initialization of frosting and provides less water adhesion during defrosting. Yet defrosting performance for hydrophobic surfaces outperforms hydrophilic and uncoated surfaces. Active and system techniques, including electrohydrodynamic (EHD), low-frequency oscillation, and ultrasonic vibration methods, hot gas reverse cycle, electric heater, desiccant dehumidifiers and controlling strategies are reviewed. The EHD defrosting method is proved to be comparatively effective in natural or laminar flow operation. Test results also indicate that utilization of alternative current source is superior to the direct current source. The electrode with negative polarity is better than positive polarity as far as frost accumulation is concerned. The low-frequency oscillation is ineffective in defrosting while ultrasonic vibration provides effective frost removal and can delay the frost growth appreciably. Test results indicate that the ultrasonic oscillation poses considerable positive influence on defrosting either operated continuously or intermittently, in direct contact or not. For system defrosting, the hot gas reverse cycle is comparatively expensive to install but the efficiency, COP, and energy consumption are superior to the other system methods. Desiccants, either solid or liquid, can be employed in association with the system defrosting methods to lower energy consumption. There were various controlling strategies to detect the frost formation and to decide the best time to initiate defrosting. However, many of them were applicable to some specific systems and environments and require further investigations to test the relevant reliability, stability, and repeatability.