Browsing by Author "Sajjad, Uzair"

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A critical review on heat transfer augmentation of phase change materials embedded with porous materials/foams
(2019-06-01)
Tauseef-ur-Rehman
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Ali, Hafiz Muhammad
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Janjua, Muhammad Mansoor
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Sajjad, Uzair
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Yan, Wei-Mon
Phase change material (PCM) is promising media for thermal energy storage owing to its extensive value of latent heat (140-970 KJ/Kg). However, thermal conductivity of PCMs is too low which obstructs energy storage and retrieval rate. In recent days, thermally enhanced PCMs are considered promising materials for efficient heat transfer in many applications. This article designates the review on improved thermal properties and heat transfer of PCMs by using porous materials. Enhanced heat transfer of PCMs can be achieved using extended surfaces (triangular, conical, square, and rectangular fins), heat pipes, and addition of highly conductive nanoparticles (e.g. Cu, Al2O3, Au, SiC, SiO2 and TiO2). Major focus of this article is to study the enhanced heat transfer of PCMs through metallic (copper, nickel, and aluminum) and carbon based (carbon, graphite and expanded graphite) porous materials/foams. Effects of porosity and pore density on heat transfer, thermal conductivity, specific heat, latent heat and charging/discharging time are critically reviewed. Porous materials/foams are reported to be efficient for heat transfer/thermal conductivity enhancement by 3-500 times. Furthermore, correlations to find the effective thermal conductivity of PCM/foam are reported. Important applications of PCM/foam reported by different researchers are also discussed in this paper. Finally, conclusions and recommendations are presented to highlight the research gap in this area. (C) 2019 Elsevier Ltd. All rights reserved.
Applications of nanofluids in photovoltaic thermal systems: A review of recent advances
(2019-12-15)
Abbas, Naseem
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Awan, Muhammad Bilal
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Amer, Mohammed
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Ammar, Syed Muhammad
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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
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Abbas, Naseem
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Abbas, Saleem
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Ali, Hafiz Muhammad
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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
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Amer, Mohammed
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Ali, Hafiz Muhammad
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Dahiya, Anurag
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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.
Effects of surface inclination and type of surface roughness on the nucleate boiling heat transfer performance of HFE-7200 dielectric fluid
(2020-02-01)
Tran, Ngoctan
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Sajjad, Uzair
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Lin, Rick
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Wang, Chi-Chuan
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機械工程學系
In the present work, the effects of surface roughness (including roughness from machined roughness and sandblasted roughness), surface inclinations, and heat fluxes on the nucleate pool boiling heat transfer of HFE-7200 dielectric liquid at a working pressure of 1 atm. are examined in detail. Five aluminum surfaces, with different roughness from 0.45 mu m to 9 mu m, are employed as test samples. The nucleate boiling phenomenon is examined with the wall-superheat temperature ranging from 5 degrees C to 30 degrees C, and surface inclinations of 0 degrees, 90 degrees, and 180 degrees, respectively. SEM images and nucleate boiling bubbles captured by a high-speed camera are utilized for further analyses. For all cases in this study, it is found that the nucleate boiling heat transfer of the sandblasted rough surfaces is superior to those of the polished and machined rough surfaces. For instance, at a wall-superheat temperature of 30 degrees C and inclination angle of 0 degrees, the heat flux is augmented up to 69.7%, and 139.3% when compared to the polished surface for the sandblasted surfaces with the roughness of 6.2 mu m, and 9 mu m, respectively. In addition, novel correlations are also proposed for predicting the nucleate pool boiling heat transfer coefficient of HEF-7200 dielectric fluid with different surface roughness, inclinations and heat fluxes. (C) 2019 Elsevier Ltd. All rights reserved.
Experimental thermal performance analysis of finned tube-phase change material based double pass solar air heater
(2019-11-01)
Sajawal, Muhammad
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Rehman, Tauseef-ur
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Ali, Hafiz Muhammad
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Sajjad, Uzair
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Raza, Ali
The present experimental study is performed to investigate the thermal performances of double pass solar air heater comprising of phase change materials (PCM) contained in metallic finned tubes to have increased energy storage and heat transfer rate. Experimental results were also helpful in the evaluation of the charging and the discharging characteristics of the PCMs. The air heater is studied for three different configurations. In the first configuration, is no PCM used. In the second configuration, RT44HC having higher melting point filled in semi-circular finned tubes (SFT) on the upper pass of double pass solar air heater (DPSAH) as a thermal storage medium (TSM) is used. While the third configuration is a combination of the second configuration and RT18HC having lower melting point, filled in circular finned tubes (FT) as TSM placed in the lower pass to enhance the thermal storage capacity of solar air heater (SAH). The heater's thermal performance is evaluated for all configurations separately. It was revealed that the third configuration containing RT44HC and RT18HC in upper and lower passes respectively is the best among others for optimum heater performance.
Experiments for suitability of plastic heat exchangers for dehumidification applications
(2019-07-25)
Amer, Mohammed
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Chen, Miao-Ru
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Sajjad, Uzair
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Ali, Hafiz Muhammad
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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
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Shad, Muhammad Rizwan
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Hussain, Muzamil
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Mehdi, Syed Muhammad Zain
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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.
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
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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
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Ahmad, Hassaan
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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
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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.
Thermal performance of LHSU for electronics under steady and transient operations modes
(2018-12-01)
Ali, Hafiz Muhammad
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Arshad, Adeel
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Janjua, Muhammad Mansoor
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Baig, Wajahat
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Sajjad, Uzair
This experimental study investigates the effect of passive cooling of electronic devices using a latent heat storage unit (LHSU) filled with n-eicosane as phase change material (PCM),under steady-state and transient heating operations. A pin-fin heat sink of square configuration, made of aluminum, pin fins acted as a thermal conductivity enhancers (TCEs), is used to augment the rate of heat transfer through n-eicosane which has low thermal conductivity. A range of input heating loads from 1.2-2.8 kW/m(2) with an interval of 0.4 kW/m(2) are applied at the base of LHSU, filled at three different volumetric fractions of n-eicosane, to quantify the steady-state and transient heat transfer characteristics for different operation modes for reliable passive cooling of electronics. The results are reported under two phases i.e. steady-state and transient heating, and thermal performance of LHSU is elucidated in terms of enhancement in operation time, enhancement ratio, effect of PCM amount and various usage modes under different heating loads. (C) 2018 Elsevier Ltd. All rights reserved.