Browsing by Author "Ali, Hafiz Muhammad"

Now showing 1 - 11 of 11

A critical review on heat transfer augmentation of phase change materials embedded with porous materials/foams
(2019-06-01)
Tauseef-ur-Rehman
;
Ali, Hafiz Muhammad
;
Janjua, Muhammad Mansoor
;
Sajjad, Uzair
;
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
;
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.
Bubble dynamics in evaporation flow of R-134a in narrow annular ducts due to flow rate oscillation
(2019-01-01)
Chen, C. A.
;
Lin, T. F.
;
Ali, Hafiz Muhammad
;
Amani, Pouria
;
Yan, Wei-Mon
This article aims to investigate the influence of imposed flow rate oscillation on the bubble behaviors of evaporative flow of R-134a in horizontal narrow annular ducts. Particularly, the effects of amplitudes and periods of the oscillating flow rates along with the vapor quality of the R-134a on the bubble characteristics are examined in details. Moreover, the R-134a flow photos captured at the middle axial location are presented to illustrate the shift between the annular two-phase flow pattern and the bubble nucleation at different operating conditions and time instances. The observations reveal that the imposed mass flow rate oscillation results in the fluctuation of bubble departure diameter and frequency along with the density of active nucleation sites with the same frequencies. The larger amplitudes and longer periods of the mass flow rate oscillation lead to the stronger fluctuations in bubble dynamics. Furthermore, it is found that the bubble nucleation on the heating surface is the dominant mechanism at the low vapor quality of 0.05. However, the annular two-phase flow prevails over a relatively large portion of the periodic cycle at the dryness fraction of 0.5 and over the entire cycle at the dryness fraction of 0.95. Finally, the evaporative heat transfer of R-134a subject to the flow rate oscillation is correlated as a function of the mass flow rate and the vapor quality.
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.
Experimental study on bubble characteristics of time periodic subcooled flow boiling in annular ducts due to wall heat flux oscillation
(2020-08-01)
Chen, A.
;
Lin, T. F.
;
Ali, Hafiz Muhammad
;
Yan, Wei-Mon
;
機械工程學系
The significant effects of imposed wall heat flux oscillation on bubble characteristics of subcooled flow boiling with R-134a in horizontal annular ducts are experimentally performed in details. Specific emphasis has been applied on the bubble dynamics of the time periodic subcooled flow boiling characteristics influenced by the mean levels, amplitudes, and periods of the wall heat flux oscillations. The obtained experimental results have disclosed that the bubble parameters like the departure diameter, frequency and active nucleation site density, do oscillate periodically in time and are at the same frequency as the imposed wall heat flux oscillation. Nevertheless, these parameters also increase at long periods, high amplitudes of imposed heat flux oscillation or high values of mean imposed heat flux. Furthermore, the bubble size reduced after the time lag when the imposed heat flux decreases with time. (C) 2020 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
;
Rehman, Tauseef-ur
;
Ali, Hafiz Muhammad
;
Sajjad, Uzair
;
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
;
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.
Nanofluid: Potential evaluation in automotive radiator
(2020-01-01)
Abbas, Farrukh
;
Ali, Hafiz Muhammad
;
Shah, Tayyab Raza
;
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.
Performance improvement of photovoltaic modules via temperature homogeneity improvement
(2020-07-15)
Muneeshwaran, M.
;
Sajjad, Uzair
;
Ahmed, Tanveer
;
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.
Thermal performance of LHSU for electronics under steady and transient operations modes
(2018-12-01)
Ali, Hafiz Muhammad
;
Arshad, Adeel
;
Janjua, Muhammad Mansoor
;
Baig, Wajahat
;
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.