ORCID Profile
0000-0002-2994-1504
Current Organisations
Tafila Technical University
,
Auburn University
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Publisher: Elsevier BV
Date: 2019
Publisher: Elsevier BV
Date: 08-2016
Publisher: MDPI AG
Date: 02-03-2020
DOI: 10.3390/SYM12030364
Abstract: Low-permeability porous medium usually has asymmetric distributions of pore sizes and pore-throat tortuosity, thus has a non-linear flow behavior with an initial pressure gradient observed in experiments. A threshold pressure gradient (TPG) has been proposed as a crucial parameter to describe this non-linear flow behavior. However, the determination of this TPG is still unclear. This study provides multi-scale insights on the TPG in low-permeability porous media. First, a semi-empirical formula of TPG was proposed based on a macroscopic relationship with permeability, water saturation, and pore pressure, and verified by three sets of experimental data. Second, a fractal model of capillary tubes was developed to link this TPG formula with structural parameters of porous media (pore-size distribution fractal dimension and tortuosity fractal dimension), residual water saturation, and capillary pressure. The effect of pore structure complexity on the TPG is explicitly derived. It is found that the effects of water saturation and pore pressure on the TPG follow an exponential function and the TPG is a linear function of yield stress. These effects are also spatially asymmetric. Complex pore structures significantly affect the TPG only in the range of low porosity, but water saturation and yield stress have effects on a wider range of porosity. These results are meaningful to the understanding of non-linear flow mechanism in low-permeability reservoirs.
Publisher: MDPI AG
Date: 03-2020
DOI: 10.3390/EN13051065
Abstract: The condensate on the surface of the minichannel heat exchanger generated during air cooling substantially reduces the heat transfer performance as it works as an evaporator in the air-conditioning system. This has received much attention in scientific communities. In this paper, the effect of operating parameters on the heat transfer performance of a minichannel heat exchanger (MHE) is investigated under an evaporator working condition. An experimental MHE test system is developed for this purpose, and extensive experimental studies are conducted under a wide range of working conditions using the water-cooling method. The inlet air temperature shows a large effect on the overall heat transfer coefficient, while the inlet air relative humidity shows a large effect on the condensate aggregation rate. The airside heat transfer coefficient increases from 66 to 81 W/(m2·K) when the inlet air temperature increases from 30 to 35 °C. While the condensate aggregation rate on the MHE surface increases by up to 1.8 times when the relative humidity increases from 50% to 70%. The optimal air velocity, 2.5 m/s, is identified in terms of the heat transfer rate and airside heat transfer coefficient of the MHE. It is also found that the heat transfer rate and overall heat transfer coefficient increase as the air velocity increases from 1.5 to 2.5 m/s and decreases above 2.5 m/s. Furthermore, a large amount of condensate accumulates on the MHE surface lowering the MHE heat transfer. The inclined installation angle of the MHE in the wind tunnel effectively enhances heat transfer performance on the MHE surface. The experimental results provide useful information for reducing condensate accumulation and enhancing microchannel heat transfer.
Publisher: Elsevier BV
Date: 10-2023
Publisher: MDPI AG
Date: 15-08-2020
DOI: 10.3390/APP10165671
Abstract: Frosting and fogging of automobile windshields is a common problem that emerges in daily driving. It is important and essential to quickly and completely defrost the windshield for safety purposes. In this study, a three-dimensional mathematical model was applied to investigate the flow distribution and flow characteristics on the windshield of a medium-size Model N800 truck. The simulation results were first compared with experimental data. The results showed that the simulation model could reliably predict the defrosting performance on the windshield. This model was then used to optimize the design of the defrosting duct that comprised the main part of the defroster. It was found that the guide plate and outlet position of the defrosting duct were the two major factors affecting the defrosting performance. Therefore, the guide plate was first optimized and the defrosting performance was analyzed. The results showed that the average pressure loss dropped by 21.56%, while the defrosting efficiency at the front white zone was improved to 89%. The position of the outlet of the airflow was further studied. The results showed that the defrosting efficiency at the front zone could be further improved to 99%.
Publisher: Elsevier BV
Date: 11-2023
Publisher: MDPI AG
Date: 23-02-2023
Abstract: Water-in-diesel (W/D) emulsion fuel is a potentially viable diesel fuel that can simultaneously enhance engine performance and reduce exhaust emissions in a current diesel engine without requiring engine modifications or incurring additional costs. In a consistent manner, the current study examines the impact of adding water, in the range of 5–30% wt. (5% increment) and 2% surfactant of polysorbate 20, on the performance in terms of brake torque (BT) and exhaust emissions of a four-cylinder four-stroke diesel engine. The relationship between independent factors, including water addition and engine speed, and dependent factors, including different exhaust released emissions and BT, was initially generated using machine learning support vector regression (SVR). Subsequently, a robust and modern optimization of the sea-horse optimizer (SHO) was run through the SVR model to find the optimal water addition and engine speed for improving the BT and lowering exhaust emissions. Furthermore, the SVR model was compared to the artificial neural network (ANN) model in terms of R-squared and mean square error (MSE). According to the experimental results, the BT was boosted by 3.34% compared to pure diesel at 5% water addition. The highest reduction in carbon monoxide (CO) and unburned hydrocarbon (UHC) was 9.57% and 15.63%, respectively, at 15% of water addition compared to diesel fuel. The nitrogen oxides (NOx) emissions from emulsified fuel were significantly lower than those from pure diesel, with a maximum decrease of 67.14% at 30% water addition. The suggested SVR-SHO model demonstrated superior prediction reliability, with a significant R-Squared of more than 0.98 and a low MSE of less than 0.003. The SHO revealed that adding 15% water to the W/D emulsion fuel at an engine speed of 1848 rpm yielded the optimum BT, CO, UHC, and NOx values of 49.5 N.m, 0.5%, 57 ppm, and 369 ppm, respectively. Finally, these outcomes have important implications for the potential of the SVR-SHO approach to minimize engine exhaust emissions while maximizing engine performance.
Publisher: MDPI AG
Date: 02-12-2022
DOI: 10.3390/APP122312364
Abstract: Due to the energy crisis and environmental impact caused by fossil fuel energy, improving the efficiency of cooling, power, and energy systems has become one of the most important aspects of energy sectors [...]
Publisher: MDPI AG
Date: 24-02-2020
DOI: 10.3390/EN13041005
Abstract: Performance assessment of a two-bed silica gel-water adsorption refrigeration system driven by solar thermal energy is carried out under a climatic condition typical of Perth, Australia. A Fourier series is used to simulate solar radiation based on the actual data obtained from Meteonorm software, version 7.0 for Perth, Australia. Two economic methodologies, Payback Period and Life-Cycle Saving are used to evaluate the system economics and optimize the need for solar collector areas. The analysis showed that the order of Fourier series did not have a significant impact on the simulation radiation data and a three-order Fourier series was good enough to approximate the actual solar radiation. For a typical summer day, the average cooling capacity of the chiller at peak hour (13:00) is around 11 kW while the cyclic chiller system coefficient of performance (COP) and solar system COP are around 0.5 and 0.3, respectively. The economic analysis showed that the payback period for the solar adsorption system studied was about 11 years and the optimal solar collector area was around 38 m2 if a compound parabolic collector (CPC) panel was used. The study indicated that the utilization of the solar-driven adsorption cooling is economically and technically viable for weather conditions like those in Perth, Australia.
Publisher: MDPI AG
Date: 23-07-2021
DOI: 10.3390/EN14154470
Abstract: Given the large demand nowadays for domestic hot water, and its impact on modern building energy consumption, air source transcritical CO2 heat pumps have been extensively adopted for hot water production. Since their system efficiency is limited by significant irreversibility, a CO2-based mixture could offer a promising drop-in technology to overcome this deficiency without increasing system complexity. Although many CO2 blends have been studied in previously published literature, little has been presented about the CO2/R32 mixture. Therefore, a proposed mixture for use in transcritical CO2 heat pumps was analyzed using energy and exergy analysis. Results showed that the coefficient of performance and exergy efficiency variation displayed an “M” shape trend, and the optimal CO2/R32 mixture concentration was determined as 0.9/0.1 with regard to flammability and efficiency. The irreversibility of the throttling valve was reduced from 0.031 to 0.009 kW⋅kW−1 and the total irreversibility reduction was more notable with ambient temperature variation. A case study was also conducted to examine domestic hot water demand during the year. Pure CO2 and the proposed CO2 blend were compared with regard to annual performance factor and annual exergy efficiency, and the findings could provide guidance for practical applications in the future.
No related grants have been discovered for Ali Alahmer.