Abdullah Al-Sharafi

A New Study for Hybrid PV/Wind off-Grid Power Generation Systems with the Comparison of Results from Homer

This article presents the development of a computational model for the sizing optimization of an off-grid hybrid solar wind electric power generation system. The model includes a PV model, wind power model, and a model for the required battery. The developed mathematical model also comprises a model for a diesel generator as an alternative for the storage battery. A simulation code has been developed using MATLAB to solve the mathematical model and simulate the performance of the hybrid system with different configuration for performance analysis and optimal sizing purpose. The mathematical model and the computer code have been developed using a general approach. This approach can be used to simulate, analyze and optimize any hybrid solar/wind/battery/diesel off-grid electric power generation systems. Also, it can be utilized for any remote area in the world depending on the weather data used as input to the developed simulation code. The results obtained via the presently developed model and code have been validated against previously published work and also against that obtained via the widely used software (HOMER). The model is used for the sizing optimization and assessment of a hybrid solar wind system based on the weather conditions for Dhahran city in the eastern province of the Kingdom of Saudi Arabia.

Marangoni convection flow and heat transfer characteristics of water–CNT nanofluid droplets

ABSTRACT The heat transfer characteristics of liquid droplets are influenced by the hydrophobicity of the surfaces. Fluid properties and surface energy play important roles in heat transfer assessment. In the present study, the influence of the contact angle on the flow field developed inside a nanofluid droplet consisting of a mixture of water and carbon nanotubes (CNT) is investigated. Flow field and heat transfer characteristics are simulated numerically in line with the experimental conditions. It is found that the flow velocity predicted numerically is in good agreement with the experimental data. Nusselt and Bond numbers increase at large contact angles and Marangoni force dominates over buoyancy force.

Silicone oil impregnated nano silica modified glass surface and influence of environmental dust particles on optical transmittance

The behavior of environmental dust particles on a silicone oil impregnated glass surface is examined in relation to optical transparent surfaces for self-cleaning applications. The characteristics of environmental dust, collected in the local area, are analyzed using analytical tools. Functional silica particles are synthesized and deposited on the glass surface prior to silicone oil impregnation. Optical properties of functionalized silica particle deposited glass surfaces are examined prior to and after oil impregnation. Further tests are conducted in the open environment to assess dust settlement in silicone oil and dust particle sedimentation on the glass surface. It is found that dust particles have various sizes and shapes, and they are composed of various metallic, alkaline, and alkaline earth metallic compounds. The average size of the dust particles is of the order of 1.2 μm. Silicone oil impregnation considerably improves the optical transmittance of functionalized silica particle deposited glass. A high spreading rate gives rise to a cloaking of dust particles on the oil surface, which gradually reduces the surface tension force and modifies the vertical force balance. Consequently, dust particles immerse into the oil film and sediment on the glass surface. This, in turn, lowers the optical transmittance of the oil impregnated glass surfaces greatly.

Reversible exchange of wetting state of a hydrophobic surface via phase change material coating

Reversible exchange of the wetting state of a hydrophobic surface is examined. Solution crystallization of a polycarbonate surface is carried out to form hierarchically distributed micro/nano size spherules and fibrils on the surface. Although the solution crystallized surface has hydrophobic characteristics, the contact angle hysteresis remains high. Functionalized silica particles are deposited on the crystallized polycarbonate surface to improve the droplet contact angle and lower contact angle hysteresis. The liquid film of n-octadecane with 1.5 μm thickness is formed on the functionalized silica particles deposited crystallized surface, which results in hydrophilic surface characteristics. The n-octadecane film solidifies upon reducing the temperature on the surface and solid flakes of n-octadecane are formed. This arrangement changes the surface wetting state to hydrophobic. Liquefaction and solidifying of the n-octadecane film at the functionalized silica deposited surface gives rise to reversible exchange of surface wetting state. This behavior is attributed to exposure of emerging functionalized silica particles to the free surface in the region of the solid n-octadecane flakes. The water droplet is cloaked by the liquid n-octadecane while forming a ridge around the droplet. In this case, the water droplet becomes mobile at the surface because flow develops in the n-octadecane liquid film at the onset of liquefaction.

Internal fluidity of a sessile droplet with the presence of particles on a hydrophobic surface

ABSTRACT Thermocapillary flow inside a sessile droplet is considered in relation to microsized particles, resembling the environmental dust particles’ removal from the hydrophobic surface. Polycarbonate surface is textured through solution-induced crystallization to generate surfaces with hydrophobic characteristics. The dusts are collected from the local environment and characterized using the analytical tools. Internal fluidity of the droplet is simulated numerically in line with the experimental conditions. An experiment is carried out to measure the velocity of the dust particles using the optical microscopic system. It is found that thermocapillary-induced forces generate counter-rotating cells in the droplet, which depends on the droplet contact angle. The percentage of dust particles removed from the hydrophobic surface into the droplet, due to droplet internal fluidity, increases with the size of the dust particles and it remains almost constant with progressing time. The dust particles follow the streamlines in the circulation cells inside the droplet.

Water Droplet Dynamics on a Hydrophobic Surface in Relation to the Self-Cleaning of Environmental Dust

The dynamic motion of a water droplet on an inclined hydrophobic surface is analyzed with and without environmental dust particles on the surface. Solution crystallization of a polycarbonate surface is carried out to generate a hydrophobic surface with hierarchical texture composed of micro/nanosize spheroids and fibrils. Functionalized nanosize silica particles are deposited on the textured surface to reduce contact angle hysteresis. Environmental dust particles are collected and characterized using analytical tools prior to the experiments. The droplet motion on the hydrophobic surface is assessed using high-speed camera data, and then, the motion characteristics are compared with the corresponding analytical results. The influence of dust particles on the water droplet motion and the amount of dust particles picked up from the hydrophobic surface by the moving droplet is evaluated experimentally. A 40 μL droplet was observed to roll on the hydrophobic surface with and without dust particles, and the droplet slip velocity was lower than the rotational velocity. The rolling droplet removes almost all dust particles from the surface, and the mechanism for the removal of dust particles from the surface was determined to be water cloaking of the dust particles.

A Water Droplet Pinning and Heat Transfer Characteristics on an Inclined Hydrophobic Surface

A water droplet pinning on inclined hydrophobic surface is considered and the droplet heat transfer characteristics are examined. Solution crystallization of polycarbonate is carried out to create hydrophobic characteristics on the surface. The pinning state of the water droplet on the extreme inclined hydrophobic surface (0° ≤ δ ≤ 180°, δ being the inclination angle) is assessed. Heat transfer from inclined hydrophobic surface to droplet is simulated for various droplet volumes and inclination angles in line with the experimental conditions. The findings revealed that the hydrophobic surface give rise to large amount of air being trapped within texture, which generates Magdeburg like forces between the droplet meniscus and the textured surface while contributing to droplet pinning at extreme inclination angles. Two counter rotating cells are developed for inclination angle in the range of 0° < δ < 20° and 135° < δ < 180°; however, a single circulation cell is formed inside the droplet for inclination angle of 25° ≤ δ ≤ 135°. The Nusselt number remains high for the range of inclination angle of 45° ≤ δ ≤ 135°. Convection and conduction heat transfer enhances when a single and large circulation cell is formed inside the droplet.

Mobility of A Water Droplet on Liquid Phase of N-Octadecane Coated Hydrophobic Surface

A water droplet behavior on the liquid n-octadecane film is investigated. The coating of hydrophobic surface by N-octadecane film provides exchange of wetting state on the surface. The polycarbonate surface is crystallized and the functionalized silica particles are placed on the resulting surface prior to thin film coating of n-octadecane. A high-speed camera is used to monitor dynamic characteristics of the droplet on the inclined film. The findings reveal that deposition of thin n-octadecane film on hydrophobic surface results in reversibly exchange of the wetting state at the surface, which remains hydrophobic when n-octadecane film is in solid phase while it becomes hydrophilic when n-octadecane film liquefies. Droplet transition velocity predicted agrees well with the experimental data. Sliding mode of the water droplet governs droplet transition on the liquid surface. Droplet pinning force, due to interfacial tension, dominates over the other retention forces including drag and shear.

2.28 Anti-Corrosive Materials

The material selection for construction of thermal energy storage and energy harvesting devices is critical for sustainable and efficient operation with minimum maintenance and replacement costs. Recent changes in climate results in storms and extended distribution of green gasses around the globe. These gases can cause acid rain and other environmental effects while influencing the quality of the surfaces of the energy storage and energy harvesting devices. In this case, chemically active fluid gradually collected on the surfaces gives rise corrosion and gradually erosion of the surfaces. Therefore, corrosion prevention of such surfaces becomes vital for sustainable and cost effective operation. On the other hand, metallic and non-metallic materials are widely used in the construction of the energy harvesting and thermal energy storage devices. The corrosion prevention of these materials in open environment requires surface treatment toward generating a passive layer while preventing surfaces from the chemical attacks. Consequently, in this chapter, the necessity of corrosion prevention of surfaces is introduced and some fundamentals of corrosion reactions and measurement techniques are presented. Generation of passive layer on such material surfaces is incorporated in the later sections. The electrochemical response and corrosion rates of treated surfaces in controlled environment is brought attention for various selective materials including alumina, titanium and copper alloys, aluminum–silicon composite, high-strength low alloy steel, and Hastelloy alloy. The findings of electrochemical tests are discussed in detail in the relevant sections. The future research direction is also included at the end of this chapter.

2.25 Hydrophobic Materials

Solar energy harvesting has many challenges, particularly for selective surfaces and cover glasses of photovoltaic panels. Recent changes in climate give rise to regular dust storms around the globe, which has an adverse effect on the optical characteristics of the solar energy harvesting devices. Dust removal from such surfaces involves with energy intensive processes and requires excessive clean water usage, which remains difficult in the areas where clean water scarcity is high. One of the solutions of such problem is introducing self-cleaning of surfaces. Hydrophobic characteristics are necessary to establish surfaces for self-cleaning. Hydrophobic/hydrophilic characteristics of surfaces are influenced by both, the surface texture and the surface energy of substrate materials. Surfaces consisting of a hierarchal texture covered with a low surface energy material show unusual water repellency, thus, termed as superhydrophobic surfaces. A water droplet on such surface rolls-off at small inclination angles, and picks and carries away small particles along its path, thereby, giving rise to the self-cleaning effect. These surfaces have attracted considerable attention in recent years due to their vast technological applications ranging from self-cleaning windows, textiles, and paints to low-drag surfaces for energy conversion. Most of the techniques that are introduced for the development of superhydrophobic surfaces require multistep procedures, longer processing times, and are not commercially scalable. Optical transmittance of surfaces is also of concern since most of the processes render surface opaque. Polydimethylsiloxane (PDMS), a transparent silicon-based organic polymer, is used in this chapter. Replication of textured surfaces by PDMS is introduced as a fast and cost-effective way of producing optically transparent superhydrophobic surfaces. Laser textured alumina tiles and photo lithographically etched silicon wafers are used as templates for replication studies. Another facile approach to obtain optically transparent superhydrophobic surfaces is through coating by silica nanoparticles. In this chapter, some fundamental aspects of surface hydrophobicity and assessment methods are presented. Later, two case studies are introduced for surface texturing. These cases include laser texturing of alumina surface and PDMS replication of textured surface toward achieving the surface hydrophobicity, and solvent crystallization of polycarbonate surface and influence of environmental dust particles on texture and optical properties of the surface. Analytical tools incorporating optical, electron scanning, and atomic force microscopes, X-ray diffraction, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy are used to assess morphological and elemental characteristics of the resulting surface. The sessile water droplet method is used to determine the water droplet contact angle and contact angle hysteresis. Microtribometer is used to determine friction coefficient of the treated surfaces. The optical transmittance is analyzed incorporating the UV–visible spectrometer. The characteristics of the textured are discussed and hydrophobic behavior of the surface together with optical transmittance are presented.