Effect of UV degradation and dynamic loading on durability of acrylic carpets using multiple regression method

26-31The effect of dynamic fatigue loading on the carpet samples subjected to long-time UV radiation exposure has been studied. The carpet samples are first subjected to different UV exposure time and then dynamic loading is imposed to the samples. In each case, the thickness loss of the carpets is measured. The results show that the UV exposure time has a slight effect on the thickness loss of the carpets. The number of dynamic impacts, on the other hand, shows a significant effect on the thickness loss with an exponential correlation. Using best curve fitting method based on least square method, a predicting equation is derived for the multiple effect of UV exposure time and number of dynamic loading on the thickness loss. The experimental verification reveals that the proposed predicting equation can be used with an acceptable accuracy

Effect of UV degradation and dynamic loading on durability of acrylic carpets using multiple regression method

The effect of dynamic fatigue loading on the carpet samples subjected to long-time UV radiation exposure has beenstudied. The carpet samples are first subjected to different UV exposure time and then dynamic loading is imposed to thesamples. In each case, the thickness loss of the carpets is measured. The results show that the UV exposure time has a slighteffect on the thickness loss of the carpets. The number of dynamic impacts, on the other hand, shows a significant effect onthe thickness loss with an exponential correlation. Using best curve fitting method based on least square method,a predicting equation is derived for the multiple effect of UV exposure time and number of dynamic loading on the thicknessloss. The experimental verification reveals that the proposed predicting equation can be used with an acceptable accuracy

Techno-Economic Analysis of Stand-Alone Hybrid Energy System for the Electrification of Iran Drilling Oil Rigs

This paper explores the potential of use of stand-alone hybrid wind/solar energy system in electrification of calibrating equipment of drilling oil rig in Iran. To achieve this, different hybrid energy system configurations based on calibration equipment demand are proposed. This study puts emphasis on the energy production and cost of energy from both wind turbine and photovoltaic (PV) in the hybrid system. In addition, to make conditions more realistic, the real meteorological data is used for HOMER software to perform the technical and economic analysis of the hybrid system. Results indicate that the PV array shares more electricity production than the wind turbine generator if both wind turbine and PV array are utilized in the wind/solar hybrid system. Moreover, results show that the operational cost will be reduced by the suggested hybrid system

Effect of users height distribution on the coverage of mmwave cellular networks with 3d beamforming

In this paper, we study the effect of users\u27 height distribution on the coverage probability of millimeter-wave (mmWave) cellular networks that utilize three-dimensional beamforming (3DBF). The users and base stations (BSs) are equipped with multiple antennas and both line-of-sight (LOS) and non-LOS links exist in the channel which are, respectively, modeled by the Nakagami-m and Rayleigh distribution. In this setup, we investigate the tilt angle optimization of the BS antenna arrays for maximizing the coverage probability under two regimes of noise limited and interference limitedd. In both cases, by adopting a stochastic geometry approach, we analytically derive the coverage probability, and then, find the optimal tilt angle that maximizes this probability. In addition, in the noise limited regime, we show that the optimal tilt angle depends on the average distance between each user and its serving BS and also their effective height. In the interference-limited regime, we further consider different rules for associating users to the BSs. Meanwhile, since in this regime, the tilt angle optimization is very complex, we propose a low complexity approach to find the optimal tilt angle that has a performance close to the optimal solution. We further study the asymptotic behavior when the density of the BSs or signal-To-interference ratio tends to infinity or zero. Finally, through the numerical simulations, we show that using the 3DBF and also incorporating the users\u27 height distribution in the tilt angle optimization lead to a substantial improvement in the coverage probability of the mmWave cellular networks

Cavitation-induced shock wave behaviour in different liquids

This paper follows our earlier work where a strong high frequency pressure peak has been observed as a consequence of the formation of shock waves due to the collapse of cavitation bubbles in water, excited by an ultrasonic source at 24 kHz. We study here the effects of liquid physical properties on the shock wave characteristics by replacing water as the medium successively with ethanol, glycerol and finally a 1:1 ethanol-water solution. The pressure frequency spectra obtained in our experiments (from more than 1.5 million cavitation collapsing events) show that the expected prominent shockwave pressure peak was barely detected for ethanol and glycerol, particularly at low input powers, but was consistently observed for the 1:1 ethanol-water solution as well as in water, with a slight shift in peak frequency for the solution. We also report two distinct features of shock waves in raising the frequency peak at MHz (inherent) and contributing to the raising of sub-harmonics (periodic). Empirically constructed acoustic pressure maps revealed significantly higher overall pressure amplitudes for the ethanol-water solution than for other liquids. Furthermore, a qualitative analysis revealed that mist-like patterns are developed in ethanol-water solution leading to higher pressures

Dual frequency ultrasonic cavitation in various liquids: high-speed imaging and acoustic pressure measurements

Ultrasonic cavitation is used in various processes and applications, utilising powerful shock waves and high-speed liquid jets generated by the collapsing bubbles. Typically, a single frequency source is used to produce the desired effects. However, optimisation of the efficiency of ultrasound reactors is necessary to improve cavitation activity in specific applications such as for the exfoliation of two dimensional (2D) materials. This research takes the next step to investigate the effect of a dual frequency transducer system on the bubble dynamics, cavitation zone, pressure fields, acoustic spectra and induced shock waves for four liquids with a range of physical properties. Using ultra-high-speed imaging and synchronised acoustic pressure measurements, the effect of ultrasonic dual frequencies on bubble dynamics was investigated. The addition of a high frequency transducer (1174 kHz) showed that the bubble fragments and satellite bubbles induced from a low frequency transducer (24 kHz) were able to extend their lifecycle, increase spatial distribution, thus, extending the boundaries of the cavitation zone. Furthermore, this combination of ultrasonic frequencies generated higher acoustic pressures (up to 180%) and enhanced the characteristic shock wave peak, indicating more bubble collapses and the generation of additional shock waves. The dual frequency system also enlarged the cavitation cloud size under the sonotrode. These observations specifically delineated the enhancement of cavitation activity using a dual frequency system pivotal for optimisation of existing cavitation-based processing technologies

In-situ observations and acoustic measurements upon fragmentation of free-floating intermetallics under ultrasonic cavitation in water

Grain refinement in alloys is a well-known effect of ultrasonic melt processing. Fragmentation of primary crystals by cavitation-induced action in liquid metals is considered as one of the main driving mechanisms for producing finer and equiaxed grain structures. However, in-situ observations of the fragmentation process are generally complex and difficult to follow in opaque liquid metals, especially for the free-floating crystals. In the present study, we develop a transparent test rig to observe in real time the fragmentation potential of free-floating primary Al3Zr particles under ultrasonic excitation in water (an established analogue medium to liquid aluminium for cavitation studies). An effective treatment domain was identified and fragmentation time determined using acoustic pressure field mapping. For the first time, real-time high-speed imaging captured the dynamic interaction of shock waves from the collapsing bubbles with floating intermetallic particles that led to their fragmentation. The breakage sequence as well as the cavitation erosion pattern were studied by means of post-treatment microscopic characterisation of the fragments. Fragment size distribution and crack patterns on the fractured surface were then analysed and quantified. Application of ultrasound is shown to rapidly (<10 s) reduce intermetallic size (from 5 mm down to 10 μm), thereby increasing the number of potential nucleation sites for the grain refinement of aluminium alloys during melt treatment

An eco-friendly solution for liquid phase exfoliation of graphite under optimised ultrasonication conditions

Ultrasonic assisted liquid phase exfoliation (ULPE) is a promising method for the large scale production of 2D materials. Currently, toxic solvents such as N-Methyl-2-pyrrolidone (NMP) are commonly used for the production of graphene. In this paper four solvents; three green solvents (water, ethanol and water/ethanol) plus NMP for comparison, were sonicated and examined in terms of their bubble dynamics and acoustic emissions. Advanced fundamental analysis was conducted using high-speed imaging synchronised with acoustic pressure measurements complemented by shadowgraphic photography of the emitted shockwaves, in order to determine a suitable eco-friendly solvent medium from a cavitation bubbles dynamics perspective. Thereafter, ULPE of graphite in the optimum solvent took place for 2 h under controlled ultrasonication parameters. The produced graphene samples were characterised by employing a series of techniques consisting of Ultraviolet–visible (UV–Vis) and Raman spectroscopy as well as transmission electron microscopy (TEM). A mixture of deionised water and ethanol was shown to produce a yield twice that of pure water, comprising of high quality few layer graphene (3–5 Ls) with an average area of ∼1.15 (μm)2 and stability of ∼78% for the duration of six months. This combination is a promising eco-friendly substitute for future commercial manufacturing of graphene

Droplet impact on superheated surfaces

The impact of droplets on heated substrates is a crucial process in a diverse range of technological and industrial applications such as thermal spray, electronics cooling and material processing. Of particular importance is the situation in which the substrate is heated above the liquid boiling point. In such case, hydrodynamic behaviors of the impacting droplets, such as spreading and possible splashing, are accompanied by boiling processes, such as liquid-vapor phase transition, bubble generation, and droplet ejection. These intangible physical processes make it challenging to understand and control quantities of practical interests such as the heat transfer rate from the surface to the liquid. In a typical boiling process, the liquid absorbs heat from the surface, vaporizes, and the generated vapor is carried away by natural convection. The heat flux remains increasing with temperature as long as the liquid maintains contact with the surface; it drops abruptly when excessive vapor completely covers the surface. The former case is commonly referred to as the contact boiling regime, while the latter one is known as the Leidenfrost regime. The transition to the Leidenfrost regime therefore is directly linked to the upper limit of boiling heat transfer. Current theories of the Leidenfrost transition assume a priori existence of the vapor layer, thus focusing on its hydrodynamics without making reference to the contact boiling regime. The main aim of this research is to obtain a physical understanding of the Leidenfrost transition. To this end, we systematically study the boiling phenomena of droplet impinging on superheated substrates made of materials having low and high thermal conductivities, namely glass and sapphire. The difference in thermal conductivity of impacted substrates results in distinct boiling behaviors of the liquids: we observe new regimes, i.e., fingering boiling and oscillating boiling regimes for substrate of low and high thermal conductivities, respectively. In particular, detailed observation and analysis of the oscillating boiling regime allows us to elucidate a new mechanism of the Leidenfrost transition based on competition between two effects: separation of liquid from the heated surface due to localized boiling, and rewetting. We show that the predicted values of the Leidenfrost temperature are consistent with the experimentally measured ones for various liquids having widely different properties, suggesting that complex entanglement between the involving hydrodynamic and thermodynamic processes of the Leidenfrost phenomenon can be understood under the newly proposed mechanism. Our findings offer a new theoretical framework to treat the Leidenfrost transition, a crucial step towards complete control of the Leidenfrost phenomenon.Doctor of Philosophy (MAE

Study of Droplet Impact on Heated Surfaces Using Total Internal Reflection

The present study reports observations of the instantaneous boiling and spreading behaviors of ethanol droplets impacting on heated glass surface. By using the total internal reflection technique, we obtain the exact contact area between the liquid and the solid surface as the drop spreads out and boils as a function of time. We show that the contact area decreases with increasing temperature due to the formation and growth of vapor bubbles at the liquid-solid interface. The technique is useful for studying phenomena involving droplet-surface interaction, which is crucial in the emerging additive manufacturing technology.ASTAR (Agency for Sci., Tech. and Research, S’pore)Published versio