Measurements of the water contact angle as a function of temperature down to freezing gives valuable information for the development of anti-icing coatings. Advancing (ACA) and receding (RCA) contact angles were measured by depositing drops of water on different material surfaces for temperatures ranging from room temperature to 0°C. No changes in the contact angles as a function of temperature have been observed for polished silicon, polished aluminum, roughened silicon, gold, high density polyethylene, PTFE (polytetrafluoroethylene), and PMMA (poly(methyl methacrylate)) for the entire temperature range. However both the ACA and RCA decrease and the hysteresis increases at temperatures below 5°C for all nanostructured materials used in this study, such as nanopatterned PMMA, PTFE nanoparticles film, and HIREC-100 (a super water-repellent coating blended with TiO 2 ; developed by NTT Advanced Technology Corporation (http:// www.ntt-at.com)). This behavior was attributed mainly to the condensation from the vapor phase of the water drop for temperatures below 5°C. The resulting thin water film decreases the contact angles, especially for the receding contact, enhancing the hysteresis and water drop adherence. These experimental results could explain the adherence of ice on superhydrophobic nanostructured surfaces.
The structural relaxation of amorphous silicon, created by ion implantation, was investigated by in situ differential scanning nanocalorimetry. Nanocalorimetry provided the possibility to measure the heat released by relaxation during annealing, for a wide range of implantation fluences and beginning at cryogenic temperatures. Ion implantation was first carried out for fluences between 10 −5 and 0.8 displacements per atom ͑DPA͒ at 133 K and 297 K, and then for temperatures ranging from 118 K to 463 K for fluences of 0.0185 and 0.37 DPA. A heat release saturation occurred above 0.1 DPA, and was found to depend on implantation temperature. The saturation level was extrapolated to 0 K, leading to an estimate of 28± 3 kJ/ mol for the maximum enthalpy that can be stored in a-Si, relative to crystalline Si.
The accumulation of dust on the solar cells panels worsens the situation and lowers the efficiency of the solar cells day by day especially in the regions known by their high rate of dust, low frequency and intensity of rain. The accumulated dust on the solar cells panel blocks the cells from the sun's rays and act as a screening effect as shown by the calculated spectral transmittance of dust which decreases the performance of the solar cells over time until the cell panels are cleaned manually or by rain. The tilt angle of the solar cell panels affects considerably the amount of accumulated dust on the surface of the panels.The study focuses on the effects of dust accumulation on photovoltaic solar panels in Jazan region. The effect is tested in outdoor measurements and it was found that regular dust accumulation reduces the solar cells efficiency by about 10% for an exposure time of 16 weeks. Moreover the tilted panel with an angle of 30° receives more dust than the panel tilted by 50° which means higher efficiency loss for the lower tilted panel. The efficiency loss is significant of large of annual monetary losses. This study can be considered as a reference to predict the level of degradation of any photovoltaic system that might be installed in the Jazan region and also to estimate the real cost include the cost of the solar panel cleaning.
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