The severe soiling of reflectors deployed in arid and semi arid locations decreases their reflectance and drives down the yield of the concentrating solar power (CSP) plants. To alleviate this issue, various sets of methods are available. The operation and maintenance (O&M) staff should opt for sustainable cleaning methods that are safe and environmentally friendly. To restore high reflectance, the cleaning vehicles of CSP plants must adapt to the constraints of each technology and to the layout of reflectors in the solar field. Water based methods are currently the most commonly used in CSP plants but they are not sustainable due to water scarcity and high soiling rates. The recovery and reuse of washing water can compensate for these methods and make them a more reasonable option for mediterranean and desert environments. Dry methods, on the other hand, are gaining more attraction as they are more suitable for desert regions. Some of these methods rely on ultrasonic wave or vibration for detaching the dust bonding from the reflectors surface, while other methods, known as preventive methods, focus on reducing the soiling by modifying the reflectors surface and incorporating self cleaning features using special coatings. Since the CSP plants operators aim to achieve the highest profit by minimizing the cost of cleaning while maintaining a high reflectance, optimizing the cleaning parameters and strategies is of great interest. This work presents the conventional water-based methods that are currently used in CSP plants in addition to sustainable alternative methods for dust removal and soiling prevention. Also, the cleaning effectiveness, the environmental impacts and the economic aspects of each technology are discussed.

• Ultrasonic vibration reduces the contact angle through the amplitude modulation. • Contact angle hysteresis and capillary waves induce a non-returning mechanism. • A thermodynamical model has been developed and validated. • Ultrasound enhanced wetting is energetically very efficient and non-polluting.

Chip evacuation is a critical issue in metal cutting, especially continuous chips that are generated during the machining of ductile materials. The improper evacuation of these kinds of chips can cause scratching of the machined surface of the workpiece and worsen the resultant surface quality. This scenario can be avoided by using a properly designed chip breaker. Despite their relevance, chip breakers are not in wide-spread use in polycrystalline diamond (PCD) cutting tools. This paper presents a systematic methodology to design chip breakers for PCD turning inserts through finite element modelling. The goal is to evacuate the formed chips from the cutting zone controllably and thus, maintain surface quality. Particularly, different scenarios of the chip formation process and chip curling/evacuation were simulated for different tool designs. Then, the chip breaker was produced by laser ablation. Finally, experimental validation tests were conducted to confirm the ability of this chip breaker to evacuate the chips effectively. The machining results revealed superior performance of the insert with chip breaker in terms of the ability to produce curly chips and high surface quality (Ra = 0.51–0.56 µm) when compared with the insert without chip breaker that produced continuous chips and higher surface roughness (Ra = 0.74–1.61 µm).

Ultrasonic cleaning is a developed and widespread technology used in the cleaning industry. The key to its success over other cleaning methods lies in its capacity to penetrate seemingly inaccessible, hard-to-reach corners, cleaning them successfully. However, its major drawback is the need to immerse the product into a tank, making it impossible to work with large or anchored elements. With the aim of revealing the scope of the technology, this paper will attempt to describe a more innovative approach to cleaning large area surfaces (walls, floors, façades, etc.) which involves applying ultrasonic cavitation onto a thin film of water, which is then deposited onto a dirty surface. Ultrasonic cleaning is an example of the proliferation of green technology, requiring 15 times less water and 115 times less power than conventional high-pressurized waterjet cleaning mechanisms. This paper will account for the physical phenomena that govern this new cleaning mechanism and the competition it poses towards more conventional pressurized waterjet technology. Being easy to use as a measure of success, specular surface cleaning has been selected to measure the degree of cleanliness (reflectance) as a function of the process’s parameters. A design of experiments has been developed in line with the main process parameters: amplitude, gap, and sweeping speed. Regression models have also been used to interpret the results for different degrees of soiling. The work concludes with the finding that the proposed new cleaning technology and process can reach up to 98% total cleanliness, without the use of any chemical product and with very low water and power consumption.

This paper reports the development of an original design of chip breaker in a metal-matrix polycrystalline diamond (MMPCD) insert brazed into a milling tool. The research entailed finite element (FE) design, laser simulation, laser fabrication, and machining tests. FE analysis was performed to evaluate the effectiveness of different designs of chip breaker, under specified conditions when milling aluminum alloy (Al A356). Then, the ablation performance of an MMPCD workpiece was characterized by ablating single trenches under different conditions. The profiles of the generated trenches were analyzed and fed into a simulation tool to examine the resultant thickness of ablated layers for different process conditions, and to predict the obtainable shape when ablating multilayers. Next, the geometry of the designated chip breaker was sliced into a number of layers to be ablated sequentially. Different ablation scenarios were experimentally investigated to identify the optimum processing conditions. The results showed that an ns laser utilized in a controllable manner successfully produced the necessary three-dimensional feature of an intricate chip breaker with high surface quality (Ra in the submicron range), tight dimensional accuracy (maximum dimensional error was less than 4%), and in an acceptable processing time (≈51 s). Finally, two different inserts brazed in milling tools, with and without the chip breaker, were tested in real milling trials. Superior performance of the insert with chip breaker was demonstrated by the curled chips formed and the significant reduction of obtained surface roughness compared to the surface produced by the insert without chip breaker.