28 research outputs found
Fabricating superhydrophobic aluminum: An optimized one-step wet synthesis using fluoroalkyl silane
No full textIn this paper we present a simple but effective procedure to impart superhydrophobicity to aluminum through a one-step wet chemistry synthesis. The synthesis is performed in one step, thanks to simultaneous etching with NaOH and grafting with fluoroalkyl silane (FAS) molecules, which allow aluminum surface functionalization. By optimizing the proper amount of reagents, controlling the reaction batch temperature and particularly by allowing pre-activation of the solution, we showed that the process can be used turn into water repellant superhydrophobic surfaces four aluminum samples in sequence, using the same reaction batch. Also, if FAS is further added to the solution the procedure can impart superhydrophobicity to further aluminum samples. The synthesis with the optimized parameters is green and cost effective, since it was developed to minimize the use of both base and fluorinated molecules. In addition, it is easy to scale up to large area treatments and to industrial application, because the procedure is one-step, is reproducible, and allows multiple use of the same reaction batch, for the treatment of multiple samples. Finally, we show that not only the surfaces show excellent non-wetting properties in quasi-static conditions, with contact angles ∼150̊ and with very low contact angle hysteresis, ∼4̊, but also in dynamic conditions, as proved by means of drop impact analysis up to Weber number of 690
Drop rebound after impact:The role of the receding contact angle
No full textData from the literature suggest that the rebound of a drop from a surface can be achieved when the wettability is low, i.e., when contact angles, measured at the triple line (solid-liquid-air), are high. However, no clear criterion exists to predict when a drop will rebound from a surface and which is the key wetting parameter to govern drop rebound (e.g., the "equilibrium" contact angle, θeq, the advancing and the receding contact angles, θA and θR, respectively, the contact angle hysteresis, Δθ, or any combination of these parameters). To clarify the conditions for drop rebound, we conducted experimental tests on different dry solid surfaces with variable wettability, from hydrophobic to superhydrophobic surfaces, with advancing contact angles 108 < θA < 169 and receding contact angles 89 < θR < 161. It was found that the receding contact angle is the key wetting parameter that influences drop rebound, along with surface hydrophobicity: for the investigated impact conditions (drop diameter 2.4 < D0 < 2.6 mm, impact speed 0.8 < V < 4.1 m/s, Weber number 25 < We < 585), rebound was observed only on surfaces with receding contact angles higher than 100. Also, the drop rebound time decreased by increasing the receding contact angle. It was also shown that in general care must be taken when using statically defined wetting parameters (such as advancing and receding contact angles) to predict the dynamic behavior of a liquid on a solid surface because the dynamics of the phenomenon may affect surface wetting close to the impact point (e.g., as a result of the transition from the Cassie-Baxter to Wenzel state in the case of the so-called superhydrophobic surfaces) and thus affect the drop rebound.</p
A novel Personal Comfort System:a radiant desk with a Loop Heat Pipe
No full textThis study is the second step toward the development and prototyping of a Personal Comfort System for tertiary sector working environments. The entire industrial sector, and in particular offices, have seen changes in working habits, with a large increase in smart working also due to the prevention of the COVID infection. The chance to partialise the HVAC system and maintain rooms in an under-conditioned state is the obligatory way towards reducing energy waste, providing each workstation with an independent system that guarantees the operator's comfort conditions. The goal of the second step presented in this work was to size and optimize the radiating desk, with the aim of testing an experimental demonstrator. A LHP was chosen to bring heat from the source to the desk, decoupling the heat generation and heat distribution system, without the need of additional parasitic power consumption or moving parts, adding to the innovation of the proposed design. The ergonomic optimisation of the surface and its power reduction did not affect its ability to improve localised comfort, since the operators' conditions move from a slightly cold to a neutral situation. Moreover, no discomforts due to vertical temperature differences or radiant asymmetries were found. Therefore, the next research step will lead to prototype creation and its analyses, conducted in a climatic room to test if the distribution system can satisfy comfort thermal requirements with probes as well as real users
Microsurgical Reconstruction with and without Microvascular Anastomosis of Oncological Defects of the Upper Limb
No full textIntroduction: The choice of the most adequate surgical technique for upper limb defects remains challenging. The aim of this article is to discuss the main microsurgical (pedicled or free) reconstructive options for the post-oncological reconstruction of different anatomical areas of the upper extremity. Materials and methods: We reviewed different reconstructive methods reported in the literature needing microsurgical expertise and compared them to our clinical experience, in order to provide further guidance in the choice of different flaps for upper limb soft tissue reconstruction. Six clinical cases, one for each anatomical district, are presented as examples of possible solutions. Results: We report the options available in the literature for post-oncologic upper limb reconstruction, dividing them by anatomical area and type of flap: local flaps, regional flaps, free flaps, and distant pedicled flaps. Our examples of the reconstruction of each anatomical area of the upper limb include one reverse ulnar pedicled perforator flap, one free Antero-Lateral Thigh (ALT) flow-through flap, one perforator-based lateral arm flap, two myocutaneous latissimus dorsi pedicled flaps, and one parascapular perforator-plus flap. Conclusions: In oncological cases, it is important to consider reconstructive options that provide stable tissue and allow for the early healing of the donor and recipient site if the patient needs to undergo adjuvant radiotherapy or chemotherapy. A wider range of flap options is essential when choosing the proper technique according to the patient's needs, surgeon's preference, and logistical possibilities. Perforator flaps combine the advantages of other flaps, but they require microsurgical expertise. Free flap reconstruction remains the gold standard to obtain a better overall and cosmetic outcome in complex and wide defects, where no suitable local pedicled flap option exists. The pedicled latissimus dorsi flap should still be included among the reconstructive options for its strong vascularization, size, and arc of transposition
Evolution of the Svalbard annual snow layer during the melting phase
No full textUnderstanding and monitoring the evolution of annual snow is an important aspect of cryosphere research. Changes in physical proprieties such as hardness, presence of melt layers, or the shape and size of crystals can completely modify the robustness, propriety and quality of the snow. Evaluating these changes can inform the study and prediction of avalanches. The annual snow layer is also a sink for several compounds and elements. In the polar environment, many compounds can be accumulated during winter depositions, especially during the polar night. During the spring, the combination of solar radiation and the melting of annual snow can release these compounds and elements into the atmosphere and groundwater. An in-depth investigation of the evolution of the first meter of the annual snow layer was conducted in the glacier of Austre Broggerbreen, Svalbard, between the 27th of March and the 31st of May, in concomitance with the start of the melting phase. The present monitoring study mainly aimed to evaluate changes in the thermal profile and water content during the formation of a new ice layer as well as the re-allocation of the total dissolved salts in the different snow layer
A Novel Personal Comfort System: A Radiant Desk With a Loop Heat Pipe
No full textThis study is the second step toward the development and prototyping of a Personal Comfort System for tertiary sector working environments. The entire industrial sector, and, in particular, offices, have seen changes in working habits, with a large increase in smart working also due to prevention of COVID infection. The chance to partialize the HVAC system and maintain rooms in an under-conditioned state is the obligatory way towards reducing energy waste, providing each workstation with an independent system that guarantees the operator's comfort conditions. The goal of the second step presented in this work was to size and optimize the radiating desk, with the aim of testing an experimental demonstrator. A LHP was chosen to bring heat from the source to the desk, decoupling the heat generation and heat distribution system, without the need for additional parasitic power consumption or moving parts, adding to the innovation of the proposed design. The ergonomic optimization of the surface and its power reduction did not affect its ability to improve localized comfort, since the operators’ conditions move from a slightly cold to a neutral situation. Moreover, no discomfort due to vertical temperature differences or radiant asymmetries were found. Therefore, the next research step will lead to prototype creation and its analyses, conducted in a climatic room to test if the distribution system can satisfy comfort thermal requirements with probes as well as real users. © 2022 Free University of Bozen Bolzano. All rights reserved
