Taking inspiration from the hydrophilic and superhydrophilic properties observed from the nanostructures present on the leaves of plants such as Alocasia odora, Calathea zebrina, and Ruelia devosiana, we were able to synthesize cupric oxide (CuO) nanostructures from the plasma surface modification of copper (Cu) that exhibits hydrophilic and superhydrophilic properties. The Cu sheets were exposed to oxygen plasma produced from the P300 plasma device (Alliance Concept, Cran-Gevrier, France) at varying power, irradiation times, gas flow rates, and pulsing duty cycles. The untreated and plasma-treated Cu sheets were characterized by contact angle measurements, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to determine the changes in the surface of Cu before and after plasma treatment. Results showed that plasma-treated Cu sheets exhibited enhanced wetting properties compared to untreated Cu. We attributed the decrease in the measured water contact angles after plasma treatment to increased surface roughness, formation of CuO nanostructures, and transformation of Cu to either CuO2 or Cu2O3. The presence of the CuO nanostructures on the surface of Cu is very useful in terms of its possible applications, such as: (1) in antimicrobial and anti-fouling tubing; (2) in the improvement of heat dissipation devices, such as microfluidic cooling systems and heat pipes; and (3) as an additional protection to Cu from further corrosion. This study also shows the possible mechanisms on how CuO, CuO2, and Cu2O3 were formed from Cu based on the varying the plasma parameters.
This study presents a mathematical model of drop size distribution during dropwise condensation on a superhydrophobic surface. The model is developed by combining a power law growth model, an exponentially decaying population model, and a Gaussian probability model for growth variations. The model is validated against experiment data, with correlations ranging from 88% to 94%. The growth model is shown to sufficiently describe the growth of drops from 0.02 mm to 0.1 mm but may be extrapolated to describe the growth of even smaller drops. The experiment data show that drop size distribution or frequency distribution of drops of different sizes varies significantly with time and may be considered pseudo-cyclic. The developed model, together with the sweep rate of drops, sufficiently describes this behavior and, consequently, may also be used to better estimate the heat transfer rate due to dropwise condensation.
A two‐step surface fabrication technique is used to modify the wetting characteristics of copper sheets for heat transfer application. It consists of oxygen plasma treatment that results in the formation of surface nanostructures, and a post‐functionalization process using self‐assembled monolayers. The copper samples are characterized by contact angle measurements, scanning electron microscopy, and atomic force microscopy. Results show that surface roughness, described using hybrid and functional roughness parameters, varies with irradiation power. The plasma‐treated copper samples become superhydrophobic with water contact angles ranging from 150° to 160° after the post‐functionalization. Condensation experiments are conducted to explore the influence of surface wettability on condensate formation. Results show that droplets formed on the superhydrophobic copper sheets are smaller and more mobile with sweep events that are 9x more frequent compared to those on untreated copper sheets. Sweep events are shown to be influenced by surface porosity, which is defined using standard roughness parameters. It is demonstrated that higher surface porosity results to higher sweep interval.
The University of the Philippines is the Philippines’ national university. It is mandated to be the leader in innovation and research. The electricity consumption of the flagship campus, the University of the Philippines Diliman, rose from 13.97 GWh in 2006 to 15.26 GWh by 2015 [1]. The electricity consumption must be managed as the university desires more students to graduate, do progressive research and creative works, and produce quality extension services. An appropriate energy policy incorporating minimum equipment standards in procuring energy consuming devices is wanting. Standardization controls the varying energy demand of equipment without compromising the quality of services delivered. The objective is to establish minimum equipment specification standards for university procurement. A framework for determining equipment standardization was developed, end-users’ need assessments and energy audits were conducted, equipment specifications were formulated, stakeholders were consulted, and equipment policy to ensure energy efficiency and sustainability were suggested. The electricity consumption was primarily due to air-conditioning (55.3%) and lighting (26.3%). Electricity savings is attained by adopting a higher standards of air conditioning energy efficiency ratio (45%), and changing to light emitting diode for lights (31%) and for monitors (5%). It is recommended that usage profiling be conducted for all the buildings.
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