The Impact of Alumina Nanofluids on Pool Boiling Performance on Biphilic Surfaces for Cooling Applications

This work aims to study the impact of nanofluids with alumina particles on pool boiling performance. Unlike most studies, which use a trial-and-error approach to improve boiling performance parameters, this study details the possible effects of nanoparticles on the effective mechanisms of boiling and heat transfer. For this purpose, biphilic surfaces (hydrophilic surfaces with superhydrophobic spots) were used, which allow the individual analysis of bubbles. Surfaces with different configurations of superhydrophobic regions were used. The thermophysical properties of fluids only vary slightly with increasing nanoparticle concentration. The evolution of the dissipated heat flux and temperature profiles for a nucleation time frame is independent of the fluid and imposed heat flux. It can be concluded that the optimal concentration of nanoparticles is 3 wt%. Using this nanoparticle concentration leads to lower surface temperature values than those obtained with water, the reference fluid. This is due to the changes in the balance of forces in the triple line, induced by increased wettability as a consequence of the deposited particles. Wherefore, smaller and more frequent bubbles are formed, resulting in higher heat transfer coefficients. This effect, although relevant, is still of minor importance when compared to that of the use of biphilic surfaces.

Can Circular Entrepreneurship Save the World Economy?

Global polarization and linear economy models has for generations been the servant of ruthless capitalism and bourgeoisie ventures. In such ruthless circumstance there has been alarming situation both globally and locally to challenge prevailing linear economy structures to question and create a sustainable platform for protecting the resources and user structures of our future generations. Life cycle assessments globally has been a case study which has shown the minimal usage of products in value based propositions and bringing the environmental ecosystem in a balanced structure irrespective of political or governmental interventions. From the birth of the Paris Agreements on Climate changes, scientists and technologists globally has stressed upon the importance of sustainability and resilience on global food security as well as natural resource management. In such scenario resource allocations even in advanced countries like Europe and America has fallen prey to gross inequality, gender gaps and faulty resource transitions even in most advanced regions. Shocking Gini coefficient figures across boundaries have led scientists and economists globally to rethink and restrategise the way strategic business management hovers globally and to better revisualise globalization and utilize the resources our earth has endowed us upon. This paper challenges prevailing notions and even best practices in current management scenario and principles of economics of entrepreneurship to jump start a society based on values, tradition and value based usage proposition; in other terms from a linear based economy to a sustainable resilient circular economy model with greater emphasis on environmental protection, poverty eradication with better integration of triple line bottom of pyramid and better community disciplines to foster a vibrant shared economy model. There is a persistent gap lying across various parameters of a linear economy which has in turn been the causal effect of human impoverishment, poverty and vast scale ecological destructions. A case based approach and exploratory study in this research paper tries to answer rising question in addressing this burning topic of circular entrepreneurship which is quite different in structure and outcome to normative economical falsifications arising out of entrepreneurship models which has till now failed to create a functional economy devoid of hazards and wastes.

Carbon dioxide as a line active agent: Its impact on line tension and nucleation rate

By considering a water capillary bridge confined between two flat surfaces, we investigate the thermodynamics of the triple line delimiting this solid–liquid–vapor system when supplemented in carbon dioxide. In more detail, by means of atom-scale simulations, we show that carbon dioxide accumulates at the solid walls and, preferably, at the triple lines where it plays the role of a line active agent. The line tension of the triple line, which is quantitatively assessed using an original mechanical route, is shown to be driven by the line excess concentrations of the solute (carbon dioxide) and solvent (water). Solute accumulation at the lines decreases the negative line tension (i.e., more negative) while solvent depletion from the lines has the opposite effect. Such an unprecedented quantitative assessment of gas-induced line tension modifications shows that the absolute value of the negative line tension increases upon increasing the carbon dioxide partial pressure. As a striking example, for hydrophilic surfaces, the line tension is found to increase by more than an order of magnitude when the carbon dioxide pressure exceeds 3 MPa. By considering the coupling between line and surface effects induced by gaseous adsorption, we hypothesize from the observed gas concentration-dependent line tension a nontrivial impact on heterogeneous nucleation of nanometric critical nuclei.

Wetting of Laser Textured Cu Surface by Ethylene Glycol and Sn

The effect of microcosmic morphologies of textured Cu surface by nanosecond laser on the inert wetting and reactive wetting, i.e., ethylene glycol/copper and tin/copper wetting systems, was studied by using modified sessile drop methods. To create different surface roughness, the microcosmic morphologies with different spacing of grooves were constructed by nanosecond laser. The results showed that the inert wetting (ethylene glycol/copper) was consistent with Wenzel model, while the reactive wetting results deviated from the model. In Sn/Cu reactive wetting system, the interfacial evolution in the early stage and the pinning of triple line by the precipitated h-Cu6Sn5 caused the rougher surface and the worse final wettability. When the scale of artificial roughness exceeded the roughness that was caused by interfacial reaction after reaching the quasi-equilibrium state at interface, the final wettability could be improved.

Oscillatory Reversible Osmotic Growth of Sessile Saline Droplets on a Floating Polydimethylsiloxane Membrane

We report a cyclic growth/retraction phenomena observed for saline droplets placed on a cured poly (dimethylsiloxane) (PDMS) membrane with a thickness of 7.8 ± 0.1 µm floating on a pure water surface. Osmotic mass transport across the micro-scaled floating PDMS membrane provided the growth of the sessile saline droplets followed by evaporation of the droplets. NaCl crystals were observed in the vicinity of the triple line at the evaporation stage. The observed growth/retraction cycle was reversible. A model of the osmotic mass transfer across the cured PDMS membrane is suggested and verified. The first stage of the osmotic growth of saline droplets is well-approximated by the universal linear relationship, whose slope is independent of the initial radius of the droplet. The suggested physical model qualitatively explains the time evolution of the droplet size. The reported process demonstrates a potential for use in industrial desalination.

Wetting Behavior of the Ag-5CuO Brazing Alloy on ZTA Composite Ceramic with/without CuO Coating in Air

The wetting of Ag-5 wt.% CuO (Ag-5CuO) alloy on initial/CuO-coated zirconia toughened alumina (ZTA) composite ceramic in air was studied in detail. The results showed that the contact angle of the Ag-5CuO/ZTA system rapidly decreased from 81° at 970 °C to 45° at 990 °C during the heating process, however, moderate reductions in contact angle were observed in the subsequent heating and temperature holding stages. In comparison with the contact angle of pure Al2O3, an increment of about 4° of the stable contact angle of Ag-5CuO alloy on the heterogeneous ZTA was observed. The reaction between Al2O3 and CuO can reduce the damage of the CuO-rich liquid to ZrO2 in the ZTA substrate. Both oxygen and CuO were helpful in reducing the contact angle of Ag on ZTA and enhancing the bonding of the Ag/ZTA interface. The continuous CuO coating on ZTA and the monotectic liquid containing more CuO in the region near the triple line induced reductions of more than 40° and about 10° in the contact angle, respectively, between the initial and the CuO coating-improved wetting systems.