According to Fourier’s law, a temperature difference across a material results in a linear temperature profile and a thermal conductance that decreases inversely proportional to the system length. These are the hallmarks of diffusive heat flow. Here, we report heat flow in ultrathin (25 nm) GaP nanowires in the absence of a temperature gradient within the wire and find that the heat conductance is independent of wire length. These observations deviate from Fourier’s law and are direct proof of ballistic heat flow, persisting for wire lengths up to at least 15 μm at room temperature. When doubling the wire diameter, a remarkably sudden transition to diffusive heat flow is observed. The ballistic heat flow in the ultrathin wires can be modeled within Landauer’s formalism by ballistic phonons with an extraordinarily long mean free path.
One of the controlling parameters of the physical and chemical effects produced by acoustic cavitation is the use of dissolved gas as it affects the temperature and pressure obtained at cavity collapse and, the reactions happening in a bubble. It also enhances the nucleation rates by decreasing the threshold required for cavitation by providing dissolved gas nuclei. The present study looks into the effect of carbon dioxide gas on cavitation using a diffusion limited model. The model couples the dynamics of a single bubble with 11 chemical reactions involving 8 reactive species. The effect of mass transport (diffusion of water vapor and radical species) and heat transport (by conduction) is included in the model. Simulations were carried out for different initial compositions of an Ar-CO bubble and the results were compared with an experimental study reported in the earlier literature. The results have indicated that intensity of collapse decreases with an increase in CO composition in the bubble thereby decreasing the yield of the oxidizing radicals like OH. This is due to the lower polytropic coefficient and higher specific heat of CO compared to that of argon. Also, the bubbles grows to a larger extent with an increase in the dissolved CO concentration thereby accommodating higher amounts of water vapor and ultimately decreasing the temperature obtained at collapse. Simulations were done for a bubble containing a mole fraction of 95% Ar and 5% CO at different values of driving frequencies (213, 355, 647 and 1000kHz) and driving pressure amplitudes (3.22, 5, 7.5 and 10bar). Higher production rate of OH radicals was predicted at a lower driving frequency, for a given driving pressure amplitude and it increased with an increase in the driving pressure amplitude. At a given driving pressure amplitude, the yield of OH radicals decreased with an increase in the CO concentration in the bubble for all the driving frequencies used in the simulations.
DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.