Experimental and simulation studies were performed to reveal local heat transfer coefficients under jet impinging in micro domain with Nitrogen gas. The experimental device was made of a 500 μm thick Pyrex and 400 μm thick silicon wafers. On the Pyrex wafer, four 100 nm thick resistance temperature detector (RTD) thermistors and a heater were fabricated from titanium. Jet orifices were etched by deep reactive ion etching (DRIE) on a silicon wafer, which was attached to the Pyrex wafer through a vinyl sticker (250 μm thick). A 1.9 mm × 14.8 mm × 250 μm micro channel was formed by laser drilling into the sticker.
Varying flow rates of Nitrogen gas and heat fluxes of the heater, temperatures of the four thermistors were collected and local heat transfer coefficients were inferred enabling to divulge the jet impinging cooling characteristics. Initial simulations were used to complement experiments and to obtain detailed flow patterns of the jet, temperature distribution on the heater area, and fluid temperature distribution.
Microbubbles (MBs) have tremendous application in a number of fields and strategies to impart them with tunable properties are of great interest to the scientific community. We recently reported a robust platform to produce polymeric MBs (more appropriately termed polymeric microcapsules, PMCs) with highly tunable materials properties by controlling the self-emulsification of oilin-water emulsions. In this study, we used design of experiments to develop a model to predict PMC internal architectures and mean particle diameter as a function of three key processing parameters: concentration of self-emulsifier (0.1% < F68 < 0.25% wt/wt), homogenization speed (1500-3000 rpm), and dilution factor (15 < DF < 30). We show that the homogenization speed and F68 concentration strongly influence both PMC morphology and size, with porous shell hollow cored PMCs being favored at low speeds and high F68 concentrations and nonporous-shelled gas-in-oil cored PMCs (g/o-PMCs) being favored at faster speeds and lower F68 concentrations. Models were subsequently validated by successfully predicting the relative percent yield and mean particle diameter of g-PMCs and g/o-PMCs for four sets of randomly selected factor settings. We anticipate that the results shown here will serve as a roadmap for other investigators interested in evaluating the utility of g-PMCs, g/o-PMCs or, combinations of the two, as novel gas carriers, diagnostic imaging agents, acoustic insulators, shock absorbers, and lightweight building materials, among many others. K E Y W O R D S bioengineering, colloids, manufacturing, surfaces and interfaces 1 | INTRODUCTION Microbubbles (MBs) are gas-filled particles with diameters ranging from a few micrometers to tens of microns. 1 The composition of the bubble shell (e.g., polymers, nanoparticles, and lipids) and the filling gas (air, oxygen, perfluorocarbons, and sulfur hexafluoride) are easily manipulated allowing one to alter important design parameters, such as stability, buoyancy, crush strength, thermal conductivity, and acoustic properties, among many others. 2-4 Intelligent design of the shell materials also permits one to engineer specific MB responses to external stimuli (e.g., to expand in response to increased temperature or ultrasound). 5 Because of this inherent tunablity, MBs continue to be evaluated for their potential use in a number of diverse industrial and medical
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