SignificanceThe treatment of hypoxemia that is refractory to the current standard of care is time-sensitive and requires skilled caregivers and use of specialized equipment (e.g., extracorporeal ...membrane oxygenation). Most patients experiencing refractory hypoxemia will suffer organ dysfunction, and death is common in this cohort. Here, we describe a new strategy to stabilize and support patients using a microfluidic device that administers oxygen gas directly to the bloodstream in real time and on demand using a process that we call sequential shear-induced bubble breakup. If successful, the described technology may help to avoid or decrease the incidence of ventilator-related lung injury from refractory hypoxemia.
•An experimental study of fluid flow and heat transfer using triethylamine (TEA)/water solution at micro scale is presented.•Liquid/liquid phase separation flow phenomena is observed via flow ...visualization and different flow regimes are identified.•The liquid/liquid phase separation process is proved to be useful in micro heat sink application.•Computational fluid dynamics (CFD) tool is used to provide physical insights.
An experimental study of liquid/liquid phase separation heat transfer at the microscale using triethylamine (TEA)/water solvent mixture is reported here. The mixture, 32.1% mass fraction of TEA, was introduced into a 22mm long, 2mm wide, and 0.4mm deep microchannel. When heated above the critical temperature, the mixture separated into distinct immiscible liquid phases. Through flow visualization, the two-phase flow patterns were determined to be predominantly mist flow, elongated droplet flow, and annular flow. Increased heat transfer coefficients of up to about 250% and reduced pressure drop were observed between cases of phase separation flow and single phase mixture flow, demonstrating the potential for applying this type of solvent mixture to miniature heat sinks. A first-order computational fluid dynamics (CFD) model was used to reveal the mechanisms controlling the hydrodynamics and thermodynamics processes. It was determined that the latent heat of mixing associated with the phase separation process contributed to the enhanced heat transfer. The self-propelled motion of components driven by chemical potential gradient further boosted the heat transport. Reduced viscosities of both phases led to the reduced pressure drop.
•Micro slot jet impingement is studied experimentally and numerically.•Local temperatures are measured within and outside the stagnation region.•3D conjugate heat transfer model captures ...thermo-hydrodynamic phenomena of slot jet.•Nusselt number correlations are presented for laminar and turbulent flow.
Local temperature measurements were made in a microchannel jet impingement cooling system with a single slot jet (Dh = 68 µm and standoff distance of 210 µm). A 40%/60% solution of propylene glycol in deionized water was used as the working fluid. Resistance temperature detectors (RTDs) were fabricated over a rectangular heater of size 1500 µm × 400 µm allowing local temperature measurements. Nominal heat fluxes ranged between 50 W/cm2 and 150 W/cm2, and jet Reynolds numbers were in the range of 122–435. A three-dimensional conduction/convection conjugated numerical model with laminar and turbulent variants was developed to predict the jet hydrodynamics and heat transfer process. Good agreement was achieved between the model and the experimental data in terms of flow coefficients and local wall temperatures. Furthermore, a generalized Nusselt number dependence on Reynolds number was formulated, taking into account the temperature-dependent viscosity of the working fluid. The results provide valuable information about local and surface-averaged heat transfer due to a flow field generated by an impinging micro slot jet.
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 oil‐in‐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.
We demonstrate the use of heat to count microscopic particles. A thermal particle detector (TPD) was fabricated by combining a 500-nm-thick silicon nitride membrane containing a thin-film resistive ...temperature detector with a silicone elastomer microchannel. Particles with diameters of 90 and 200 μm created relative temperature changes of 0.11 and −0.44 K, respectively, as they flowed by the sensor. A first-order lumped thermal model was developed to predict the temperature changes. Multiple particles were counted in series to demonstrate the utility of the TPD as a particle counter.
Design of electronic equipment has evolved over the past few decades to incorporate advanced functionality while simultaneously reducing their dimensions. An undesirable consequence of such progress ...is the tendency of contemporary electronics to dissipate heat over diminishing length scales, leading to increased heat fluxes and surface temperatures. Equipment designers are faced with the predicament of engineering their products to reject any excess heat that will result in unsafe operating temperatures. Steady advances in the electronics industry have rendered air cooled heat exchangers inadequate. Furthermore, single-phase liquid flow is also being stretched to its limits by increasing heat fluxes. Liquid cooling with phase change, or flow boiling, offers promising solutions to the challenge posed by heat generation in electronics. However, multiphase flow in narrow conduits comes with associated concerns such as unstable operation, dryout and critical heat flux (CHF), all of which result in high surface temperatures. Practical realization of two-phase heat exchangers in the electronics industry is hindered by the lack of universal predictive tools and control mechanisms that will address these concerns. In this dissertation, a novel approach is presented to control surface temperatures and enhance heat transfer in microchannel flow boiling. Experiments were performed using a microdevice with resistance-temperature detectors (RTDs) as heating and sensing elements. The flow was visualized through a high-speed imaging system. A transverse jet in crossflow was used to control surface temperatures and to effectively suppress dryout, at nominal heat fluxes up to 14 W/cm2. A setpoint-based feedback control mechanism was evaluated under conditions of steady and transient heating, and its performance was compared to the reference case without active control. Maximum surface-averaged heat transfer enhancements of 130% and 127% were obtained with active control for steady and unsteady heating respectively. Transient local temperature measurements were made and used to compute the corresponding heat transfer coefficients. Active control allowed the local surface temperatures to be maintained in the vicinity of the specified setpoint in most cases.
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