Search

The current work presents a study of qualitative relationships between the flow unsteadiness, induced by nozzle geometry variation, and non-equilibrium condensation behavior at high temporal scales for supercritical carbon dioxide (sCO 2) flow. A closed sCO 2 loop facility is used to drive a supercritical carbon dioxide flow through a rectangular converging–diverging channel. As the flow traverses through the channel, it experiences a local pressure reduction in a stalled region, eventually leading to non-equilibrium condensation of the working fluid. The flow is visualized using high-speed shadowgraphy and schlieren techniques to characterize the unsteady flow dynamics at the diverging section of the nozzle. Spectral information of the condensation behavior is retrieved from the optical diagnostics using power spectral density calculations, revealing multiple dominant frequencies in the diverging section of the nozzle. Three different nozzles are studied to understand how these dominant frequencies of condensation phenomenon change with respect to the nozzle geometry. Each nozzle design is distinguished with a unique dominant frequency, which is significantly impacted by the effect of flow throat velocity and the degree of adverse pressure gradient. Nozzles with divergence of 15° shows a dominant frequency in the range of 5 – 6.25 kHz in condensing behavior while nozzles with 6° divergence exhibited half the frequency of the phase change. These effects resulted from the extent of adverse pressure gradient imposed by the divergence angle of the nozzle. Additionally, these dominant frequencies are also compared to the wall-pressure signals acquired from high-frequency pressure transducers. Spectral analysis of wall-pressure signals, which are directly linked to nozzle designs, reveals a strong coupling between the condensation behavior and the wall-pressures. • Non-equilibrium condensation visualized using high-speed optical diagnostics. • A dominant frequency observed from unsteady flow fluctuations in a nozzle • Dominant frequencies are correlated to the flow inlet conditions and nozzle geometry. [ABSTRACT FROM AUTHOR]

• Refractory granular media enable high temperature solar thermal energy storage. • High temperature granular flows are characterized with particle flow properties. • High temperature discrete element method models predict granular flow behavior. • High temperature flows are characterized with velocity and mass flux contours. High temperature particle flow properties necessary to predict granular flow behavior for solar thermal energy storage applications were measured and calculated for Carbobead CP 30/60 up to 800 °C. The measured properties included elastic and shear moduli, particle–particle coefficients of static sliding and rolling friction, and particle–particle coefficients of restitution. Poisson's ratio was calculated with elastic and shear moduli. The flow properties were used as inputs for a numerical model using the discrete element method to examine granular flows along an inclined plane at high temperature. The flow behavior was strongly influenced by the coefficients of static friction, which impacted the particle residence time, shear effects from the side walls, and particle flow mass flux. An 8.7%, 15.6%, and 8.5% increase and 37.9% decrease in steady state mass flow rate was observed for 200 °C, 400 °C, 600 °C, and 800 °C, respectively, when compared to room temperature simulations. A 52%, 59%, and 33% decrease in the time to reach steady state was observed for 200 °C, 400 °C, and 600 °C, respectively, while a 53% increase in time was observed for 800 °C. A significant delay in the flow development at 800 °C was observed due to significantly higher frictional forces. [ABSTRACT FROM AUTHOR]

• Selectivity of competitive consecutive Bourne reaction in jet in coflow mixer. • Non-intrusive experimental measurements of competitive consecutive Bourne Reaction. • LES modeling of competitive consecutive Bourne Reaction. Dynamic inline spectroscopic measurements and Large Eddy Simulation (LES) observe the products of a competitive-consecutive test reaction system within a well-characterized coaxial flow. The test reaction is a competitive consecutive chemistry which produces two spectrophotometrically measurable products. For the first time, these products are measured spatially throughout the reactor. Experimental and computational results map the reaction progress and product distribution. The evolution of this chemical process is explained in terms of the inlet, jet, and pipe flow regimes of the confined jet. The inlet and jet regimes were demonstrated to produce the majority of the desired product, whereas the undesired product is predominantly generated in the pipe regime. [ABSTRACT FROM AUTHOR]