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Rosný bod spalin: teoretické modelování a předběžné měření
Krejčí, A. Petr ; Hrubý, Jan ; Ždímal, V. ; Trávníček, Zdeněk
Based on industrial needs, the dew point temperature of flue gases is re-examined, both theoretically and experimentally, with mixture of sulphuric acid and water vapors as a flue gas model. This work is motivated by inconsistency and unsufficient accuracy of previous works, which differ significantly in data on sulphuric acid saturation pressure. Experimental setup based on the Laminar co-flow tube is used to express saturation pressure of sulphuric acid via measurements of binary homogeneous nucleation rate.
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Aplikace gradientní teorie fázových rozhraní na modelování nano-kapiček
Hrubý, Jan
The gradient theory (GT) is the simplest theory giving a physically sound picture of fluid-fluid phase interfaces. The density of the fluid varies in a continuous manner across the phase interface. In the GT, energy comprises the kinetic energy due to the macroscopic motion, internal energy of homogeneous fluid, and a gradient-square term, representing the effect of phase interfaces. Somewhat surprisingly, attempts to apply GT to nucleation are very scarce. A fundamental problem of the nucleation theory is determination of the so-called work of formation. In this work we solve numerically the differential Euler-Lagrange equations in spherical symmetry simulating a droplet of mixture of n-nonane and methane. The density of n-nonane is monotonously decreasing function of the radius. The density of methane shows a “hump” located on the outer side of the interface, corresponding to the known effect of gas adsorption.
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Dvou-strukturní model termodynamických vlastností a povrchového napětí podchlazené vody
Hrubý, Jan ; Holten, V.
A thermodynamic model was developed describing the liquid and gaseous phases of water. The model correctly represents the strong anomalous behavior of supercooled water. The anomalies are due to the vicinity of liquid-liquid critical point. The model approximates liquid water as a mixture of two competing structures (high- and low-density structure) and cavities. The thermodynamic state is found by minimizing the Gibbs free energy with respect to the proportion of the two structures and number of cavities. The mixture approach is further used to model the surface tension.
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Smoke visualization of jet and wake flows
Trávníček, Zdeněk
Flow visualization, as a part of experimental fluid mechanics, is a typical initial step of many experimental studies. It can contribute significantly to the understanding of mechanisms involved in flow fields. Moreover, it can be helpful in the selection of the flow parameters and regions of interest for local and detail point measurements. The visualization can be very beneficial for a precise adjustment of a chosen flow field pattern in a test section if alternative flow field modes are possible. Typical case is a bistable and hysteretic behavior of complex flows. The paper shows a few cases of complex jet and wake flows, namely impinging jets from standard and special nozzles (round and slot nozzles, annular nozzle with a fluidic or acoustic control, two-slot nozzle, and slot nozzle with the Coanda effect), and a non-isothermal wake flow behind a cylinder in the cross flow.
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