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Density gradient theory combined with the PC-SAFT equation of state used for modeling the surface tension of associating systems
Vinš, Václav ; Planková, Barbora ; Hrubý, Jan ; Celný, D.
The density gradient theory (GT) combined with a SAFT-type (Statistical Associating Fluid Theory) equation of state has been used for modeling the surface tension of associating fluids represented by a series of six alkanols ranging from methanol to 1-pentanol. The effect of nonzero dipole moment of the selected alkanols on the predicted surface tension was investigated in this study. Results of the GT + non-polar Perturbed Chain (PC) SAFT equation of state were compared to predictions of GT combined with the PC-polar-SAFT, i.e. PCP-SAFT, equation. Both GT + PC-SAFT and GT + PCP-SAFT give reasonable prediction of the surface tension for pure alkanols. Results of both models are comparable as no significant difference in the modeled saturation properties and in the predicted surface tension using GT was found. Consideration of dipolar molecules of selected alkanols using PCP-SAFT had only minor effect on the predicted properties compared to the non-polar PC-SAFT model.
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Gliding Arc
KALA, Jaroslav
The thesis is focused on increasing the surface tension of polyethylen, using plasma. A gliding arc was chosen for this surface modi cation. The theoretical part includes an overview of gas discharges, their classi cation, properties and technical applications, and deals with an in uence of surface tension on surface modi cations of materials. The experiment is explained in the practical part, a jet analysis carried out before the experiment is described. Results of the experiment are presented.
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Material hydrophility and hydrophobicity measurements
SEDLÁK, Jiří
The aim of this thesis is to find out using a method based on the size of the contact angle as changes over time surface free energy density polyethylene. Measured samples of discharges were adjusted by varying plasma and increased its surface tension. The theoretical part deals with the surface tension, contact angle and the Young's equation, which describes the relationship between wetting angle and energy at the interface states of matter. This work also mentions the ways in which the measurement is made. In the practical part of the thesis there is described not only the process of measuring, but also the own experiments and their results.
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Microbubble Generation by Fluidics. Part II: Bubble Formation Mechanism
Tesař, Václav
Author develops a facility for generation of sub-millimetre sized air bubbles in water. A promising and economically viable method, based on author's earlier experience, is fragmentation of bubbles by oscillation while they are still at the aerator exit locations. Understanding the mechanism by which the oscillation affects bubble formation is a pre-requisite to new aerator design. Results obtained so far reveal a strange bubble size independence on the applied acoustic power, frequency of oscillation and the character of aeratoir body.
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Přechodové teplotní pole v komoře pro měření povrchového napětí podchlazených kapalin
Hrubý, Jan ; Müller, M. ; Richtr, K. ; Mareš, R.
Results of mathematical modeling of the transient temperature field in a new chamber developed to measure surface tension of supercooled liquids are presented. The chamber is designed to enable a very fast (within 0.1 s) formation of a homogeneous temperature field (within 0.02 K) after a temperature jump of 60 K. The interior of the chamber of dimensions 20x16x32 mm is filled with dry nitrogen surrounding the measuring capillary and thermometers (very fine thermocouples and RTD’s). The temperature jump is generated by switching the flow direction of the nitrogen serving as a heat transmitting fluid. To reduce the thermal boundary layer near the bottom and ceiling walls, they are made permeable and some gas is sucked out. The flow in the chamber is laminar. We compute the temperature field analytically and numerically, using the commercial software Fluent. The results indicate that the design objectives of the experimental device were met.
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Povrchové napětí čisté vody
Richtr, K. ; Hrubý, Jan ; Mareš, M.
The problem of surface tension of supercood water is briefly reviewed. A device is described, developed for measurements of the surface tension of supercooled water. Some preliminary experimental data are given and compared with IAPWS values.
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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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Polymer surface tension and properties of state
Jůza, Josef
This contribution presents transformation of some well-known equations expressing surface tension using state properties and other parameters to express the ratio of the surface tension to the drop density, which is more reliable and available even if density is unknown.
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