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Improvements of the experimental apparatus for measurement of the surface tension of supercooled liquids using horizontal capillary tube
Vinš, Václav ; Hošek, Jan ; Hykl, Jiří ; Hrubý, Jan
An experimental apparatus with a horizontal capillary tube for measurement of the surface tension of supercooled liquids was designed and tested in the previous study [V. Vinš et al., EPJ Web Conf. 92, 02108 (2015)]. In this work, recent modifications of both the experimental setup and the measurement analysis are described. The main aim is to improve the accuracy and the reproducibility of measured surface tension and to achieve higher degrees of supercooling. Among other modifications, the optical setup observing the liquid meniscus at the open end of the horizontal capillary tube together with the video analysis were thoroughly revised. The modified apparatus was used for the measurement of surface tension of supercooled water at temperatures down to – 11 °C. The new data have a lower scatter compared to the previous horizontal measurements and show a good agreement with the other data obtained with a different measurement technique based on the modified capillary rise method.
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An apparatus with a horizontal capillary tube intended for measurement of the surface tension of supercooled liquids
Vinš, Václav ; Hošek, Jan ; Hykl, Jiří ; Hrubý, Jan
New experimental apparatus for measurement of the surface tension of liquids under the metastable supercooled state has been designed and assembled in the study. The measuring technique is similar to the method employed by P.T. Hacker [NACA TN 2510, 1951]. A short liquid thread of the liquid sample was located in a horizontal capillary tube partly placed in a temperature-controlled chamber. One end of the capillary tube was connected to a setup with inert gas which allowed for precise tuning of the gas overpressure. The open end of the capillary tube was precisely grinded and polished in order to assure its planarity and perpendicularity. The liquid meniscus at the open end was illuminated by a laser beam and observed by a digital camera. Application of an increasing overpressure of the inert gas at the inner meniscus of the liquid thread caused variation of the outer meniscus such that it gradually changed from concave to flat and subsequently convex shape. The surface tension at the temperature of the inner meniscus could be evaluated from the overpressure corresponding to exactly planar outer meniscus.
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EXPERIMENTAL APPARATUS FOR MEASUREMENT OF DENSITY OF SUPERCOOLED WATER AT HIGH PRESSURE
Hrubý, Jan ; Hykl, Jiří ; Peukert, Pavel ; Šmíd, Bohuslav
Thermodynamic behavior of supercooled water (metastable fluid water existing transiently below the equilibrium freezing point) at high pressures was subject to many recent theoretical studies. Some of them assume that a second critical point of water exists, related to two liquid phases of supercooled water: the low-density liquid and the high-density liquid. To test these theories, an original experimental cryogenic apparatus is being developed. The volume changes are measured optically in custom-treated fused-silica capillary tubes. The capillaries are placed in a metal vessel designed for pressures up to 200 MPa. The vessel is connected to a circulation thermostat enabling a rapid change of temperature to prevent freezing. A new high-vacuum device was developed for degassing of the ultrapure water sample and filling it into the measuring capillaries. The experiments will contribute to fundamental understanding of the anomalous behavior of water and to applications in meteorology, aerospace engineering, cryobiology etc.
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Povrchové napětí čisté vody
Richtr, K. ; Hrubý, Jan ; Mareš, M.
Je podán stručný přehled problematiky měření povrchového napětí podchlazené vody. Je popsán přístroj, vyvinutý pro měření povrchového napětí podchlazené vody. Jsou uvedena předběžná experimentální data a jejich srovnání s daty IAPWS.
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Dvou-strukturní model termodynamických vlastností a povrchového napětí podchlazené vody
Hrubý, Jan ; Holten, V.
Byl vyvinut termodynamický model popisující kapalnou a plynnou fázi vody. Model správně reprezentuje silné anomální chování podchlazené vody. Anomálie jsou způsobeny blízkostí kritického bodu kapalina-kapalina. Model aproximuje kapalnou vodu jako směs tvou soutěžících struktur (vysoko- a nízko-hustotní struktura) a kavit. Termodynamický stav je nalezen minimalizací Gibbsovy volné energie vzhledem k proporci obou struktur a počtu kavit. Tento přístup je dále použit pro modelování povrchového napětí.
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