Homogeneous nucleation in liquid nitrogen at negative pressures
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Homogeneous Nucleation in Liquid Nitrogen at Negative Pressures V. G. Baidakov*, V. E. Vinogradov, and P. A. Pavlov Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620016 Russia *e-mail: [email protected] Received April 4, 2016
Abstract—The kinetics of spontaneous cavitation in liquid nitrogen at positive and negative pressures has been studied in a tension wave formed by a compression pulse reflected from the liquid–vapor interface on a thin platinum wire heated by a current pulse. The limiting tensile stresses (Δp = ps – p, where ps is the saturation pressure), the corresponding bubble nucleation frequencies J (1020–1022 s–1 m–3), and temperature induced nucleation frequency growth rate GT = dlnJ/dT have been experimentally determined. At T = 90 K, the limiting tensile stress was Δp = 8.3 MPa, which was 4.9 MPa lower than the value corresponding to the boundary of thermodynamic stability of the liquid phase (spinodal). The measurement results were compared to classical (homogeneous) nucleation theory (CNT) with and without neglect of the dependence of the surface tension of critical bubbles on their dimensions. In the latter case, the properties of new phase nuclei were described in terms of the Van der Waals theory of capillarity. The experimental data agree well with the CNT theory when it takes into account the “size effect.” DOI: 10.1134/S1063776116100010
1. INTRODUCTION Liquids under certain conditions are capable of withstanding large tensile stresses in both the static and dynamic regimes. The boundary of maximum tensile stress corresponds to the state in which a liquid loses its recovery response to arbitrarily small mechanical and/or thermal disturbances [1]. However, even before attaining this boundary (spinodal), tensilestressed liquids exhibit instability in the form of discontinuous changes in the parameters of state. Under “pure” conditions, the loss of continuity and formation of vapor bubbles (i.e., cavitation) in liquids take place spontaneously due to thermal fluctuations (homogeneous nucleation). For temperatures below about 0.9 Tc (where Tc is the temperature at the critical point), homogeneous nucleation proceeds at a significant rate only at negative pressures (p < 0). There are no principal differences in the behavior of the properties of liquids at p > 0 and p < 0. However, while the limiting values of stretching (superheating) achieved at positive pressures agree with the results predicted by classical (homogeneous) nucleation theory (CNT) [1, 2], the experimental and theoretical values of the tensile strength of liquids at negative pressures differ by a factor of ten or more [3–5]. Indeed, in the original experiments of Misener and Hedgcock [3] on stretching of liquid nitrogen in metal bellows, the tensile strength was –0.35 MPa (T = 71 K). Beams [4] studied the cavitation strength of cryogenic fluids by
the inertial loads method and obtained the tensile strength (–p) of liquid nitrogen at T =
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