Activation of freons cavitation by polyethylsyloxane liquid additives

Аuthors

Vinogradov V. E.

Institute of Thermal Physics of the Ural Branch of the Russian Academy of Sciences , Amundsena St., 107a Ekaterinburg, 620016, Russia

e-mail: vinve@mail.ru

Abstract

Limiting superheating and cavitation strength of weak solutions (up to 5%) of a polyethylsiloxane liquid (PES-4) in freons at pulse stretching up to – 4 MPa was experimentally studied. Two methods for recording the onset of cavitation in a stretched liquid were employed: by photographing the cavitation region in a negative pressure wave at room temperature, and by the boiling signal on a wire heater at high temperatures. The nucleation rate in the first case was 10¹²—10¹⁴ m^—3s^—1. With the second method, the nucleation rate reached 10²⁰—10²⁴ m^—3s^—1. Experiments were performed with a Freon 11 — PES-4 solution in the temperature range from 25 to 160 °C with PES-4 concentration of 5 %, and a of Freon 113 — PES-4 solution in the temperature range from 25 to 190 °C at a PES-4 concentration of 5 %. At 25 °C, exponential dependences of the centers of cavitation densities in the studied liquids on the stretching magnitude were obtained. Experimenting with PES-4 solutions revealed that the slope of experimental dependencies of cavitation centers density on pressure was less than predicted by the theory of homogeneous nucleation. A supposition on the heterogeneous cavitation centers presence in the liquid was made. The PES-4 additives activate the heterogeneous centers, increasing thereby the cavitation density observed in the experiment. At positive pressures, the dissolution of PES-4 in Freons 11 and 113 raises the temperature of the limiting superheating of liquids. The obtained results are consistent with calculations using the homogeneous nucleation theory formulas. In the area of negative pressures exceeding the absolute value of 5 MPa, a decrease in freons cavitational strength was found when dissolving polyethylsiloxane liquid in them. It was shown, that small additions of a high-molecular liquid activated the centers of heterogeneous cavitation in a liquid with a small number of atoms in the molecule (Freon 11, Freon 113) within the temperature range from 25 to 100 °C.

Keywords:

fluctuation nucleation, negative pressure, cavitation, freons

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