The results of an investigation of thermodynamic effects are presented. Distributions of temperature and pressure in a developed cavity were measured for zero- and quarter-caliber ogives. A semiempirical entrainment theory was developed to correlate the measured temperature depression, ΔT, in the cavity. This theory correlates ΔTmax expressed in dimensionless form as the Jakob number in terms of the dimensionless numbers of Nusselt, Reynolds, Froude, and Pe´cle´t, and dimensionless cavity length, L/D. The results show that in general ΔT increases with L/D and temperature and the cavitation number based on measured cavity pressure is a function of L/D for a given model contour, independent of the thermodynamic effect.
The net positive suction head (NPSH) requirements for a pump are determined by the combined effects of cavitation, fluid properties, pump geometry, and pump operating point. An important part of this determination is the temperature depression (ΔT) defined as the difference between ambient liquid temperature and cavity temperature. Correlations are presented of the temperature depression for various degrees of developed cavitation on venturis and ogives. These correlations, based on a semiempirical entrainment theory, express ΔT in terms of the dimensionless numbers of Nusselt, Reynolds, Froude, Weber, and Pe´cle´t, and dimensionless cavity length (L/D). The ΔT data were obtained in Freon 114, hydrogen, and nitrogen for the venturis and in Freon 113 and water for the ogives.
The results of an experimental investigation into the effect of gas diffusion on the volume flow-rate of gas needed to sustain a ventilated cavity are presented. Oas diffusion was found to have a significant effect on the ventilated flow rate required to sustain a cavity of a given size. An analysis for the gas diffusion effect was conducted based on a mathematical model of diffusion proposed by Brennen. The results compare favorably with experimental data. Also, an empirical scaling relationship is proposed for ventilated cavity flows.
Journal of Fluids Engineering
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