Critical Flow of Water Under Supercritical Pressures

Abstract

An experiment on critical flow of water was conducted in two nozzles of 1.41 mm in diameter and 4.35 mm in length with rounded-edge and sharp-edge respectively, covering the ranges of inlet pressure of 22.1–29.1 MPa and inlet temperature of 38–474 °C. More than 200 data points were obtained. The characteristics and the parametric trends were investigated. In the region of near and beyond pseudo-critical temperature the thermal equilibrium is dominant, and the flow rate can be represented by the modified homogeneous equilibrium model reasonably. In the below pseudo-critical region the results exhibit scattered feature as a result of hysteresis effect in the onset of vaporization, characterizing a bifurcation behavior. This effect is more significant in the nozzle with sharp-edge, especially at higher pressure. For the temperature well below the pseudo-critical point the flow is not at critical condition and is represented by the Bernoulli equation.