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.

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