New paper on chocked flow in nozzles

The paper entitled Choked liquid flow in nozzles: Crossover from heterogeneous to homogeneous cavitation and insensitivity to depressurization rate has been published in Chemical Engineering Science.

The critical mass flow rate is the maximum flow rate that can pass through a constrained geometry such as a nozzle. In the paper linked to above, we demonstrate that a delay of the phase transition is necessary to reproduce experiments. Two methodologies are presented: (1) the delayed homogeneous relaxation model (Delayed HRM), and (2) the metastable isentrope model (MIM). Delayed HRM is a relaxation model that can readily be incorporated into a spatially distributed description of the fluid flow, e.g. in ejectors. MIM assumes isentropic flow and instantaneous equilibrium up to the limit of metastability, and yields a geometry-independent critical mass flux as the solution of a set of algebraic equations. We compare the two methodologies to available experimental data on the critical mass flow rates of carbon dioxide and water through nozzles, finding that they give nearly identical predictions. Using the limit of metastability predicted by homogeneous nucleation theory works well at high temperatures, rendering the methodologies completely predictive. They deviate on average 11% from experimental data on CO2, and thus outperform homogeneous relaxation models by a large margin, even when the latter employs several fitted parameters. For water and carbon dioxide, we find a crossover between homogeneous and heterogeneous nucleation at T=590 K and T=285 K respectively. Moreover, the predicted limit of superheat falls on a single curve in the temperature–pressure space of water as shown in the figure below. By combining this expression with the above methodologies, we obtained an average deviation of 3% with available experimental data on critical mass flow rates for water.