The effects of metastability in the phase transition processes for the transcritical R744 converging-diverging nozzles were investigated in this study. The research comprised both numerical simulations and experimental measurements, performed for the operating conditions typical for a R744 heat pump. The computational approach utilized the Delayed Equilibrium Model based on superposition of the homogeneous and heterogeneous nucleation. The research was performed at the test facility specially designed for experimental investigation of the small-scale, ejector-equipped heat pumps. Based on the results for a sample conical geometry, the authors developed and validated a correlation equation for the nucleation work reduction factor. Once validated, the model proved to yield acceptably low discrepancies between the simulation and the experimental results, also for other nozzle geometries.
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