Investigation of unsteady flow behavior of cryogen-spray coupled with cold air jet

Abstract

Cryogen spray cooling (CSC) coupled with cold air jet (CAJ) was used to mitigate Cryogen consumption. However, the CAJ interaction could affect the flow structure and spray's unsteadiness, permitting coolant intermittency. In this study, the unsteady behavior and flow structure of CSC coupled with CAJ have been qualified. During the experiment, CAJ at an inclined angle of 30°, temperature of 266 K, flowrate of 0.0, 3.0, 6.0 m3/h, and axial distance of 20 mm from the spray-nozzle was injected into a typical R-134a spray system. A high-speed camera was used to capture the unsteady spray through the Mie-scattering technique, while large-eddy simulation (LES) coupled with discrete-phase model (DPM) was used to predict the vortical structure. The spatial correlation was used to identify the coherent structures, while the proper orthogonal decomposition (POD) was used to demonstrate their unsteady signatures. The results showed a significant impact of the CAJ on the spray-pattern and associated unsteadiness, providing an asymmetric spray-plume at the CAJ windward side. The CAJ increased the fluctuating energies of the unsteady coherent structures by 32 % through CAJ-to-spray interactions. It contributed to the unsteady spray through the counter-rotating vortex-pairs (CRVP) at the lateral sides and hairpin vortices along the injection line. The CRVP clustered the spray in recirculating regions, introducing unsteady CAJ entrainment at the leeward and thermal field at the windward. This work could insight into our understanding of unsteady multiphase flow, promoting advanced cooling technology by uncovering their causes and effects.