Abstract
Drag force plays an important role in determining the momentum, heat and mass transfer of droplets in a flashing spray. This paper conducts a comparative study to examine the performance of drag force models in predicting the evolution of droplet evaporation for R134a single droplet and spray characteristics for its flashing spray. The study starts from single moving R134a droplet vaporizing in atomispheric environment, to a fully turbulent, flashing spray caused by an accidental release of high-pressure R134a liquid in the form of a straight-tube nozzle, using in-house developed code and a modified sprayFoam solver in OpenFOAM, respectively. The effect of the nozzle diameter on the spray characteristics of R134a two-phase flashing spray is also examined. The results indicate that most of the drag force models have little effect on droplet evporation in both single isolated droplet modelling and fully two-phase flashing spray simulation. However, the Khan–Richardson model contributes to different results. In particular, it predicts a much different profile of the droplet diameter distribution and a much lower droplet temperature in the radial distance. The nozzle diameter has a significant impact on the flashing spray. A smaller diameter nozzle leads to more internse explosive atomization, shorter penetration distance, lower droplet diameter and velocity, and a faster temperature decrease.
Highlights
Two-phase flashing spray is usually caused by a sudden release of high-pressure liquid or liquified gas into a low-pressure environment below its saturation pressure in the form of leakages or nozzles.The liquid pressure will experience a rapid decrease while its temperature usually has very little change during this ultra-short period, which makes the liquid superheated
The results indicated that spray characteristics played a decisive role in determining surface transient heat transfer, and the cooling performance could be effectively enhanced by adjusting the spray conditions
R134asingle singledroplet droplet evaporation evaporation will firstly, andand thenthen it followed by the flashing spray.spray
Summary
Two-phase flashing spray is usually caused by a sudden release of high-pressure liquid or liquified gas into a low-pressure environment below its saturation pressure in the form of leakages or nozzles. Zhou et al [13] experimentally investigated the global distributions of droplet diameter, velocity and temperature, and the empirical correlations of droplet velocity and temperature variations were proposed Afterwards, they comparatively investigated the spray behavior and surface heat transfer of flashing spray cooling with 50 ms spray duration using different refrigerants of R134a, R407C and. How the drag force coefficient influences vaporizing droplet evolution of the diameter, velocity and temperature for a single isolated droplet and for droplets in flashing spray with low saturation temperature and high volatile cryogens is still unclear. This paper conducts a comparative study to examine the performance of several selected drag force models in predicting the evolution of droplet evaporation for R134a single droplet and spray characteristics for its two-phase flashing spray through a two-stage procedure. FOR PEER REVIEW flashing by a selected drag force model
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