Study on water droplet flash evaporation in vacuum spray cooling

- Droplet heat and mass transfer during vacuum spray cooling are investigated.
- An analytical model on droplet flash evaporation has been developed.
- Droplet vapor concentration affects droplet phase transition and lifetime greatly.
- Droplet phase transition accelerates the evaporation of the droplets.
- The study contributes to advanced industrial applications of vacuum spray cooling technique.

Droplet flash evaporation plays an important role in determining the performance of the vacuum spray cooling, but the properties of the droplet flash evaporation on the micrometer scale are less reported. In this article, a one-dimensional droplet flash evaporation model has been proposed by introducing a simple heat balance correlation and a phase transition model to Fick's law. Both the performance and applicability of the present model are validated against the published experimental data. Based on the current model, the thermal effects including temperature, heat transfer coefficient, phase transition and droplet lifetime are analyzed in order to offer a guidance for future numerical models of the droplet impingement cooling in vacuum condition. The effects of various parameters including ambient pressure and temperature, droplet size and the fraction of vapor concentration on the droplet phase transition are also addressed from the standpoint of vacuum spray cooling. The numerical results obtained will provide deep insight into the heat transfer mechanisms of the vacuum spray cooling and contribute to advanced industrial applications of the vacuum spray cooling technique.

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