# Fast transient spray cooling of a hot thick target

## TL;DR

This paper investigates transient spray cooling of hot targets by measuring heat flux and temperature changes during different boiling regimes, supported by a theoretical model that accurately predicts the thermal behavior.

## Contribution

It introduces a comprehensive experimental and theoretical analysis of transient spray cooling, including a new model for heat conduction and heat flux prediction across boiling regimes.

## Key findings

- Theoretical model accurately predicts target temperature evolution.
- Experimental data aligns well with theoretical predictions.
- Spray parameters significantly influence boiling regimes and heat flux.

## Abstract

Spray cooling a hot target is characterized by strong heat flux density and fast change of the temperature of the wall interface. The heat flux density during spray cooling is determined by the instantaneous substrate temperature, which is illustrated by boiling curves. The variation of the heat flux density is especially notable during different thermodynamic regimes: film, transitional and nucleate boiling. In this study transient boiling curves are obtained by measurement of the local and instantaneous heat flux density produced by sprays of variable mass flux, drop diameter and impact velocity. These spray parameters are accurately characterized using a phase Doppler instrument and a patternator. The hydrodynamic phenomena of spray impact during various thermodynamic regimes are observed using a high-speed video system. A theoretical model has been developed for heat conduction in the thin expanding thermal boundary layer in the substrate. The theory is able to predict the evolution of the target temperature in time in the film boiling regime. Moreover, a remote asymptotic solution for a heat flux density during the fully developed nucleate boiling regime is developed. The theoretical predictions agree very well with the experimental data for a wide range of impact parameters.