Subcooled flow boiling of a citric acid aqueous mixture

In the present research, an experimental investigation was conducted to assess the heat transfer coefficient of aqueous citric acid mixtures. The experimental facility provides conditions to assess the influence of various operating conditions such as the heat flux (0–190 kW/m2), mass flux (353–1059 kg/m2s) and the concentration of citric acid in water (10%–50% by volume) with a view to measure the subcooled flow boiling heat transfer coefficient of the mixture. The results showed that two main heat transfer mechanisms can be identified including the forced convective and nucleate boiling heat transfer. The onset point of nucleate boiling was also identified, which separates the forced convective heat transfer domain from the nucleate boiling region. The heat transfer coefficient was found to be higher in the nucleate boiling regime due to the presence of bubbles and their interaction. Also, the influence of heat flux on the heat transfer coefficient was more pronounced in the nucleate boiling heat transfer domain, which was also attributed to the increase in bubble size and rate of bubble formation. The obtained results were also compared with those theoretically obtained using the Chen type model and with some experimental data reported in the literature. Results were within a fair agreement of 22% against the Chen model and within 15% against the experimental data.