Interaction of the Nucleation Phenomena at Adjacent Sites in Nucleate Boiling

Abstract

<p> This investigation is an original study in nucleate pool boiling heat transfer, consisting of two parts: an experimental study and a theoretical study. The experimental study was performed with water boiling at atmospheric pressure on a single copper surface. Two different levels of heat flux were investigated. For the lower level of heat flux (92.21 kW/m2), three different levels of subcooling (0, 6.5, 12°C) were studied and for the higher level of heat flux (192.11 kW/m2), two different levels of subcooling (0, 7.5°C) were studied as well. </p> <p> The cross-spectral density function ·and the crosscorrelation function were used to determine the time elapsed (-r) between the start of bubble growth at two neighbouring active sites with separation (S). The experimental results indicate that for the lower level of heat flux at three different levels of subcooling, the separation (S) and the time elapsed (-r) are related. For the higher level of heat flux at 0°C subcooling it was not possible to detect any correlation, but for the 7.5°C subcooled condition a weak correlation was found to exist. For the lower level of heat flux, all the experimental data for the saturated and subcooled boiling conditions plotted as (S-Rd) versus (T-Tg) drew together into a single curve, indicating that a single relationship could fit all the data. </p> <p> Three different theoretical models were devised in an attempt to·explain the experimental observations. The first model involved heat diffusion in the water; the second model was based upon the disturbance caused by the propagation of a pressure pulse in a mixture of water and vapour and finally the third model involved heat diffusion in the solid. The first two models failed to give satisfactory agreement with the experimental results, but the theoretical predictions corresponding to heat diffusion through the solid gave good agreement with the experimental findings. </p>