Onset of convective flows in a near-wall granular layer during nonstationary liquid boiling

The onset and development of convective flows during nonstationary conductive heating of a cell with a layer of cylindrical pebbles placed in a liquid medium have been studied using a proposed and implemented optical method. The temperature fields have been measured using a holographic interferometry technique with immersion optical tomography elements, which is based upon the dependence of the index of refraction on the temperature and properties of a continuous medium. The mechanism of the pebble-bed influence on the time and character of microconvection formed near the cell wall heated from below has been studied for variable thermal properties of the liquid medium and pebbles in the granular layer and supplied heat flux. Data on the visualization of temperature fields and the development of convective flows in a pebble-bed reactor cell of complicated shape during nonstationary heating have been obtained for the first time.