Onset of nucleate boiling in minichannels

Heat transfer characteristics during flow boiling in a minichannel were stu died. For these investigations a thermographic measuring method was used. T he axial distribution of the external wall temperature was measured, from w hich the internal wall temperatures and the local heat transfer coefficient are calculable. Detailed investigations were carried out in particular for the onset of nucleate boiling. The results of the measurements on a vertic al evaporator pipe with an internal diameter of 1.5 mm are presented in dep endence on the mass flux and the heat flux. A model for the prediction of t he initial point of boiling and the wall-superheat has been derived based o n the experiments. (C) 2000 Editions scientifiques et medicales Elsevier SA S.