Spatio-temporal analysis of nucleate pool boiling: identification of nucleation sites using non-orthogonal empirical functions

The analysis of spatio-temporal data and the physical understanding of the systems generating them are often limited by the available techniques. Thes e limitations are especially evident in nucleate boiling. This paper invest igates the analysis of a sequence of temperature fields obtained from a poo l nucleate boiling experiment. Spatio-temporal data for the wall temperatur e in pool nucleate boiling of water on a thin, horizontal, stainless steel plate were obtained by liquid crystal thermography and high speed video rec ording. A previous analysis provided examples of the thermal conditions for activation of individual nucleation sites, for the heat transfer mechanism s during bubble growth and for the consequent interactions between adjacent sites. Principal component analysis (PCA) is shown to provide a reconstruc tion of the temperature fields that is accurate in the root mean square sen se but which obscures information about the underlying physics, such as pos itions of the nucleation sites. In contrast, a new approach using non-ortho gonal empirical functions (NEFs) encodes the relevant physical constraints (e.g., each NEF has a radially symmetrical form as suggested by the pattern of cooling during bubble growth). NEFs provide an efficient identification of the positions of active sites in successive frames; they are better sui ted to the analysis of non-stationary dynamics than PCA and allow for infor mation compression. (C) 2001 Elsevier Science Ltd. All rights reserved.