In this paper, quantitative and qualitative investigations on the unstable fluctuations of wall temperature signals in a multiple-tube evaporator with a vapor-liquid-solid boiling flow were carried out by employing the nonlinear analysis tools including reconstructed phase space analysis, correlation dimension analysis and Kolmogorov entropy analysis besides the traditional analysis methods such as power spectral analysis and autocorrelation analysis. The values of Kolmogorov entropy are positive and finite, and the values of correlation dimension are from 1.5 to 2.0. The analysis results indicate that the physical parameter fluctuations of the system with a vapor-liquid-solid three-phase boiling flow are chaotic. Based on the estimates of correlation dimension, it can be found that at least two independent variables are needed in order to describe the flow boiling behavior of such system. The curve shapes of correlation integral versus radius of hypersphere vary with the variations of multi-phase flow regimes or states. So do the curve shapes of slope or Kolmogorov entropy versus radius of hypersphere. And the multi-phase flow regimes or states at given operation conditions in such system may be identified or characterized by the shape variations of these curves. In the estimations of chaotic invariants including correlation dimension and Kolmogorov entropy at the same given operation condition, the multi-value phenomena are found. The phenomena reflect the multi-scale behavior occurred in such multi-phase flow boiling systems. (c) 2005 Elsevier B.V. All rights reserved.