INVESTIGATION OF POOL BOILING DYNAMICS ON A RECTANGULAR HEATER USING NANO-THERMOCOUPLES: IS IT CHAOTIC OR STOCHASTIC?

摘要

The non-linear dynamical model of pool boiling on a horizontal rectangular heater is assessed from experimental results in this study. Pool boiling experiments are conducted over a horizontal rectangular silicon substrate measuring 63mmX35mm with PF-5060 as the test fluid. Novel nano-thermocouples, micro-machined in-situ on the silicon substrate are used to measure the surface temperature fluctuations for steady state pool boiling. The acquisition frequency for temperature data from the nano-thermocouples is 1kHz. The surface temperature fluctuations are analyzed using the TISEAN package. A time-delay embedding is employed to generate higher dimensional phase-space vectors from the temperature time series record. The optimal delay is determined from the first minimum of the mutual information function. Techniques such as recurrence plots, and false nearest neighbors tests are employed to assess the presence of deterministic chaotic dynamics. Chaos quantifiers such as correlation dimensions are found for various pool boiling regimes using the raw data as well as noise-reduced data. Additionally, pseudo-phase spaces are used to reconstruct the 'attractors'. The results after non-linear noise reduction shows definitive presence of low-dimensional (d <= 7) chaos in fully developed nucleate boiling, at critical heat flux and in film boiling.