Chaotic dynamics of the pool boiling was intensively investigated over the last couple of decades due to its importance for the boiling theory, and the practical applications of the phenomenon in real equipment. This work provides further development of the experimental and theoretical analysis methods for chaotic boiling investigation and delivers new results using these methods for the flow boiling conditions of the refrigerant R134a. Experiments were conducted at pressures up to 3 bar, heat fluxes up to 125 kW/m2, and mass flow rates between 2 and 3 kg/(m2s) in a real evaporator of a heat pump, equipped with an original enhanced microstructured surface. The enhanced surface was manufactured using a novel machining method, leaving no chippings, or cutting waste for a metallic material.
Experimental results on distribution of vapor bubbles departure diameters were obtained using enhanced optical methods, based on reflected low radiation He-Ne laser source at several heat fluxes, including near critical values. The common problem of optical methods limited application at high heat fluxes was successfully overcome, using a new theoretical analysis, combining the Mie scattering and Beer−Lambert−Bouguer law. Investigated enhanced surface produces a much wider range of vapor bubbles departure diameters due to its branched microstructure. The width of the corresponding spectra is 50 times higher than for a smooth surface. This results in higher heat transfer coefficients due to a higher nucleation sites density. Another heat transfer mechanist could be attributed to the micro convection, arising around an oscillating vapor bubble. These oscillations were analyzed using the Poincare phase portraits and auto correlation functions.