An optical method for measuring the bubble dynamic data subject to an isolated bubble model is presented at low heat flux q⩽1kW/m2; while the operating heat fluxes are up to 30 kW/m2. By simultaneous measurements of departure diameters, velocities, frequencies and nucleation site densities, the heat transfer contribution of an individual active site is evaluated. A single phase heat transfer correlation was used to model the present heat transfer data. The test specimens consisted of tubes with porous copper (Cu) and molybdenum (Mo) plasma coated surfaces. The porosity (ε), the thickness of the porous layer (δ), and the mean pore diameter (η) of the tested tubes are the following: 0.055⩽ε⩽0.057,100⩽δ⩽300μm, and 3⩽η⩽4μm. The tests were carried out using R-134a and R-600a as working fluid at a saturation temperature of 18°C and with low and moderate heat fluxes (⩽1 kW/m2) for boiling visualization and related measurements (⩽30 kW/m2).

Issue Section:
Evaporation, Boiling, and Condensation
Keywords:
boiling, heat transfer, bubbles, flow visualisation, Boiling, Bubble Growth, Enhancement, Heat Transfer, Refrigeration
Topics:
Bubbles, Heat transfer, Heat flux, Boiling, Plasmas (Ionized gases)
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