Experimental investigations and a simplified model for pool boiling on micro-fins with sintered perforated foil

• Object of analysis: plain micro-fins and micro-fins with perforated foil covering.
• Boiling curves for water and FC-72.
• Simplified model for heat flux determination at pool boiling.
• Prediction of heat flux ±35% for boiling water and ±40% for FC-72.

The paper presents experimental data for two kinds of copper enhanced surfaces: micro-fins with sintered perforated foil (MFP, hole diameter 0.05–0.3 mm) and a micro-fin structure without a covering (MF). The experiments were carried out for water and FC-72 at atmospheric pressure. Micro-fins of 0.5 and 1 mm in height were uniformly spaced on the base surface. At all heat fluxes for water and low heat fluxes (below 25 kW/m2) for FC-72, surfaces with micro-fins covered with perforated foil produced the highest heat transfer coefficient. Maximum heat flux from the MFP surface increased 130% for water and 75% for FC-72 in relation to the smooth surface.The results for both working fluids were compared in terms of the dimensionless Bond number.The simplified model was proposed for determining total heat flux for the studied surfaces. It was assumed that the structure formed a system of connected perpendicular horizontal tunnels between the micro-fins confined by a top porous covering. The heat fluxes were determined for evaporation in the tunnels and for convection on the perforated foil based on the calculated departure bubble parameters (diameter, nucleation sites density, frequency). The predicted heat fluxes, when compared with the experimental results, showed satisfactory agreement for boiling water at medium and high superheats.