Experimental Investigation of Bubble Dynamics in Nucleate Pool Boiling for TiO2 nano particle coated surface

Enhancement of CHF of heater in the nano-fluid or nano-particle coated surface in the fresh water has been intensively studied. It was known that the wettability change and formation of the micro-porous structure on the nano-particle coated heater surface cause CHF enhancement. These changes on the heater surface will affect bubble departure dynamics but studies on the bubble dynamics on the nano-particle coated surface are rare. Therefore, the present study is performed to measure the bubble departure characteristics experimentally and to find one of reasons of CHF enhancement. Zuber correlated the multiplication of the bubble diameter and departure frequency as the drift velocity which appear again in his CHF correlation: fD = 0.092m/ s for the boiling water on the copper heater at atmospheric pressure. However, Ivey categorized three distinguished region based on the dominant physics: fD3/4 = 0.44 for the small bubbles from 0.2 to 0.5cm, fD1/2 = 0.90g1/2 for the mushroom like large bubble (D > 0.5cm) but for the thermal region fD2 = consant . All of these correlations are applicable to the bare heater on the fresh water not for the bare heater in the nano fluid or nano-particle coated heater in the fresh water. Therefore, in the present study, we measured bubble departure diameter and frequency for both bare surface heater and TiO2 nano-particle coated heater to explain partly why CHF of nano-particle coated surface is enhanced in term of macrolayer under the mushroom bubble