Study of pool boiling on flat and micro-grooved brass and copper surfaces

Abstract

Among the different ways of achieving heat transfer enhancement in pool boiling, modification of surface roughness and the associated change in the surface wettability are two widely studied methods. It is well established that microstructure can play an important role in varying surface roughness and improving interfacial wettability. In the present study, pool boiling heat transfer on a number of micro grooved and flat (brass and copper) surfaces with water as the working fluid is investigated experimentally for enhancement of critical heat flux. The micro structured sample surfaces feature parallel grooves having dimensions of tens of microns and are fabricated using a mechanical micromachining process. Classical pool boiling experiments are conducted for three different values of heat flux (75 kw/m2, 100 kw/m2, 125 kw/m2). The bubble nucleation process is visualized and the bubble departure diameter is measured with the help of a high speed camera. It is observed that the nucleation site density and departing bubble diameter increases, while the bubble departure frequency decreases with an increasing heat flux for both kind of surfaces and materials. Comparison of the results among the flat and micro-grooved surfaces reveals that the boiling on micro-grooved surfaces results in higher heat transfer coefficient, more nucleation sites, lower bubble departure frequency and larger bubble diameter under similar operating conditions.Among the different ways of achieving heat transfer enhancement in pool boiling, modification of surface roughness and the associated change in the surface wettability are two widely studied methods. It is well established that microstructure can play an important role in varying surface roughness and improving interfacial wettability. In the present study, pool boiling heat transfer on a number of micro grooved and flat (brass and copper) surfaces with water as the working fluid is investigated experimentally for enhancement of critical heat flux. The micro structured sample surfaces feature parallel grooves having dimensions of tens of microns and are fabricated using a mechanical micromachining process. Classical pool boiling experiments are conducted for three different values of heat flux (75 kw/m2, 100 kw/m2, 125 kw/m2). The bubble nucleation process is visualized and the bubble departure diameter is measured with the help of a high speed camera. It is observed that the nucleation site density and d...