Effects of Pore Diameters and System Pressure on Saturated Pool Nucleate Boiling Heat Transfer From Porous Surfaces

The porous surface structure was manufactured with precision for the experimental study of nucleate boiling heat transfer in R-11. Boiling curves and the data of bubble formation were obtained with a variety of geometrical and operational parameters; the pore diameters were of 50, 100, 150 μm, there was a combination of pores of different sizes; and the system pressures were of 0.04, 0.1, 0.23 MPa. The boiling curves exhibit certain trends effected by the diameter and population density of pores. A combination of high system pressure and pore sizes of 100 or 150 μm dia enables boiling to persist even when the wall superheat is reduced to an extremely low level of 0.1 K. A noteworthy feature of porous surface boiling is that intense bubble formation does not necessarily yield a high heat-transfer performance. Examination of the data indicates that liquid suction and evaporation inside the cavities are a proable mechanism of boiling with small temperature differences.