A Parametric Study of Nucleate Boiling on Structured Surfaces, Part II: Effect of Pore Diameter and Pore Pitch

Abstract

This two-part experimental work identifies the effect of geometric dimensions on the boiling performance of “tunneled” enhanced boiling surfaces, which is similar to the Hitachi Thermoexcel-E surface. Tests were performed on a horizontal tube using R-11 and R-123 at 26.7°C for heat fluxes from 2 to 70 kW/m2. This second part of the study defines the effect of the pore dimensions (pore diameter and pore pitch). The pore diameters are 0.12, 0.18, 0.23, and 0.28 mm and the pore pitches are 0.75, 1.5, and 3.0 mm. The results are interpreted to explain the relationship between pore diameter and pore pitch on the boiling performance.

Boiling heat transfer enhancement in subsurface horizontal and vertical tunnels

“…One may suppose that due to a low value of heat of vaporization for R-123 (h fg % 170 kJ/kg), the tunnel is dried out because of insufficient amount of liquid, which agrees with the results obtained by Chien and Webb [6,7] and Nakayama et al [4,5]. The surface with pores of 0.4 and 0.5 mm ensures the balance between liquid supply and its evaporation in tunnel menisci ( Table 2).…”

“…According to Chien and Webb [6,7] and Nakayama et al [4,5], the feeding rate of the tunnel with liquid will be higher than the evaporation intensity with increasing total surface of pores (pore diameters). Then a larger foil pore diameter may cause the flooding of the tunnel when too much liquid flow into it.…”

“…Chien and Webb [6,7] presented the effect of the tunnel dimensions (fin height, fin pitch, tunnel shape) for a limited range of pore diameters (0.12-0.28 mm) and pore pitches (0.75-3.0 mm) on boiling heat transfer. The surface was formed on an integral-fin tube having a copper foil wrapped over the fin tips.…”

Effect of pore size on the nucleate pool boiling of structured enhanced tubes

“…A systematic study on the boiling performance of tubes having surface pores has been performed by Chien and Webb [3,4]. They investigated the effect of pore diameter, pore pitch and tunnel shape using R-11 and R-123.…”

Heat flux determination for nucleate boiling in subsurface tunnel structures

“…The proposed new model for boiling heat transfer in tunnel structures was based on Nakayama et al model [9], later improved by Chien and Webb [4] for surfaces investigated in [2,3]. The quoted model was developed through experimental studies of pool boiling on cylindrical surfaces with subsurface tunnels, formed by placing foil with small holes on a finned tube.…”