EXPERIMENTAL INVESTIGATION OF STEEL SPHERES AS A PASSIVE ENHANCEMENT TECHNIQUE FOR FLASH BOILING OF HCFC-22

An experimental investigation was conducted to study the influence of a layer of 3.6-mm-diameter steel spheres on the mass flow during flash boiling in a glass pressure vessel. It was observed that the steel sp heres added numerous heterogeneous nucleation sites within the liquid and promoted abundant vapor bubble growth during depressurization. The steel spheres were in contact with each other and with the interior o f the glass vessel. The data from these experiments were compared with baseline experimental results primarily with regard to the mass flow. Each test was run for 60 s, using controlled variables of orifice dia meters (1.59 and 5.56 mm), initial refrigerant amounts (0.23, 0.45, an d 0.68 kg), initial pressures (575 and 840 kPa), and vessel geometries (665 and 1110 ml). Pressures, temperatures, and mass how rates, along with calculated saturation temperatures, amount of superheat, mass fl ux, and total mass hashed, were used to compare the baseline experimen ts with the enhanced boiling method. Results showed an increase in the total mass flashed at each test condition, ranging from an average; o f 22% to 81% with respect to baseline experiments. (C) Elsevier Scienc e Inc., 1997.