Pool Boiling Heat Transfer of Borated (H₃BO₃) Water on a Nanoporous Surface

With regard to potential application in pressurized water reactors (PWRs), a nanoporous heated surface was tested in pool boiling of an aqueous solution of boric acid (H₃BO₃), or borated water (1% volume concentration). The effect of different system pressures and different surface orientations on pool boiling heat transfer was studied. The nanoporous surface consisted of a coating of alumina nanoparticles applied on a 1 cm² flat copper surface through nanofluid boiling. An uncoated surface in borated water was similarly tested, and due to boric acid deposition, the boiling heat transfer (BHT) degraded and the critical heat flux (CHF) enhanced relative to pure water. Also, the possibility of transient pool boiling behavior of borated water was investigated but none was detected. For all pressures and orientations, the nanoporous surface further enhanced the CHF of borated water to the CHF produced by the nanoporous surface in pure water. Over the nanoporous surface, the CHF of borated water was increasingly better with decreasing pressure, than that over the plain surface. However, BHT degraded slightly further. Boric acid deposition over the nanoporous surface was believed to be the source of this BHT degradation, but played no apparent role in the further CHF enhancement.