Natural convection heat transfer enhancement using bubble injection between vertical parallel plates

Abstract

We experimentally study natural convection heat transfer enhancement using bubble injection between a vertical heated plate and a flow guiding plate in water. While heat transfer is more than tripled with bubble injection, the introduction of the flow guiding plate parallel to the heated plate further increases heat transfer by up to 12% despite attenuating the wall-normal liquid fluctuating velocity. We attribute further heat transfer enhancement to increased wall-parallel liquid velocity driven by bubbles rising at high speeds. We also perform temperature calculations incorporating experimentally measured mean liquid velocities, which permit a quantitative evaluation of the wall-parallel mean liquid velocity and wall-normal liquid fluctuating velocity contributions to heat transfer. The calculations show that the fractional contribution of wall-parallel mean liquid velocity with bubble injection to heat transfer is high, especially in the upstream region of the heated section, and the presence of the flow guiding plate near the heated wall increases the contribution by up to 30% compared with the case without the plate.