PHENOMENOLOGICAL STUDY OF BOILING IN A NARROW SPACE FROM AN ISOLATED NUCLEATION SITE

The aim of the present work is to identify the mechanisms of heat tran sfer enhancement during natural convective boiling in confined spaces. The influences of gap-size (0.3 to 2 mm), of pressure (1 to 3 bar), o f heating surface orientation (vertical or horizontal) and chat of the number of nucleation sites (no site, single site or several sites) fo r boiling R-113 in a narrow channel are investigated. Results for unco nfined boiling are also presented as a reference. It is shown that lat ent heat transfer is improved when the bubbles are squeezed against th e heated wall. The heat transfer enhancement is greater for a vertical than for a horizontal orientation because the two-phase fluid velocit y is increased when the gap-size decreases, which enhances the sensibl e heat transfer. Finally, the confinement reduces the effect of an inc rease in pressure, which limits the influence of confinement. indeed, both parameters lead to contrary effects on the bubble diameter.