ENHANCED NUCLEATE BOILING HEAT-TRANSFER IN A NARROW CONFINED SPACE BETWEEN A HEATING SURFACE AND A SLITTED PLATE

Systematic experiments were conducted of nucleate pool boiling of wate r and R113 for a confined space created by a narrow gap between a rect angular vertical heating surface set parallel to an opposed unheated g lass plate. Three parameters are assumed significant to confined space boiling heat transfer: gap size between the heating surface and the u nheated glass plate; number of slits equally dividing the unheated pla te; and the peripheral condition of the space, whether it is partly cl osed or open. The present findings are summarized as follows: (1) The heat transfer coefficient is a complicated function of gap size, numbe r of slits, heat flux, and the lateral closure conditions of the boili ng space. (2) Boiling behavior and heat transfer coefficient are simil ar to that of unconfined nucleate boiling for gap sizes larger than 2 mm. (3) For a gap size less than 2 mm, compared to unconfined boiling, heat transfer is enhanced for a wide range of heat flux and deteriora tion begins at higher heat fluxes. (4) Critical heat flux decreases co nsistently with decreasing gap size. (5) Slits on the unheated plate a re effective in extending enhanced heat transfer up to higher heat flu xes and consequently in increasing critical heat flux. (6) Optimizatio n of the gap size and the number of slits gives for water, a six-fold; and for R113, a three-fold increase in maximum enhancement of heat tr ansfer over that of unconfined boiling.