要約

Systematic experiments were conducted of nucleate pool boiling of water and Rl 13 for a confined space created by a narrow gap between a rectangular vertical heating surface set parallel to an opposed unheated glass plate. Three parameters are assumed significant to confined space boiling heat transfer: gap size between the heating surface and the unheated glass plate; number of slits equally dividing the unheated plate; and the peripheral condition of the space, whether it is partly closed or open.
The present findings are summarized as follows: (1) The heat transfer coefficient is a complicated function of gap size, number of slits, heat flux, and the lateral closure conditions of the boiling space. (2) Boiling behavior and heat transfer coefficient are similar 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 deterioration begins at higher heat fluxes. (4) Critical heat flux decreases consistently with decreasing gap size. (5) Slits on the unheated plate are effective in extending enhanced heat transfer up to higher heat fluxes and consequently in increasing critical heat flux. (6) Optimization 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 transfer over that of unconfined boiling.