A comparison of the flow boiling performance characteristics of partially-heated cross-ribbed channels with different rib geometries

Abstract

Measured local heat transfer data and the results of flow visualization experiments are reported for convective boiling of R-113 and methanol in vertical cross-ribbed channels similar to geometries used in formed-plate compact heat exchangers. Experiments are conducted using a test section in which one wall of the channel is heated while the opposite wall is adiabatic and transparent to allow visual observation of the flow. Heat transfer data are obtained for three different rib crossing patterns at coolant mass flux values between 40 and 230 kg m −2 s −1 and mass qualities between 0.10 and 0.80. Comparison of these data, together with those for a fourth geometry previously reported, indicate that variations of the rib spacing and angle have a significant effect on boiling heat transfer performance. Variation of the rib crossing pattern in these channels is found to have only a small effect on heat transfer. The swirl and agitation induced by the ribs are found to increase the convective boiling heat transfer coefficient by as much as a factor of 4 above that for a round tube under comparable flow conditions. Methods of correlating the heat transfer data for annular film-flow boiling in these geometries are also discussed.