Influence of condensate inundation on heat transfer of R134a condensing on three dimensional enhanced tubes and integral-fin tubes with high fin density

High performance integrally-finned tubes with external fin density of 54 and 56 fpi are designed and manufactured. The condensing heat transfer of R134a on five tubes with integral-fin density of 20, 37, 48, 54, 56 fpi and five different high performance three dimensional enhanced tubes are studied for their single horizontal tube. Condensate inundation experiment of the integrally-finned and three-dimensional enhanced tubes is also performed. The experimental results indicate that the specially-designed integrally-finned tubes No.4 and No.5 of high density show the highest overall heat transfer performance over the three dimensional enhanced tubes about 8%. For the lower fin density integrally-finned tube, the results show apparently no condensate inundation influence effect. For the higher fin density tubes, the heat transfer is firstly enhanced more or less with the condensate impinging from the above tube, then maintains nearly unchanged. For the 3-D enhanced tubes, the heat transfer is also enhanced with condensate inundation firstly except tube No.7, while it is all followed by a mild drop as the increase of condensate rate. As a whole, the performance of the integral-fin tube with high density is better than that of the 3-D enhanced tubes.

► All integrally-finned tubes tested show basically no row effect in condensing.
► Row effect is observed for all 3-dimensional enhanced tubes tested.
► Integrally-finned tube with high fin density performs better than 3-D enhanced tubes.