Studies on the Enhancement of Forced Connective Heat Transfer in Three-Dimensional Rib-Roughened Tubes : 1st Report, In-line Arrangement

Abstract

In order to improve the performance of heat transfer inside a tube, an investigation of three-dimensional rib-roughened surfaces was undertaken to determine the effects of rib shape and pitch along the tube circumference (the number of ribs) on flow friction and heat transfer characteristics. All ribs were in the shape of a regular triangle whose vertical angle was 60'. Four types of rib height were tested. Also, five types of ring height were tested for comparison. They were arranged in line with a constant pitch along the flow direction by varying the pitch along the tube circumference. Finally, as a result of performance comparisons of heat transfer enhancement under the condition of constant pumping power, (1) High-performance was given in the case of a small number of ribs in which three dimensionality was shown in the local heat transfer coefficient distribution. (2) But by increasing the number of ribs, the distribution changed into two djmensional and these performances were lower than or equal to that of the ring. (3) Under the condition of a constant number of ribs, the rib height for excellent performance can be found.