09. Heat and Mass Transfer

Flow boiling in a header-shared parallel tube system with normal diameter is prone to instability. In the case of a small diameter tube system, the surface tension of fluid dominates the liquid-vapor two-phase flow pattern in the flow conduit, and boiling phenomena is significantly dif-ferent compared to normal diameter tubes. In this study, the unstable flow boiling phenomena occurring in three parallel small diameter tubes with a shared inlet and outlet header has been investigated. The experiment used a sy-ringe pump to maintain a constant flow rate to the inlet header and three small diameter tubes electrically con-nected in series and energized to maintain a constant heating heat flux. The experimental setup was carefully designed to minimize external disturbances. The test heat-ed tubes were made of stainless steel with an inner diame-ter of 0.51 mm, an outer diameter of 0.81 mm, and a heated length of 130 mm. FC-72 was used as the test fluid. The flow and heat transfer characteristics of flow boiling in parallel small diameter tubes were investigated by measuring the temperature distribution on the outer sur-face of the tubes and its temporal variation using an in-frared thermography camera. In particular, the temporal and space variation of dryout occurrence in each heated tube were investigated in detail.