Boiling heat transfer from inclined channels in a natural circulation loop

Boiling heat transfer was investigated in a rectangular channel heated from the bottom and inclined at 30° to the horizontal. The channel is installed in a two-phase closed thermosyphon loop where water is circulated naturally. One of the experimental parameters is heat flux (16.10, 13.82, and 9.09 W/cm²) from the immersed heater surface, and the other is channel spacing in the range of 1-20 mm between the adiabatic upper wall and the heated bottom wall. At constant imposed heat flux, the superheat at the wetted heater surface declined as the channel spacing narrowed from about 10 mm to 1 mm and was in inverse proportion to the average mass velocity through the channel. The heat transfer coefficient at the immersed surface of heater increased as the average mass velocity increased. On the other hand, in the slower mass velocity region, the heat transfer coefficient at the higher heat flux was larger than that at the lower one, but this trend was reversed in the faster mass velocity region. The turning point was about 90 g/cm ² s. These data are applicable to actual cooling system designs for multilayer printed circuit boards where guide vanes are attached to the inlet of each channel