Experimental Investigation On Forced Flow Boiling Heat Transfer In Vertical Narrow Rectangular Channel

Flow pattern characteristics of forced flow boiling heat transfer, characteristics of wall temperature variation and boiling heat transfer characteristics in vertical narrow rectangular channel under atmospheric pressure with pure water as experimental medium was investigated. The width of narrow channel in testing section was 2 mm, and single wall vapor heating and visualization were introduced in the experiments. The variation of flow pattern characteristics in channel and the procedure of boiling generating can be observed directly from one side, with the channel heated from the other one.The variation procedure of forced flow boiling heat transfer in narrow rectangular channel was photographed in the experiment. There was difference between transition of flow pattern in narrow rectangular channel and transition of flow pattern in common tube.Corresponding for three phases in variation of wall temperature in the experiment of start-up, there were three different modes of heat exchange. Heating power, volume flow rate and condensate depression in entrance all influenced the variation of wall temperature, OSV (initial point of net vapor generation) and hysteresis of saturated boiling.According to the experiment observation, the position of OSV existed in state of dynamic balancing under definite experimental condition. By the verification, the position of OSV which calculated from model Levy and model Saha was far from the experimental one. While the conclusion drew from model SUNQI tally with experimental value preferably under condition that volume flow rate was 60L/h, with relative error less than±20 %.In the process of saturated boiling, the instability of flow, the weak symmetry of vapor-liquid two-phase flow in narrow channel and other factors had some influence on temperature fluctuation of heating wall and medium. Volume flow rate had notable influence on the medium only in section of subcooled boiling.