Investigation of flow boiling in narrow channels by thermographic measurement of local wall temperatures

Flow boiling heat transfer characteristics of water and hydrocarbons in mini and microchannels are experimentally studied. Two different test section geometries are employed; a circular channel with a hydraulic diameter of 1,500 mu m, and rectangular channels with height values of 300-700 mu m and a width of 10 mm. In both facilities, the fluid flows upwards and the test sections, made of the nickel alloy Inconel 600, are directly electrically heated. Thus, evaporation takes place under the defined boundary condition of constant heat flux. Mass fluxes between 25 kg/m(2) s and 350 kg/m(2) S and heat fluxes from 20 kW/m(2) to 350 kW/m(2) at an inlet pressure of 0.3 MPa are examined. Infrared (IR) thermographv is applied to scan the outer wall temperatures. These allow the identification of different boiling regions, boiling mechanisms, and the determination of the local heat transfer coefficients (HTC). Measurements are carried out in initial, saturated, and post-dryout boiling regions. The experimental results in the region of saturated boiling are compared with currently available correlations and with a physically founded model developed for convective boiling.