Experimental boiling heat transfer study of vertical water flow through multiple thin rectangular channels with side -vent cross-flow

An experimental study of two-phase flow and boiling heat transfer in vertical thin rectangular channels of high aspect ratio with side vents was conducted. A multiple-heated channel configuration with up-flow, forced, and natural convection flows was investigated. By using unheated rectangular flow channels running parallel to the heated channels, the effects of side-vent cross-flow and channel-to-channel heat transfer on critical heat flux (CHF) were examined. The working fluid was water. Experimental test parameter ranges include absolute inlet pressures from 89.8 to 115.4 kPa, inlet water temperatures from 290.7 to 305.6 K, and water mass flow rates from 9.5 to 39 kg/m 2s. The test apparatus was instrumented in order to obtain global and local pressure and substrate temperature data. In addition, several viewing windows provided a visual survey of the boiling regimes and side-vent cross-flow patterns. Aluminum plates embedded with bar heaters provided a uniform heat flux to the flow channels. The primary objectives of this study were to determine the effects of heat and mass transfer between adjacent channels as is permitted by side-vent cross-flow and to obtain two-phase-flow and heat transfer data, with side-vent effects. The results enabled the development of a low-flow CHF correlation for flow geometry typical of plate-type nuclear reactors and heat exchangers. This new correlation incorporated several parameters that helped quantify the effects of conjugate heat transfer due to the thermodynamic properties of both the cooling fluid (water) and the heated substrate (aluminum). An analysis of the data, through comparison with previous flow boiling studies, provides a better understanding of how the geometry, flow conditions, and channel configurations affect the fluid mechanics and heat transfer characteristics of interior channel flows, which is essential in understanding heat transfer and CHF phenomena. The CHF correlation developed in this study compares the reported results from this study and three previous INEEL studies within an error of +/-5%. By including the uncertainties associated with this study's results, the margin of error is +/-8.5% with a 95% confidence.