Flow boiling critical heat flux on small heated regions

Often, in optical and electronic equipment, heating is concentrated in very small regions, and, because of materials constraints, cooled walls must be as thin as possible. Also, for efficiency, many high-flux cooling designs involve forced-convection boiling heat transfer. Though efficient, a design with boiling heat transfer can be difficult for it must properly account for the complexities of the boiling flux-temperature relationship. Of concern is locating the point of incipience to boiling and the point of maximum nucleate boiling heat flux, Critical Heat Flux (CHF), and describing the complex behaviors in the vicinities of these points. Characteristics of boiling near these points are discussed in terms of boundary layer behavior. Changes in either the heater size or the wall thickness affects the boiling curve, particularly the CHF behavior. Results from experiments which were conducted on small, heated regions are discussed in light of their application to the design of high-power optical and electronic devices. The effects of flow velocity, subcooling, pressure, heating length, dissolved gas content, and flow streamline curvature are addressed.