Critical heat flux in cooling channels for flow-field probes

Probes (sampling, temperature, pressure) for high-temperature environments, such as gas turbine combustors, can survive only if they are cooled. To keep probe size small, the cooling passages must be microchannels, [O] 100 micrometer internal diameter. For logistical reasons, the length-to-diameter ratio is considerable. Heat fluxes are high, so that boiling occurs even with high velocities. The limiting factor for probe survivability, then, is the critical heat flux (CHF). This paper summarizes an experimental study of CHF in cooling channels that might be used for probes. A CHF correlation for water coolant is developed for design. An orifice at the channel inlet, originally conceived for enhancement, was found to dramatically improve the flow stability and increase the CHF. Pumping power requirements for plain tubes and orificed tubes are also documented.