Direct Measurement of Hot-Wall Heat Flux

The implementation and use of high-temperature-capable heat flux sensors is investigated in several different hot-wall measurement scenarios. A graphite flat-plate heater was used to generate high heat fluxes representative of hypersonic flight. This allowed the comparison of cold-wall and hot-wall heat flux measurements under carefully controlled experimental conditions by using a high-temperature heat flux sensor mounted on three very different substrates, from an actively cooled body to a well-insulated body. A water-cooled Gardon heat flux sensor was used to measure the incident radiation in all cases. Incident radiation heat fluxes as high as 65 W cm(-2) and high-temperature heat flux sensor surface temperatures as high as 1130 degrees C were realized. A unique data-processing scheme rendered the high-temperature heat flux sensor virtually insensitive to the material on which it is mounted and accounted for the sensor's temperature-dependent properties. Because of the emitted radiation and natural convection from the high-temperature heat flux sensor surface, the net heat flux was very different from the incident heat flux measured by the cold sensor (water-cooled Gardon). For these idealized cases, the incident radiation could be predicted from the hot-wall total heat flux measurements. For more realistic conditions, however, it is important to be able to measure the actual heat flux desired.