The development and use of a new heat flux gage system that is made using microfabrication techniques is proposed. The goal is to produce a system that has the capability to accurately measure time-resolved heat flux in unsteady flows. To accomplish this, novel heat flux gages have been designed that are small, have high frequency response, and are capable of measuring very high convective heat flux rates. By using high-temperature metals and ceramics as the gage components, operation over a wide temperature range can also be achieved (0 to 1000 Degrees Celsius). In addition, a new calibration system has been designed for the gages by making use of their very fast time response. The gages will consist of a thin layer of insulating material with many thermocouples positioned across it to form a differential thermopile. The overall thickness of approximately 1 micrometer will give negligible flow and thermal disruption with response times on the order of 5 microseconds. The surface size will be on the order of 0.2 mm by 2 mm. This will be achieved using thin film techniques associated with photolithography as commonly used for miniature electronic circuits. The measurement capabilities of the gages will be demonstrated in unsteady flows over a frequency range of 10 to 10,000 Hz and for flow velocities from low speed to supersonic. The combination of all of these characteristics in one heat flux gage would make this a major advancement in heat transfer instrumentation. Measurements would be possible that simply couldn't be made previously. The high frequency response allows direct measurement of time-resolved heat flux to observe the details of turbulent flows, the details of rotor wake effects at operating speeds of gas turbine engines, the details of the two- phase flow in fluidized beds, the effects of tube vibration in heat exchangers, and numerous other applications. Although it is very commonplace to make detailed fluid dynamic measurements of such unsteady flows, the capability to make corresponding unsteady heat transfer measurements has not been well developed. In addition, applications where the high heat flux capability are important include fundamental and applied heat transfer in such diverse fields as boiling and condensation, hypersonic flow, flow in shock tubes, high-sped turbomachinery (including gas turbine engines), processes using jet impingement heat transfer, and high-speed planes and rocket nozzles. As can be seen, much further research would be made possible by the development and demonstration of this heat transfer measurement capability.
