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DEVELOPMENT OF AN OPTICAL CONVOLUTION VELOCIMETER FOR MEASURING STACK FLOW
Citation:
Rudd, M. DEVELOPMENT OF AN OPTICAL CONVOLUTION VELOCIMETER FOR MEASURING STACK FLOW. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/2-78/049 (NTIS PB279013), 1978.
Description:
A new type of instrument has been developed and tested for the measurement of stack flow velocities. The instrument is optical and generates a shadowgraph pattern of the wake from a small heater. This shadowgraph is projected on a mirror grating of precise dimensions and the reflected light detected by a photodiode. The output of the photodiode fluctuates at a frequency that is related to the velocity with which the turbulence is convected across the grating. By measuring this frequency, the flow velocity is determined. A version of this optical convolution velocimeter (OCV), as it is called, has been built to withstand a temperature of 200C and combustion gases. This unit has been tested in both a wind tunnel and EPA's stationary source simulation facility (SSSF). The agreement with a pitot tube was close, 1% in the wind tunnel and 2 - 2.5% in the SSSF. Some difficulty in signal processing was found at high speeds and high temperatures or dust loadings, but this can be cured. The OCV promises to be a much more accurate and easier to use instrument than the pitot tube, at little additional cost.