Frequency response of fine wire thermocouples and cold wires over a large temperature range in airflows

The theoretical and experimental investigation of frequency response of cold wires and fine wire thermocouples is presented for the case of heated airflows (T less than 600 K). Over this temperature range transfer functions of these thermal sensors show the same behavior as already observed for the case of slightly heated flows. Experimental tests of frequency response are performed using an 'external heating technique' where the sensor is actually submitted to calibrated temperature fluctuations over a large frequency range (.01-500 Hz). The good agreement found between experiments and predictions show that significant errors can be made for cold wires if prong-wire thermal interaction is not taken into account.