Effect of the sensor sensitivity on the temperature fluctuation measurement in a turbulent thermal mixing region

The sensitivity of a sensor is an important parameter to measure the temperature fluctuation with high frequency in the turbulent thermal mixing region. In order to compare the sensitivity of the sensors, an experiment has been carried out for measuring the temperature fluctuation in a turbulent mixing region formed by two or more jets using cold wires and thermocouples which have different diameters. The dimensionless temperature fluctuation (θ*) measured at the same condition shows much difference according to the time constant of the sensor, and the frequency of the fluctuation was about 100Hz at 12m/s flow velocity but in a broad range of 50 ∼ 300Hz. When the flow velocity is in a 4.5∼16m/s range, the ratio of temperature fluctuation (θ*B/θ*A) measured by two sensors decreases with the increase of flow velocity, and decreases linearly with the log value of the response time ratio. When the ratio of temperature fluctuation is compared according to the time constant based on the diameter of sensor, There exists a differnet trend between the ratio of temperature fluctuation by the pair with cold wire and thermocouple and that by pair with thermocouple and thermocouple