FIG. 3. Dimensionless Fréchet kernel F*(X,0,) for a dual-probe heat-pulse sensor with heater probe at (X,Y) = (–,0) and temperature probe at (X,Y) = (,0). Results are from Eq. [32] with Y = 0 for dimensionless times = 0.21, 0.23, 0.25 0.27, and 0.29. The curve for = 0.25 is the special case of Eq. [34] for which there are no singularities at the heater probe or temperature sensor.