Application of thermistors to measure air flow velocities very close to surfaces

Problems using thermistors close to plane walls are discussed. Analysis of the thermistor probe heat balance shows that reducing the measurement height to 2 mm has no important consequences. At still lower heights direct heat conduction to the wall can play a role. Flow interference effects between wall and thermistor at small heights are unclear. Experimental investigation shows that the thermistor probe accuracy at 2 mm from the wall is the same as at 8 mm. Conditions for extrapolation in order to assess the shear stress are given.