In order to assess the effect of frequency on transport of a passive scalar contaminant in an oscillatory flow, a piston-driven pipe flow is established. Two pipe test section geometries are used: one straight, round and uniform and the other uniformly tapering (i.e. conical). Flow is driven at frequencies characteristic of human breathing, both resting, normal and high frequency. A screen of closely spaced, parallel, thin wires is placed perpendicular to the flow, in the test section and is heated so as to dissipate a constant power into the fluid. The subsequent time-average and instantaneous temperature fields are measured, as functions of position. The results are shown to be consistent with the consequences of transport of heat by a combination of convection and diffusion. Convective transport is found to increase with frequency, at constant amplitude, but the effective diffusivity does not obey the predictions of theories which are based on an assumption of constant average axial gradient of the scalar field.