Finite-size effects on the thermal conductivity of He4 near the superfluid transition

We report new high-resolution measurements of the thermal conductivity very near the superfluid-transition temperature T on a thicker sample (0.57 cm) than had been used previously (0.22 cm) by Lipa and Chui (LC). Our results deviate less from the conductivity expected for a bulk sample than do the LC data. Our data, the results of LC, and previous measurements on a 0.0025-cm-thick sample are consistent with a simple phenomenological model for the effect of the solid boundaries uponz.