Olafsen, JS; Behringer, RP, *Dynamic measurements of thermal transport coefficients and boundary resistance I. Normal*^{4}He,
Journal of Low Temperature Physics, vol. 106 no. 5-6
(1997),
pp. 673-704 .
**Abstract:**

*The thermal conductivity, κ, and the thermal diffusivity, DT, of normal liquid 4He have been obtained from the temperature response, T((ω), across a fluid layer of thickness, d, to an ac heat flux, Q(t) = Q0exp(iωt). Previous transient heat flux experiments measured the thermal relaxation of the fluid towards equilibrium and assumed the dominance of a single slowest mode. The present ac technique allows measurements under steady-state conditions while driving the system at a single frequency, ω. The response curve for T(ω)/Q0 yields data for κ, DT and the boundary resistance, Rb. Boundary effects appear at frequencies higher than τ-1 ≡ DT/d2 where the fluid is unresponsive to bulk heat transport. We use this fact to obtain Rb with high accuracy in the normal phase from the high frequency response. In addition, the apparatus permits the fluid thickness, d, to be varied continuously and in situ from zero to 3 nun, allowing for further consistency in the fluid measurements. This work also includes data for the onset of convection where Q0 > Qc. and Qc corresponds to the heat amplitude at convective onset.*