This study experimentally examines the heat transfer across surfaces which contact and separate at regular intervals. The results are presented for the case of low contact pressure, moderate interface temperature, equal contact and separation times during a cycle, and identical materials on either side of the contact interface. The results are presented in two basic areas: 1) the behavior of the thermal contact resistance during the quasi-steady state; and 2) the length of time required for the temperature distribution in the material to approach the temperature distribution observed in the quasi-steady-state condition. The results indicate that the thermal contact resistance should not be considered a constant for contacts of short duration; and that relatively few cycles are required for the temperature distribution in the material to approach that observed in the quasi-steady state.
Nomenclature
A-cross-sectional area, m 2 Bi = contact conductance parameter = h c .L/k, dimensionless Fo = Fourier number a t/L 2 , dimensionless h c = thermal contact conductance = l/R c , W/m 2 C h c ss = steady-state thermal contact resistance, W/m 2 C h () = convective coefficient at x = 0, W/m 2 C h -, / = convective coefficient at x = 2L, W/m 2 C k = thermal conductivity, W/mC L = specimen length, m L* = dimensionless length = x/L n = number of cycles required to reach the quasi-steady state, dimensionless Q = heat transfer at the contact interface, W R c = thermal contact resistance, m 2 C/W T(x,t) = generalized temperature distribution, C T c = heat sink fluid temperature, C T /f = heat source fluid temperature, C r* = dimensionless temperature = [T(
x 9 t) -T(2L,t)]/[T(Q,t) -T(2L,t)] t-time variable, s t c = contact time, s x = spatial variable, m a = thermal diffusivity, m/s 2
