Abstract
Either top or bottom wall temperature of an infinite horizontal fluid layer is time-dependently and sinusoidally oscillated with the constant average temperature on the opposing horizontal wall. This is the system with no temperature difference between the top and bottom walls in a time-averaged sense, as studied by Kalabin et al. for a square channel. The fluid is Newtonian and Boussinesq approximation is made. The fluid layer of height 1 versus the horizontal width 4 is adopted and numerical computation is carried out. The time-averaged heat flux is always positive, i.e., upward, even if the time-averaged temperature difference is zero between the top and bottom walls. This holds even if the oscillating temperature is on either the top or bottom walls.
