Abstract:
The effect of pulsating laminar flow of a Bingham plastic fluid on heat transfer from a
constant temperature cylinder is studied numerically over wide ranges of conditions as
Reynolds number (0.1 Re 40) and Bingham number (0.01 Bn 50) based on the
mean velocity, Prandtl number (10 Pr 100), pulsation frequency (0 x* p), and
amplitude (0 A 0.8). Results are visualized in terms of instantaneous streamlines, isotherms, and apparent yield surfaces at different instants of time during a pulsation cycle.
The overall behavior is discussed in terms of the instantaneous and time-averaged values
of the drag coefficient and Nusselt number. The size of the yielded zone is nearly in phase
with the pulsating velocity, whereas the phase shift has been observed in both drag coefficient and Nusselt number. The maximum augmentation (30%) in Nusselt number occurs
at Bn ¼ 1, Re ¼ 40, Pr ¼ 100, x* ¼ p, and A ¼ 0.8 with respect to that for uniform flow.
However, the increasing yield stress tends to suppress the potential for heat transfer
enhancement. Conversely, this technique of process intensification is best suited for Newtonian fluids in the limit of Bn ! 0. Finally, a simple expression consolidates the numerical values of the time-averaged Nusselt number as a function of the pertinent
dimensionless parameters, which is consistent with the widely accepted scaling of the
Nusselt number with Pe1/3 under these conditions
