Heat transfer enhancement in oscillatory flows of Newtonian and viscoelastic fluids

The work by U.H. Kurzweg for the enhanced longitudinal heat transfer of a Newtonian fluid in zero-mean oscillatory laminar flows in tubes subjected to an axial temperature gradient [U.H. Kurzweg, J. Heat Transfer 107 (1985) 459–462] is generalized for the case of a viscoelastic Maxwell fluid. While Kurzweg discovered that a Newtonian fluid exhibits a single maximum value of the effective diffusivity for a specific oscillation frequency, several maxima for different resonant frequencies are found in the case of the Maxwell fluid. The absolute maximum of the enhanced thermal diffusivity for the viscoelastic fluid and, consequently, the axial heat transfer in the tube, may be much higher than those for the Newtonian fluid. Since this absolute maximum increases as the radius of the tube decreases, a possible application may be to improve the efficiency of micro- and nano-thermal devices through the enhancement of the heat transfer rates in those devices. We provide two specific examples of heat transfer enhancement: a standard viscoelastic fluid (CPyCl/NaSal) oscillating in a macroscopic tube (scale of centimeters) and water oscillating at high frequencies in a tube of nanometric scale under conditions similar to those used experimentally in water nanoresonators.