Enhanced heat conduction in oscillating viscous flows within parallel-plate channels

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Abstract
The hydrodynamics of enhanced longitudinal heat transfer through a sinusoidally oscillating viscous fluid in an array of parallel-plate channels with conducting sidewalls is examined analytically. Results show that for fixed frequency the corresponding effective thermal diffusivity reaches a maximum when the product of the Prandtl number and the square of the Womersley number is approximately equal to α2 Pr = π Under such tuned conditions the axial heat transfer achievable is considerable and can exceed that possible with heat pipes by several orders of magnitude. The heat flux between different temperature reservoirs connecting the parallel-plate-channel configuration is shown, under tuned conditions, to be proportional to the first power of both the axial temperature gradient and the flow oscillation frequency and to the square of the tidal displacements. A large value for the fluid density and specific heat is also found to be beneficial when large heat-transfer rates are desired. The process discussed involves no net convection and hence achieves large heat-transfer rates (in excess of 106 W/cm2) without a corresponding net convective mass transfer. A discussion of the physical origin for this new heat-transfer process is given and suggestions for applications are presented.

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