Acoustically Coupled Heat Transfer Enhancement

Most conventional methods of convective heat transfer enhancement rely on improved mixing via introduction of surface modifications, which entail large disturbances to the mainstream. Accordingly, an enlarged pressure drop penalty is inevitable, and in turn, imposes a restrictive trade-off between increased heat transfer performance at the expense of higher losses. However, determined by the resistance of the thermal boundary layer, convective heat transfer is undoubtedly a surface phenomenon, which takes place where the inertial effects are small with respect to the viscous shear forces. Therefore, in practice, enhancement of heat transfer is possible by acoustic excitation of the fluid. By avoiding surface modifications, this methodology has the capacity to extend the current state-of-the-art in forced convection heat transfer absent of significant pressure drop penalties.

Effect of Perturbation Type on Heat Exchanger Performance

 The research effort is geared towards an improved understanding of the underlying physical mechanisms of aero-thermal laminar and turbulent boundary layer development under the influence of directed sound excitations.To this end,  a versatile small-scale low-speed wind tunnel facility, which can be equipped with various types of acoustic drivers, is built in order to carry out experiments on sound excited heat transfer in forced convection.

Schematic of Experimental Wind TunnelMeasurement of time-averaged convective heat transfer is conducted by means of wide-band liquid crystal (LC) thermometry, which provides high-resolution surface temperature distributions. In order to provide uniform heat flux distribution along the investigation surface, the entire side wall facade is heated by means of a 25μm thick Inconel sheet connected to a 60V-50A DC power supply. The current is dissipated as thermal energy by the Joule effect and, at steady state, the heat is convected away primarily by the fluid in contact. A sample data image, where the color variations depict the temperature distribution along the test section, can be found below.

Thermochromic Liquid Crystals