Okke Ouweltjes

Synthetic Jet Cooling Part II: Experimental Results of an Acoustic Dipole Cooler

The paper discusses experimental results for a typical embodiment of synthetic jet cooling technology: an acoustic dipole cooler comprised of a standard loudspeaker in a housing provided with two pipes. A transient measurement set up is used to measure the average heat transfer coefficient based on cooling a 5*5 cm2 metal plate. Heat transfer and noise results are presented for a range of frequencies, pipe lengths and diameters. The results are compared with a standard 60*60 mm fan. It is concluded that, at least for the cases studied, the synthetic jet is superior on all fronts: heat transfer performance, noise level and dissipated power.

Finite difference time domain electroacoustic model for synthetic jet actuators including nonlinear flow resistance

A lumped element electroacoustic model for a synthetic jet actuator is presented. The model includes the nonlinear flow resistance associated with flow separation and employs a finite difference scheme in the time domain. As opposed to more common analytical frequency domain electroacoustic models, in which the nonlinear resistance can only be considered as a constant, it allows the calculation of higher harmonics, i.e., distortion components, generated as a result of this nonlinear resistance. Model calculations for the time-averaged momentum flux of the synthetic jet as well as the radiated sound power spectrum are compared to experimental results for various configurations. It is shown that a significantly improved prediction of the momentum flux-and thus flow velocity-of the jet is obtained when including the nonlinear resistance. Here, the current model performs slightly better than an analytical model. For the power spectrum of radiated sound, a reasonable agreement is obtained when assuming a plausible slight asymmetry in the nonlinear resistance. However, results suggest that loudspeaker nonlinearities play a significant role as well in the generation of the first few higher harmonics.

Synthetic Jet cooling using asymmetric acoustic dipoles

In two earlier papers [1, 2] the principles and experimental results have been discussed for a typical embodiment of synthetic jet cooling technology: an acoustic dipole cooler comprised of a standard loudspeaker in a housing provided with two pipes. The current paper shows experimental and numerical results for another type: the asymmetric dipole. Basically, this type consists of a loudspeaker with a minimal volume attached to it with one or more holes with or without pipes. Results for driving power and noise are presented for a number of actuators covering a large parameter space: frequency, pipe dimensions and driving voltage were varied over a large range. A relatively simple acoustic model extended to include separation losses matched the experimental results very well. The results indicate promising heat transfer performance with minimal noise combined with a large degree of freedom.

An electro-acoustic implementation of tibetan bowls: Acoustics and perception

Tibetan singing bowls are employed worldwide for meditation, music, relaxation, personal wellbeing, and religious practices. Each Tibetan bowl can produce a limited number of sounds, defined by the size and material of the bowl, and the actuator device used. Usually, there is a need for a second person to actuate the bowl. Addressing these limitations, we built an electronic device, named eBowl, which can mimic the acoustics of Tibetan bowls, and beyond that, can produce a wide range of other sounds. Furthermore, it can be used for relaxation and sound massage without the need for a second person. The eBowl generates auditory beats that are in EEG alpha frequency range, which can cause brainwave entrainment and lead to relaxation. User tests measuring physiological parameters revealed the eBowls effectiveness for relaxation, showing that eBowl influences skin conductance, heart rate, and respiration rate and induces relaxation.