Experimental investigation of the effect of multiple synthetic jets on heat transfer and pressure loss in minichannels

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Synthetic jets can enhance minichannel thermal performance by adding net momentum flux into a fluid stream without adding mass flux. When incorporated into minichannels, these jets can impinge on the far wall, disrupt boundary layers, and enhance mixing within the channel, leading to high heat transfer coefficients. Many researchers have examined the effects of synthetic jets in microchannels and minichannels with single- and multi-phase flows using various fluids. This study aims to characterize the use of synthetic jets in minichannels that utilize an aqueous-glycol mixture with multiple jets along the length of a channel. Previous research has shown the use of synthetic jets can augment local heat transfer coefficients by two to three times the value of steady flow conditions using refrigerant as the working fluid. In this investigation, average heat transfer coefficients and pressure loss were measured experimentally for a range of synthetic jet operating conditions. Experiments were conducted with a minichannel array containing embedded thermocouples in order to directly measure local wall temperatures. Wall temperature measurements taken at various locations along the channel indicated that when synthetic jets were used the average heat transfer coefficient along the channel increased up to 81%. The effects of momentum ratio, frequency, and bulk Graetz number on heat transfer and pressure loss is presented. This research shows that by using a synthetic jet array the pressure loss (i.e., pumping power) can be reduced by 78% while maintaining the heat transfer coefficient. Finally, an empirical correlation is presented that predicts the heat transfer enhancement due to synthetic jets over the range tested that has a mean absolute error (MAE) of only 5.5%.