Thermal analysis of piezoelectric actuators for active cooling of RF phased array radars
RF communications and radar systems present an extreme thermal management challenge. These systems are comprised of tightly packaged high wattage components requiring a controlled temperature to meet performance and reliability parameters. One approach being pursued to meet this thermal challenge is embedding piezoelectric actuators within the electronics to create synthetic air jet drives for localized cooling. U.S. Army AMRDEC is developing and testing actuator test beds to mature the concepts and develop practical solutions. This investigation attempts to model these actuators in a CFD thermal analysis program, verify the results of the models with the current test beds, and then insert the model in conceptual designs of phased array antennas. The goal of the investigation is to gain insight into the practical application of a maturing thermal management concept in a real world application. These cooling devices have achieved over 2.5 W/cm2 cooling capacity in a 1.3 cm3 package.
Local Convective Heat Transfer From a Constant Heat Flux Flat Plate Cooled by Synthetic Air Jets
The effects of a small-scale, rectangular synthetic air jet on the local convective heat transfer from a flat, heated surface were measured experimentally. The synthetic jet impinges normal to the surface and induces small-scale motions by zero-net mass flux, time-periodic entrainment, and ejection of ambient air at frequencies whose periods are far higher than the characteristic thermal time scale. The velocity field between the jet orifice and the target plate is measured in planar cross sections using particle image velocimetry and is related to the local heat transfer from the plate. The present work suggests that synthetic jets can lead to substantial enhancement of the local heat transfer from heated surfaces by strong mixing that disrupts the surface thermal boundary layer. The dependence of the local heat transfer coefficient on the primary parameters of jet motion is characterized over a range of operating conditions.
Preparation of hydrophilic poly(vinyl butyral) hollow fiber membrane via thermally induced phase separation
Abstract Hydrophilic microporous hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Poly(vinyl butyral) (PVB) and three kinds of polyethylene glycols (PEG) with the molecular weight of 200, 400 and 600 were used as polymer and diluents. In all cases, liquid–liquid (L–L) phase separation occurred and asymmetric cellular structures with the smaller pores at the outer surface were obtained. The properties of membranes such as pore size, water permeability, solute rejection and intensity were investigated by changing molecular weight of PEG, concentration of PVB, composition of the bath and air gap distance. The smaller molecular weight of PEG, the more PEG in the bath and the shorter air gap distance resulted in the higher water permeability, the lower solute rejection property and the lower mechanical strength.