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.
Integrated PCB active cooling with piezoelectric actuator
Thermal management is challenging in RF communication and radar systems that require high-power levels for operation and reliability as well as small footprints to control intrinsic losses and meet design constraints. An interesting approach uses discrete, in-situ fluid handling and embedded synthetic jet drivers to enhance local cooling at the component. In this approach, fluid cavities and actuators are integrated into the PCB near the component. Magnetic and piezoelectric actuators have proven effective in other less-demanding applications. The challenge to adapting from magnetic to piezoelectric actuators is to achieve high flowrates because piezo-actuators have lower displacement and higher frequencies. This investigation explores frequency and displacement effects on cooling rates for piezo-actuators embedded in PCB. Further concept development includes integration with thermal ground planes.
Evaluation of CuAl2O4 as an Oxygen Carrier in Chemical-Looping Combustion
The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with intrinsic separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor where the fuel, or gasification products of the fuel, reacts with the solid oxygen carrier. In this work, copper(II) aluminate (CuAl2O4) was assessed as a potential oxygen carrier using methane as fuel. The carrier particles were produced by freeze–granulation and calcined at 1050 °C for a duration of 6 h. The chemical-looping characteristics were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900–950 °C during 45 alternating redox cycles. The oxygen carrier exhibited reproducible and stable reactivity behavior in this temperature range. Neither agglomeration nor defluidization was noticed in any of the cycles carried out at 900–925 °C. However, after reactivity tests at 950 °C, soft agglomeration and particle fragmentation were observed. Systematic phase analysis of the Cu–Al–O system during the redox cycle was carried out as a function of duration of reduction and oxygen concentration during the oxidation period. It was found that the CuAl2O4 is reduced to copper(I) aluminate (CuAlO2; delafossite), Cu2O, and elemental Cu. The CuAlO2 phase is characterized by slow kinetics for oxidation into CuO and CuAl2O4. Despite this kinetic limitation, complete conversion of methane with reproducible reactivity of the oxygen carrier is achieved. Thus, CuAl2O4 could be a potential oxygen carrier for chemical-looping combustion.