Liquid metal based magnetic cooling: velocity measurements

Heat transfer enhancement in a segment of the active magnetic regenerator (AMR), consisting of a magnetocaloric material (Gadolinium) and a heat transfer fluid in between, which is periodically magnetized and demagnetized, is investigated in this work. After giving a brief account on how magnetohydrodynamic (MHD) convection can be used to enhance the heat transfer from flat plate gadolinium toward the heat transfer fluid we apply two different techniques for MHD flow generation. In the first approach, an electric current I was injected into an electrically conducting, aqueous heat transfer fluid (NaOH). A heat transfer enhancement of about 40% (I=3mA) was found by means of a Mach-Zehnder interferometer. In the second approach, a liquid metal (GaInSn) was used which is potentially an interesting candidate for a heat transfer fluid in an AMR operating with high cycling frequency. Velocity measurements by means of ultrasound doppler velocimetry with a quasi uniform static magnetic field (220mT) in the gadolinium channel are presented.