Isothermal velocity measurements in two HyperVapotron geometries using Particle Image Velocimetry (PIV)

Abstract

HyperVapotron beam stopping elements are high heat flux devices able to transfer large amounts of heat (of the order of 10–20MW/m2) efficiently and reliably making them strong candidates as plasma facing components for future nuclear fusion reactors or other applications where high heat flux transfer is required. They employ the Vapotron effect, a two phase complex heat transfer mechanism. The physics of operation of the device are not well understood and are believed to be strongly linked to the evolution of the flow fields of coolant flowing inside the grooves that form part of the design. An experimental study of the spatial and temporal behaviour of the flow field under isothermal conditions has been carried out on two replicas of HyperVapotron geometries taken from the Mega Amp Spherical Tokamak (MAST) and the Joint European Torus (JET) experiments. The models were tested under three isothermal operating conditions to collect coolant flow data and assess how the design and operational conditions might affect the thermal performance of the devices for single phase heat transfer. It was discovered that the in-groove speeds of MAST are lower and the flow structures less stable but less sensitive to free stream speed perturbations compared to the JET geometry. The MAST geometry was found to suffer from hydrodynamic end effects. A wake formation was discovered at the top of the groove entrance for the JET geometry, while this is absent from the MAST geometry. The wake does not affect significantly the mean operation of the device but it may affect the coolant pumping load of the device. For the JET variant, there is evidence that the typical operation with free stream flow speed of 6m/s is advantageous.