The effects of imperfect insulator coatings on MHD and heat transfer in rectangular ducts

The integrity of the electrically insulating coating at the coolant channel walls represents a feasibility issue for a self-cooled liquid metal blanket. The effects of cracks in the insulating layer on MHD pressure drop are investigated, for various crack locations, sizes and resistivities. It is shown that, once the crack resistance exceeds the Hartmann layer resistance, the MHD pressure drop increases significantly. Using the 2-D fully-developed MHD flow code, it has been found that the crack location has a large impact on the MHD pressure drop: for the same crack sizes and resistivities, the pressure gradient increases as the cracks move towards the central plane. The effect of the insulation on heat transfer is discussed. The heat transfer capability is reduced in the presence of the insulator coating.