I am using anys to create a heat exchanger containing parallel slabs. the heat exchanger is defined as a solid body i need it to be hollow to allow air flow. any ideas?

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I started by sketching the heat exchanger as a solid rectangle and extruded it then i sketched the slabs and extruded them i used bolean to define the heat exchanger without the slabs the empty space between the slabs is not hollow but filled with solid i need air to be passing between the slabs