An electroplating apparatus includes an electrode at the bottom of a chamber, an ionically resistive element with through holes arranged horizontally at the top of the chamber, with a membrane in the middle. One or more panels extend vertically and parallelly from the membrane to the element and extend linearly across the chamber, forming a plurality of regions between the membrane and the element. A substrate with a protuberance extending along a chord of the substrate and contacting a top surface of the element is arranged above a first region. An electrolyte flowed between the substrate and the element descends into the first region via the through holes on a first side of the protuberance and ascends from the first region via the through holes on a second side of the protuberance, forcing air bubbles out from a portion of the element associated with the first region.