The Closed Feedwater Heaters with Cascaded Drains receive two liquid flows and one steam flow. This configuration is used in a large number of power plants, both nuclear and fossil-fueled.

Cold feedwater enters from the bottom and flows inside a tube. It is first preheated by the condensate from the downstream feedwater heater, then by heat exchange with the steam, before being directed downstream.

The condensing steam mixes with the condensate coming from downstream, with the total condensed flow being directed upstream.

The Thermoptim model includes an external three-branch inlet mixer and an external two-branch outlet divider