Rankine Cycle

Hi Norm – I am an ME and working with an associate who is not technically inclined. I am trying to provide him a layman’s explanation as to why the waste heat in a condensing turbine is unrecoverable for process uses and why a topping turbine is so much less efficient at making electricity than a condensing turbine.

            Do you know of anything that explains these principles in simple terms or with an illustration?

--Kerry, Florida

            Kerry – When steam expands into a vacuum, its volume gets a lot bigger. At a bigger volume, the steam’s velocity is much greater. It’s the velocity of the steam striking the turbine wheels that spin the turbine. Like the wind causing a windmill to turn. The faster the steam or air, striking the turbine blades, or the air striking the windmill sails, the more work that can be extracted (or electric power, which is work) from the spinning turbine.

--Norm