Stirlingengineforum.com

One of my ideas is to use flattened tubing to increase surface area and heat capacity. The evenly flattened tube has a rectangular path for the gas to flow, and the flat shape lends itself for heat transfer in either direction. The increased amount of metal per unit volume of gas should also increase heat capacity. It is known that a rectangular port flows more freely than a circular if it is bent along the longitudinal axis. The counter argument is that increased internal surface area equals increased friction. I will be putting this to the test in my v-twin compressor conversion......if the tube bending doesn't give me arthritis, that is. It should help me keep dead volume down, also.

You mean like this?

For a small engine, yes. For a big stirling engine, no. This is what I mean for the large stirling engine. The flat jawed geared pliers are made by knipex and are a favorite among many.