Jones writes: "it was claiming that there was neither room nor extra mass for fins or channels. I listed that as the caveat. Rossi also says the water flow is straight thru." Ever look at how a steam locomotive boiler is constructed? The flow is straight thru and the heat xfer surface area is many many times the surface area of the outer enclosing cylinder. I posted a reply about this and attached a jpeg, but I guess Bill hasn't had time to let it thru the filter. Come to think about it, a nuclear reactor core looks similar, but is vertically oriented instead of horizontal...
-Mark
