“…In [11], the actual pipes are deployed in a helical coil pattern. Other enhanced double-pipe heat exchangers involved features such as [12,13] (fins), [14] (louvered strips), [15] (ring protuberances), [16] (twisted inner square tube in an outer circular tube), [17] (bulbous protrusions in the inner tube wall), and [18,19] (two helically-wrapped circular tubes). The literature involving corrugated double pipe heat exchangers is virtually exclusively concerned with experimentation.…”