Helical tube bundle arrangements for heat exchangers

A heat exchanger for underwater operation comprising:

• a plurality of tube bundles each being a same first length that extends from a first end of the plurality of tube bundles to a second end of the plurality of tube bundles, each tube bundle comprising a plurality of tubes helically wound about a central axis, each tube configured to carry a fluid from a first tube end to a second tube end;
• a plurality of tube shrouds being the same first length, each tube shroud circumferentially enclosing a respective one of the tube bundles and forming a passage about the respective one of the tube bundles that is fluidically isolated from the tubes of the respective one of the tube bundles;
• a first tube sheet fixed with respect to first ends of the plurality of tube shrouds and having a plurality of first openings configured to facilitate a flow of separate fluids through the plurality of tube shrouds and the plurality of tube bundles;
• a second tube sheet fixed with respect to second ends of the plurality of tube shrouds and having a plurality of second openings configured to facilitate the flow of the separate fluids through the plurality of tube shrouds and the plurality of tube bundles;
• and
• a shell coupled to the first tube sheet and to the second tube sheet and defining a chamber in which the plurality of tube shrouds is disposed.