A coaxial-flow heat exchanging structure for installation in the Earth, and facilitating the transfer of heat energy in an aqueous-based heat transfer fluid, between said aqueous-based heat transfer fluid and material beneath the surface of the Earth, said coaxial-flow heat exchanging structure comprising:
- a proximal end and a distal end;
- an input port, provided at the proximal end, for receiving said aqueous-based heat transfer fluid at a first temperature from a heat exchanging subsystem, and an output port, provided at the proximal end, for outputting said aqueous-based heat transfer fluid at a second temperature to said heat exchanging subsystem;
- an inner tube section having an outer wall surface extending between the proximal and distal ends, the inner tube section supporting an inner flow channel having a substantially uniform inner diameter along its length and along which the aqueous-based heat transfer fluid can flow in a substantially laminar manner;
- a thermally-conductive outer tube section, disposed coaxially around said inner tube section, and having an inner wall surface extending between said proximal and distal ends, and a cap portion at said distal end sealing off said thermally conductive outer tube section from fluid leaks at said distal end;
- wherein an outer flow channel is formed between the outer wall surface of the inner tube section and the inner wall surface of said thermally-conductive outer tube section, and is capable of conducting said aqueous-based heat transfer fluid flowing from the distal end of said inner flow channel, and past said cap portion, and along said outer flow channel towards said proximal end, so that said aqueous-based heat transfer fluid can exit from said output port and flow into said heat exchanging system;
- wherein a helically-arranged fin structure is disposed along a portion of said length of said outer flow channel so as to introduce turbulence into the flow of said aqueous-based heat transfer fluid flowing along said outer flow channel, thereby improving the transfer of heat energy between the aqueous-based heat transfer fluid and material beneath the surface of said Earth along the length of outer outer flow channel;
- wherein the heat transfer process occurring between said aqueous-based heat transfer fluid and material beneath the surface of said Earth is carried out without a change in state of said aqueous-based heat transfer fluid flowing within and along said inner and outer flow channels of each said coaxial-flow heat transfer structure;
- and
- wherein the cross-sectional dimensions of said outer flow channel produce fluid flows therealong having optimal vortex characteristics that optimize heat transfer between said aqueous-based heat transfer fluid within said outer flow channel and the inner wall surface of said thermally-conductive outer tube section.