 As a result of these limitations, different solutions involving structural modifications to the conventional heat pipe have been proposed.Some of these modifications incorporate arterial tubes with considerably low hydraulic resistance for liquid return to the heat source (arterial heat pipes), while others provide spatial separation of the vapor and liquid phases of the working fluid at the transportation section (separated line heat pipes).Though these new forms of heat pipes are able to transfer significant heat flows and can increase heat transport length, they remain very sensitive to spatial orientation relative to gravity.