Experimental characterization of welding joint effects on multi-segment annular wick heat pipe for heat pipe microreactor

Heat Pipe MicroReactors (HPMRs) rely on passively operated heat pipes for core heat removal and energy conversion, making wick manufacturing quality a key reliability concern. Long heat pipes required for HPMR often exceed the practical manufacturing length of a single continuous wick, making welding joints a necessary step – yet their quantitative impact on heat pipe performance remains poorly characterized. This study experimentally evaluates how the number of welding joints (0, 1, and 3) in a manually fabricated SS316L annular-screen wick affects thermal resistance, capillary limit, and local dry-out risk in a 1-m water heat pipe. Rate-of-rise (ROR) test showed localized permeability reductions of up to 62.42% at welding sites, but Darcy's law scaling – validated against a reverse capillary-limit formulation – revealed this translates to only 0.5–1.48% loss in global effective permeability converging to under 1% at HPMR scale (4 m). Steady state test (50–130 W) confirmed stable global vapor core transport, though localized effective thermal conductivity showed non-linear, power-dependent behavior. Deliberate dry-out test at 200 W revealed a counterintuitive relationship; the 3-welding joint outlasted the 1-welding joint by 1089 s, driven by weld-induced flow resistance raising operating temperature and lowering liquid viscosity. These findings show welding joints introduce negligible global performance loss but create non-linear, local uncertainties for HPMR wick design.