Acceleration effect on operating behavior of a visual loop heat pipe without a bayonet

This study proposes a newly designed ammonia-stainless steel dual compensation chamber loop heat pipe without a bayonet and experimentally investigates its operating performance under high acceleration (3–15 g) across four typical directions (A, B, C, and D), thermal loads (30–400 W), and heat sink temperatures (10–25 ℃), using visual windows at the ends of the two compensation chambers to observe the internal vapor–liquid phase distribution. Experimental results indicate that (i) higher thermal loads increase operational temperature while thermal conductance initially increases and then stabilizing or decreasing, with stable operation achieved even under the most adverse direction A of 30 W and 9 g; (ii) directional effects are significant, with operational temperature decreases and thermal conductance increases sequentially from directions A to D. Direction D yields the lowest operational temperature of 27.8 ℃ at 3 g and 150 W, and highest thermal conductance of 23.12 W/K at 12 g and 200 W; (iii) vapor backflow may occur in the liquid pipe before startup in direction C, while high thermal loads operating during steady state could induce two-phase states in both condenser and liquid pipe; (iv) increased acceleration degrades operational performance in direction A, but slightly increases temperature in directions C and D, with thermal conductance varying by thermal load; and (v) higher heat sink temperature elevates operational temperature and thermal conductance while altering two-phase distribution in both the liquid pipe and condenser.