The heat transfer performance of nitrogen PHPs with different heat transmission distances (100 mm and 500 mm) and tube configurations (single-loop and complex-loop) were experimentally investigated. Experiments were conducted in the vertical bottom heat mode with different filling ratios (15 %–70 %). The results showed that the maximum effective thermal conductivity increased proportionally with the heat transmission distance whereas the thermal resistance remained constant (0.2 K/W at a filling ratio of 31.8 %). This verified the outstanding long-distance heat transfer advantage of the nitrogen PHP. Experiments at different filling ratios showed that the maximum thermal conductivity decreased as the filling ratios increased. A filling ratio of 31.8 % was recommended. Under this operating condition, the PHP can load the maximum heat input while exhibiting relatively high effective thermal conductivity. Compared to the single-loop configuration, the complex-loop exhibited higher effective thermal conductivity, and this enhancement in thermal performance was more pronounced for the longer PHP.