<p>The extruder is prone to heat accumulation, which could affect production processes. Thus, this study explored the effectiveness of incorporating variable-diameter pulsating heat pipes into an extruder heat exchange system. The gas–liquid two-phase flow process within a pulsating heat pipe extruder was simulated, and the heat transfer effects of pulsating heat pipes with different diameters, as well as the heat transfer effects and temperature distribution of an extruder with a variable diameter condensing pipe, were examined. The findings revealed a substantial enhancement in performance when pulsating heat pipes were employed in the extruder’s heat exchange system, outperforming conventional gravity heat pipes. Specifically, the cooling start-up time was reduced by one-third when variable-diameter pulsating heat pipes were used. Moreover, the maximum temperature difference within the evaporation chamber at the same height was reduced by 5.5 K. This result suggests that the variable-diameter pulsating heat pipes promote a more uniform temperature distribution within the extruder. In summary, the variable diameter pulsating heat pipe demonstrates superior heat transfer efficiency and a more rapid response time than the gravity heat pipe does. This enhanced performance translates into reduced temperatures within the extruder, offering a significant advantage for the thermoplastic extrusion process. This innovation mitigates the risk of heat-related issues during operation.</p>