Experimental study on thermal performance of a loop heat pipe with a bypass line

The loop heat pipe with both flat evaporator and boiling pool (NLHP) has much higher maximum heat flux than conventional loop heat pipe (LHP). However, the serious temperature overshoot and the startup time difference between the evaporator and boiling pool have become a bottleneck of the NLHP. In this study, a loop heat pipe with a bypass line (BLHP) is proposed to improve the startup characteristics of the NLHP. The effects of the bypass line, time difference, boiling pool heat load and evaporator heat load on the thermal performance of the BLHP are experimentally investigated. The results indicate that the bypass line, which is installed between the condenser outlet and the first vapor line, accelerates the return of working fluid and reduces the adverse effect of the heat leakage. The temperature overshoot is virtually eliminated and the BLHP can operate stably at various evaporator and boiling pool heat loads under a broad range of time differences. Furthermore, the BLHP reduces the heating wall temperature by 3.9–8.1 °C and thermal resistance by more than 10% under various heat loads compared with the NLHP. While maintaining the heating wall temperature within 85 °C, the maximum heat flux is 39.3 W·cm⁻², which is much higher than most conventional LHPs using methanol as working fluid.