This paper constructs a flat heat pipe model suitable for medium and low temperature thermal energy storage scenarios (50-150°C). The pipe is 200 mm long and 50 mm wide, and uses a copper-based wick (porosity 0.65) and deionized water as the working fluid. The COMSOL simulation analysis is performed. Results show that at a heat source temperature of 100°C and a heat load of 500 W, the temperature difference between the center and edge of the evaporator reaches 17°C. In contrast, the temperature difference in the condenser is only 3°C. Heat transfer efficiency increases with heat load, reaching 89.2% at 800 W under 100°C, significantly higher (p < 0.05, one-way ANOVA) than 86.1% at 80°C and 88.5% at 120°C. Heat storage capacity reaches a maximum of 14,580J at a tube length of 200 mm and a porosity of 0.65, a 13.6% increase over the 150 mm tube length model, calculated as [(14580-12840 J)/12840 J]×100%. The 10-hour heat loss rate is 5.1% at a porosity of 0.65. While the loss rate is slightly lower (4.8%) at a lower porosity (0.55), the heat storage capacity is insufficient. This study provides a parameter optimization basis for heat pipe design in medium and low temperature waste heat recovery systems.