Numerical investigation of a three-medium plate-fin latent thermal energy storage unit using two-phase working fluids for compact high-power laser thermal management

Managing transient high-power heat loads under strict mass and volume constraints is a key challenge for high-energy laser systems. Conventional latent thermal energy storage (LTES) systems using single-phase heat transfer fluids experience streamwise temperature variation, which weakens the local thermal driving force and limits power density. This study proposes a three-medium plate-fin LTES unit driven by two-phase working fluids to improve transient charging/discharging performance under compact and lightweight constraints. By exploiting latent heat transport and nearly isothermal phase-change behavior, the working fluids help maintain a higher average thermal driving force along the channel. A finite-volume numerical model was developed to quantify the effects of fin geometry and operating conditions on LTES-unit performance. The results show that the optimized corrugated fin improves phase-change response by balancing fin-PCM interfacial heat transfer and transport resistance, reducing the charging and discharging durations by 6.86% and 5.54%, respectively, compared with rectangular fin. The best-performing design among the investigated cases, with a fin period of 4 mm, amplitude of 1.5 mm, thickness of 0.4 mm, height of 8 mm, and percentage of PCM of 0.8, achieves volumetric and gravimetric power densities of 299.0 kW m⁻³ and 0.285 kW kg⁻¹ during charging, and 294.6 kW m⁻³ and 0.281 kW kg⁻¹ during discharging, respectively. Under the same initial thermal driving force, single-phase water reaches only 45.9% of the power density obtained with the two-phase working fluid, even at a 40-fold higher mass flow rate. These findings indicate that the proposed plate-fin LTES unit using two-phase working fluids is a promising candidate for compact and lightweight thermal management of high-energy laser systems.