Thermal Resistance Effects in Additively Manufactured Polymer Heat Exchangers for Latent Heat Energy Storage

Abstract

Polymer heat exchangers are attractive for compact thermal energy storage (TES) systems due to their compatibility with additive manufacturing, corrosion resistance, and geometric flexibility; however, their low thermal conductivity introduces uncertainty regarding achievable performance. This study experimentally evaluates additively manufactured polymer heat exchangers using lithium nitrate trihydrate (LiNO3·3H2O) as a phase change material (PCM) and investigates the influence of wall thickness and system geometry on TES behavior. Two polymer heat exchangers with wall thicknesses of 0.55 mm and 0.75 mm were fabricated using vat photopolymerization and tested under controlled melting and freezing conditions. At a flow rate of 200 mL/min, the 0.55 mm configuration achieved an average heat transfer rate of 74 W, an overall heat transfer coefficient of 184 W/(m2·K), and an effectiveness of 0.49. Increasing wall thickness resulted in only minor changes in performance, indicating limited sensitivity to wall conduction resistance within the range considered. Comparison with a geometrically similar aluminum heat exchanger shows that comparable heat transfer rates can be achieved at intermediate flow conditions. However, the polymer configurations exhibit reduced total energy transfer due to incomplete PCM utilization associated with larger characteristic encasement length scales. These results highlight the distinction between rate-limited and capacity-limited performance in TES systems. The findings demonstrate that system performance is governed primarily by geometric design and PCM-side heat transfer rather than material conductivity alone, and suggest that polymer heat exchangers designed to reduce PCM length scales can achieve competitive TES performance.