Tailored flow condensation of low surface tension fluids via additively manufactured gradient wick structures

• A novel 3D-printed gradient wick structure is proposed for enhanced flow condensation of extremely wetting fluids. • The new condenser concept tunes pore size distribution to account for local variations in two-phase flow characteristics. • The gradient wick flow condenser demonstrated an increase in local condensation heat transfer coefficient as vapor quality decreases. • The gradient wick flow condenser showed a 21 % higher normalized power density compared to its uniform counterpart. State-of-the-art enhanced flow condensation techniques perform poorly with low surface tension fluids due to unfavorable filmwise condensation behavior and limited long-term durability. To overcome this challenge, a novel internal flow condenser is developed to tailor flow condensation of commonly used low surface tension fluids by accounting for spatial variations in two-phase flow characteristics. The proposed design conceptualizes gradient wick structures with tuned pore size distributions that reflect the local vapor quality and convective effects as vapor gradually transitions to liquid, while enabling capillary-assisted condensate drainage. Experiments were employed to establish the effectiveness of the gradient wick flow condenser concept against a benchmark uniform wick flow condenser of a similar average porosity. The gradient wick flow condenser, featuring progressively narrowing pores in both longitudinal and lateral directions, not only outperformed the uniform wick flow condenser but also demonstrated a tailored flow condensation performance. In particular, the gradient wick flow condenser unveiled an increase in the local condensation heat transfer coefficient as vapor quality decreases, which is in sharp contrast to conventional flow condensers that suffer declining condensation rates due to condensate film thickening. Additionally, a semi-analytical model was developed to elucidate local flow condensation physics associated with the gradient and uniform wick flow condensers. Findings of the present study underscore the promise of gradient wick flow condensers in enhancing flow condensation performance of extremely wetting fluids such as dielectrics and refrigerants in future thermal management systems.