Hygroscopic film integrated with the fin structure: a long-term cooling solution for fin heat exchanger

Abstract

Integrating the hygroscopic heat dissipation layer with the fin represents an innovative approach to enhance the heat transfer coefficient, while simultaneously reducing the overall volume, weight, and material requirements for the fin heat exchanger. However, designing a hygroscopic layer that seamlessly integrates with the fin structure, has an excellent hygroscopic heat dissipation effect, and long-term enhanced heat dissipation after the liquid has dissipated poses a significant challenge. Here, we report a flexible, self-adhesive, adjustable thickness, high heat transfer coefficient desorption radiation film (DRF) for long-term heat dissipation enhancement through integrating desorption cooling and radiation-enhanced cooling, along with controlling the thermal resistance for conduction. Using a hydrophilic sodium alginate-CaCl2 crosslinked adsorption medium and polyvinyl alcohol to enhance radiation and adhesion properties, a porous hygroscopic film is fabricated with fast moisture adsorption, no leakage, high emissivity, controllable thermal resistance, and strong adhesion. The flexible film can be directly attached to the fin surface, maintaining the original advantages of the fin structure with minimal modification, making it excellent in adhering effectively. Compared to an aluminum plate, the system reduces the temperature rise rate by 21.3 times and lowers the steady-state temperature by 9℃ even staying lower than the graphene-coated surface over time. After three cycles (1 hour for desorption and 1 hour for adsorption in each cycle), the cooling efficiency only decreased by 4%, showing minimal impact from the short adsorption time. After applying to the real fins and optimizing the corresponding structure, the cooling down of the same volume reaches 8.5℃, and the heat transfer coefficient is increased by 18%. In photovoltaic panel tests, the system reduced temperature by 3.5℃. Our strategy offers a novel, simple, cost-effective solution for long-term enhanced heat dissipation of fin heat exchangers, while also providing insights into desorption cooling for reducing heat transfer resistance.