Investigation of the cooling performance of a radiative sky water-cooling module with serpentine channels: experiments and CFD simulation

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The radiative sky water-cooling module (RSWCM) utilizes a radiative cooling surface to reject heat to the cold sky, thereby cooling circulating water. This technology has potential applications in building energy savings, auxiliary cooling in air-conditioning systems, and condenser cooling in power plants. While previous research to enhance cooling performance has focused primarily on optimizing the optical properties of radiative cooling materials, the influence of internal flow-channel structures on water-side heat transfer in RSWCMs remains inadequately investigated. To address this gap and enhance water-side heat transfer through optimized internal flow routing, this study proposes a serpentine-channel RSWCM and comprehensively evaluates its dynamic cooling performance through outdoor experiments and numerical simulations. The results reveal that the serpentine channel re-routes the internal flow, leading to a moderate increase in the average cooling power from 65.18 to 66.72 W/m 2 . Increasing the channel number enhances water-side heat transfer, albeit with diminishing marginal returns in cooling gain. Furthermore, as the channel height increases from 5 to 15 mm, the average cooling power decreases from 65.59 to 49.44 W/m 2 , indicating that a smaller channel height is more advantageous for water-side cooling performance. Increasing the flow rate from 30 to 480 mL/min raises the average cooling power from 58.50 to 71.94 W/m 2 , but simultaneously reduces the average temperature drop from 2.46 to 0.21 °C. Additionally, as the tilt angle increases from 0° to 90°, the average cooling power decreases from 66.59 to 33.61 W/m 2 , indicating that a horizontal orientation is preferable under the investigated nighttime conditions.