Air side enhancement of heat transfer in an additively manufactured 1 kW heat exchanger for dry cooling applications

Additive manufacturing is a fast-growing technique due to its ability to fabricate complex objects layer by layer from a preprogrammed digital model. Additive manufacturing can greatly enhance the heat exchanger manufacturing field, as it makes possible the fabrication of complex heat exchanger designs that are challenging to fabricate using conventional methods. In the present work, an air-to-water manifold-microchannel heat exchanger made of titanium alloy (Ti64) with size of 15 cm x 15 cm x 3.2 cm was fabricated using direct metal laser sintering (DMLS) additive manufacturing technique. The manifold-microchannel feeds the fluid flow into an array of parallel microchannels for better flow distribution as well as short flow travel length, thus yielding significantly enhanced heat transfer performance with low pressure drop penalty. Upon successful fabrication, the heat exchanger was experimentally tested, and the results were analyzed against conventional heat transfer surfaces. Based on the experimental results, for the case where the heat exchanger heat flow rate is 900 W, air-side Reynolds number is less than 100 and the temperature difference between the inlet air and water temperature is 27.5°C, heat transfer coefficient of 180 W/m²K and pressure drop of 100 Pa are observed. Compared to the conventional surfaces like wavy fin, louvered fin, and plain plate fins, up to 80%, 120%, and 190% improvement in air-side heat transfer coefficients were recorded, respectively, with an air-side pressure drop of less than 100 Pa. The results strongly suggest that additive manufacturing could be implemented for materials and complex designs that are otherwise difficult to fabricate with conventional technologies.