3D Printed Air-Side Heat Transfer Surfaces for Air-Cooled Heat Exchangers

The objective of this Department of Energy ARPA-E project is to improve the thermal efficiency of dry-cooled condensers by reducing the air-side thermal resistance without significantly increasing either the capital cost or the fan power required to operate these devices. This project applies the additive manufacturing via Fused Filament Fabrication (FFF) to develop air-cooled heat exchangers. The designs of the air-side heat transfer surfaces are dictated by FFF manufacturing constraints as well as by the thermal-fluid performance. The FFF additive manufacturing technique that allows unprecedented design freedom for the optimization of the air-side heat transfer surfaces, leading to a substantial enhancement in the overall heat transfer coefficient. The performance targets for the proposed 3-dimensional heat exchanger are 7.8 kW of heat transfer rate, $10/kW, and a COP greater than 200.

In order to produce competitive and effective plastic heat exchangers, the base polymer material should be strong at elevated temperatures, and the thermal conductivity of the matrix should be enhanced with fillers. Due to their high thermal conductivity and relative cost-effectiveness, copper, carbon fiber, graphite, and aluminum fillers have been investigated in a PA6 and a PC matrix. Small batches are compounded and benchmarked, then filament is produced at the PEC via twin screw and/or single screw extrusion. Computational fluid dynamics is used to model the air flows over the heat exchange surfaces in order to understand their relationship to the heat transfer, which can then be used to optimize the geometry. The materials, design and manufacturing constraints all interact to govern the key outcomes of the project: high performance and low cost.