Compact Condensers Enabled by Additive Manufacturing

The project goal is to develop an ultra-compact water-cooled condenser heat exchanger (HX) using generative design algorithm (GDA) and additive manufacturing (AM). The condenser HX will use fresh water at 25°C to remove 50kW of heat from condensing R134a at 35°C or lower saturation temperature. The project aims to design a HX with high power density while minimizing pressure drop. The approach presented in this project has shown that additive manufacturing can enable more complex structures yielding to heat transfer enhancement through internal structures and novel heat exchanger designs. A 50 kW water-cooled condenser heat exchanger with a power density of 27 MW/m3 was designed during Phase I of this project.  The high-power density is enabled by a novel 3D spiral geometry and additive manufacturing. Throughout this project, a generative design software tool designed to automatically find the highest performing and most efficient designs and optimized fin shapes has been developed and verified through experimental validation. The validation was achieved by generating a scaled-down heat exchanger design with the model and fabricating an additively manufactured prototype. A test facility containing an R134a refrigeration system was customized to incorporate the prototype and to enable experimental investigation. Furthermore, this system was designed to allow testing under off-design conditions such as two-phase inlet to the condenser. The prototype heat exchanger was tested over a range of operating conditions and achieved heat transfer as high as 5.4 kW successfully meeting the smaller scale design targets. The results indicate that the model predicts capacity and refrigerant side pressure drop very well and the prototype performed consistently over a period of 6 weeks. To our knowledge, this is the first demonstration of an AM heat exchanger in an R-134a condensing / freshwater coolant application. The simulation tool was used to generate a variety of heat exchanger designs and showed trade-offs between power density and pressure drop. In addition, it was shown, that the proposed designs have higher power density compared to commercial 50 kW heat exchangers. The manufacturability, scalability, and cost of the proposed heat exchanger were evaluated and show that the selected spiral design has several advantages. We explored and identified transition opportunities and propose to proceed with Lockheed Martin and HII as the main Phase II transition partners which positions a potential Phase II effort well to design, fabricate, and test prototypes to meet specific shipboard conditions and applications.