Development and characterisation of a Ti6Al4V additive manufactured compact counterflow heat exchanger for application in Organic Rankine Cycles

Abstract

Reducing greenhouse gas emissions is a vital component in mitigating the effects of global warming. While engineers across the globe are focused on finding new viable sources of clean energy, increasing the efficiency of current power-producing equipment would alleviate the pressure for finding and implementing these new technologies. Various technologies exist to achieve greater efficiency, including Organic Rankine Cycles (ORCs). These systems have been successfully implemented in various large-scale industrial sectors, capturing and utilising low-grade waste heat from their processes. With great potential for increased efficiency within the domestic sector (less than 10 kW), intricate components in these small-scale systems require advanced traditional manufacturing processes that drive up cost and lead times. The study aims to demonstrate the viability of using additive manufacturing (AM) for component fabrication, specifically focusing on developing and characterising an additively manufactured compact counter-flow heat exchanger for application in ORCs. A theoretical model was developed to size a baseline heat exchanger. The heat exchanger core consisted of 0.5 mm square channels with a length of 30 mm packed in an array. The model was also used to size two more heat exchangers, each with different channel sizes and lengths; one with a core of 1 mm x 40 mm square channels and one with a core of 2 mm x 50 mm square channels. With the preliminary sizing completed, the geometric data from the theoretical model was used to develop CAD models of the heat exchangers for production in Ti-6Al-4V using additive manufacturing. The heat exchangers were then experimentally characterised using a purpose-built test bench, capturing all relevant data. Each heat exchanger was characterised with 12 different flow settings, running five tests per flow setting. The test results were evaluated for validity and processed into useful data for comparison to the mathematical model results. Additionally, computational fluid dynamics analyses were conducted and compared to the theoretical and experimental results. An acceptable level of agreement was obtained between the theoretical, experimental and CFD results.