Design and techno economic optimization of an additively manufactured compact heat exchanger for high temperature and high pressure applications

Abstract

Additive manufacturing (AM) has tremendous potential to produce high-power-density heat exchangers. However, manufacturing AM-heat exchangers at a competitive cost impedes their commercial adoption. In this paper, a novel design of an AM counter flow pin–fin compact recuperator, and its manufacturing costs when using laser powder bed fusion method, are presented. The compact recuperator, which can operate at a high temperature of 800 °C, a high fluid pressure (250 bar) on the cold side and withstand a differential pressure of 170 bars across the fluid streams, as seen in supercritical carbon dioxide power cycles, is designed for a lifetime of 40,000 h. Numerical models to predict the thermo-fluidic performance, and a simplified mechanical model based on plate theory to predict the mechanical stresses, of the recuperator are presented. The recuperator's thermal performance and compactness are studied, and its manufacturability is evaluated via a multi-objective techno-economic optimization. The optimization process considers thermo-fluidic, structural, and manufacturing constraints. The recuperator was fabricated using Haynes 282, and the printability of the design features using a laser-powder-bed-fusion machine is demonstrated. The choice of employing two different AM machines, with different build plate dimensions, number of lasers, and design constraints, on the recuperator's cost/unit, cost/UA, and cost/kW-th o are examined. It is observed that the cost/UA and cost/kW-th decrease exponentially from 13,839 USD-K/kW to 1,994 USD-K/kW and from 80 USD/kW-th to 18 USD/kW-th, respectively, with the size and thermal rating of the recuperator. The exponential decrease in cost/UA and cost/kW-th with increase in power rating opens the possibility of manufacturing large-scale additively manufactured recuperators at a competitive cost. The recuperator, including headers, can achieve a maximum volumetric heat density of 200 MW/m3. The optimization framework can be used to obtain optimal pin-array heat exchanger dimensions for other applications and materials using laser powder bed fusion method.