PERFORMANCE ENHANCEMENT OF A HIGH-CONCENTRATION RATIO PARABOLIC TROUGH SOLAR COLLECTOR USING SUPERCRITICAL CO2 WITH A MODIFIED TWISTED TAPE INSERT

The parabolic trough solar collector (PTSC) technology is the most technically and commercially developed concentrating solar power (CSP) technology. However, several research initiatives are still needed to make it cost-competitive, such as increasing the PTSC’s concentration ratio, using cheaper working fluids with desirable thermal transport properties, and enhancement of the receiver heat transfer performance in order to reduce temperature gradients and increase the system’s overall efficiency. Supercritical CO2 (sCO2) is favored as a working fluid for next-generation PTSCs due to its availability, affordability, and stability at high temperatures. However, given that sCO2 has poor temperature-dependent thermal transport properties, enhancing the heat transfer performance of receivers using it becomes critical. In this study, a combined and thoroughly validated approach using Monte Carlo ray tracing for optical analysis and computational fluid dynamics (CFD) simulation for thermo-hydraulic modeling were used to determine the influence of a novel twisted tape insert on the overall performance of a high-concentration ratio PTSC using sCO2 as the heat transfer fluid. Numerical simulations were performed for a PTSC with a concentration ratio of 121, sCO2 operating pressure of 8 MPa, inlet temperature of 700 K, Reynolds number ranging from 137,000 to 3,428,000, and twist ratios ranging from 2 to 4. Results show that the twisted tape insert improves the heat transfer performance by up to 73% compared to a plain receiver tube. However, the use of smaller twist ratios of the twisted tape improves heat transfer but increases friction factor and pumping power needs.