Abstract
The supercritical carbon dioxide (sCO2) based Brayton cycle is a proposed alternative to replace conventional Rankine cycles in terms of high cycle efficiency, compact turbomachinery and heat exchangers. In the sCO2 cycle, however, the existing heat exchangers have been challenged by large portion of heat transfer (approximately 60–70% of total cycle heat transfer) and high cycle efficiency required. In the present study, two novel heat exchangers were proposed by utilizing triply periodic minimal surface (TPMS) structures. i.e. the Gyroid structure and Schwarz-D surface, to enhance heat transfer and improve cycle efficiency. TPMS structures are a class of structures composed of two distinct inter-penetrating volume domains separated by an area-minimizing wall, which have been observed as biological membranes and co-polymer phases. Two heat exchangers along with a reference printed circuit heat exchanger (PCHE) were investigated numerically by computational fluid dynamics simulations when the hot and cold sCO2 fluids pass through them at various Reynolds numbers. Effects of geometrical shapes and Reynolds number on the hydraulic and thermal performances were identified. It was demonstrated that two heat exchangers with TPMS can improve overall thermal performance by 15–100%, and the Nusselt number is raised by 16–120% for a given pumping power in comparison with the PCHE. Hence, heat exchangers with TPMS have a very good potential to enhance sCO2 cycle efficiency.
Highlights
The supercritical CO2 Brayton cycle has the potential to replace steam Rankine cycles in electricity generation, due to its higher efficiency and compactness compared with steam Rankine cycles [1,2,3,4]
The results indicated that the UCPHE has a better overall performance than the Printed Circuit Heat Exchanger by about 15% within the investigated range of the Reynolds number
A novel heat exchanger based on triply periodic minimal surface structures was proposed and studied through computational fluid dynamic simulations
Summary
The supercritical CO2 (sCO2) Brayton cycle has the potential to replace steam Rankine cycles in electricity generation, due to its higher efficiency and compactness compared with steam Rankine cycles [1,2,3,4]. The heat transfer performance and pressure loss of PCHE in sCO2 cycle have been investigated experimentally and numerically, but in most of studies the conventional PCHE with continuous zigzag channel were focused. Ngo et al [18] experimentally studied the S-fin-type PCHE and the zigzag-type PCHE, compared their thermal–hydraulic performance, and proposed correlations of the Nusselt number and the pressure-drop factors. Pei et al [21] proposed a honeycomb Ultra-compact Plate Heat Exchanger with hexagonal channels as recuperator in the SCO2 Brayton cycle They varied the geometry parameters and evaluate the performance via Nu/f1/3. Two heat exchangers with TPMS structures of the Gyroid and Schwarz-D types were designed, and the corresponding numerical simulations were launched to identify detailed flow fields, hydraulic loss and heat transfer characteristics, and overall thermal performance. It was identified that the heat exchangers with TPMS can enhance overall thermal performance by 15–100% compared with the PCHE, and for a given pumping power, the new exchangers can intensify Nusselt number by 16–120%
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