Design and analysis of a natural draft direct dry cooling system for a supercritical carbon dioxide power cycle for CSP application
type: CreativeWork
description: Natural draft direct dry cooling systems (NDDDCSs) offer a modern alternative to conventional dry cooling systems such as mechanical draft direct air coolers or natural draft indirect dry cooling systems. This technology combines the benefits of both, promising reduced auxiliary power consumption, decreased system complexity and better efficiency from direct cooling. In this work, such an NDDDCS with vertically arranged heat exchangers around the tower circumference is designed and evaluated for a supercritical carbon dioxide (sCO2) power cycle for a concentrated solar power application. The system is configured to house both the precooler (PC) and intercooler (IC) heat exchangers within the same tower. Three numerical models are developed to simulate NDDDCS performance, each with an increasing order of fidelity aimed at addressing the limitations of the preceding approach. Initially a lumped parameter model is used to explore a larger design space, intended to obtain a best-performing system geometry by minimising the total system material cost and lost work. The results indicate that cost-effective NDDDCSs for sCO2 applications favour smaller cooling towers with taller heat exchangers. Further, employing complex multi-pass counterflow heat exchanger geometries allow for enhanced heat rejection capacities along with reduced cooling tower footprints. The second model extends the analysis to a 1-D discretised heat exchanger network to capture parameter distributions resulting from the highly variable property gradients of sCO2 near the critical point. These results confirm that lumped parameter models overpredict performance as property gradients are not accounted for accurately. The 1-D model shows a 4.66 % reduction in overall heat rejection at design point, split between decreases of 2.35 % at the PC and 7.35 % at the IC. The discretised 1-D model also investigates the effects of off-design ambient temperatures and approximated crosswinds on system performance cha…
abstract: Natural draft direct dry cooling systems (NDDDCSs) offer a modern alternative to conventional dry cooling systems such as mechanical draft direct air coolers or natural draft indirect dry cooling systems. This technology combines the benefits of both, promising reduced auxiliary power consumption, decreased system complexity and better efficiency from direct cooling. In this work, such an NDDDCS with vertically arranged heat exchangers around the tower circumference is designed and evaluated for a supercritical carbon dioxide (sCO2) power cycle for a concentrated solar power application. The system is configured to house both the precooler (PC) and intercooler (IC) heat exchangers within the same tower. Three numerical models are developed to simulate NDDDCS performance, each with an increasing order of fidelity aimed at addressing the limitations of the preceding approach. Initially a lumped parameter model is used to explore a larger design space, intended to obtain a best-performing system geometry by minimising the total system material cost and lost work. The results indicate that cost-effective NDDDCSs for sCO2 applications favour smaller cooling towers with taller heat exchangers. Further, employing complex multi-pass counterflow heat exchanger geometries allow for enhanced heat rejection capacities along with reduced cooling tower footprints. The second model extends the analysis to a 1-D discretised heat exchanger network to capture parameter distributions resulting from the highly variable property gradients of sCO2 near the critical point. These results confirm that lumped parameter models overpredict performance as property gradients are not accounted for accurately. The 1-D model shows a 4.66 % reduction in overall heat rejection at design point, split between decreases of 2.35 % at the PC and 7.35 % at the IC. The discretised 1-D model also investigates the effects of off-design ambient temperatures and approximated crosswinds on system performance cha…
author: Van Niekerk, Christoffel Hendrik
language: en
date published: 2026-03
date modified: 2026-07-24T04:40:06Z
provider: Stellenbosch University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Stellenbosch : Stellenbosch University