English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The paper aims to improve the understanding of the dependency of compressor inlet conditions close to the critical point in supercritical CO2 (sCO2) cycles on different volumetric cycle designs. The compressor inlet conditions are fixed by the specific static outlet enthalpy of the main cooler and the static pressure determined by the mass of CO2 in the closed cycle. While in a previous study the authors analyzed effects on the compressor inlet conditions with respect to the specific static enthalpy in the pseudocritical region for constant inlet pressure, this paper focuses on the influence of the volume of the heater and cooler. The analysis is based on experimental observations from two different experimental sCO2 cycles, the SUSEN loop and the HeRo loop. The change of compressor inlet pressure upon change of the cooling power is substantially different and caused by the different volumetric design of the cycles. A simple model based on the volumes of the hot and cold sections in the cycle is developed to understand the dependency of compressor inlet conditions on the volumetric design. In terms of the volumetric design of the cycle, the paper will improve the knowledge of the challenges in stable compressor operation close to the critical point. INTRODUCTION Currently many researchers investigate power cycles with supercritical CO2 (sCO2) as a working fluid. Several publications suggest that these power cycles have potential to achieve higher efficiency and flexibility while featuring simpler and more compact cycles (e.g. Ahn et al., 2015 and Brun et al, 2017). Moreover, they can be used for various applications, such as waste heat recovery, fossil fuel or solar power plants. One special application, however, is the use in a novel emergency heat removal system for nuclear power plants. This system is called the supercritical CO2 heat removal system (sCO2-HeRo) and consists of a simple Joule cycle. It is retrofittable to existing nuclear power plants and removes residual decay heat from the nuclear core in case of a station blackout (Benra et al., 2016). The experimental observations serving as foundation for the analysis in this paper are made in the sCO2-HeRo and the follow-up sCO2-4-NPP project. For this system, the compactness and simplicity of the cycle are key requirements and lead to the application of sCO2 as working fluid. Increased simplicity means the reduction or simplification of the auxiliary systems, such as the inventory control for regulating the mass of CO2 in the cycle. Simplification is also interesting for sCO2 power cycles in other applications as it may be a driver for the reduction of system costs. Furthermore, it is important to understand cycle behavior when inventory control fails. Therefore, it is also interesting for large power systems such as the one investigated in the sCO2-Flex project. Both, the benefit for the simplification of sCO2 cycles and for the failure analysis of the inventory control serve as motivation for the following analysis. It studies the effect of the change of static compressor inlet temperature by adjusting the cooling power on its inlet pressure with constant mass of CO2 in the cycle. The sCO2-HeRo system is also supposed to be robust while the compressor works close to the (pseudo-)critical point. Close to this point, which is the intersection of an isobaric (black) and the pseudocritical (dotted red line) line in Figure 1 defined by the local maxima of isobaric heat capacity, sCO2 shows large gradients of e.g. density upon static pressure and temperature (Figure 1, left). Therefore, it is crucial to understand the influences on the compressor inlet conditions which determine the performance of the compressor. In a previous study, the authors showed that even though large gradients in e.g. density upon static pressure and temperature in the pseudocritical region exist (Figure 1, left), a change of cooling power will not lead to sudden changes of compressor inlet density. That is presented in Figure 1 on the right (Hacks et al., 2019a). Because of the almost linear trend of specific enthalpy and density even in the pseudocritical region, there are no sudden changes of compressor pressure ratio. However, the previous study is limited to a shift of compressor inlet

Impact of volumetric system design on compressor inlet conditions in supercritical CO2 cycles