The steady behavior of the supercritical carbon dioxide natural circulation loop

TL;DR

This study investigates the steady state behavior of supercritical carbon dioxide natural circulation loops through experiments and a predictive equation, highlighting the effects of thermodynamic states and viscous losses on flow rates.

Contribution

It introduces a generalized predictive equation for steady state behavior of supercritical CO2 NCLs and assesses its accuracy against experimental data.

Findings

Predictive equation accurately captures flow rate changes due to thermodynamic state variations.

Viscous losses significantly limit steady state flow rates in the loop.

Experimental data confirms the model's effectiveness across a range of pressures and temperatures.

Abstract

The steady state behavior of thermodynamically supercritical natural circulation loops (NCLs) is investigated in this work. Experimental steady state results with supercritical carbon dioxide are presented for reduced pressures in the range of 1.1-1.5, and temperatures in the range of 20-65 {\deg}C. Distinct thermodynamic states are reached by traversing a set of isochors. A generalized equation for the prediction of the steady state is presented, and its performance is assessed using empirical data. Changes of mass flow rate as a result of changes of thermodynamic state, heating- and driving height are shown to be accurately captured by the proposed predictive equation. However, the enhanced viscous losses in the instrumentation of the loop and in the proximity of heat transfer equipment are shown to significantly limit the steady state flow rate. Subsequently, the findings are put forward in aid of the development of safe, novel supercritical natural circulation facilities.