Instability mitigation by integrating twin Tesla type valves in supercritical carbon dioxide based natural circulation loop

Highlights: • Tesla type valve is used in natural circulation loop (NCL) to mitigate instability. • Effect of heat input on the stability at supercritical pressures is studied. • Tesla valve reduces flow reversal and prescribes flow direction in NCL. • Fluctuations in temperature and velocity get reduced with Tesla-NCL. • Maximum reduction in heat transfer capability with Tesla NCL is ≤3%. Flow instability in supercritical fluid based natural circulation loop (NCL) is still an investigation aspect of physical and mathematical problems to comprehend. Therefore, NCLs require precise design assessment that focuses on the interaction of all the transient responses of buoyancy and friction forces which can ensure a stable zone of operation. To promote the uni-directional circulatory movement of loop fluid and to decrease the magnitude of instability, this research emphasizes the development of NCL integrated with two modified Tesla type valves. In this article, numerical simulations have been carried out for a range of supercritical pressures (80–100 bar) and heat inputs (500–2000 W) to do the comparative investigation of instability phenomenon in supercritical carbon dioxide based regular natural circulation loop and a new modified twin Tesla NCL. Results show that the use of modified Tesla valves leads to better stabilization for all supercritical pressures and heat inputs considered in the study. It is also found that the proposed Tesla NCL mitigates the temperature and velocity oscillations with a marginal drop of $⩽$3% in the heat transfer performance. Using asymmetrical flow resistance to stimulate directional circulation is an efficient technique to combat this instability issue. Obtained results are validated with the existing correlations, and a good agreement is obtained.