Flow stability and linear disturbance analysis of single-phase natural circulation loop under different thermal boundaries

PIV measurements of natural circulation driven flow inside and around SMR fuel assemblies

Numerical investigation of thermohydraulic performance in supercritical CO2- based dual natural circulation systems

Experimental study on natural circulation cooling system for core catcher with downward-facing heating channel

Dynamic modeling and control strategy study for a natural circulation small lead-cooled fast reactor with supercritical CO2 recompression Brayton cycle system

Assessment of TRACE for predicting startup transients in natural circulation boiling water reactors

Thermo-neutronic analysis of natural circulation in the ABV small modular reactor under ocean-induced motions

A comprehensive investigation of computational analysis on flow characteristics, stability and safe limits of a supercritical natural circulation loop for different heating power profiles

Stability threshold for stratification-induced flowrate oscillations in PLANDTL-2 sodium natural circulation experiment

Experimental study of natural circulation phenomena in a micro prismatic modular reactor core channel

Analyzing the influence of rifled tube and magnesium oxide (MgO) nanoparticle on the performance of flat-plate solar collector under natural circulation

ABSTRACT In natural circulation loops (NC loops), flow initiation is driven by the difference between the heat source and the heat sink density variations. Given that the flow rates within these loops are lower than those in forced convection channels, surface characteristics can significantly influence the flow. No heat transfer studies have been found that describe the effects of UV‐irradiated PDMS surface modifications in NC loops. The study focuses on evaluating the thermal performance of surface‐modified natural circulation mini‐loops with a hydraulic diameter of 3 mm. The impact of surface modifications at the mini‐loop heater section, under different power inputs (10, 15, and 20 W) and temperatures at the heat sink (20°C and 30°C), is investigated. The performance of 0.01 and 0.02 vol.% Al 2 O 3 and SiO 2 nanofluids was measured and compared with that of D.I. water. The initial experiment involved a channel with untreated polydimethylsiloxane (PDMS) coating on the heater section (contact angle of 86.2 ± 2.7°). Subsequently, the experiment was repeated with a vacuum UV (VUV)‐treated PDMS coating (contact angle of 2.7 ± 2.1°). The heat transfer coefficient within the heater section was estimated using a nonintrusive interferometric technique. The thermal performance of a 3 mm hydraulic diameter mini‐loop with dilute metal oxide nanofluids was compared with deionized water (D.I. water), and the results were validated against Vijayan's correlation. Figure of Merit (FOM) analysis indicated that, for the designed mini‐loop, 0.02 vol.% alumina nanofluid exhibited the best performance. At 10 W and 283 K, the surface‐tuned heater section with 0.02 vol.% alumina nanofluid demonstrated a 12.42 ± 1.6% enhancement in the local heat transfer coefficient. However, the Nusselt number increment was only 5.39 ± 1.7%. The high wettability of the heater section hinders the slip flow. The rise in the thermal conductivity of the basefluid due to nanoparticle addition also reduces the Nusselt number. The surface effects being comparable with the buoyancy forces, the Reynolds number inside the loop is lower.

Study on scaling analysis methods based on Lead-Bismuth loop with natural circulation

Investigation of natural circulation flow instability based on thermal effect during steady-state condition using wavelet and chaotic analysis

Numerical study on thermal stratification and asymmetric flow heat transfer characteristics of S-CO2 natural circulation

Study on safety of advanced integrated natural circulation reactor of NHR200-II under LOCA condition

Dynamic oscillations in the supercritical carbon dioxide natural circulation loop

Pipeline systems are essential across various industries for transporting fluids over various ranges of distances. A notable application is natural circulation through thermo-syphoning, driven by temperature-induced density variations that generate fluid flow in closed loops. This passive mechanism is widely employed in sectors such as process engineering, oil and gas, geothermal energy, solar water heaters, fertilizers, etc. Natural Circulation Loops eliminate the need for mechanical pumps. While this passive mechanism reduces energy consumption and maintenance costs, maintaining stability and efficiency under varying operating conditions remains a challenge. This study investigates thermo-syphoning in a rectangular closed-loop system and develops optimal control strategies like using a Linear Quadratic Regulator (LQR) and Model Predictive Control (MPC) to ensure stable and efficient heat removal while explicitly addressing physical constraints. The results demonstrate that MPC improves system stability and reduces energy usage through optimized control actions by nearly one-third in the initial energy requirement. Compared to the LQR and unconstrained MPC, MPC with active constraints effectively manages input limitations, ensuring safer and more practical operation. With its predictive capability and adaptability, the proposed MPC framework offers a robust, scalable solution for real-time industrial applications, supporting the development of sustainable and adaptive natural circulation pipeline systems.

Dimensionless analysis of the influence of secondary water level on the single-phase reverse flow in the inverted U-tube of steam generators with natural circulation

Influence of rolling motion on two-phase flow in narrow rectangular channel under natural circulation and forced circulation