Natural convective flow and heat transfer studies for supercritical water in a rectangular circulation loop

• Natural circulation experiments conducted with supercritical water.
• The instability observed in the pseudo-critical temperature range of operation.
• Instability is found for small power range bounded by upper and lower stable zones.
• Instability is observed at low supercritical pressure range of 22.1–22.9 MPa.
• No instability observed at higher supercritical pressures.

A closed Supercritical Pressure Natural Circulation Loop (SPNCL) has been set up to generate data on flow and heat transfer behavior for supercritical fluids (i.e. water and carbon dioxide) under natural circulation conditions. Experiments were conducted in SPNCL with water as working fluid. Instability was observed over a narrow window of power in the pseudo-critical temperature region for horizontal heater horizontal cooler orientation. Instability was observed at low supercritical pressure range of 22.1–22.9 MPa, however it got suppressed at higher pressures. An in-house developed computer code NOLSTA has been used to perform steady state and stability analysis of SPNCL and predictions are compared with experimental data. The heat transfer data generated in the test facility has been compared with various heat transfer correlations for supercritical fluids available in literature. The present paper describes the experimental results and comparisons in detail.

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