Experimental study on flow and heat transfer of High-Pressure helium flow in compact helical tube heat exchanger in HTGR

In this study, experiments were conducted on helium flow within a compact helical tube heat exchanger. High-temperature helium and deionized cooling water, flowing in opposite directions, were allocated to the shell side and tube side, respectively. The Reynolds number of helium ranged from 3 × 10³ to 1.6 × 10⁴ under an operational pressure of 2.1 MPa. Measurements were taken for helium temperature, tube outer-surface temperature distribution, pressure, and mass flow rate to illustrate the flow and heat transfer characteristics. Sensitivity analysis of thermal–hydraulic parameters, including heat transfer power and efficiency under various operational conditions, was performed. The convective heat transfer coefficient and pressure drop were calculated. The transition point (Re = 9000) between laminar and turbulent flow of helium on the shell side was identified, and empirical correlations for the Nusselt number and friction coefficient were proposed. The experimental results indicate that the heat transfer performance of helium in the compact helical tube heat exchanger exceeds that of water in large-scale helical tube heat exchanger by approximately 20.75 % under fully developed turbulence, while the flow resistance characteristics remain essentially consistent.