Effect of Helium Pressure on Natural Convection Heat Transfer in a Prismatic Dual-Channel Circulation Loop


The effects of helium pressure on the convection heat transfer coefficient and temperature fields (helium and wall surface temperatures) in a unique scaled-down dual-channel natural circulation loop with upper and lower plena have been investigated in this study. Natural convection is one of the passive safety systems of the prismatic very high-temperature reactors (VHTRs) during the accident scenarios. The operating helium pressure was varied from 413.47 to 689.12 kPa in the temperature range from 6 to 196°C. Radial and axial measurements were carried out along the flow channels using a new sophisticated flush wall-mounted heat transfer coefficient probe in conjunction with the radial adjuster for T-thermocouple that are integrated in a novel way to characterize natural convection heat transfer in terms of heat transfer coefficient, Nusselt number, helium temperature, and wall surface temperature. The obtained experimental results along the flow channels showed the dependence of natural convection on the system's pressure in which the Rayleigh number is proportional to the square of the helium pressure (Ra α P2). Also, it was found that upon increasing the helium pressure from 413.47 to 689.12 kPa, the heat transfer coefficient and Nusselt number are increased by 30% and 35%, respectively. Moreover, the wall surface temperature along the downcomer and riser channels are decreased by 12.7% and 18% with increasing the helium pressure from 413.47 to 689.12 kPa, respectively.


Nuclear Engineering and Radiation Science

Second Department

Chemical and Biochemical Engineering

Research Center/Lab(s)

Center for High Performance Computing Research


The authors acknowledge the financial support provided by the U.S. Department of Energy-Nuclear Energy Research Initiative (DOE-NERI) Project (NEUP 13-4953 (DENE0000744)) for the 4th generation nuclear energy, which made this work possible.

Keywords and Phrases

Accidents; Atmospheric Temperature; Channel Flow; Heat Convection; Heat Transfer Coefficients; Helium; High Temperature Gas Reactors; High Temperature Reactors; Natural Convection; Nusselt Number; Probes; Surface Properties; Thermocouples; Accident Scenarios; Helium Pressure; Helium Temperatures; Natural Circulation Loop; Passive Safety Systems; Prismatic Very High-Temperature Reactors (VHTRs); Temperature Range; Wall Surface Temperature; Heat Transfer; Heat Transfer Coefficient Probe; Helium Pressure

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Article - Journal

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© 2018 Elsevier, All rights reserved.

Publication Date

01 Feb 2018