The liquid lead-bismuth eutectic (LBE) is a highly promising coolant for new generation nuclear reactors. The experimental loop is usually arranged inclination or vertical for preventing LBE clogging tube at emergency conditions. Because of the high density and low Prandtl number, LBE natural convection due to buoyancy is significant in the inclined tube. In present work, the influence of buoyancy on LBE convective heat transfer is numerically investigated in a three-dimensional circle tube under different inclined angles and length-to-diameter ratios. The turbulent disturbance resulted from buoyancy reinforces convective heat transfer performances of LBE in the inclined tube. The smaller inclined angle and the larger diameter are helpful to enhance convective heat transfer. The dominant factor effect on convective heat transfer is inclined angles rather than length to diameter ratios. Further numerical investigations of LBE heat exchanger with/without buoyancy are performed. The results indicate that LBE heat exchanger of 5°inclined angle can significantly enhance convective heat transfer with the acceptable pressure drop. This structure is also sufficient to ensure LBE flow back to the storage tank when the pump stops. A reasonable and widely applicable selection criterion of inclined angles is necessary to be constructed to guide engineering applications.

Conclusions

In this paper, the flow and heat transfer characteristics of LBE in tubes under different inclination angles and length to diameter ratios are investigated numerically using standard k-e turbulent model in the software ANSYS CFX. The effects of buoyancy resulted from local temperature difference on convective flow state, velocity and temperature distributions, heat transfer coefficients and pressure drops are analyzed in order to understand the variation of LBE heat exchanger performance in the engineering application. Further numerical investigations of LBE heat exchanger with and without buoyancy in LELA are performed to discuss the effect of the inclined angle. Based on the numerical results and detailed analysis, the following conclusions can be drawn.

The effect of buoyancy force on convection heat transfer of LBE cannot neglect due to its high density and good heat conduction. At the considering buoyancy condition, LBE natural convection in the inclined tube is reinforced. And the velocity and temperature distributions are asymmetric and distorted in the cross section of inclined tube. The turbulent disturbance resulted from buoyancy reinforces the convective heat transfer performance of LBE in the inclined tube. The smaller of inclined angle and the larger of tube diameter are helpful to enhance convective heat transfer. The dominant factor effect on convective heat transfer is the inclined angle of tube rather than the length to diameter ratio. As the inclined angle of tube increases, the LBE pressure drop along the tube increases. The effect of length to diameter ratio on the pressure drop is relatively smaller.

In the engineering applications of LBE, in order to prevent the tube clogging, the proper inclined angle of tube must be maintained to ensure that the LBE flows back to the storage tank when the LBE pump stop. This structure is also helpful to enhance the convective heat transfer of LBE. A reasonable and widely applicable selection criterion of inclined angle tube is necessary to be constructed to guide the engineering application.

The results have been published on Applied Thermal Engineering 127 (2017) 846–856.