Pressure drop characteristics of spiral tube heat exchangers in molten salt reactor

BackgroundSpiral tube heat exchanger (STHE) is simple, compact, and able to accommodate large temperature differences, which can fulfill the heat transfer demand of molten salt reactor. However, research on the thermo-hydraulic characteristics under high-temperature molten salt conditions is scarce. There are no suitable correlation equations for heat transfer and flow resistance applicable to STHE used in molten salt reactor.PurposeThis study aims to develop pressure drop correlation formulas for the tube-side and shell-side flow of the STHEs which use molten salt as a heat transfer medium.MethodsFirst, the Ø12 mm×1.6 mm spiral tube heat exchanger was taken as the research object, and three-dimensional models of the STHE with similar Prandtl number (Pr) as that of the molten salt reactor, were established. Then, the pressure drop characteristics of the tube-side and shell-side of the STHE under different flow velocities and geometric parameters were obtained by CFD simulation. The geometric parameters included layer spacing, tube spacing, number of layers, and helical winding diameter. Thereafter, the flow velocity was characterized by the Reynolds number (Re), and all geometric parameters were divided by the spiral tube diameter. The pressure drop was expressed in the form of the friction factor, so that all variables involved in the analysis were transformed into dimensionless parameters. On this basis, the quantitative relationships and variation trends of the dimensionless parameters were systematically analyzed. The sensitivity analysis of the influence of shell-side geometric parameters on the friction factor was performed. Finally, nonlinear regression of the numerical simulation results was conducted to establish correlation equations for the pressure drop characteristics of the tube-side and shell-side flows.ResultsThe results show that the friction factor of the tube-side flow changes conversely with increasing Re and winding diameter. The winding diameter plays a dominant role in pressure drop of the tube-side flow when Re is small. While Re is large, the influence of flow velocity becomes essential. On the shell side, the friction factor is negatively correlated with Re, layer spacing and tube pitch, but is positively correlated with the number of layers. Among these geometric parameters, layer spacing has a significant impact on the shell-side pressure drop, substantially exceeding the influence of layer count and tube pitch. The average deviations between the results given by the correlation equations and the numerical data are 0.62% for the tube side and 2.5% for the shell side.ConclusionsThe established equations in this study can be used to describe the pressure drop characteristics on both sides of the spiral tube heat exchangers, which provide a theoretical basis for heat exchanger design.