Numerical and experimental study on natural convection outside tube bundle under small convection temperature difference

The Passive Residual Heat Removal Heat Exchanger (PRHR HX) is the key equipment of the Passive Residual Heat Removal System (PRHRS). In the Swimming Pool-type Low-Temperature Heating Reactor (SPLTHR), the reactor core pressure and outlet/inlet temperature are 0.32 MPa and 100/80 °C, respectively. In this case, the convection temperature difference of natural convection heat transfer outside PRHR HX is small, which affects the operation of PRHRS, so it is necessary to carry out related research. In present work, numerical and experimental study on the outside heat transfer characteristics of the tube bundle under the small convection temperature difference has been carried out. The results show that the high Reynold number k-ε turbulence model with enhanced wall treatment is suitable for simulating the outside natural convection of the tube bundle, and the simulation results are consistent with the experimental data. For fluid-solid-fluid coupled heat transfer process, the heat transfer temperature difference should be used as the parameter of Gr number. Within the boundary conditions of this study, the Nu numbers predicted by traditional correlations are 1.4–2 times lower than the experimental and the simulation results. According to the results of simulation and experiment, an outside natural convection heat transfer correlation of the tube bundle is proposed, and the error between the predicted value and the experimental data is within −3%–10%. The results of this study can provide a basis and reference for engineering design of the PRHRS. •Carried numerical and experimental researches on natural convection heat transfer outside the tube bundle under small temperature difference.•The calculation method for the Gr number outside the tube bundle in the process of fluid-solid-fluid heat transfer is given.•The experimental and simulation results of natural convection heat transfer outside the tube bundle under the small temperature difference are compared with the traditional correlation.•The correlation for predicting the natural convection heat transfer outside the tube bundle under the condition of small temperature difference is given.