In order to improve the safety and economy of lightweight designs of large pressure vessel tube sheets, the effects of temperature load model, convection load model and fluid-solid coupling load model on the temperature field and stress field of isothermal reactor tube sheets have been compared through numerical simulation. The stress distribution rule at the key position of the tube sheet was obtained, and the equivalent stress of each model was evaluated by means of the pressure vessel standard. The results show that the temperature gradient of the tube sheet of the temperature load model is the largest, and the stress concentration of the tube sheet is the most prominent. The temperature gradient of the tube sheet of the fluid-solid coupling load model is the smallest, and the stress concentration of the tube sheet is greatly alleviated. The local film stress and the primary + secondary stress of the tube sheet increase with the increase of the temperature gradient of the tube sheet. The two stresses of the temperature load model are 36.49 MPa and 155.73 MPa, respectively. The two stresses of the convection load model are 31.40 MPa and 132.74 MPa, respectively. The two stresses of the fluid-solid coupling load model are 27.84 MPa and 112.84 MPa, respectively. Compared with the other two thermal load models, the stress of the tube sheet calculated by the fluid-solid coupling load model corresponded more closely to actual conditions, and the reliability of the optimized design of the large pressure vessel tube sheet was the highest.

Liquid-solid two-phase flow technology is widely applied to the heat transfer enhancement in heat exchanger design, the key lies in guiding low-volume-fraction particles to the wall region to disrupt the thermal boundary layer and thereby improve the heat transfer efficiency. The movement behavior of particles is a key factor for deep analysis of heat transfer enhancement mechanism. Non-spherical particles have better disturbance effects and more complex movement behaviors due to the anisotropy of their shapes. This paper takes regular tetrahedral particle groups as the research subject to analyze their motion and distribution law in liquid-solid two-phase flow in vertical uppipe. In the investigation, the effects of particle inlet volume fraction (1%, 2%, 3%, 4% and 5%) and liquid inlet velocity (1.0, 1.2, 1.5, 1.8 and 2.0 m/s) on the average velocity and relative volume fraction distribution of particle groups in tubes are simulated based on CFD-DEM (Computational Fluid Dynamics-Discrete Element Model) coupling method, and the accuracy of the numerical simulation is verified by PIV (Particle Image Velocimetry) experiments. The results show that, within the studied parameter range, the average velocity of particle groups exhibits axial fluctuations, with a fluctuation amplitude intensifying as the liquid inlet velocity increases, and decreases radially from the pipe center to the wall. Furthermore, the velocity distribution becomes increasingly centralized as the fluid flow develops axially. Along the radial direction, the relative volume fraction of particles follows the double peak law, that is, being higher in the central area and near the wall of the tube, while being lower in the transition area. When the particle inlet volume fraction is 1% and the liquid inlet velocity is 2.0 m/s, the particle volume fraction near the pipe wall is the highest.