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The heat transfer characteristic of supercritical water is one of the crucial issues in SuperCritical Water-Cooled Reactors (SCWRs). The efficiency and safety of the SCWR system are largely dependent on the local heat transfer performance. This paper establishes the numerical model for supercritical water in a long vertical circular loop (inside diameter = 10 mm) and analyzes the flow and heat transfer mechanism during the transition process from subcritical to supercritical states under various heat fluxes (uniform and nonuniform). The results reveal that the difference in thermophysical properties between the boundary layer and the core region is the main reason for the heat transfer behavior, especially during the transition from subcritical to supercritical and liquidlike to gaslike. The flow structure on the buffer layer is a dominating factor for heat transfer deterioration. The cases under variable nonuniform heat fluxes have a higher heat transfer coefficient compared with uniform heat fluxes. But, this will cause large changes of the parameter locally. The dominating factors of heat transfer deterioration under these conditions are also identified. [ABSTRACT FROM AUTHOR]

The virtual boundary meshfree Galerkin method (VBMGM) is given to calculate the multi-domain transient heat conduction with heat source problem. The radial basis function interpolation is used to obtain the virtual source function on the virtual boundary, the heat source, the particular solutions of the temperature, and the heat flux in the computational domain. The formula of the proposed method is gotten by the Galerkin method and the control equations of the multi-domain transient heat conduction with heat source. Therefore, there are the advantages of the Galerkin method, the boundary element method, and the meshfree method for the multi-domain transient heat conduction with heat source problem by VBMGM. The numerical meaning of the weighted values are definite for the multi-domain transient heat conduction with heat source problem through VBMGM, such as the partial derivatives of the temperature, the heat flux, the heat source, and the continuity conditions on the public boundary at time. The detailed calculation scheme of VBMGM is deducted for the multi-domain transient heat conduction with heat source problem. Two numerical examples, four subdomains with the time-dependent heat source problem and two subdomains with the constant heat source and mixed boundary condition problem, are computed. The accuracy and the stability of VBMGM for the multi-domain transient heat conduction with heat source problem are verified. [ABSTRACT FROM AUTHOR]

This article presents a virtual boundary meshless with Trefftz method for calculation of the two-dimensional steady-state heat conduction crack problem, which is based on the idea of multidomain combination. The virtual source function is constructed by the radial basis functions approximation in the subdomain not containing the crack. The temperature or heat flux is calculated by crack special solution of Trefftz function in the crack subdomain. Thus, the proposed method has the advantages of both the boundary-type meshless method and the Trefftz method. No nodes or elements are distributed on the crack, because the boundary condition of the crack is automatically satisfied by employing the crack special solution of the Trefftz function. The heat stress intensity factor is simply and directly calculated. [ABSTRACT FROM PUBLISHER]

The boiler equipment should be able to adapt to the load requirements and overcome the interference of various external conditions. By establishing a one-dimensional single-channel general numerical calculation model suitable for flow instability analysis of ultra-supercritical boilers at 700 °C, the rules of flow in the tubes are calculated. The 7th loop and the 22nd loop of the boiler water wall are selected as typical loops, and the dynamic characteristics of the two loops are calculated. The results show that after applying different multiples of heat flux disturbance, regardless of whether metal heat storage is considered, the inlet and outlet mass flow rates of the two circuits show inverse dynamic responses and eventually return to a steady state. When considering heat storage, it takes about 63 s for the 7th loop to return to stability. The recovery and stabilization time of the 22nd loop is about 60 s. Metal thermal storage has a positive effect on the settling time of the pipe section after heat flux disturbance. And when the maximum heat flux disturbance is applied, the maximum wall temperatures of the two loops are 443.9 °C and 446.5 °C, and the boiler can operate safely and stably. [ABSTRACT FROM AUTHOR]

A numerical study is conducted to investigate heat transfer characteristics of supercritical water flowing upward in an inclined smooth tube under uniform heating conditions. In this study, model verification was performed under the conditions of low heat flux and high heat flux to ensure the accuracy of experimental data. Inner wall temperature and heat flux distribute non-uniformly on the circumference due to the influence of natural convection. The increase of heat flux enhances the non-uniform circumferential distribution, while the increase of mass flux reduces the non-uniform circumferential distribution. Heat transfer of upward vertical and inclined flows is compared under low and high heat flux conditions. Radial distributions of fluid temperature, density, specific heat capacity, velocity, and turbulent kinetic energy are presented and analyzed. The analysis shows that the increase of heat flux reduces radial turbulence and heat-absorbing capacity of the boundary fluid, while increases radial temperature and density gradient. Three dimensionless buoyancy parameters are used to evaluate the buoyancy effect of inclined flow. [ABSTRACT FROM AUTHOR]