Numerical Simulation Method Of Multi-physics Couping For Heat Exchange Tube And Fluid

Shell-and-tube heat exchanger is widely used in the process industry. Heat transfer efficiency analysis, and equipment safety evaluation is the key technical issues in heat exchanger design, operation and maintenance. In this paper, tube-side and shell-side fluid is combined with the structure of heat exchange tube, numerical simulation method of multi-physics couping with flow and temperature field in fluid domain, and displacement and temperature field in structure domain, is carried out. It has important academic value and good prospects for engineering applications. Multi-field coupling analysis of shell-and-tube heat exchanger is numerical simulation, involving multi-field calculation, multi-interface coupling and multi-parameter iterative. At the point of gradual research principle from the simple to complex issues, the research work are as follows.First, select casing heat exchanger as the research object, use finite volume method to analysis multi-physics of fluid domain, use finite element method to analysis multi-physics of solid domain. Under the condition of small deformation, the multi-field coupled model of axisymmetric fluid and solid is established. For two-way transfer of temperature and heat flux and one-way transfer of force at the two-dimensional coupling interface, the interpolation formula and iterative is derived. Direct transfer method of exactly match grid, the minimum distance method and interpolation function matrix method of non-matching grid is established. The example shows that non-matching grid interfaces with the matching grid interfaces have the same numerical results. The accuracy of non-matching grid interpolation algorithm is verified. Compared the numerical result of multi-field coupling with analytical formula, the maximum error of the overall heat transfer coefficient is 10.2%. It provides numerical model and method for the heat transfer coefficient calculation of complex heat exchange tube.Second, under the condition of large radial deformation, the multi-field coupled model of the symmetry structure and tube-side fluid is established. For two-way coupling of displacement and force at the coupling interface, the interpolation formula and iterative scheme is derived. The example shows that, under the low speed laminar flow, with the increase of radial displacement, inlet pressure decreases, temperature difference between the inlet and outlet increases, wall heat transfer coefficient decreases, but the mainstream flow velocity and temperature has no expansion, the heat transfer performance is decreases. Third, under the condition of lateral vibration, the multi-field coupled transient dynamic model of three-dimensional shell-and-tube structure and fluid is established. Considering the advantages and disadvantages of Lagrangian and Eulerian description, ALE moving grid method is established to solve the flow of fluid domain, and the problems of large deformation and transient problems of solid domain. Basis on the conditione of the interface displacement compatibility, load balance, temperature continuity and energy conservation, iterative scheme of temperature and heat flux, displacement and force for multi-field coupling is derived, and convergence criterion is given. According to theory of fluid-structure interaction, the full algorithm of multi-physics couping to promote physical value with synchronization time. The example shows that tube without damping vibration has periodic motion attenuation, attenuation frequency is 80.1 Hz, it decreases by 21% from natural frequency. The inflence of the exciting force, the exciting force frequency, shell-side fluid velocity, density, viscosity, size of the outer boundary of the shell side on transient response of casing heat exchanger, is also received.Fourth, under the condition of rotate movement, the dynamics model of fluid-structure interaction for slender tube with its inner pipe fluid and outer annular fluid is established. The slender tube discretes into beam elements, based on the relationship of beam element and volume element, interpolation formula of displacement and force is derived, and the convergence criterion is given. The example shows that horizontal trajectory of rotating slender tube is diferent at different parts, and the phenomenon of revolution and rotation occures. Slender tube with its fluids has a strong coupled phenomenon.Finally, under the condition of transverse vibration, the multi-field coupled transient dynamic model of multi-tube bundles and fluid is established. Iterative scheme of multi-interface and multi-field is derived, and the convergence criterion is given. The problem of physical interaction and iterative convergence between tubes is solved. Using distributed technology, the caculation of large-scale multi-bundle and multi-field coupling numerical simulation is realized. The example shows that the flexibe tube in rigid tubes has cyclical divergence transient state. The inflence of flexibe multi-bundles on transient response is received. Multi-bundles and fluid presents complex multi-field coupling phenomena.This research also provides the theoretical basis and numerical methods for thermal recovery wells, offshore drilling riser tubes and other oil drilling enginering in the multi-field coupling analysis.