A new concept of “Sideling Flow” in shell side of shell-and-tube heat exchanger is presented, which is relative to the cross flow, longitudinal flow and helical flow in heat exchanger. A type of new energy saving shell-and-tube heat exchanger with sideling flow in shell side, shutter baffle heat exchanger is invented, which exhibits the significant heat transfer enhancement and flow resistance reducement performance. The “Field Synergy Principle” is adopted to analyze the heat transfer enhancement mechanism of sideling flow, it is indicated that the shutter baffle heat exchanger exhibits the perfect cooperativity between velocity field and temperature grads field. Effects of the structure and processing parameters on the fluid flow and heat transfer are also investigated through numerical simulation, both the correlative equations of heat transfer coefficient and pressure drop in shell side are deduced, which provide references for the design and popularization of this new type heat exchanger.
The crack growth behaviors loaded in mode I under strain and stress control at different temperatures were presented in α-Fe by atomistic simulations using LAMMPS code. The interatomic bonds of atoms were characterized using the embedded atom method interatomic potential. The simulation models were built with initial edge crack subjecting to cyclic uniaxial constant strain rate and constant stress. A temperature range from 100 K to 1200 K was considered to probe the influence of the temperature on crack growth. The crack growth mechanism and the radial distribution function (RDF) during crack growth were investigated. The results indicated that the crack propagation mechanisms were sensitive to temperature and the boundary conditions. By proposed image adjusting technology the dislocation slip bands can be more clearly displayed on screen. In order to include the effect of temperature on crack growth, a temperature factor defined as a function of temperature in exponential form was introduced to modify the theoretical expressions based on thermal activation theory. Its coefficient and index can be determined by the RDF peak value obtained from atomistic simulations. For cyclic loading the crack growth process was dependent on both temperature and cyclic loading period in terms of simulations.
The variable cross-section H-type structure, which is used in the new type of heat exchanger with longitudinal flow of shell side, could reduce the scour action of imports fluid on the tube bundle and prevent vibration of the tube bundle. It could also improve the state of the shell side fluid flow, reducing the flow dead zone, allowing for a more efficient use of the heat transfer area and improving the energy efficiency. The new structure will make the temperature and stress distribution in the heat distribution more complex, so it is necessary to analyze the stress intensity of the variable cross-section H-type structure. A three-dimensional finite element model of the variable cross-section H-type structure is established in this paper, and the surface temperature of the various parts of the heat exchanger are determined through temperature analysis. Using ANSYS Workbench software, thermal-stress analysis of the H -type structure with different structural parameters is tested, and the temperature and stress field are obtained. The results show that a Ring plate of H-type structure has a larger temperature gradient along the thickness direction. The maximum stress of the heat exchanger is 203.13 MPa, which occurred on the connections of the ring plate and jacket in the lower temperature side. The ring plate thickness of the H-type structure has a significant influence on its maximum stress. Therefore, a reasonable selection of ring plate thickness is important for the safety of the heat exchanger.
The physical model and analytical method are put forward for considering the molecular interaction between solid wall and gas fluid when dealing with convective heat transfer in macro/mini/micro channels based on the boundary layer theory concept, the molecular kinetic theory of gases, structural chemistry and continuum hypothesis. The influence rule of wall-fluid intermolecular forces to the transport properties of gases located in boundary layer region is studied applying proposed models. The gas density variation distribution equation including the wall-fluid molecular interaction is derived with continuum media integral approach. The theoretical results show that the fluid diffusion is independent of the wall-fluid interaction but visosity and heat conductivity not. According to the gas molecular density distribution function and molecular dynamics, new formulae were developed for calculating viscidity coefficient and thermal conductivity with wall-fluid interacting effect for a fluid. The research results provide scientific reference for further study and exploitation on fluid flow and heat transfer of mini/micro channels. In addition, the formulae offered in this paper to compute the transport properties of gases are also suitable for fine analysis of boundary layer in macro-scale channels.
For heat exchanger tube of steam generator, the relation between heat exchanger tube and fluid is typical fluid-structure interaction problem. Flow induced vibration has been found so far to be responsible for fatigue damage and failure of steam generator tubes, which will result in large economic loss and radioactive pollution. So the steam generator tubes are the weakest link in the primary coolant loop. Based on the synthesis of all sorts of factors influencing the dynamic characteristics of steam generator heat transfer tubes, establishing the heat transfer tube model, research on the weakening effect of fluid hole on fluid, the natural frequencies of the heat transfer tubes are analyzed under different fluid holes and fluid hole distance by numerical simulation.
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