Astudy Of The Flowand Heat Transfer Characteristic For Corrugated Tube Bundlesand Structure Optimal

The research of this article is forced on corrugated tube heat exchanger, which canbe divided into two parties, one is flow and heat transfer between tube bundles and theother one is flow homogeneity in the shell side. First the different distributed corrugatedtube bundles are compared with each other, Then different parameters of tube bundles isstudied with CFD method and optimized by minitab. At last, the new structure of shellside inlet is contrasted with the traditional structure and analyzed deeply under differentinfluence factors. All the above content is detailed as followings:(1) The triangular central subchannel is abstracted from corrugated tube bundlesand meshed with size of0.55which is verified though the grid independence. Thencombined with empirical formula, the computations are performed on model of smoothtube bundles by two different turbulence model. After analysis, it is found theRealizable k-ε model fits empirical formula better and the error of it can be controlledwithin15%. Compared maplosed corrugated tube bundles with traditional corrugatedtube bundles under different Re, it is discovered that the state of corrugation aggregationhas a huge influence on flow and heat transfer characteristics. After malposed the tubes,the disturbance of corrugation decreases sharply, while disturbance frequency increasesthree times, which could enhance resistance performance drastically on condition of thesimilar heat transfer performance, thus the overall heat transfer performance ofmalposed corrugated tube bundles could improve by7-24%.(2) Combined with local Nu andΔP, the heat transfer, resistance and overall heattransfer performances are detailed with paramaters of corrugation height, corrugationpitch, tube space and Nusselt number changed. It’s found when corrugation pitchincreased, heat transfer performance and resistance decrease and its amplitude reducegradually, causing overall heat transfer increase gradually. When corrugation heightincreased, heat transfer performance and resistance increase proportionally. Consideringthe amplitude of resistance is lager relatively, the overall heat transfer performancedecreases. When tube space increased, heat transfer performance of maplosed tubebundles decreases and its amplitude gradually compared with smooth tube bundles,while its resistance enhances relatively, making overall heat transfer performancedecreases accordingly. (3) The distributions of velocity, temperature, pressure, turbulent kinetic energyand turbulent dissipation rate are detailed on malposed tube bundles with differentstructure paramaters. When corrugation pitch increased, the disturbance of discretecorrugation don’t change while mean velocity decreases nonlinearly, making rate of heattransfer and resistance decline nonlinearly and its amplitude decrease gradually. Whencorrugation height increased, the disturbance of discrete corrugation and rate of heattransfer increase linearly. Due to the overlay of the turbulence area, resistance increasesnonlinearly and its amplitude increase gratually. When tube space increased, thevelocity decreases accordingly, the disturbance of discrete corrugation declines sharply,causing effect of heat transfer worse and turbulence area smaller.(4) Minitab is used to conduct the response surface analysis including four factorsand five response values. The effect of the linear term, interactive term and quadraticterm are analyzed based on the value of P and F in the variance and detailed with theresponse surface analyses. After ignoring the insignificant factors, the optimal binaryregression equation is fitted. Considering the conflict relationship between Nuc/Nusandfc/fs, the Pareto curve is utilized to obtain an optimum design (minimum of fc/fs) forspecified Nuc/Nus. When set the specific constraint of Nuc/Nusas1.43, the minimum fc/fsof1.585and the maximum η of1.845is obtained naturally.(5) For different inlet structure of the shell side, Realizable k-ε model is used tostudy the fluid flow state. It’s found the velocity is higher and flow longitudinally alongthe tube bundles in the new heat exchanger than in the traditional heat exchanger. Thenafter changing the structure of comb baffle, it’s discovered when comb baffle is the typeone and Φ is12.81%, the length fluid get steady flow is shorter, the peak of unevennessis minimum and the uniformity on one cross section is best. Velocity relative deviationin central zone of shell side possessing a decrease tend and velocity relative deviation inmarginal area possessing a increase tend is lager. Sandwich structure affects form of themost streamline, thus the type of velocity relative deviation in the shell side isdetermined, while comb baffle can perfect the velocity relative deviation within limits.The uniformity in shell side can also be improved under low Re which is a insignificantfactor for velocity relative deviation.