Numerical Simulation Of Heat Transfer Process And Structure Optimization Design In Mechanical Vapor Compression System (MVR)

Mechanical vapor recompression(MVR) technology is widely used in Many industrial production field such as wastewater treatment,water desalination,alkali production,fermentation and food processing,for a series of advantages such as remarkable energy saving effect,simple structure and low running cost.Whether the inland MVR technique can continue to develop and achieve advantages in the world depends on the optimization design of MVR system process network,safe and reliable steam compressor and independent research of high efficiency evaporator. Heat exchanger as the core components of evaporator, the heat transfer performance has extremely influence on energy saving efficiency of MVR system.Therefore the study of the characteristics of the fluid flow and heat transfer in heat exchanger has very important significance to optimize the heat exchanger structure and increase heat transfer efficiency.This paper studing the tube heat exchanger which uses CFD and ANSYS FLUENT 14.0 proceed the three dimensional numerical simulation for the flow and heat transfer in a tube heat exchanger and shell heat exchanger process on the basis of reasonable simplified model. Based on the calculating model of the standard k—ε two equation model,this paper using pressure correction SIMPLE algorithm to solve problem.The fluid flow and heat transfer process in the heat exchanger is complex. The study of the process use the wall temperature subjunctive at present.wall temperature subjunctive is a kind of simplified algorithm which imaging outer wall heat of heat exchanger for constant temperature uniformity and ignored the influence of heat transfer in the pipe fluid. In order to explore the constant wall temperature to impact on the simulation of the heat exchanger shell side heat transfer fluid, the study adopts the method of interior and exterior fluid coupling heat transfer to comparing and analying the wall temperature subjunctive in different tube side flow rate. The calculation results of that two methods have differences, and the difference decreases with the increase of tube side fluid flow. This match classic theory of heat transfer and the actual situation perfectly. By comparing, this paper argues that you can use the wall temperature subjunctive to numerical simulation when the tube side fluid flow is larger and heat transfer of heat exchanger performance is good,so that you can improve calculation efficiency and guarantee accuracy. Otherwise we should adopt interior and exterior fluid coupling heat transfer.The law can reveal the actual situation of local temperature change in heat exchanger better and make the results more accurate and reliable. In the process of research, this paper has adopted the interior and exterior fluid coupling heat transfer.Baffle plate is an important heat transfer parts in heat exchanger. This paper mainly studied the influence which the baffle structure change(including the baffle spacing and baffle plate gap height changes) to the heat exchanger shell side fluid flow and heat transfer. Through the simulation calculation we can obtained shell side fluid, the distribution of velocity, temperature and pressure under the different baffle plate structure, and then obtained import and export temperature difference, pressure drop and characteristic curve that heat transfer coefficient changing with baffle structure. This paper uses h/Δ P index which we often use in the engineering application as an evaluation standard of comprehensive performance of the heat exchanger. Comprehensive performance of the heat exchanger increases baffle plate space decreasing and gradually reducing of the gap height through the analysis.