Development And Research Of New Heat Exchangers Based On High-efficiency Heat Exchange Tubes And HDD Baffles

Shell-and-tube heat exchnagers are the most widely used heat transfer equipment in engineering.Developing high-efficiency heat exchangers is of great importance for saving energy and reducing resource consumption and constitutes continuous research topcs in science and technology.Baffles with holes in different diameters(or HDD baffles)and conically-corrugated tubes are the longitudinal flow baffles and high-efficiency heat exchange tubes proposed by Beijing University of Chemical Technology.In this dissertation,experiments and numerical simulation were carried out to study the effects of reducing tube bundle vibration when using HDD baffles and the effects of heat enhancement when using conically-corrugated tubes,study the fluid flow and heat exchange in some new heat echangers constructed by HDD baffles and/or conically-corrugated tubes and develop the process calculation software of heat exchangers.The main work and conclusions are as follows:(1)Numerical models for the heat exchanger with traditional segmental baffle,the heat exchanger with HDD baffles and the heat exchanger with segmental HDD baffles were established.Two-way fluid structure coupling analysis was peformed and results were compared between heat echangers.It is found that compared with the traditional segmental baffle,the vibration of the tube bundle in heat exchangers with HDD baffles can be effectively reduced.(2)The fluid flow and heat transfer performance in conically-corrugated tubes were numerical simulated and compared with those in other highefficiency heat exchange tubes.It is found that under the given conditions,the conically-corrugated tube is the best for heat enhancement.With suffient simulation results,correlation equations for the Nusselt number and friction coefficient in high-efficiency heat exchange tubes were proposed.The mechanism for the heat enhancement was studied based on the synergy angle analysis.(3)The mechanical properties of the conically-corrugated tube after forming from a smooth tube were studied with experiments and numerical simulation.Results show that different from the smooth tube,the conicallycorrugated tube has three-dimensional stresses under the axial load,and the maximum axial stress of the conical tube is much greater than that of the smooth tube under the same nominal diameter,thickness and axial load.Compared with the smooth tube,the axial stiffness of the conically-corrugated tube is significantly reduced.Although the fatigue fracture resistance of conicallycorrugated tube is lower than that of smooth tube,it still meets the requirements of engineering application.In addition,the axial stress concentration factor and stiffness equivalent factor of conically-corrugated tube are defined and regressed into the function of structural parameters for engineering application.(4)A new type of heat exchanger with conically-corrugated tubes and HDD baffles was developed.Taking water and oil as the media,the heat transfer performance of the heat exchanger was studied with experiments and numerical simulation,and compared with the heat exchanger with traditional segmental baffle.Results show that compared with the traditional segmental baffle heat exchanger,when water and oil are used as the media on the shellside,the total heat transfer coefficient of the heat exchanger with conicallycorrugated tubes and HDD baffles increases by 10%-66% and 4%-20%respectively under the experimental conditions.In addition,correlation of the shell-side Nusselt number in the heat exchanger with conically-corrugated tubes and HDD baffles was proposed.(5)The heat exchanger with arc-corrugated tubes which are commonly used and HDD baffles was constructed.The shell-side flow and heat transfer performance of the heat exchanger were studied with numerical simulation,and compared with the heat exchanger with traditional segmental baffle,heat exchanger with smooth tubes and HDD baffles and heat exchanger with smooth tube and segmental HDD baffles.Results show that the heat exchanger with arccorrugated tube and HDD baffles has the best heat transfer performance among these four heat exchangers.With sufficient simulation results,correlation of shell-side heat transfer coefficient of high-efficiency heat exchanger was also fitted.(6)To facilitate engineering application,the process calculation software was developed using Py Qt5 for heat exchangers including some new highefficiency heat exchangers such as the heat exchanger with conically-corrugated tubes and HDD baffles and the heat exchanger with arc-corrugated tubes and HDD baffles.Examples show the software is easy and reliable to use.