Development And Research Of High Efficiency Heat Exchanger With Lower Flow Resistance

It is the main purpose of research on heat exchanger to increase heat transfer efficiency and reduce pressure drop. The important factor which affects the comprehensive performance of heat exchanger is fluid flow conditions in heat exchanger. So, only by understanding the law of fluid flow can it be found to improve heat transfer efficiency and reduce pressure drop. In this paper, the spiral flows have been studied as research object, the influential factors of the heat transfer coefficient and pressure drop has been analyzed, and the new type of tube and heat exchanger has been researched and developed by using the results. The performance of this new type of heat exchanger has been tested by experiment. The results show a better performance of this kind of heat exchanger than the rod baffler heat exchanger. The main works and productions in this paper are as follows:(1) The spiral flows in the tube have been analyzed by using method of numerical and analyses in which the model of tube with twisted tape inserts had been set up. The effects of twist ratio and Reynolds number on fluid flow and heat transfer have been discussed. The enhanced heat transfer mechanism of spiral flow is: twisted tape can induce spiral flow so that the flow velocity and the secondary flow are increased, the flow boundary layer and heat transfer boundary layer are thinned, and the convection heat transfer is enhanced. The cross-sectional area of spiral duct along the axis doesn't change, and fluid doesn't produce vortex and return fluid flow, and the movement of fluid is fluent and stable continuously. The velocity and heat transfer coefficient can be increased by increasing Reynolds and reducing twist ratio, thus convective heat transfer is enhanced.(2) Spiral flows around tube have been researched by using the same method in which the model of double-tube heat exchanger with spiral tape has been set up. The effects of helical angle and Reynolds number on fluid flow and heat transfer have been discussed. The results reveal the same mechanism of enhanced heat transfer of spiral flows both in tube and around tube. The cross-section area of spiral duct around tube along the axis will not change, so vortex and return fluid flow fluid will not be produced. The difference between spiral flow around tube and in tube is the action area. The spiral tape exert less influence on fluid than twisted tape because its small action area. It is necessary to enlarge action area of spiral tape in structure design.(3)A new type of tube, helical rib tube, and heat exchanger, helical ribbed self-support type heat exchanger, have been developed based on above research and the merits of helical baffle heat exchanger. The structure of this new type of tube has been designed. This new type of tube has been manufactured by designing a proper processing technique. The helical ribs in heat exchanger can substitute for baffle plate because it will increase heat transfer area, induce spiral flow, and support tube bundle and tube. The structure and assembly method of this new type of heat exchanger have been designed. The helical ribbed self-support type heat exchanger has the merits of higher heat transfer coefficient, lower pressure drop, good compressive performance, and simple structure. The supports and restrictions for tubes are so many that can produce the favorable antivibration capability.(4) The three dimensional models of two kind of tube bundle have been set up, the velocity field, the pressure field and temperature field have been simulated. The results reveal the enhanced heat transfer and lower pressure. The different spiral flows are promoted each other because of the tube bundle arranged ribs with the different spiral directions. The comprehensive performance of tube bundle with different spiral direction is better than the same direction. The best range of spiral angle has been determined which is from 20°to 25°by optimizing.(5) The performance of helical ribbed self-support type heat exchanger has been tested by experiment, and the results have been contrasted with the simulation results which show the feasibility of numerical simulation. The performance experiment of rod baffle exchanger with the same conditions with helical ribbed self-support type heat exchanger has been done, and the results have been contrasted. The conclusions are attained that the total transfer heat coefficient of helical ribbed self-support type heat exchanger is higher than that of rod baffle heat exchanger and the pressure drop is lower than its, the comprehensive performance is heightened distinctly. The relationship formula of heat transfer has been attained by disposing the data of experiments, and can provide reference for engineering application.