Experimental And Theoretical Investigation Of Heat And Mass Transfer In Plate Heat Exchanger

Plate heat exchangers have been widely used in the practical industrial applications for perfect performance including high efficiency, power saving and compact size. However, more investigations are needed in the researches of heat and mass transfer performance in plate heat exchangers, which make great influences in applications. Experimental and theoretical analyses of heat and mass transfer characteristics in plate heat exchangers are provided, in which different flow parameters, different fouling patterns and different geometry designs have been concerned. Geometric parameters include plate height, plate spacing, and plate angle. The results are valuable for the applications and designs of plate heat exchangers. Main contents of this paper are shown as follow:Firstly, Summaries about heat, flow and mass transfer characteristics in plate heat exchangers have been done. Empirical formulas for heat transfer coefficient and friction factor are listed in the paper. Also, fouling mechanisms and fouling models of precipitation fouling, particulate fouling and composite fouling are analyzed.Secondly, fouling model in this paper is based on mass balance model of Kern and Seaton. The basic method of heat and mass problems in turbulence is analogy. Four analogies including Reynolds analogy, Prandtl-Taylor analogy, Von-Karman analogy and j factor analogy, which have different applied condition, are systematically discussed. A semi-theoretical fouling model has been established based on a group of fouling experiments using Prandtl-Taylor analogy, Von-Karman analogy and j factor analogy. Von-Karman analogy shows the best accuracy and the applied condition of Von-Karman analogy is the widest among the three analogies. Also, the fouling model based on Von-Karman analogy is the most suitable more in turbulence comparing with the other two. Therefore, Von-Karman analogy is chosen to be the basic theory in our fouling model. Thirdly, experiment rig has been established with the coordination of Shandong University. Experiments for testing the heat transfer coefficient and friction factor in four plate heat exchangers have been finished. Modified Wilson plot method and equal Reynolds method are used in the tests of heat transfer coefficient. Simulation results of heat and flow characteristics in four plate heat exchangers have been given. In addition, three fouling tests including precipitation fouling tests, particulate fouling tests and composite fouling tests have been finished, which are focused on the influences of temperature, concentration and average velocity, respectively. Also, geometry parameters and flow parameters are concerned in fouling tests. A type of Teflon coated plates has been used for testing the anti-fouling characteristics and well anti-fouling performance is shown in the coated plates comparing with the common SS-304plates. The largest reduction of fouling resistance in the anti-fouling tests is36.8%and the anti-fouling effects in precipitation fouling tests are much better than particulate fouling tests.Finally, the fouling models of plate heat exchangers including precipitation fouling, particulate fouling and composite fouling, which are based on Von-Karman analogy, have been established. The fouling models in plate heat exchangers show-well predictions, which are all less than±20%comparing with the experiment results. The fouling models in particulate fouling tests show the best predictions, which are all less than±6%comparing with the experiment results. In addition, the fouling mechanisms of precipitation fouling, particulate fouling and composite fouling have been discussed. The micro structures of the fouling deposition have been investigated using Scanning Electron Microscopes. Micro structures of the fouling depositions give more results about the processes of fouling deposition and discussions between the fouling mechanisms and the micro structure of fouling deposition have been given.