Study On Falling Film Dynamics And Interfacial Absorption Performance Of Horizontal Tube Bundles

To increase the primary energy ratio(PER), vertical array of horizontal tube bundles under vacuum condition, as one kind of falling film thermal-dynamic device, is used widely in the absorption refrigeration system. For a long time, the heat transfer calculation and structure design of absorption chiller is in rough status at the absence of the study of falling film flow over the horizontal tube bundles and the fundamental theory of heat and mass transfer. For the same reason, research about the enhancement of thermal component performance is hardly to carry out. At the basis of the past research, three experiments were set up to study the falling film flow microcosmic mechanism of different fluids on horizontal tube bundles and the process of the heat and mass transfer. The first experiment is primarily on the falling film flow mode transition on horizontal tube bundles; the second is on the digital graph high speed collection of the droplet deformation on horizontal tube bundles and and the third is on the interface absorption performance on horizontal tube bundles.The concept of horizontal tube bundles falling film dynamics and interface transfer process is proposed for the first time. Based on the common dynamic characteristic of four main thermal processes such as falling film absorption, falling film evaporation, falling film condensation and falling film generation in the absorption chiller, the falling film flow mode transition on the horizontal tube bundles and the microcosmic mechanism of flow mode transition is investigated. By introducing the concept of interface phenomenon, the common characteristic in the four thermal processes of heat and mass transfer over free surface can be concluded to the interface transfer process. By the integration of falling film dynamics and interface phenomenon, the fundamental theory frame of horizontal tube bundles falling film thermal device is built up.Transition from macroscopical statistics to microcosmic mechanism of horizontal tube bundles is realized by the concept of Unit Fluid. The map of Unit Fluid-Mode Transition Mechanism (UF-MTM) on horizontal tube bundles is given for the first time. The microcosmic mechanism that drives the flow mode from droplet to sheet is interpreted. The main results are that the transition from droplet to columns mode is driven by the continuous liquid neck; the transition from inline columns to stagger column flow is driven by the formation of the surface crest; the pendant liquid under the horizontal tube is the source force of the merging between the adjacent columns; the generation of the liquid tooth and the stagant point is the inevitable phenomenon during the adjacent column merging process; the transition from columns to sheet mode is driven by the merging deformation.The microcosmic development mechanism of droplet formation process on horizontal tube bundles is investigated using high speed video. A series of complex topology structures such as the droplet generation ,growing up, elongation, breakup of the main droplet at the bottom of the liquid neck, the saddle extension on the tube surface, the self-similar shrink of liquid neck, the breakup at the top of the aculeate liquid neck, the generation of the satellite droplets etc. are observed. The innovative significant concept of RSB is proposed to describe the effect of the Ratio of tube Spacing to total Breaking length on the topology structure during droplet formation. The nine important topology transition phases of droplet formation on horizontal tube bundles are proposed for the first time and the topology transition difference of droplet formation under various RSB is analyzed.Based on the graphic information treatment technology, the digital description of microcosmic mechanism of the droplet and columns mode on horizontal tube bundles is presented and the variation of surface area and the volume of unit droplet from its existence duration is analyzed by using the methods of conversion of the pixel coordinate system to the Cartesian coordinate system, the edge detection, the cubic spline smooth curve fitting and self-adaptive Simpson integral, Through the topology similarity analysis of droplet formation process from the macroscopic dimension to microcosmic dimension, the droplet mode on the horizontal tube bundles is involved in the multifarious droplet formation nonlinear dynamics scopes. The topology similar expression near the breakup point of the minium liquid neck of complex fluid is introduced using dimension theory and similar analysis.Based on the mixing level multi-factorial experiment and the multi-factorial Response Surface Methodology, the regression equation of interface heat transfer and mass transfer coefficients is educed. The visualization study platform based on Matlab of horizontal tube bundles falling film thermal-dynamic device has been set up.Throgh above study, the primary discuss on falling film dynamic characteristic of horizontal tube bundles is carried out, the basis of next study about the interface transfer performance of falling film thermal-dynamic device is thereforce established.