Research On Momentum,Heat And Mass Transfer Of Falling Film Absorption In A Vacillating Tube

In recent years, fishing vessels have had to go to deep sea for fishes mainly due to the lack of offshore fish resources and to the limits of fishery areas. Refrigeration, therefore, has been paid close attention for playing an important role in freezing and chilling of fish. In order to overcome some disadvantages that compression refrigeration systems used on most present fishing vessels are unfavorable to energy saving and environmental protection, an absorption refrigeration system with a new working pair of TFE/NMP(2, 2, 2-Trifluoroethanol/N-Mehtyl-2-Pyrrolldone)are proposed to be installed on a fishing vessel in this paper. And for this reason, a lot of theoretical and experimental research on falling film flow characteristics and the coupled momentum, heat and mass transfer of falling film absorption in a vacillating absorber梐 key component of the absorption system is carried out here. The main work is as follows:1 According to boundary layer theory, a physical and mathematical model of falling film absorption in a vacillating vertical tube with TFE/NMP solution is presented for the first time based on the study of that absorption inside a static vertical tube. The model, which includes the effect of additional inertia forces by vacillation, describes a problem of unsteady three-dimension wavy laminar falling film absorption.2. The similarity of velocity, temperature and concentration distributions in the direction normal to the falling film surface is assumed. The original governing differential equations are transformed into integral equations by integration in the whole film. The integral equations are discretised implicitly using two-order upwind finite volume method and solved by Gauss-Seidel point iteration method. The computation program for the discretised equations is worked out and the distributions of some parameters such as velocity, temperatures and concentrations are obtained by processing the calculation results with the soft ware of TechPlot.3. The computation results show that vacillation has a significant effect on falling film absorption in a vertical tube with TFE/NMP solution. Firstly, the related parameters are distributed periodically in the falling film and their periods all equal to that of vacillation of fishing vessel. Secondly, the film tangent and radial velocity components are not zero because of vacillating additional inertia forces and furthermore, in one vacillation period, most parameters are distributed quite regularly in the tangent and radial directions. Thirdly, when other parameters are kept constant, the falling film absorption is enhanced if theamplitude or the period of vacillation is moderately decreased and this result conforms to the theoretical qualitative analysis. Finally, falling film absorption changes with the solution parameters at inlet and system pressure and the change trend is very similar to what happened in the static tube.4. An experimental apparatus of falling film absorption in a vacillating is set up to check the reliability of theoretical model and to have a deep understanding of heat and mass transfer of practical falling film absorption. Falling film absorption with TFE/NMP solution in a static vertical tube and that in a vacillating tube are investigated respectively.5. The experiment results show that when other initial parameters are kept constant, the heat and mass transfer of falling film absorption under the condition of normal vacillation of fishing vessels is better than that in static status; The amplitude and period of vacillation directly influence the performance of the absorber and an adequate decrease of vacillation period or vacillation amplitude is beneficial to the absorption performance. This conclusion tallies with the numerical results;6. Both the experimental and numerical studies indicate that the TFE/NMP absorption refrigeration system can completely meet the demands of the refrigeration of fishing vessels when the sea wind is not strong. The above study p...