Performance Research Of Horizontal Tube Falling Film Evaporator

Horizontal-tube falling film evaporator has many advantages such as high heat transfer coefficient,small heat transfer temperature difference and sufficient refrigerant amount,which has attracted the attention of a large number of scholars.However,the phenomenon of“dry patch" is likely to appear on the outer wall of the heat exchange tube bundle of the falling film evaporator.Some studies have proposed the use of an ejector recycling system to reduce this phenomenon.However,there are few studies on it.It is difficult to directly optimize it.Therefore,it is very important to provide theoretical reference for the design of horizontal-tube falling film evaporator.On the basis of consulting a large number of factors related to the heat transfer performance of the horizontal-tube falling film evaporator and using the research data of the liquid recirculation system.After analyzing the influence of various factors on the performance of horizontal-tube falling film evaporator,the structure of falling film evaporator is optimized,and a new patented falling film evaporator structure is designed.The structure of the new horizontal-tube falling film evaporator not only uses the liquid recirculation system,but also sets the first and two stage distributor.Trying to make the outer wall of the tube in the bottom heat pipe more uniform and reduce the phenomenon of local "dry patch".In this paper,a finite difference model for the evaporation heat transfer of a horizontal-tube falling film evaporator is established.In the model,the variation of heat transfer performance along tube side fluid flow direction,tube array vertical and horizontal direction,as well as the effect of dry patch on the performance are considered.Here adopt Roques'correlations based on experimental data to solve heat transfer coefficients of falling film on horizontal tube surfaces.Through the theoretical model,two kinds of simulation programs for falling film evaporators with different structures are programmed using Visual Basic language.The performance parameters of the four prototypes are simulated and calculated by this software,and the error analysis is checked through the calculation results,which shows that the software can be applied to this research.For comparison and analysis of the data,it is concluded that the performance of falling film evaporator and recirculation ratio etc,the relationship between the and verify the design of new type falling film evaporator can reach the expected effect.Conclusion:In order to completely eliminate the phenomenon of dry patch on the surface of the reinforced heat transfer tube bundle,the value of the recirculation ratio R1 should be more than 1.5;The suitable recirculation ratio R1 is about 1.2,and the integrated falling-film factor ? is about 0.78;It shows that for a given heat transfer tube,the falling film evaporator should have the appropriate refrigerant recirculation flow value,making the falling film evaporator high heat transfer performance and avoiding the excessive waste of refrigerant;In the new design of falling film evaporator,only in the small flow rate of refrigerant recycling situation;In order to achieve the expected results,and to achieve the best state of falling film evaporator,the refrigerant flow rate required is about 1.5 times the existing use of liquid recirculation system of falling film evaporator;Although the bottom heat exchange tube bundle of the secondary recirculating falling film evaporator is better than the primary recycle structure in achieving the original design of the falling film evaporator,the effect is not significant,and the local "dry patch" phenomenon of the upper heat exchange tube bundle is intensified.