Study On The Influence Of Rolling On Falling Film Absorption Characteristics Of Marine Falling Film Absorber

Absorption refrigeration is an important renewable energy application technology,which can use low-grade heat energy to provide heating and cooling.And there is a great amount of waste heat in the ship,especially in the marine diesel engine,some of which could be used again.The waste heat is suitable for air-conditioning system of ship and be used as driving heat source of the LiBr Absorption refrigerator.The rolling state when shipping sails will affect the absorption effect of falling film in absorber.Up to now,the research in this respect is not enough.Therefore,the study of the mechanism of falling film absorption under rolling state not only is of strong theoretical significance,but also has important practical value.Based on the study of the characteristics of heat and mass transfer of absorption,the numerical model to simulate the process of falling film absorption with LiBr solution on a static vertical wall and that on a rolling wall,are established respectively.The main research contents are given as follows:On the basis of the parameters of a 600-ton passenger ship's diesel engine,the quantitative analysis feasibility of to use the waste heat in diesel engine as driving heat source of the LiBr Absorption refrigerator has been studied.1)Thermodynamic analytical study is made on the diesel engine.The results show that the exhaust heat accounted for 23.32%of total fuel combustion heat and the exhaust exergy accounts for 29.55%of total fuel exergy.The exhaust contains vast amounts and high grade of energy,which is suitable to be used as heat source to drive the LiBr absorption refrigeration air conditioner.2)Air conditioning load of the ship was calculated to know that whether the exhaust heat can meet the demand of the air conditioning load or not.The ship's total cooling load is 54kw.Air conditioning load of the ship was calculated to know that whether the exhaust heat can meet the demand of the air conditioning load or not.The ship's total cooling load is 54kw.So,if using single-effect LiBr absorption refrigeration system,exhaust only need to reduce 24.2?;using dual-effect LiBr absorption refrigeration system,exhaust only need to reduce 14.5?.The exhaust temperature reduced so little.It is little effect on the exhaust system.Therefore,the analysis result shows that the scheme of using the exhaust heat of marine diesel engine to drive the absorption refrigeration air-conditioning is feasible.A numerical model to simulate the process of absorption of LiBr solution in static state is established.The variation of the film surface wave,the distribution variation of temperature field and concentration field in interface and bulk are got.The influences of fluctuant of interface concentration and temperature on the heat and mass transfer are discussed.Simulating results show that fluctuation enhances the absorption capacity of film,and fluctuation falling film absorption model is better than smooth falling film absorption model.Simulation results indicate that the velocity of liquid film along the wall decreases and the radial velocity increases,which have a good effect on falling film absorption.When the wall is slightly rolling,the effect of falling film absorption is good,and when the wall is rolling violently,the effect of falling film absorption becomes worse.Under the rolling conditions,the outlet temperature and outlet concentration change with the rolling angles and times are constantly changing.The change is periodically,and the period of change and the rolling are uniform.This paper also investigates the instability of the film in the rolling state.It is found that there may be five surface wave regions,which are the monochromatic wave region,the sine wave region,the solitary wave region,the merged wave region and the fall off region.Rolling angle has an important impact on the change of film surface wave.The evolution process of the film surface wave regions accelerated as the rolling angles get bigger.The instability of falling film in rolling state also affected the concentration gradient of film.When the wall is slightly rolling,the surface wave regions of film are monochromatic wave region,sine wave region and solitary wave region.The concentration gradient of film becomes larger than that of static state.The falling film absorption is promoted.When the wall is rolling violently,the surface wave regions of film appeared merged wave region and fall off region.Liquid film is falling off the wall.The concentration gradient of film becomes smaller than that of static state.The falling film absorption is hindered.The Reynolds number and Sherwood number of film also changed under rolling state.With the same rolling amplitude,the smaller the rolling period is,the faster the Reynolds number increases,the faster liquid film surface wave evolution.As the Reynolds number changes within certain range,the Sherwood number increases along with the increasing of the Reynolds number.However,as the Reynolds number changes without certain range,the Sherwood number decreases along with the increasing of the Reynolds number.