The Heat And Mass Transfer Characteristics Of The Falling Film Absorption Process In The Absorption Power Circulation Tube

The absorption power cycle system can efficiently recover low temperature waste heat or low-grade thermal energy,and the absorber is one of the key components of this system.The enhancement of heat and mass transfer for the absorber will improve the performance of the absorption power cycle system.In this paper,the numerical simulation of the heat and mass transfer characteristics for falling film absorption in the vertical tube of absorber installed in the absorption power cycle system is carried out.The main research work is as follows:The commercial CFD code,ANSYS FLUENT,is used to solve the governing equations,in which,the VOF model and CSF model are both considered.The effect of the inlet temperature and concentration of solution,the inlet mass flow rate of the solution,the inlet temperature of the cooling water,and the contact angle between the liquid film and the wall surface on the heat and mass transfer for the falling film absorption in vertical tube are studied.The results reveal that the heat and mass transfer flux of falling film absorption increases first and then decreases with the increase of the inlet mass flow rate of the solution,that is,there is an optimal inlet mass flow rate of the solution,which presents the heat and mass transfer flux for the falling film absorption.The heat and mass transfer flux decrease with the increase of the cooling water inlet temperature,the solution inlet temperature and the concentration.The heat and mass transfer flux decrease when the contact angle increases.Comparing the CFD numerical simulation results with the experimental correlation calculation results,it can be found that the relative errors of them are less than 25%.CFD numerical simulation is carried out to study the effects of porosity and thermal conductivity of porous media on heat and mass transfer for the falling film absorption in porous media when Brinkman-Forchhiemer extended Darcy equation is considered.The results reveal that the average heat and mass transfer coefficient,heat and mass transfer flux for the absorption increase first and then decrease with the increasing of porosity,that is,there is an optimal porosity,which presents the best heat and mass transfer performance.The optimum porosity is about 0.8.When the thermal conductivity of porous media increases,the average heat and mass transfer coefficient,and average heat and mass transfer flux increase,but the increment decrease.CFD numerical simulation is carried out to study the heat and mass transfer performance for falling film absorption in a vertical threaded tube.The heat and mass transfer performance of the smooth pipe and the four threaded tube with different structural parameters(pitch and groove depth)are compared,the effect of the pitch and groove depth on the heat and mass transfer for falling film absorption are studied respectively.The results reveal that the threaded pipe with a pitch of 6mm and a groove depth of 0.75 mm exhibits the best heat and mass transfer performance among these four kinds of threaded pipes,and the heat and mass transfer coefficient of the threaded pipe are 149% and 87.2 % higher than that of the smooth pipe,respectively.With the increasing of the pitch,the average heat and mass transfer coefficient of the absorption first increase and then decrease,that is,there is an optimal pitch(6 mm),which present the largest heat and mass transfer coefficient.With the increase of the groove depth,the average heat transfer and mass transfer coefficient of the absorption process first increase and then decrease,that is,there is an optimal groove depth(0.55 mm at the tube diameter of 22mm),which presents the best heat and mass transfer performance.