Investigation Into The Falling Film Formation Of Lithium Bromide Solution On The Inside Surface Of A Horizontal Tube And Its Enhanced Mass Transfer

Absorber is the key part in the absorption refrigeration cycle. The behaviors ofthe absorber directly affect the refrigerating performance in absorption refrigeratingsystem. In the view of absorption mechanism, the falling film formation, masstransfer ratio of water vapor on the way from the vaporizer to the absorber and thediffusion of water vapor on the surface of Lithium Bromide falling film play a keypart in absorption process. Therefore, the investigation into the falling film formationof Lithium Bromide on the surface of absorber and the way of enhanced mass transfercan not only be helpful in industrial application for a better absorption behaviors, andits results may also make contribution to the theoretical progress in mass transfer.A theoretical model for describing falling film formation and mass transfer ofLithium Bromide solution on the inside surface of a horizontal tube was establishedbased on the boundary layer coordinate system and numerical solution was obtainedby using TDMA method, combining theoretical analysis to its mechanism. The localvelocity and thickness of falling film of Lithium Bromide were solved numerically foreach case, and discussions to the flow behaviors of falling film were made combiningsolving the local liquid film temperature and water vapor distribution. The masstransfer coefficient can also be made out by this and it shows that the enhancement ofmass transfer can bring about a better absorption behaviors. An experimentalapparatus was developed to investigate absorption behaviors of falling film ofLithium Bromide solution on the inside surface of a horizontal tube in the case offorced convection mass transfer and the convection mass transfer coefficient wasobtained experimentally. The result shows that a suitable vapor velocity and lowervacuum pressure can bring about a better absorption behavior in the case of forced convection water vapor transfer, and theoretical analysis suggested that the thinnerboundary layer thickness, the lower mass transfer resistance in the case of forcedconvection water vapor transfer on the Lithium Bromide solution surface. Numericalsolution to the temperature distribution in the falling film of Lithium Bromidesolution and water vapor density distribution in the absorber show that there is largevariations of falling film temperature and water vapor density in the circumferencedirection rather than radial direction.5m/s of water vapor velocity can provide bestabsorption behavior in the case. An experimental comparison with falling filmabsorption of Lithium Bromide solution on the outside surface of horizontal tube wasmade in the case of forced water vapor convection. The result shows that masstransfer enhancement of falling film absorption inside the tube is superior to thatoutside the tube for the smaller size and more suitable structure for heat transferenhancement. Thus, liquid falling film absorber inside the tube maybe the best choicefor the engineering application.