Heat falling film absorber

Falling-film absorbers. These are usually vertical heat exchangers with the cooling medium in the shell and the absorption taking place in the tubes. The solvent flows downward, while the gas may enter either at the bottom (countercurrent flow) or at the top (cocurrent flow). 

Mass transfer in falling-film absorbers is strongly dependent on the gas velocity in the tubes, the liquid and gas distribution, and the tube surface conditions. The maximum capacity of falling-film absorbers is normally restricted either by flooding or by pressure drop. Another important limit in these absorbers is film breakup. If heat flux is excessive, dry areas may form at the tube wall and reduce mass transfer. 

Falling-film absorbers make continuous heat removal possible and are therefore extensively used in applications where the heat released during absorption is high, such as in the absorption of hydrogen chloride to form hydrochloric acid. 

Uddholm, H., and Setterwall, F. (1988) Model for Dimensioning a Falling Film Absorber in an Absorption Heat Pump, International Journal of Refrigeration, Vol. 11(1), pp. 41-45. 

Related topics are evaporation (Section 16.11.4.1) for gravity and agitated falling films, absorbers (Section 16.11.4.8), and shell-and-tube heat exchangers (Section 16.11.3.3). 

Desorphon technology has been developed primarily for absorption-cycle heat pumps. The counter flow falling film absorber developed by Garimella has been tested by Determan as a desorber, requiring only modification of the flow distribution and enclosure [259]. The desorber (18 X 18 X 51 cm) could transfer... 

For example, vaporization may occur as a result of heat absorbed, by radiation and convection, at the surface of a pool of hquid or as a result of heat absorbed by natural convect ion from a hot wall beneath the disengaging surface, in which case the vaporization takes place when the superheated liquid reaches the pool surface. Vaporization also occurs from falling films (the reverse or condensation) or from the flashing of hquids superheated by forced convec tion under pressure. 

A very early application of liquid film flow in the chemical industry is mentioned in a patent of 1836 (G5) hydrogen chloride gas produced in the Leblanc soda process was absorbed by water films flowing over packings. Much later the film coolers and evaporators used in the German beet sugar industry inspired the earliest detailed theoretical and experimental studies of flow and heat transfer in falling films (CIO, N6, N7). Chemical engineering interest in film flow has increased rapidly in recent years. 

Jeong, S., and Garimella, S. (2002) Falling-Film and Droplet Mode Heat and Mass Transfer in a Horizontal Tube LiBrAVater Absorber, International Journal cf Heat and Mass Transfer, Vol. 45(7), pp. 1445-1458. 

Killion, J. D., and Garimella, S. (2005) Simulation of Pendant Droplets and Falling Films in Horizontal Tube Absorbers, Journal of Heat Transfer, Vol. 127 (in press). 

As discussed in the section on absorbers (Section 7.7.4), falling films used in microchannels have shown potential for ammonia-water systems [279]. The military has shown interest in these absorption systems due to their inherently low electrical requirements and low noise. However, military application requires orientation independence, even more restrictive size requirements, and a heat rejection temperature of 50 °C (120 °F). To address this need, wicking and fractal microchannel technology has been developed that allows orientation independence and control of the liquid film thickness, which in turn controls the majority of mass... 

Film-type tube apparatus) Multitube apparatus with an absorbent falling-film on the tube insides. Cocurrent and countercurrent flow of gas phase and falling-film (both phases are coherent). Simple design with the possibility of heat removal by a cooling agent outside the tube shell. Low gas pressure drop, small interfacial area, small liquid mass transfer coefficient. 

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