SURFACTANTS AND FLUID PROPERTIES

Investigations were made to clarify if the change in the surface tensi on and the viscosity of aqueous solution of LiBr due to small amounts of surfactants can explain the observed enhancement of the heat-transf er coefficient in a falling film absorber with horizontal tubes. It is expected that, especially for this type of absorber, the surface tens ion has an impact on the absorber performance. Yet it will be shown in this study that the effect of the reduced surface tension alone canno t explain the changed heat-transfer behavior for all investigated surf actants. This also applies to the viscosity. Measurements of this quan tity which will be presented show that the decrease of the viscosity i s too small to be responsible for the enhancement. Effects creating tu rbulence, such as Marangoni convection, or the drop characteristics ha ve to be taken into account. Further investigations, particularly of t he surface tension, are necessary to understand the mechanism of enhan cement due to surfactants. Copyright (C) 1996 Elsevier Science Ltd and IIR