The instability of a liquid layer heated from the side when the upper surface is open to air

When a liquid layer is heated from the side, a monocellular flow develops immediately, no matter how small the temperature difference is. If the temperature gradient between the side walls is increased, this flow becomes unstable. Laser Doppler velocimetry measurements are reported here in an attempt to describe the main features of both the basic flow and the instability modes. It is found that before the appearance of traveling waves ~the most dangerous mode as predicted by the theory!, stable rolls with their axes perpendicular to the temperature gradient, span over the whole liquid layer, starting from the hot side, even if the aspect ratio ~the length of the layer divided by its thickness! is very high. This unexpected situation modifies the basic flow. A further increase of the temperature gradient leads to the appearance of a time periodic motion. © 1996 American Institute of Physics

Experimental Correlation of Combined Heat and Mass Transfer for NH 3 -H 2 0 falling film absorption

vection. The main conclusion from this study is that the negative concentration gradient of the surface tension is a trigger for inducement of Marangoni convection before the additive solubility, while the imbalance of the surface tension and the interfacial tension is a trigger after the solubility limit. Acknowledgment The authors thank Mr. K. Iizuka, Tokyo University of Agriculture and Technology, for his experimental assistance. The authors acknowledge that this work has been partially funded by the Japan Science and Technology Corporation (JST). References Beutler, A., Greiter, I., Wagner, A., Hohhmann, L., Schreier, S., and Alefeld, G., 1996, "Surfactants and Fluid Properties," Int. J. Refrigeration, Vol. 19, No. 5, pp. 342-346. Chavepeyer, G" Salajan, M., Platten, J. K., and Smet, P., 1995, "InterfacialTension and Surface Adsorption in j-Heptanol/Water Systems," Journal of Colloid and Interface Science, Vol. 174, Daiguji, H,, Hihara, E., and Saito, T., 1997, "Mechanism of Absorption Enhancement by Surfactant," Int. J. Heat and Mass Transfer, Vol. 40, No. 8, pp. 1743-1752. Fujita, T., 1993, "Falling Liquid Films in Absorption Machines," Int. J. Refrigeration, Vol. 16, No. 4, pp. 282-294. Hihara, E" and Saito, T., 1993 Journal of Heat Transfer TL = temperature of the fluid far away from the plate t' = time t R = reference time u = velocity of the fluid UD = reference velocity at' = frequency X,, = distance of the transition point from the leading edge |3 = coefficient of volume expansion p = density e = amplitude (constant) 9 = nondimensional temperature u = nondimensional velocity i = y-i Introduction Transient laminar-free convection flow past an infinite vertical plate under different plate conditions was studied by many researchers. The first closed-form solutions for Prandtl number Pr = 1.0 in case of a step change in wall temperature with time was derived by Illingworth (1950) and for Pr # 1.0, he derived the solution in integral form. Siegel (1958) studied the unsteady freeconvection flow past a semi-infinite vertical plate under stepchange in wall temperature or surface heat flux by employing the momentum integral method. Experimental evidence for such a situation was presented by Goldstein and Eckert (1960). For a semi-infinite vertical plate, unsteady free-convection flow was studied analytically b

Intérêt de la méthode des différences finies pour l'étude non linéaire du problème de Bénard dans les mélanges

Le problème de Bénard dans les mélanges présente des difficultés particulières dans le cas non-linéaire et pour des surfaces aux limites rigides. La méthode des différences finies présentée dans cette communication permet une simulation plus fidèle d'un appareil de Soret plan de dimensions finies. Elle complète ainsi la littérature récente sur le sujet.Chavepeyer G. Intérêt de la méthode des différences finies pour l'étude non linéaire du problème de Bénard dans les mélanges. In: Bulletin de la Classe des sciences, tome 60, 1974. pp. 1433-1467

The instability of a liquid layer heated from the side when the upper surface is open to air

When a liquid layer is heated from the side, a monocellular flow develops immediately, no matter how small the temperature difference is. If the temperature gradient between the side walls is increased, this flow becomes unstable. Laser Doppler velocimetry measurements are reported here in an attempt to describe the main features of both the basic flow and the instability modes. It is found that before the appearance of traveling waves ~the most dangerous mode as predicted by the theory!, stable rolls with their axes perpendicular to the temperature gradient, span over the whole liquid layer, starting from the hot side, even if the aspect ratio ~the length of the layer divided by its thickness! is very high. This unexpected situation modifies the basic flow. A further increase of the temperature gradient leads to the appearance of a time periodic motion. © 1996 American Institute of Physics