![]() ![]() ![]() In section II the fall of the heat transfer coefficients is less than in section I because the heat transfer is improved by the waviness of the condensate film. In zone I and II the heat transfer coefficient falls with increasing vapor rate because the condensate film becomes thicker. Zone III from Re = 1600 with turbulent condensate flow Zone II between Re = 40 and Re = 1600 with laminar wavy flow Zone I up to Re = 40 with laminar condensate flow without waves In gravitation region, three different flow types are formed depending on the condensate Reynolds number. Heat transfer coefficients of ethanol and cyclohexane in the condensation in vertical tubes.Ī distinction is made between the shear stress-controlled and the gravitation-driven heat transfer. If the liquid film thickness is less than or comparable to the pore size, the local volume average will no longer be applicable and a direct simulation at the pore level must be performed.įigure 8.8. This is referred to as a thick-film region, and the local volume average is applicable ( Kaviany, 1995). The discussion in this section is limited to the case where the thickness of the liquid film is much greater than the diameter of the pore size. The temperature in the liquid region is below saturation temperature, while the temperature in the two-phase region is at saturation temperature. It is assumed that the vapor temperature is equal to the saturation temperature, i.e., there is no superheat in the vapor phase. The latter will create a two-phase region between the liquid film and the vapor region, where both condensate and vapor are present. In addition to gravity-driven downward liquid flow, the liquid also infiltrates the vapor region due to capillary force. Film condensation occurs when the temperature of a vertical, impermeable, and wettable wall next to a porous medium saturated with vapor falls below saturation temperature ( Fig. ![]()
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