Experimental work about counter current two-phase flow of air and gas in nearly horizontal pipe has been performed. The work was performed in a 1.1？m long circular transparent acrylic pipe with 50？mm inner diameter, in two inclination angle settings (20° and 10° from horizontal). The smooth liquid and air inlet was used. Porous liquid inlet and a nozzle connected with calm section were used as liquid and gas inlet. The effect of liquid properties is examined by using five different working fluids (Water, two different concentration of butanol and glycerin aqua solutions). As for results. (1) CCFL causes a drastic change in the delivered liquid to the lower plenum. (2) The effect of inclination angle is significantly observed. The flooding gas superficial velocity decreases with inclination angle. (3) The liquid viscosity affects the flooding phenomena. 1. Introduction Counter current flow in vertical tube has many applications in a diverse range of process industries. The phenomenon of flooding is of considerable technological importance, as flooding can be limiting factor in the operation of equipment. For example, in a pressurized water reactor (PWR), the counter-current flow of steam (upward) and cold water (downward) may take place in vertical channels when the emergency core cooling (ECC) water is injected into the reactor vessel. This leads to complex processes including the condensation of steam due to the introduction of cold water in to the reactor core. Most importantly upward steam flow may prevent sufficient cooling of reactor component by ECC water. Flooding phenomena have been studied in order to develop analytical models to predict the onset of flooding velocity. As a result, a large number of correlations have been proposed in the literature to predict it for given set of condition. In spite of the large number of reported results, there is still considerable uncertainty concerning the phenomena at the onset of flooding. A previous work by Wallis [1] who studied counter current of liquid-gas flow in vertically channel found the inversely proportional relationship of the liquid and gas velocity. To provide a further observation, Hewitt [2] and Barnea et al. [3] performed an experiment in inclined pipe and showed the effect of inclination angle. They found that the effect of inclination angle is complicated. The flow rate at which flooding occurs increases and then decreases as the inclination angle is changed from horizontal to vertical. In the other hand, Pantzali et al. [4] showed the tendency of the flooding gas flow rate increase with
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