Experimental slug flow dissipation analysis in pipes with horizontal to inclined downward direction change

•Experimental study on gas–liquid two-phase slug flow in ducts with slightly direction changes was realized.•Three slug dissipation phenomena, namely, gas plug, stratification and wave flooding, were observed.•Bubble rear velocity tends to exceed that its front in downward inclined cases.•Froude number and superficial gas–liquid velocities are used to classify the Gas plug, the stratification and, the wave flooding.•Gas plug, stratification and wave flooding were analyzed with the aid of average values and Probability Density Functions.