Validation of the Time Model in Gas–Liquid Horizontal Pipe Flow

In a stratified gas–liquid (water–air in our case) horizontal pipe flow, the growing long wavelength waves may reach up to the top of a pipe and form a slug or evolve into the roll waves. At certain flow conditions, the slugs may grow to become extremely long, up to 500 times pipe diameter (Kadri et al. “On the development of waves into roll waves and slugs in gas/liquid horizontal pipe flow,” in ICMF 98, 2007). Existence of such a long slug may create problems like reduction in operational efficiency (Andritsos et al. in Int J Multiph Flow 15:877–892, 1989). It is important to know at what flow conditions the roll waves start to occur from a wavy stratified flow. It is also necessary to find out the certain critical parameters beyond which the flow starts to form a slug. This can be analysed by tracing the horizontal and vertical time required by the crest to reach at the top pipe wall with the help of the high speed camera (Kadri et al. in Int J Multiph Flow 35:1001–1010, 2009). In this paper, the wave transition time model proposed by (Kadri et al. “On the development of waves into roll waves and slugs in gas/liquid horizontal pipe flow,” in ICMF 98, 2007) is validated using the flow visualization technique considering the average height of liquid \({\mathrm{h}}_{\mathrm{avg}}\) as the input parameter. When the time required by the wave crest to overtake downstream end is less, the roll wave is formed, if not slug formation occurs. Experiments for the validation were performed on the gas–liquid horizontal pipe set-up with 0.05 m internal pipe diameter. The obtained results are in adequate concurrence with the time model (Kadri et al. “On the development of waves into roll waves and slugs in gas/liquid horizontal pipe flow,” in ICMF 98, 2007). The flow visualization analysis is also extended to obtain the wave crest tracking and its characteristics.