HTRI research focusing on large diameter pipes led to improved prediction of flow patterns and valuable guidance to operators.

Siddharth Talapatra, Senior Project Engineer, Research
December 11, 2016

Liquid-gas two-phase flow can be challenging for the oil and gas, process, and nuclear industries due to the fact that a liquid-gas interface can take on various shapes that strongly impact the transfer of mass, momentum and heat. Better prediction of liquid holdup and two-phase pressure drop can lead to improved prediction of circulation rate and duty of thermosiphon reboilers, among other applications. The flow regime for vertical pipes with upflow can have an impact on pressure pulsations, circulation rates, and thermosiphon instabilities, which are important for the process and power industries.

HTRI recently concluded research on vertical upflows, with a focus on large diameter pipes

We compared a wide range of pressure drop methods against recent air-water data collected in the 12.7-cm diameter transparent flow loop (Figure 1) as well as data collected for saturated steam and hydrocarbons in the outlet piping of a thermosiphon reboiler. This led to the identification of a liquid holdup model that is an improvement over our current methods (HTRI report TPF-14).

We also examined the applicability of the HTRI-recommended Fair [1] and Dukler [2] flow regime maps. We compiled an extensive dataset of flow regimes in large diameter pipes, consisting of open literature and HTRI data, and used it to evaluate various flow regime maps.

Our findings led to some clear guidelines regarding the applicability of Fair and Dukler maps, and we developed a new flow regime map for large diameter pipes (HTRI report TPF-15). This improved prediction of flow patterns in thermosiphon outlet piping can provide valuable guidance to operators and designers.

Figure 1. Picture of the 12.7-cm diameter transparent flow loop, used to acquire pressure drop,
void fraction and flow visualization data for air-water flows
HTRI members can read more about this subject in our recent technical reports:
  • S. Talapatra, Pressure drop and void fraction for vertical upflow in large diameter pipes, TPF-14, Heat Transfer Research, Inc., Navasota, TX (2016).
  • S. Talapatra, New flow regime map for vertical upflow in large diameter pipes, TPF-15, Heat Transfer Research, Inc., Navasota, TX (2016).


  • J. R. Fair, What you need to design thermosiphon reboilers, Petro. Refiner 39(2), 105 – 123 (1960).
  • Y. Taitel, D. Barnea, and A. E. Dukler, Modelling flow pattern transitions for steady upward gas-liquid flow in vertical tubes, AIChE J. 26(3), 345 – 354 (1980).