Non-Boiling Heat Transfer in Gas- Liquid Flow in Pipes – A Tutorial

Abstract :-
In this tutorial the fundamentals of non-boiling heat transfer in two-phase two component gas-liquid flow in pipes are presented. The techniques used for the determination of the different gas-liquid flow patterns (flow regimes) in vertical, horizontal, and inclined pipes are reviewed. The validity and limitations of the numerous heat transfer correlations that have been published in the literature over the past 50 years are discussed. The extensive results of the recent developments in the non-boiling twophase heat transfer in air-water flow in horizontal and inclined pipes conducted at Oklahoma State University’s Heat Transfer Laboratory are presented. Practical heat transfer correlations for a variety of gas-liquid flow patterns and pipe inclination angles are recommended.

Keywords:- Two-phase flow, gas-liquid flow, heat transfer, horizontal flow, upward inclined flow.

Introduction :-
The expression of ‘two-phase flow’ is used to describe the simultaneous flow of a gas and a liquid, a gas and a solid, two different liquids, or a liquid and a solid. Among these types of twophase flow, gas-liquid flow has the most complexity due to the deformability and the compressibility of the phases. Two-phase gas liquid flow occurs extensively throughout industries, such as solar
collectors, tubular boilers, reboilers, oil and geothermal wells, gas and oil transport pipelines, process pipelines, sewage treatments, refrigerators, heat exchangers, and condensers. 1
The knowledge of heat transfer in two-phase gas-liquid flow is important in these industrial applications for economical design and optimized operation. There are plenty of practical examples in industries which show how the knowledge of heat transfer in two phase flow is important. As an example, since slug flow, which is one of the common flow patterns in two-phase gas-liquid flow, is accompanied by oscillations in pipe temperature, the high pipe wall temperature results in ‘dryout’, which causes damages in the chemical process equipments, convectional and nuclear power generating systems, refrigeration plants and other industrial devices (Hestroni et al., 1998a,b; Mosyak and Hestroni, 1999).
Another example is in the field of petroleum industry. The petroleum productions, such as natural gas and crude oil, are often collected and transported through pipelines located under sea or on the ground. During transportation, many pipelines carry a mixture of oil and gas. In the process of transportation, the knowledge of heat transfer is critical to prevent gas hydrate and wax deposition blockages , resulting in repair, replacement, abandonment, or extra horsepower requirements (Kaminsky, 1999; Kim, 2000). Some examples of the economical losses caused by the wax deposition blockages cited by Fogler (2004) are: direct cost of removing the blockage from a sub-sea pipeline - $5 million; production downtime loss (in 40 days) - $25 million, and cost of oil platform abandonment (Lasmo, UK) -$100 million.

The objectives of this tutorial are to briefly present the fundamentals of non-boiling heat transfer in two-phase gas-liquid flow in pipes, review the available non-boiling heat transfer data and correlations that exist in the open literature, and present an overview of the research that has been conducted at Oklahoma State University’s Heat Transfer Laboratory over the past several years on non-boiling, two-phase, air-water flow in vertical, horizontal, and inclined pipes for a variety of flow patterns.

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