Estimating Void Fraction and Frictional Pressure Gradient — Lesson 8

This lesson covers the estimation of void fraction and frictional pressure gradient in two-phase flow systems. The lesson begins with a discussion on the empirical approach to finding the frictional pressure gradient, which is primarily expressed in terms of two-phase multipliers. The lesson then delves into the Lockhart and Martinelli correlation, which is widely used to express the two-phase frictional pressure gradient in terms of equivalent single-phase pressure gradient terms. The lesson also discusses the limitations of the separated flow model and the assumptions it is based on. The lesson concludes with a comparison of the separated flow model and the actual annular flow situation, highlighting the discrepancies between the two.

Video Highlights

00:17 - Introduction to the topic of estimation of void fraction and frictional pressure gradient
04:19 - Explanation of the assumptions made in the correlation
05:33 - Discussion on the derivation of phi l square for annular flow
43:09 - Explanation of the correlation between void fraction and X
43:27 - Discussion on the modifications and improvements of the Lockhart and Martinelli correlation

Key Takeaways

- The frictional pressure gradient in two-phase flow systems is primarily estimated using empirical correlations.
- The Lockhart and Martinelli correlation is a widely used method to express the two-phase frictional pressure gradient in terms of equivalent single-phase pressure gradient terms.
- The separated flow model, while useful, is based on certain assumptions and has its limitations.
- A comparison of the separated flow model and the actual annular flow situation reveals discrepancies, primarily due to the neglect of interaction between the two phases.