Turndown Curve and Flow Map

What is the Turndown Curve (TDC)?

The turndown curve (TDC) is a graph that represents the pressure drop versus the mass flow rate in a flow line vulnerable to terrain slugging, It is represented by a convex curve.

The left zone to the inflection point in the TDC represents the zone where the gravity forces are preponderant. On the other hand, the right zone to the inflection point in the TDC represents a zone where the friction forces are preponderant.

 

Why the Turndown Curve (TDC) is helpful?

The TDC is helpful for this project since it shall suggest the start point to simulate the transition between a stable flow (No severe slugging) and a no stable flow (severe slugging). This start point should be the lowest point of the TDC.  

It is important to note that the lowest point of the TDC does not always represent the transition point between a stable and a no stable flow. It only indicates the starting point. This subject will be broaden in the next sections

How to calculate the Turndown Curve (TDC)?

  1. Liquid and gas mass fraction are fixed.
  2. A total mass flow rate is fixed.
  3. All the parameters and variables are introduced in LedaFlow.
  4. The simulations is run with the steady-state pre-processor. 
  5. The pressure is measured. 
  6. The differential pressure is calculated by subtracting the atmospheric or outlet pressure of the system.

These are the steps to calculate one point of the TDC. The same procedure is repeated (from #2 to #6) in order to calculate the rest of the points, just the liquid and gas mass fraction remains constant and fixed. 

What is the Flow Map?

As its name indicates, the flow map is a map that shows at which conditions of superficial velocity of liquid, superficial velocity of gas, liquid mass fraction and gas mass fraction the flow is stable, where there is no severe slugging, and no stable, where there exist severe slugging. 

This flow map is a result of the transient simulation of each point of the different Turndown Curves.