Question

Prepare 5 pages (max. ) brief description about Multiphase flow pumps that work at high gas volume fraction or percentage ( high GVF).

The report should address the following important points:

1- Differences between multiphase flow pump (for gas and liquid mixture) and single phase flow pump (for liquid).

2-Difference between multiphase (gas-liquid) flow pump at high gas percentage (say 80% and above gas) and a compressor.

3-Differences in pump head, pump speed, design and stages should be addressed.

4-How can we modify a single phase flow pump (liquid only) to handle gas-liquid flow

5-How can we modify a gas-liquid flow pump to handle gas percentage rather than low percentage of gas

Answer 1

1. Differences between multiphase flow pump (for gas and liquid mixture) and single phase flow pump (for liquid).

• In the case of steam and liquid water the density of the two phases differs by a factor of about 1000. Therefore the influence of gravitational body force on multiphase flows is of much greater importance than in the case of single-phase flows.
• The sound speed changes dramatically for materials undergoing phase change, and can be orders of magnitude different. This significantly influences a flow through an orifice.
• The relative concentration of different phases is usually a dependent parameter of great importance in multiphase flows, while it is a parameter of no consequence in single-phase flows.
• The change of phase means flow-induced pressure drops can cause further phase-change (e.g. water can evaporate through an orifice) increasing the relative volume of the gaseous, compressible medium and increasing efflux velocities, unlike single-phase incompressible flow where decreasing of an orifice would decrease efflux velocities.
• The spatial distribution of the various phases in the flow channel strongly affects the flow behavior.
• There are many types of instabilities in multiphase flow.

2-Difference between multiphase (gas-liquid) flow pump at high gas percentage (say 80% and above gas) and a compressor.

Pumps and compressors use very similar mechanisms, and basically perform the same action, but in different fluid regimes. At some point there is a crossover point in terminology, but here are some stereotypes:

• Compressors operate on compressible fluids, typically gases. Pumps operate on fluids, typically liquids, approximated as incompressible.
• Compressors are intended to develop a very high pressure rise against a closed system; pumps are designed to develop relatively little pressure against a free-flowing system with minimal backpressure.
• Pumps are often used in continuous-flow operation, while many lower-end compressors must have intermittent duty cycles.
• Compressors usually have a feedback sensor to shut off when they reach a desired pressure; pumps have a fixed design and operate freely across their performance curve as conditions change.

3-Differences in pump head, pump speed, design and stages should be addressed.

Pump head is the pressure developed.

pump speed is how fast the rotor or crankshaft turns.

pump design is how you select a pump to do what you want it to do.

pump stages refers to the number of rotors or the number of times pump energy is imparted to the pumped fluid within a single pump unit..

4-How can we modify a single phase flow pump (liquid only) to handle gas-liquid flow

With reference to the phase diagram shown .let us say you start with a liquid i the region labelled “liquid phase.” You would increase the pressure at constant temperature into the “compressible liquid” region, then increase the temperature at constant pressure into the “supercritical fluid region. In this region the distinction between liquids and vapors is lost. Then you could decrease the pressure at constant temperature into the gaseous phase region. If desired, you could even then decrease the temperature at constant pressure into the vapor region. All this would happen without there ever being two phases present. This process isn’t very practical but it can be done.

5-How can we modify a gas-liquid flow pump to handle gas percentage rather than low percentage of gas

In general, a reciprocating pump is more efficient than a centrifugal pump. Reciprocating machines are generally applied on low-flow/high-head service. Centrifugal pumps can have efficiencies as low as 40 percent on low-flow/high-head service. A reciprocating machine can have efficiencies greater than 90 percent on the same service. Using reciprocating machines can help end users achieve considerable power savings.