I know that you're gonna have it your way or nothing at all
But I think you're moving too fast

("Waterfalls," by TLC, 1996)

 

RIGID VERSUS NON-RIGID PIPING SYSTEMS

PTOA Readers and Students also recently learned in PTOA Segment #233 that the PV Flowrate is delivered to where it is needed via an extensive Piping Network.

Guess what?  The human body also has an intricate network of piping called the Blood Circulation System.

The Blood Circulation System in the human body even has a Positive Displacement Pump called The Heart. The Heart discharges blood into a Blood Supply Header that divides up into arteries that deliver blood where it is needed.  The Return Header supplies blood to the suction-side of The Heart through a network of veins. 

Here's an important difference between the Blood Circulation System in the human body and the Piping Network in a processing facility:

The content of the PTOA PV Flowrate Focus Study Area DOES NOT apply to flexible piping like arteries and veins in a human body.

All of the content in the PTOA PV Flowrate Focus Study Area assumes that the pipes in the Piping Network are rigid. The fluid flowing through the the pipes completely fills the pipes; there are no pockets of air.

Furthermore, the PV Flowrate content does not apply to water flowing through open channels.

Otherwise stated: All of the Piping and Pipe Fittings featured in the PTOA PV Flowrate Focus Study Area are rigid and completely filled up by the flowing fluid.

Once again, Fred is confused!

Fred wants to know what the big deal is about "rigid" versus "non-rigid" Piping.

Knowing that the Piping Network pipes are rigid infers that any change in the PV Flowrate is due to a change in the flowing fluid's Velocity.

Why?

 

THE TWO COMPONENTS THAT DETERMINE A VOLUMETRIC FLOWRATE.

PTOA Segment #159 featured the PV Pressure ↔ Fluid Velocity Swap and also defined the two components that determine the Volumetric Flowrate of a fluid:

• The Flow-Through Area of the Pipe (A) is the same as the formula from geometry books to determine the area of a circle. Flow-Through Area of a Pipe = π * (Internal Radius of Pipe).²   For example, assume that water is flowing through a 1-foot diameter pipe.  The Flow-Through Area of a Pipe with an internal pipe diameter equal to 1-foot diameter is 3.14 * 0.5 ft² = 0.785 ft.²
• The Velocity (V) of a flowing fluid is simply how fast fluid is flowing through the pipe. Velocity is always expressed as a distance divided by a time.  For example, a fluid flowing 10 feet per 1 minute has a Velocity of 10 ft/min.
• When the Velocity (V) of the example fluid is multiplied by the Flow-Through Area of the Pipe (A), the Volumetric Flowrate of the example fluid (sometimes called Q) can be quantified: Q =(0.785 ft²) * (10 ft/min) = 7.85 ft³/min.

 

Conversion Factors were featured in PTOA Segment #148.  A Volumetric Flowrate (Q) of 7.85 ft³/min can be converted into gallons/min by accessing any on-line conversion tool and learning 1 ft³=7.48 US liquid gallons. Thus 7.85 ft³/min*7.48 gal/ft³= (7.85) * (7.48) gal/min = 58.72 gpm (gallon per minute).

In conclusion, Fred:

First point: Since a rigid pipe will have a constant Flow-Through Area, the only changes observed in a PV Volumetric Flowrate must be attributable to a change in the fluid's Velocity factor!

Second point: The Velocity factor of a flowing fluid will also change as predicted by the PV Pressure ↔ Fluid Velocity Swap; the Velocity factor of a Volumetric Flowrate will increase if the pipe diameter decreases and vice versa.

Got it, Fred?

 

 

VOLUMETRIC FLOWRATES MUST BE CORRECTED TO STANDARD CONDITIONS

Brilliant PTOA Readers and Students already learned how molecules are excited by an increase in PV Temperature.

As the PV Temperature steadily increases, the molecules in a substance get excited and start banging into each other ...and then ricochet off of each other ...eventually making a solid substance melt into a liquid and a liquid substance vaporize into a vapor or gas.

All PTOA Readers and Students learned the definition of Density and Specific Gravity in PTOA Segment #145.

Density is the Mass of a substance divided by the Volume of the substance.

The Specific Gravity of a Gas is the Density of the Gas divided by the Density of Air (at 60 °F).

The Specific Gravity of a Liquid is the Density of the Liquid divided by the Density of Water (at 60 °F).

And all PTOA Readers learned the following interrelationships of fluid properties in PTOA Segment #162 (↑ means "Increases" and ↓ means "Decreases").

Fluid Temperature ↑ =

Fluid Volume ↑ & Volumetric Flowrate ↑
& Density ↓ & Specific Gravity ↓

and vice versa:

Fluid Temperature ↓ =

 Fluid Volume ↓ & Volumetric Flowrate ↓
& Density ↑ & Specific Gravity ↑ 

Why does all the above matter with respect to measuring a Volumetric Flowrate?

The Actual Flowing Temperature and the Actual Flowing Pressure of the flowing fluid must be corrected to Standard Temperature and Standard Pressure so that an accurate Volumetric Flowrate can be determined based on a known Temperature and Pressure.

In the industrial USA, Standard Temperature has been defined as 60 °F (aka, 519.67 °R).

In the industrial USA, Standard Pressure has been defined as 14.7 psia (0 Gauge Pressure).

The Standard Temperature and Standard Pressure are defined differently in other industrial processing areas of the world.

The Specific Gravity of the flowing gas or liquid can be corrected to Actual Flowing Specific Gravity after lab results reveal what the Actual Flowing Specific Gravity is.

The nearby calculation shows how an Actual Gas Flowrate of 0.032 ACFM (Actual Cubic Feet per Minute) is corrected to 0.48 SCFM (Standard Cubic Feet per Minute).

Note that the Standardized Flowrate of 0.48 SCFM is 1.5 times greater than the Actual Flowrate of 0.032 ACFM ...quite a difference!

Furthermore, the standardization calculation is fairly complicated. Fortunately, today's Smart Transmitters and/or the Distributed Control Systems "bloc calcs" perform the standardization calculations.

The output of the calculations will be represented as Flowrates in units of SCFH (Standard Cubic Feet per Hour) or perhaps MMSCFD (Millions of Standard Cubic Feet per Day). The "S" denotes that the PV Flowrate measurement has been corrected to Standard Temperature (60 °F=519.67 °R) and Standard Pressure (14.7 psia).

A few more points on the subject of correcting PV Volumetric Flowrates:

Brilliant PTOA Readers and Student will also remember that a change in the PV Pressure will change the Density and hence Specific Gravity of a gas or vapor. (Hey! That's an application of the Gas Laws that are Always and Yet Never Used!).

However, a change in PV Pressure does not significantly impact the Density and Specific Gravity of liquids. Why? Because liquids are not compressible! Otherwise stated, a liquid's Volume does not change much when Pressure is increased or decreased.

 

MASS FLOWRATES

Wow! A man was put on the moon and returned back to Earth in 1969. Why hasn't a technology to accurately measure a Flowrate without all the correcting to Standard Temperature and Standard Pressure been developed?

A Flowrate Device that could accurately measure Mass ... not Volume ... would simply quantify how fast an amount of stuff ... aka, Mass ... is flowing over a unit of time.

 

 

A Mass Flowrate is expressed in a unit of Mass divided by a unit of time. Examples include Pounds Mass/hr or Kilograms/hr.

PTOA Readers and Students are already aware of one important use of Mass Flowrate in process industries ...  the production of Steam.

The thing about Steam is that it is 100% composed of Water.  All the properties of Water as it changes phases have been well studied and appear in what are called Steam Tables. The Mass Flowrate Meters used for the production of Steam work because the Boilers operate at Pressures that define how much mass of Steam is generated ... according to the laws of The Universe.

Most other process streams are a combination of compounds and are nowhere near as pure as Steam.

Within the past few decades, the Coriolis Mass Flowrate Meter has earned industrial acceptance with respect to accurately measuring the Mass Flowrates of liquids (not so successful for gases).

The proven accuracy of the Coriolis Mass Flowrate Meter has established its service in the custody transfer of products. The buyer of feedstocks pays for exactly the mass of feedstocks received. And the seller of products does not give away product for free.

The Coriolis Mass Flowmeter will be featured in the upcoming PTOA PV Flowrate Focus Study featuring the Detection, Measurement, and Transmission of the PV Flowrate.

Any person who understands the Coriolis technology well enough to troubleshoot these Flowrate Devices will have job security for life!

 

TAKE HOME MESSAGES:  All of the content in the PTOA PV Flowrate Focus Study Area assumes the fluids are flowing through rigid ... not flexible ... pipes, valves, and fittings.

A Volumetric Flowrate (Q) can be calculated Q= V* A, where V and A are defined as follows:   

• The Flow-Through Area (A) is the area of a circle with the internal diameter of the Pipe.
• The Velocity Factor (V) is the velocity (distance/time) that the fluid flows through the Pipe. 

 

Because fluids are flowing through rigid pipes, any change in Volumetric Flowrate is due to a change in the Velocity factor of a Volumetric Flowrate. 

The Velocity factor of a Volumetric Flowrate will increase when the diameter of the pipe decreases, and vice versa.

A change in Temperature will impact a fluid's Density and Specific Gravity, hence change the fluid's Volume and Volumetric Flowrate. A change in Pressure will impact the measurement of a Gas Flowrate. To be able to compare Volumetric Flowrates throughout a processing facility, the Actual Flowrate detected and measured by a Flow Meter Device must be corrected to Standard Temperature and Standard Pressure.  In the industrial processing USA, Standard Temperature is 60 °F (519.67 °R) and Standard Pressure is 14.7 psia.

The difference between the Actual Gas Flowrate and the Standardized Gas Flowrate can be significant.

To improve the accuracy of a Volumetric Flowrate measurement, the assumptions regarding the Specific Gravity of the flowing fluid should be corrected to the Actual Specific Gravity of the flowing fluid.  The correction is more important for gas flowrates than liquid flowrates. 

Process Operators are not accountable for correcting Flowrates to Standard Conditions; smart transmitters and software perform these calculations.  

However, Process Operators should be aware what that the "S" in a Gas Flowrate measurement (e.g., SCFM, SCFD) reveals that the gas flowrate measurement has been corrected to Standard Temperature and Standard Pressure. 

Mass Flowmeters would eliminate the need for adjusting to Standard Conditions. Steam production is measured by Mass Flowmeters. However, gas and liquid process streams are not as homogenous as Steam.

A Mass Flowmeter based upon Coriolis technology is gaining credibility measuring the Mass Flowrate of Liquids.

 

©2022 PTOA Segment 0235

PTOA PV FLOWRATE FOCUS STUDY AREA
PV FLOWRATE FUNDAMENTALS FOCUS STUDY

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