Volumetric, Mass and Thermal Flow Measurement

Question 1

Explain the basic principle of operation for liquid volumetric flow meters.

Answer 1

The flow stream gets broken up into discrete volumes and measured. An odometer typically counts the amount of these discrete volumes.

Question 2

Explain the operation of a nutating disk volumetric flow meter and give a common
application for this meter.

Answer 2

The disk has 2 volumes above and below the disk. Each rotation of the disk displaces a volume of the metering chamber minus the volume of the disk. These meters are commonly used to measure residential water.

Question 3

Explain the effect that viscosity, temperature, and pressure have on volumetric flow
meters.

Answer 3

Temperature: changes meter dimensions due to thermal expansion

Viscosity: less viscous fluids will have more slippage (leakage)

Pressure: minimal effect and is often neglected

Question 4

Explain how a meter factor is determined for a volumetric meter, what this factor
accounts for, and how this factor is used.

Answer 4

Meter factor is determined from a proving procedure and adjusts gross volume using temperature and pressure correction factors.

Question 5

Gas flow measurements made with volumetric type flow meters equipped with an
odometer type readout are always at ________.

Answer 5

flowing or line conditions

Question 6

List four types of gas volumetric flow meters with their main application.

Answer 6

Bellows: custody transfer for a gas process, domestic and industrial

Geared Lobbed Propeller: gas measurement, high pressure

Sliding or Rotating Vane: metering for a gas or liquid process

Liquid Sealed Drum: laboratory, secondary standard used for testing

Question 7

Explain the basic principle behind gas volumetric flow meters.

Answer 7

Gas flow is separated into volumetric compartments. A mechanical gear train turns an odometer type of display. The display indicated certain flow units.

Question 8

Rate the four types of gas volumetric flow meters as to their capacity.

Answer 8

1) Sealed Drum (lowest)
2) Diaphragm
3) Vane
4) Rotary (highest)

Question 9

How is the volume of the measuring chamber determined for a gas volumetric
type flow meter?

Answer 9

Proving the meter against a known volume

Question 10

What is a dry test meter?

Answer 10

Diaphragm/Bellows type meter that is highly accurate, and negates temperature as pressure on both sides of the meter stays constant, has a high TDR and good reliability

Question 11

What attributes to the bellows gas meter popularity?

Answer 11

Simplicity, durability and high accuracy

Question 12

How is the bellows type gas volumetric flow meter temperature and pressure
compensated?

Answer 12

Pressure is kept constant by using a regulator and temperature is compensated for automatically

Question 13

Explain the operation of the Coriolis meter.

Answer 13

A D-tube in the mass meter is vibrated at it’s natural frequency. Once fluid starts passing through the tube the fluid’s mass provides resistance to the up and down movement of the tube. This resistance causes the tube to twist causing a phase shift that is proportional to the mass flow rate.

Question 14

Explain how density can be determined from a Coriolis Mass Flow Meter.

Answer 14

Resonant frequency of the Coriolis flow meter.

Question 15

Explain what effect temperature has on the Coriolis Mass Flow Meter tube.

Answer 15

Temperature affects the volume meter due to thermal expansion of the meter parts which in turn will affect the mass meter.

Question 16

List the two parts of the load that a gas meter must overcome.

Answer 16

Friction losses and differential pressure losses although these are small

Question 17

Explain why the pressure drop across a Coriolis Mass Flow Meter is quite large.

Answer 17

Once the process fluid enters the tube it undergoes a change in direction due to vibration. Additionally, the older models had small diameter tubes than the process line.

Question 18

State and explain the basic principle behind Thermal Mass Flow Meter.

Answer 18

A heater is installed between two temperature sensors in the pipe. Since one sensor is upstream from the heater and does not heat up a change in temperature occurs. The difference in the temperature is proportional to the velocity.

Question 19

Explain two complications introduced when going to a non-intrusive Thermal Mass
Flow Meter design.

Answer 19

1) Heat can be conducted through the pipe
2) Mass flow and temperature difference in non linear

Question 20

Explain the principle of operation of a Hot Wire Anemometer.

Answer 20

A constant temperature difference is maintained by varying the power to the heated sensor. The power required to maintain this temperature difference is a function of the mass flow.

Question 21

Where are hot wire anemometers commonly used?

Answer 21

Air ducts and flow switches