A text book explanation of Fluid flows normally will state that flow in a conduit will occur either as Laminar , Transitional or Turbulent. These concepts are important to those who manufacture flowmeters that measure flow using an inferential method as opposed to direct reading methods, especially if the flow being measured is going to see a distinct change in the Reynolds number.
The term “transitional” means exactly that ! The flow is going through a transition e.g. from Laminar to Turbulent. You may find that certain individuals using the term “ Laminar Flow” are actually not talking about a laminar flow but about an axially symmetric flow profile .
A laminar flow looks like a cone shaped flow where the velocity in the centre of the pipe is very much greater than that of the outside of the pipe. A typical example of a Laminar flow in liquids could be seen in a viscous oil where frictional forces at lower flow rates tend to hold back the fluid nearer to the pipe wall .
At the same time, a similar sized pipe filled with free flowing water will exhibit a turbulent flow regime.
WHY IS THE REYNOLDS NUMBER IMPORTANT?
The Reynolds number is of extreme importance to certain manufacturers using an inferential method of flow measurement on certain fluids that change state at different velocities. It will important for them to know exactly when the transition occurs so that adjustments can be made internally to output the corrected flow rate.
GAS - MASS FLOW VS VOLUMETRIC FLOW
There are different units used to measure Volume and Mass
THERMAL MASS FLOWMETERS
These are flowmeters that measure the total mass flow rate of a fluid. They are very popular devices for the measurement of gases flowing through pipes and tubes.
The Mass Flow Meter or MFC (mass flow controller ) works on a principle where the heat is transferred to the boundary layer of the fluid flowing over the heated surface.
The industrial applications extend to gas flow in pipes and ducts. For measurement of smaller flows of clean gases or liquids in tubes a capillary type flowmeter might be used.
The laminar mass flow meter is a product which is designed normally as a stand alone meter. It has its own digital display and normally is configurable to be used with several gas type options. Laminar mass flow meters can measure gases such as sulfur hexafluoride, butane, ethane, compressed air, methane, CO2, CO , Helium, Oxygen and many other types of gas if they have been set and calibrated to the particular gas.
Normally the manufacturers of laminar mass meters will have options set for a choice of a long list of gases. They also have a high turndown ratio and lower end mass flow devices are now able to compete with the price of the rotameter.
