Flow sensors

Flow sensors are devices that sense the rate of fluid or gas flow. There are many types of flow sensors, but basically they all measure volume or area per unit time.

The most common flow sensors in our daily life are those used to measure water flow and electrical consumption in people’s homes. A lot of offices and schools use flow sensors to measure the air velocity indoors, so the ventilation can be automatically controlled.

Flow sensors are used for much more than I thought when I began researching on the topic of this post. Apparently, the dynamic of fluids is the foundation of the understanding of flow of air, water, lava, glaciers, and the Earth’s mantle. The Bernoulli’s principle is the basic concept behind all of the abovementioned. The Bernoulli’s principle describes the relationship between the velocity and pressure exerted by a moving liquid: as the velocity of a fluid increases, the pressure exerted by that fluid decreases.

In the design phase of a building, it is possible to test the BIM model’s performance according to fluid or gas flows. Computational fluid dynamics, usually known as CFD, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. For example are all airplanes tested with CFD before they are built in mini-scale and tested in a wind tunnel. The same can be done with buildings and urban planning, using programs like Autodesk Ecotect. I will continue this post writing about CFD, as it is one step ahead of the flow sensors in the building phase. 

CFD works by dividing a space in a BIM model into a grid containing a large number of cells. The grid can simulate everything from the wind flow when building a new building, temperature outside and inside a building, effectiveness of building services, consequences of fire, ventilation and natural ventilation, and positioning for sensors. It is very important when for example placing temperature sensors in a tall space, as the temperature is very different at the top than at the bottom. By simulating it before sensors are being placed, you can make sure that the operating isn’t unnecessarily.

Sources:

http://www.ldeo.columbia.edu/~martins/hydro/lectures/fluid_dynamics.html

http://library.thinkquest.org/27948/bernoulli.html

http://www.designingbuildings.co.uk/wiki/Computational_fluid_dynamics_for_buildings

Comments:
Nameita's post: Very informative and nice post! I had no idea how a humidity sensor worked (and never actually really thought about it), so thanks for explaining it so well. It seems like a pretty old school principle with the metal pieces and then the moisture that creates voltage. Impressive stuff! 

Dave's post: Interesting post! I am surprised that you can get a sensor of the size of a quarter for just 10 dollars!