Free Teledyne Hastings Mass Flow Converter APP

Teledyne Hastings Mass-Flow Converter
Post publication date: 
Monday, October 20, 2014

Schaefer is proud to inform their website visitors that Teledyne Hastings is offering, for free, a very handful tool, the Mass Flow Converter app. Teledyne has created a version for iPhone and iPad, and Android. There's also a web-based version, you can find it at www.massflowconverter.com

In the following paragraphs we will tell you the reasons that have driven Teledyne to build the app, how it works, and how it can be used.

Converting between mass flow units is not always that straight forward. That's why they have developed a tool that makes it easy.

 
What is mass flow

What we mean by mass flow? Mass flow, in few words, can be defined as the flow of individual molecules. So while flow meters are often specified by units like sccm (standard cubic centimeters per minute) or scfm (standard cubic feet per minute), the mass flow rate is about the number of molecules (n) moving through a given cross sectional area per unit time.

An example of conversion to molecular flow rate

So as our first example, let's take a look at the conversion of 10,000 sccm (10,000 cm3/min) to a molecular flow rate. The main question is: "How many molecules are in 10,000 sccm?" In the figure, we show a container that is 10,000 cm3 in volume. Before we can calculate the number of gas molecules in a volume, we need to know the pressure and temperature of the gas. That's wen it comes in handy the ideal gas law:

n = (P * V) / R*T where n is the number of molecules, P is the pressure, V is the Volume, R is the Universal Gas Constant and T is the Temperature.

At this step we will have to use/specify the so called "reference conditions" or "STP" (Standard Temperature and Pressure). In many cases, 0°C and 760 Torr are used for the STP. But this is not always the case. So it is always very important to specify the reference conditions (STP) any time you use a standardized mass flow unit like sccm, slm, scfh, etc (any mass flow unit that starts with "s" is going to need the reference conditions or STP specified). In our example, we are going to use STP of 0°C & 760 Torr.

OK, so here we go: n = (1 atm) * (10,000 cc) / (82.053 cc * atm / K * mole) * (273 K)

Note that we have used a value of R in terms of pressure in Atmosphere (760 Torr = 1 atm), and Temperature in Kelvin (0°C = 273K).

n = 0.45 mole

In other words, a flow rate of 10,000 sccm (0C, 760 Torr) is the same as a molecular flow rate of 0.45 Mole / minute.

The Mass Flow converter App

OK that is the hard way. It's much easier to use the mass flow converter app. In the example shown above, we would dial sccm on the left and Mole/Min on the right. Then to select the reference conditions, we use the menu in the center.

If you are like me, you will start to play with the App. And soon you will notice that the user can change the gas using the pull down menu at the top. But notice that in the case of our first example (converting from standardized mass flow units to molecular flow units), that the gas selection has no effect on the conversion. This is because the standardized flow units (e.g. sccm, slm, scfh, etc.) are actually molar flow units based on reference conditions (STP) and the ideal gas law.

So, why do we allow the user to select gas? In the case of units like gm/sec, Kg/hr, or lb / min, we are going to need to know the gas so that we can calculate the mass. Let's take a look at the case of converting from slm to grams/second. We will use as our same example of 10,000 slm (0°C & 760 Torr) and we will use methane (CH4) as our gas.

We showed earlier that 10,000 sccm is a molecular flow rate of 0.45 Mole / Min. And since 1 slm = 1000 sccm, it is easy to see that 10,000 slm = 450 Mol/min. And since we know that our unit of choice (gm/sec) is in terms of seconds, let's go ahead and convert our time units now:

10,000 slm = (450 Mole / Min) * (1 Min / 60 sec) = 7.5 Mole/ sec.

Now we need to know how much mass there is in a Mole of methane. Google is very nice for getting this number – just type, "Molecular weight of methane" and here is the result: 16.04 g/mol.

By the way, Google will do this for almost all gases. So now we can finish our conversion and we get: 7.5 Mol / sec * (16.04 g/mol) = 120 g/sec.

The mass flow converter app and website www.massflowconverter.com takes all the work out of these conversions and we hope that you will find this tool helpful. If you have any questions about mass flow meters and controllers, Application Engineers at Teledyne Hastings are always happy to help.

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Teledyne Hastings