Flow Rates

Upon studying this section, you should be familiar with the following:

The notation used to express quantities (such as mass) as a rate (such as mass/time).
The usefulness of refering to quantities as rates in chemical engineering.

The Dot means a Rate.

Explanation:
The dot above each quantity, say mass, signifies that we are refering to the quantity per time, a rate, say mass per time.

Three popular quantities which are often referred to as rates in chemical engineering are mass, moles, and volume. These rates are referred to as flow rates, that is, mass flow rate, molar flow rate, and volumetric flow rate.

The following table shows these quantities as rates.

Why is it important to refer to quanties as flow rates rates?

In the home, any time something flows, you are concerned with its flow rate. When you turn on your kitchen facet to wash you hands, the flow rate of the water must be just right. Too slow, and you can be washing your hands for an hour, too fast, and water rushes out and gets your clothes wet. Maintaining specific flow rates are important in many aspects of life, whether it be pouring a glass of milk, gasing up your car, or pumping water from the Colorado river.

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