Process Data and Process Variables
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- Info Page links lead to definitions, expanded explanations, and related material—because sometimes you really do need to explain it.
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Why Process Data and Process Variables
Many engineers—chemical engineers in particular—design, analyze, and operate processes that transform inputs such as chemical reagents, heat, and electricity into outputs such as other chemical products.
The design and analysis of processes requires knowledge of the types of measurements or data that are obtained from a process, and the variables used to model that process. This section discusses many of the variables, measurements, and data that are common in chemical and thermal processes, how they are defined, what they mean, and how they are used, presented, and analyzed.
Conversions
We begin with units, conversions, and dimensionless numbers. In spite of the desire to perform all calculations in SI units, practicing engineers must be comfortable working with both familiar and obscure units. This set of videos discusses several common techniques for working with diverse units.
The topics in this section are:
Dimensional Equation Unit Conversions
Is Furlongs Per Fortnight a Thing?
Unit Conversion
Video, Info Page, Visuals.
Dimensional equations are frequently used to convert data, measurements, and variables from one set of units to another. They will not solve all unit-conversion problems, but they will solve many of them. A web-search calculator is usually the easiest way to implement dimensional equations, but by no means the only way. Dimensional equations are used when units are related through multiplication and division.
Temperature Conversions
How Keen Is Your Rank? Just the Facts
Temperature Conversion
Video, Info Page, Visuals
How Keen Is Your Rank?, The Full Story
Temperature Conversion
Video, Info Page, Visuals
Converting temperatures and temperature intervals among \(\mathrm{K}\), \(^\circ\mathrm{C}\), \(^\circ\mathrm{F}\), and \(^\circ\mathrm{R}\) applies the principles discussed in the previous and next video set. Because temperature is such an important measurement, datum, or variable, these videos discuss precisely how to make these conversions.
Is It Hot in Here, or Is It Just My Thermistor?
Thermistors, Thermocouples, and Other Temperature Sensors
Video, Info Page, Visuals
The most commonly measured process variable is temperature. This video discusses several temperature-measurement techniques. It is optional because, at this level, it is not necessary to know how to measure a temperature, but it is valuable for anyone who actually needs to measure a temperature or must specify how a temperature measurement should be made.
Converting Equations with Units
The Most Annoying Equation Conversion
Unit Conversion of Equations
Video, Info Page, Visuals
When units have a more complex relationship than simple multiplication—such as \(^\circ\mathrm{C}\) and \(^\circ\mathrm{F}\)—the relationship is expressed in an equation with dimensions. In addition, there are times when equations, particularly empirical equations, are expressed in SI units but need to be converted into American Engineering units. The procedure for deriving such equations with units is presented in this video.
Dimensionless Numbers or Groups
Where Does Sherwood Hide His Unit? Principles
Dimensionless Numbers Principles
Video, Info Page, Visuals
What the Schmidt? Examples
Applications of Dimensionless Numbers
Video, Info Page, Visuals
In the early days of engineering there were huge data sets that needed to be regressed and correlations developed. The Buckingham pi theorem provided a way to reduce the dimensionality of these data sets and simplify calculations.
In addition, normalizing ordinary and partial differential equations—essentially making the variables dimensionless by choosing a scale—gives rise to dimensionless parameters. The most well-known of these is the Reynolds number, but there are many others. This set of videos discusses dimensionless parameters and dimensionless numbers, where they come from, and how they are used.
Pressure
The second most commonly measured process variable is pressure.
Under Pressure Part 1, Just the Facts
Pressure Basics
Video, Info Page, Visuals
Under Pressure Part 1, The Full Story
Pressure Basics
Video, Info Page, Visuals
Part 1 discusses the common pressure units and hydrostatic pressure.
Under Pressure Part 2, Just the Facts
Abs., Atm., Gauge, Barometric Pressure
Video, Info Page, Visuals
Under Pressure Part 2, The Full Story
Abs., Atm., Gauge, Barometric Pressure
Video, Info Page, Visuals
Part 2 discusses absolute, atmospheric, barometric, gauge, and vacuum pressure.
Mass, Moles, and Mass and Mole Fractions
When purchasing, ordering, selling, or processing raw materials and chemical reagents, one has to specify the mass or weight of solids, the mass, weight, or volume of liquids, and the mass or pressure and volume of gases. However, when calculating the amount needed for a given chemical reaction, the number of moles needed needs to be calculated. The practicing engineer needs to be able to convert back and forth between mass and moles. The two video sets in this series are:
What is a Mole? Just the Facts
What a mole is
Video, Info Page, Visuals
What is a Mole? The Full Story
What a mole is
Video, Info Page, Visuals
What the Frac?
Mass, Moles, Mass Fractions, Mole Fractions
Video, Info Page, Visuals
When dealing with mixtures, there are times that one needs to calcuate what mass fraction of each species is present and times to calculate the mole fraction of each species. This video explains how to calculate mass and mole fractions, how to convert between the two, and how to calculate mass- and mole-averaged molecular weight.
Volume, Density, and Flow Rates
Are You Dense? Crank Up the Volume and Go With the Flow! Just the Facts
Mass, Moles, Density, Volume, and Flow Rates
Video, Info Page, Visuals
Are You Dense? Crank Up the Volume and Go With the Flow!, The Full Story
Mass, Moles, Density, Volume, and Flow Rates
Video, Info Page, Visuals
In Chemical and Thermal Processes, the flows are often calculated and/or measured as mass flow rates, molar flow rates and/or volumetric flow rates. The video explains how the three flow rates are defined, and how to convert among them.