"Guess what? I got a fever, and the only prescription is more cowbell!"

(American pop culture phrase originating in a 4/8/2000 Saturday Night Live comedy sketch. Google "more cowbell" to fully understand.)

 

Your Mentor has Temperature Measurement Fever ... and the only cure is to finish learning the Must-Knows about Temperature Measurement!

In the prior PTOA Segment, PTOA Readers and Students reviewed and/or learned these 4 facts about temperature:

• The definition of temperature.
• Temperature and electrical conductivity are physical properties of a substance.  The relationship between the temperature and conductivity of a substance (aka electron movement) can be used to measure temperature.
• There is a direct relationship between increases/decreases in  temperature and increases/decreases in molecular activity.
• The two common temperature scales are °F and °C.

This PTOA Segment #96 continues the list of Temperature Measurement Must-Knows so that PTOA Readers and Students are prepared to learn how temperature measuring devices work.

 

5. ABSOLUTE TEMPERATURE SCALES: DEG K and DEG R

Anyone reading the PTOA Segments in sequential order as intended already knows that heat energy radiated from the sun is absorbed by everything on the surface of the earth.

Radiation heat transfer was featured in PTOA Segment #66 entitled "The Mother of All Heat Transfer."

Around 160 years ago, some scientists/engineers wanted to know what happened to Stuff/Matter/Mass when temperatures were lowered to the point that no molecular bumping and jiving was possible.

These scientist theorized that molecular activity does not totally stop until the temperature is lowered to -273.15 °C which is equal to -459.7 °F.

Two new "Absolute Temperature Scales" that included the new definition of absolute zero were thus created.

On the Kelvin Scale (°K) "absolute zero" is equal to -273.15 °C, much colder than the 0 °C that defines where water freezes on the Celsius/Centigrade temperature scale.

On the Rankin Scale (°R)  "absolute zero" is equal to -459.67 °F, much colder than the 32 °F that defines where water freezes on the Fahrenheit scale.

PTOA Readers and Students encountered references to the two Absolute Temperature scales throughout the PTOA Heat Transfer Focus Study Area.

The Kelvin absolute temperature scale was used to define the Thermal Conductivity Factor in PTOA Segment #63 entitled "A-OK!":

k = Thermal Conductivity Factor
expressed in [Watt / (meters-deg K)]
which is equal to 0.5779 [BTU / (foot-hr- deg F).

The Kelvin absolute temperature scale was also used to quantify radiation heat transfer:

The T⁴ temperature in the radiation heat transfer equation shown below (and which appeared in PTOA Segment #66 entitled "The Mother of All Heat Transfer") was a Kelvin scale temperature.

Process Operators will not encounter Kelvin or Rankin scale temperatures in a real day-to-day situation. However, Absolute  Temperature Scales will be show up occasionally; for example:

• In process industry paperwork like the Mass and Energy Balance Sheets that accompany Process Flow Diagrams and various reference tables.
• In the rare event of performing ideal gas law calculations because all those PV=nRT type calculations require the T to be in absolute temperature units. PV=nRT is featured in future PTOA segments so do not stress about it now.
• FOR INSTRUMENT TECHS ONLY: Instrument Techs may not realize that they are performing an ideal gas law calculations when adjusting the coefficient for an orifice plate to accommodate actual flowing temperature from the orifice design temperature.

In summary, do not stress about Absolute Temperature Scales.

Just be aware:

To convert a Celsius/Centigrade degree to the Kelvin scale equivalent, just add 273 to the Celsius/Centigrade scale temperature and °C becomes °K.

To convert a Fahrenheit degree to the the Rankin scale equivalent, just add 460 to the Fahrenheit scale temperature and °F becomes °R.

Better yet, just use THIS UNIVERSAL TEMPERATURE LINK to convert between °C, °F, °K, and °R and thank the csgnetwork.com for making your life easier!

 

6. MORE TEMPERATURE = MORE AGITATION AND MOLECULAR ACTIVITY = MORE VOLUME OF STUFF/MATTER/MASS

Hey! Two things to notice about Temperature Measurement Must-Know #6:

First, Temperature Measurement Must-Know #6 just builds upon Temperature Measurement Must-Know #3 which stated:

MORE TEMPERATURE = MORE AGITATION AND MOLECULAR ACTIVITY!

Second,  Temperature Measurement Must-Know #6 is oldy, moldy news!

PTOA Readers and Students that read the PTOA Segments in the intentional sequential order are already expertly aware that when Stuff/Matter/Mass absorbs sufficient thermal energy the molecules get so agitated they want to be further apart, thus increasing volume while changing their physical state.

The graphic to the above left was featured in PTOA Segment #2 entitled "Four Great Reasons to Monitor Temperatures." PTOA Segment #2 included the first introduction to the relationship between temperature and changes of state ... ergo changes in volume.

The below graphic was featured in PTOA Segment #25 entitled "Another One Bites the Dust" which was part of the PTOA Focus Study on Process Industry Temperature-Increasing Equipment.

PTOA Readers and Student should notice that only 3 molecules of the original 20 molecules of solid Stuff/Matter/Mass is shown in the far right side picture on the graphic; all the other molecules got so agitated and excited in the gas state that they moved out of the picture frame!

The compared pictures of solid, liquid, and gas molecules illustrate that more volume is needed to accommodate all of the originally solid stuff when it melts into a liquid. And MUY MUCHO MORE volume is needed to accommodate the originally solid molecules when they change from a liquid into a gas or vapor!

 

7. HOTTER/COLDER TEMPERATURES CAUSE MATERIALS TO EXPAND/CONTRACT 

Every new Process Operator trainee at a processing facility will eventually come across what strange piping and will wonder ... what the heck is going on?

Sure seems like making a straight run of pipe would be easier and a lot less costly, eh?

The answer is "Nope!"

The strange run of pipe is providing sufficient room for the entire pipe to expand when a hot process stream is flowing through it.

The same line will contract when the processing facility is shutdown  under controlled conditions for a scheduled Turnaround.

In the graphic below, the red lines show where this pipe is designed to expand when operating at a hot temperature.

Process lines also contract rapidly when an emergency event  interrupts the flow of process streams that are expected to keep lines warm. Emergency events include power outages and losses of strategic pumps or compressors.

PTOA Readers and Students have probably deduced that during emergency shutdowns Outside Process Operators must be alert for leaks between flanges on shell and tube exchangers and pipes that contract too rapidly. A series of emergency shutdowns will eventually fatigue pipes.

In summary:

The relationship between a temperature increase/decrease and the linear thermal expansion/contraction of materials ... especially metals ... can be used in some temperature measuring devices.

A link to a table that compares the ability of materials to expand when heated is below:

 TABLE OF LINEAR THERMAL EXPANSION COEFFICIENTS

Did you notice?

The units of linear thermal expansion use the Absolute Temperature Scales, °K and °R!  Good thing PTOA Readers and Students know what they are!

Yet it is not necessary to understand the units; just comparing the relative rates that the materials expand will prove the utility of the table:

An alloy of iron and nickel called Invar has an expansion coefficient of 1.5 (left side column in the table).

An alloy of copper and zinc called Brass has an expansion coefficient of 18.7.

Conclusion:  Brass expands 12 times faster than Invar when heated.

PTOA Readers and Students will soon learn how the different rates of linear expansion can be used to make devices that measure temperature.

 

TAKE HOME MESSAGES: This PTOA Segment #96 featured facts all PTOA Readers and Students must understand about temperature to gain future core competency understanding how the Process Variable Temperature is measured in the process industries.

The two absolute temperature scales are Kelvin (°K) and Rankin (°R).

The absolute temperature scales were created to theorize what happens at "absolute zero" ... a temperature at which no molecular activity occurs.

PTOA Readers and Students will not use Absolute Temperature Scales on a day to day basis but will notice references to them in process industry design paperwork.

Temperature measuring devices can be manufactured that use the direct relationship between a change in temperature and:

• a change in the volume that contains a specific amount of Stuff/Matter/Mass.
• a change in the length of Stuff/Matter/Mass, especially when the stuff is made out of metal. This change in length is also called "change in linear expansion."

 

©2016 PTOA Segment 00096
PTOA Process Variable Temperature Focus Study Area
PTOA Process Industry Automation Focus Study Area

 

 

 

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