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We just HAD to share this white paper from Exergen explaining emissivity using Alice and the White Rabbit. Such a great way to explain a relatively complex concept.
Through the Looking Glass: The Story of Alice’s Quest for Emissivity
by Dr. Frank Pompei, all content courtesy of Exergen Global Industrial Sales
“It’s all done with mirrors!’’
“What do I see when I look in my mirror?” asked Alice. “I see myself, of course.”
“But what about the mirror why can’t I see the mirror itself” she pondered. “Maybe it’s because the mirror is invisible? Na, if it were, I would be able to see the wall behind it.” Just then she had an idea, “I know, if I put spots of crayon on the mirror, then I can see the mirror!”
She put spots of crayon on the mirror and sure enough, she could see the mirror, wherever she put the spots! “The crayon spots are now part of the mirror, and I can see them!”
“Hmm . . .” she thought. “I still can’t see the whole mirror. All I can see is the part covered by the spots. In between, I still see my face, not the mirror.”
A magical white rabbit who had been watching Alice appeared and said, “Why, my dear girl, you are almost there! A little further and you will understand the concept of EMISSIVITY!”
“Emissivity?” queried Alice. “What is that?”
The rabbit, being patient as well as an expert on matters of light and heat, continued: “Alice, what do you see in your mirror?”
Alice replied, “Why. . . I see the mirror where crayon spots are, and my reflection where they are not.”
“Of course.” replied the rabbit. “You can see the visible part of the mirror, as crayon, but the rest, let’s call it ‘not-mirror: you cannot see because it REFLECTS.
“Does this mean that light bounces off the not-mirror part?” asked Alice.
“Why yes, of course, you are beginning to see it!” cried the rabbit. “What about the crayon marks? Does light bounce off them?”
“No!” said Alice. “I can see those for what they really are: the mirror itself and not my face.”
“Splendid!” cried the rabbit. “Now, what if we counted up all your dots and added them together to see how much of the mirror they cover. Let’s suppose that they added up to 10% of the mirror. What does that mean?”
“Hmmm . . .” said Alice, being thankful she always did her arithmetic homework. “That means that I can see 10% of the mirror!”
“And . . ,” encouraged the rabbit.
“And that 90% is left for me to see my reflection?” cried Alice.
“Absolutely correct,” stated the rabbit in his most authoritative voice. “Now you see a great principle— when you look at a surface, the sum of the amount you can see and not-see is 100%.”
“And . . ,” giggled Alice, anticipating his next statement. (You see, Alice is a very bright girl.)
“And . . ,”said the rabbit. “The part that you cannot see is replaced by a REFLECTION. What you see is not the object itself. The missing not-seen part is replaced by a reflection which can be seen! You see, Alice, nature insists that when you not-see something, you must see something else!”
“Wow!” thought Alice. “I wonder how Mother Nature knows when to do all this? She then asked. “What happens if I use more crayon and cover 90% of the mirror?”
“Why then, how much is left to reflect?” continued the rabbit.
“Of course,” answered Alice, “only 10%.”
‘Nature insists on the total of the mirror and not-mirror adding up to 100%,” explained the rabbit.
Suddenly, another thought struck Alice. “What if I wished to see all of the mirror? Would I then have to cover the whole thing with my crayon?”
“That’s one way,” said the rabbit as if he read her thoughts. “But there is a better way, especially if you do not wish to disturb the mirror.” Alice was puzzled, reasoning that to see 100% mirror, she would have to see 0% not-mirror, and not be able to see herself at all!
“It’s all done with mirrors!” exclaimed the rabbit with a twinkle in his eye. He then produced a hollow, shiny, metal beach ball (proving white rabbits are not only smart, but magical) which he proceeded to divide in half, and put a small hole in the center of one of them.
“Why, it’s a round mirror!” cried Alice as she peered inside it. “Right.” said the rabbit as he placed it over the mirror with the crayon spots covering 10%. “Now look inside this hole, Alice, and tell me what you see.”
Alice carefully peered into the hole and gasped at what she saw. “I see all 100% as crayon!” she cried.
Not believing her eyes. She quickly removed the beach-ball half and looked at the mirror. It was the same as it was before! Ninety percent was reflecting the light from her face, while 10% was covered with crayon dots. Carefully replacing the beach-ball-half on the mirror and looking inside again, she insisted, “You must be using your magic to do this.”
“No,” said the rabbit softly. ‘“It is the nature of things which makes you see 100% mirror now, when there is only 10% of the mirror visible without the beach-ball-half.”
“The 90% of the mirror which is reflecting is continuing to reflect. However, the light which it reflects has as its source only the crayon dots. The light from the crayon dots is reflected by the beach-ball-half BACK to the mirror. If the light happens to hit a reflecting part, it reflects BACK to the beach ball again, and back to the surface. Eventually the light hits a crayon dot. Then it is absorbed and does not reflect.
“When you look inside the hole, you see the result of zillions of reflections and absorption’s of light. The entire reflecting part of the mirror is covered, not by the crayon dots themselves, but by the REFLECTIONS OF THE CRAYON DOTS!
“And that is why, my dear Alice, you see 100% of the crayon/mirror and 0% of anything else. For when we reach 100% of something, we can have 0% of not-something.” concluded the rabbit.
After a long pause, Alice asked, “What does all this have to do with EMISSIVITY? You said I was well on my way to understanding it.”
“Well’ said the rabbit. “Light energy and heat energy are identical. Both follow the very same rules. The difference is that heat energy, sometimes called INFRARED, cannot always be seen by your eyes. You can sometimes feel it, such as when you place your hand near a hot stove. Most of the time a sensitive instrument, such as a MICROSCANNER, is required.
“All materials, like your mirror with crayon dots, will partly reflect and partly emit its own heat radiation.
The part which is emitted because of its own heat is called EMISSIVITY. The part which is reflected from other objects nearby is called REFLECTIVITY.
“Just like your mirror with the dots, nature insists that the sum of EMISSIVITY and REFLECTIVITY is 100%. If a surface has an emissivity of .8, that means it emits heat energy as if 80% of its surface were emitting at 100%. The remaining .2 reflectivity means that heat energy is reflected by 20% of the surface reflecting at 100%.
“So you see Alice, emissivity is not so mysterious. It is just the part of the surface that you can see, concluded the rabbit.
“I understand!” said Alice, “but what about the beach-ball-half with the shiny inside? How does that work in infrared?”
“Why that’s a very, very good question, Alice.” replied the rabbit, and he proceeded to explain.
“One of the purposes of using infrared is to measure the temperature of surfaces—much, much more quickly than can be done by other methods. However, there was a nagging problem of EMISSIVITY.
“The engineers at Exergen were gravely concerned with this problem, because their customers could not always know what the exact value of the emissivity is on any particular surface.
“You see, Alice, if a sensitive instrument is ‘looking’ at a surface, it sees, like your eyes do, a combination of emitted and reflected heat radiation. Unless you know how many ‘crayon dots’ there are and what the reflections are, then you cannot know the temperature of the surface.
“What you really want to know, to get temperature, is the average heat emitted by the ‘crayon dots: since they are really the surface. The reflective portion only tells you that the surface reflects—not what the surface is.
“Therefore, the Exergen engineers, in designing the MICROSCANNER D-SERIES, had a bright idea-use a shiny beach-ball-half! They called it the Automatic Emissivity Compensation System (AECS), a rather complicated name. Most people just call it a ‘reflective cup’.
“You see, Alice, the shiny, reflective cup on the D-series does the same thing that you saw in your mirror. Instead of your eyes, a sensitive detector is used to look into the hole.
“The heat emitted by the ‘crayon dots’ reflect and re-reflect until 100% of the surface is covered with the dots. Then the heat detector sees 100% dots and 0% not-dots. Therefore, the EMISSIVITY IS ONE.
“With the emissivity at 1.0, Alice, an exact temperature may be calculated by the electronic circuits in the MICROSCANNER D-SERIES.” concluded the rabbit.
“Well, how about that!” said Alice. Now I understand emissivity, and also how to deal with it! If anyone ever asks how the MICROSCANNER D-SERIES works its magic, now I can tell them:
Did you know Pfannenberg’sDTS cooling units don’t require a filter? Unlike other brands that include built-in filters that eventually need servicing, the DTS series was designed for easy use and maintenance.
As Pfannenberg points out, “if a dirty filter is not cleaned or replaced, it can become clogged which severely limits its efficiency and result in poor performance.” Knowing this, Pfannenberg designed the DTS cooling units with features for use in both indoor and outdoor environments while protecting against ambient air, dust and humidity.
1) High Airflow Backward Curve Impeller Fan
Provides high airflow in a long lasting, single bearing design. Higher airflow pushes dirt through wider fin spacing allowing for less clogging which avoids system failure.
2) Large Fin Spacing
Large condenser fin spacing allow for longer maintenance periods, even without an additional Nano coating. They are less susceptible to clogging from dirt buildup which can cause the unit to work harder and hamper efficiency.
3) Corrosion Protection
The DTS Outdoor and wash-down units have a special coating on pipes and coils on the ambient side of the unit to provide maximum protection from saltwater, sour gas, and other corrosive substances.
4) Self-Protected Electronics
Our unit is uniquely designed to protect itself in NEMA 3R, 4, and 4X environments. An example of this is the location of our control electronics within our dry, cool interior circuit.
That doesn’t mean you can install and forget your cooling unit. As with any unit located in a dirty environment, the components around the external air circuit require periodic cleaning. To avoid any critical component failure, follow the 3 simple steps below to help ensure your enclosure cooling units stay up running:
3 Simple Steps to Keep Your Enclosure Cooling Units Running - YouTube
How to Avoid System Failure
STEP 1: Make Sure your Condenser Coils are Clean
When dirt, dust or debris builds up on your condenser coils, it can have a major effect on the performance of your cooling unit.
STEP 2: Check your Fan Motors and Inside/Outside Electrical Components
The fan motor and fan blades need to be inspected to determine wear and damage. Also make sure electrical components aren’t damaged or loose.
STEP 3: Set your Unit to the Recommended Proper Temperature
Pfannenberg recommends the dip-switches on the control board to 95°F/35°C in the factory.
*All maintenance should be performed by qualified personnel, following all safety procedures.
Filterfans® force surrounding air into the electrical enclosure so that a slight overpressure builds up inside the enclosure. The surrounding air enters the enclosure via the Filterfan® which ensures that it is filtered.
The ambient (outside of the enclosure) temperature is lower than inside the enclosure and stays within an acceptable range
The application is in a clean, non-hazardous environment
Filterfans® are very cost-effective and work great if you need multiple configurations, they can be located in a range of locations within complex enclosure configurations.
We recommend installing Filterfans® in the lower third of the enclosure and the exhaust filter as close to the top as possible. This helps avoid hot spots within your enclosure.
Pfannenberg cooling units work as a heat pump that basically pumps the thermal energy transferred from the enclosure up to a higher level of temperature. The air inside the enclosure is cooled down by the evaporator and at the same time dehumidified.
The ambient (outside of the enclosure) temperature is higher than the target internal temperature of the enclosure
Active cooling is required
If you have a NEMA rating that is required, closed loop cooling can maintain the NEMA rating of the enclosure. For harsh environments where ambient air must be kept out of the enclosure cooling units seal out the ambient air, cooling and re-circulating clean, cool air throughout the enclosure.
When would I need an Air to Water Heat Exchanger?
Air to water heat exchangers use a water source to remove the heat from the enclosure. The heat is transferred to fluid and the heated fluid is them removed, adding no heat to the ambient (outside of the enclosure) environment.
There is a chilled water source readily available at the enclosure
The application has extreme conditions; high ambient temperatures, extremely dirty or caustic or other issues that make other solutions unusable
There is no heat transfer to the ambient environment so there is no need to de-rate the units in high ambient applications.
When would I need to use a Chiller?
Chillers use a refrigeration cycle to remove collected heat from a circulating liquid. As the liquid moves through tubes and pipes it absorbs the heat generated by equipment and processes. The generated heat is transferred back to the chiller where it is dissipated. Fluid is cooled and sent back into the system.
You need to manage higher heat loads that exceed traditional enclosure cooling methods
Precise temperature control is required in the manufacturing process
Large fluctuations in heat load requirements need to be managed
The source of cooling can be located separately from harsh environments
Want to learn EVEN more?
Check out these other blogs covering other thermal management and enclosure protection topics below!
We recently had a customer, Future Tech Electric, contact us looking for a variable frequency drive panel with an extra tap for an external motor starter. The application was for sand washing/drying.
Our UL508A panel shop engineers contacted the customer, Russ, with a few questions and then we sent a quote. Russ immediately called and asked how fast we could get it done because the machine was down and they were losing money.
We did what we do best; got the parts ordered, the panel built and shipped out. In this instance we were able to do it all within 7 business days!
Russ sent a follow up email letting us know the panel worked out perfectly and thanking our panel shop team for all their help finding the right solution for their application.
“The VFD Controller worked out perfectly! Thanks again for all your help in choosing the right VFD for the job!”
Clean and consistent electrical currents are optimal for the health of your industrial equipment.
The addition of a line reactor, sometimes known as a choke or inductor, helps protect your equipment from input power disruptions that damage the drive.
Line reactors are electro-magnetic devices which consist of a steel core wrapped with copper coils. The coils form a magnetic field which current flows through limiting the rate of rise of current, reducing harmonics and protecting additional electrical devices. There are generally two types of line reactors used with VFDs; AC & DC.
When a reactor is installed between the power system and the VFD, it is known as an AC line reactor. When a DC reactor is inserted into the DC link of a drive, it is known as a DC link reactor.
Both AC and DC reactors act as harmonic current limiters but the AC reactor protects more equipment due to being installed between the VFD and power source limiting exposure to power system surges and fluctuations. This limits exposure to power system surges and fluctuations. Reactors can prevent overvoltage trips, increase the reliability and life span of the VFD, improve total power factor, and reduce nuisance tripping.
What is Impedance?
“Resistance in ohms but also commonly referenced in terms of percent when combined with the system voltage and line current flowing through the reactor.
That percentage then becomes the common term used to define the level of impedance for each rating of line reactor. That impedance functions to slow the rate of current changes in the line. The greater the current through the reactor, the greater the percentage of applied impedance will be.
If a reactor is said to have an impedance rating of 3% or 5%, that means the reactor will apply that specified percent of impedance when the current flowing through the reactor is at the rated current of the device,” TCI, Line and Load Reactor Basics.
Installing a line reactor on the input side of the VFD ensures protection to the drive but line reactors also have the capacity to be installed on the output side of the drive blocking potential incoming background line voltage harmonics.
“In almost all drive applications, the addition of an input AC line reactor is a low cost solution for drive protection and harmonic mitigation,” TCI, Line and Load Reactor Basics.
Want to learn more?
TCI has all sorts of helpful guides for incorporating a line reactor into your application:
The input line power is known to have power surges, spikes, transients, etc.
The supply line power is very stiff; greater than 10 times the kVA rating of the connected VFD.
Where harmonic distortion is a concern. (IEEE-519 Harmonic Control in Electrical Power Systems)
You want a buffer between your VFD and your motor to temper the waveform and reduce voltage stress on the motor
The general consensus seems to be the more current regularity the better, for all equipment across the board. If you’re ready to take the next step in harmonic mitigation; feel free to contact our sales staff at: email@example.com or get some help figuring the right reactor from our tech support at: firstname.lastname@example.org.
Schmersal and EHS Today have paired up to release this safety quiz to test your knowledge. Machine guarding is rated one of OSHA’s top ten most cited violations of the year so why not review some of the most common machine safety integration practices?