Physics for HVAC&R Techs

[DTLarca]

I'm going to be writing a series of articles on specifically HVAC&R physics that might last 12 months, maybe 24 or maybe even beyond 36 months. I will write the first one, the intro, this Friday. The idea is that by the end of the series any level 3, 4 or 5 tech who says he/she does not understand all the physics and formula used in HVAC&R will no longer have any valid excuse. No lecturer should ever after say they have no easy to understand material to teach thermodynamics (including PH charts and Psychrometrics) or fluid dynamics etc with/from.

<Moderators remove if necessary>
The articles will be published in the ACR Today magazine - I make no money out of writing these articles - I just get to enjoy a few more hours a month thinking
</Moderators remove if necessary>

Does anybody have any ideas about what of physics they would like to read about?

Is physics easy but boring? Is it interesting but too difficult? Or are there other opinions/perceptions?

[Gary]

'How things work' is interesting... 'physics' is boring. Figuring it out is interesting. Calculation is boring. Understanding it is interesting. Memorizing it is boring. Interesting is not too difficult, boring is too difficult.

[DTLarca]

'How things work' is interesting... 'physics' is boring. Figuring it out is interesting. Calculation is boring. Understanding it is interesting. Memorizing it is boring. Interesting is not too difficult, boring is too difficult.

I like it - that is the sort of approach I am looking to take - short little essays with diagrams that illustrate the real field life events of a Technician but from a view that invokes a sort of "Damn - so that's how it goes - that's so easy but also so useful - I could have worked that out myself - well - I'll work the next one out myself"

I might copy and paste your words into the article Gary - crediting you and where you said it of course

[nevgee]

'How things work' is interesting... 'physics' is boring. Figuring it out is interesting. Calculation is boring. Understanding it is interesting. Memorizing it is boring. Interesting is not too difficult, boring is too difficult.

Gary does have a point here, however defining it a different way, I notice people clam up at the thought of such subjects . . "physics" .... algebra .... etc

They say "I don't do algebra .... can't do math" but the reality is so not true. When it's pointed out they do algebra every waking moment, and they see "physics" in action all the time but just don't realise it. It's just that they've never seen the connections. Bringing the connections between simple analogy to the compex technical description is one of those routes of understanding and exploration that enlivens the mind.

And so another way forward.

[DTLarca]

Gary does have a point here, however defining it a different way, I notice people clam up at the thought of such subjects . . "physics" .... algebra .... etc

They say "I don't do algebra .... can't do math" but the reality is so not true. When it's pointed out they do algebra every waking moment, and they see "physics" in action all the time but just don't realise it. It's just that they've never seen the connections. Bringing the connections between simple analogy to the complex technical description is one of those routes of understanding and exploration that enlivens the mind.

And so another way forward.

People might "see" that there is "physics" all around them but people don't automatically see physics as in what actually happens all around them.

What is an enlightened person? Perhaps the best definition of an enlightened person is someone who has read "The Outlines of Skepticism" by Sextus Empiricus - the book that not just freed Europe from the tyranny of religion but because of this Europeans rediscovered Greek science - Galileo rediscovered Epicurus (all weights fall at the same speed in a vacuum) and Newton/Leibniz brought back to life Archimedes calculus. Darwin was accused of simply paraphrasing Epicurus's 3rd century BC theory of evolution. It's fascinating stuff reading how Eratosthenes calculated the circumference of the earth already in about 270BC http://en.wikipedia.org/wiki/Eratosthenes

All of this and much more Greek science was lost at the utter collapse of European civilisations when the nonsense of monotheistic religions came into place. The dark ages were indeed very dark.

But, after Galileo, an enlightened person was one who not only learned that all religiously motivated metaphysics were logically contradictory but also understood such things as that throwing an apple twice as hard was not the same thing as twice as fast and that throwing an apple twice as fast did not carry it twice as far - in other words an enlightened person was one who realised that common sense had only ever brought ignorance and misery and that is why the Greeks, before but especially Socrates, battled against it. Because common sense is false and leads to amplified falsities, it is what governments govern nations with - one fools a nation by constantly appealing to common sense - while in fact doing something very different.

But a mind is enlivened, as you say, when taking the time to understand especially energy. If you understand energy you immediately understand for instance the difference between throwing a ball twice as hard and twice as fast. I have not yet spoken to a person who understands energy - and I have spoken to many degreed engineers. They use physics like I use a hammer - they cannot build tools out of physics like I cannot build my own hammers (metallurgy).

[mikeref]

'How things work' is interesting... 'physics' is boring. Figuring it out is interesting. Calculation is boring. Understanding it is interesting. Memorizing it is boring. Interesting is not too difficult, boring is too difficult.

Gary, i wish i had thought of thoes words for my signature. How about classrooms are boring in longwinded sessions but practical experience goes all too fast. Textbooks are boring when various examples do not include suitable illustrations to break up the endless sentences. Also, skimming over important basics like Q=MC deltaT, then using change in temperature in degrees K but later it changes to degrees C, where did that come from? 5/9(f-32)=degreeF to degreesC, do we need to have that crammed in as well, Maybe? Going out on a limb here(pointing to branch bending), the average human retains around 10% of information provided in a so called lecture so its necessary to reinforce information provided.. mike.

[Gary]

Telling someone that frog legs tastes like chicken is meaningless to someone who has never tasted chicken. He can memorize the phrase, but he doesn't understand it. Then moving on to explain the subtle differences in flavor has him completely lost. Each bit of knowledge must be linked to previously held knowledge, which is ultimately linked to sensorial input or there is no learning and no teaching, there is only preaching to the choir.

You may find this more difficult than you imagine. The opening post in my "Refrigeration 101" thread would be an example of my feeble attempt to begin with sensorial input and then progress step-by-step to the more complex.

http://www.refrigeration-engineer.co...ad.php?t=19701

[nevgee]

Telling someone that frog legs tastes like chicken is meaningless to someone who has never tasted chicken. . . . . . . You may find this more difficult than you imagine. The opening post in my "Refrigeration 101" thread would be an example of my feeble attempt to begin with sensorial input and then progress step-by-step to the more complex.

You're quite right ..... hence my point about the day to day analogy, it's essential to bring the connections to the known knowledge then building the connections by creating more of the links.

It's just a mental jigsaw really, identify the colours, join them up to create a picture with supporting over views.

Never the less it's often very interesting to be able to read or hear someone else's approach in describing a process or technical feature. There are often little gems in there that hadn't been considered previously.

[DTLarca]

You're quite right ..... hence my point about the day to day analogy, it's essential to bring the connections to the known knowledge then building the connections by creating more of the links.

It's just a mental jigsaw really, identify the colours, join them up to create a picture with supporting over views.

Never the less it's often very interesting to be able to read or hear someone else's approach in describing a process or technical feature. There are often little gems in there that hadn't been considered previously.

Just to add to yours and Gary's comments...

John Locke's Tabula Rasa http://en.wikipedia.org/wiki/Tabula_rasa

David Hume's "Impressions versus Ideas" http://en.wikipedia.org/wiki/David_Hume

Man can predict nothing about the natural world by merely rational means. Empiricism wins every time.

The rationalists say that the sun orbits the earth, that heavy stones fall faster than light stones, that the planets have to orbit in perfect circles, that if you fire one electron at a time at a double split you will have no interference patterns etc etc. But the empiricists find, when they test these thesis experimentally, that the arguments and evidence always point to something quite clearly the opposite of common sense.

Two of Socrates dialogues called Meno and Theaetatus are devoted to the theory of knowledge (Epistemology)

http://www.sacred-texts.com/cla/plato/meno.htm
http://www.sacred-texts.com/cla/plato/theaetet.htm

In the Meno Socrates explains that people are able to work many things out for themselves but only if they experiment and never if they just sits and thinks alone. He gives the example of a square having it's sides or peripheral dimensions being doubled - he is explaining to a slave boy how it works but not by telling the slave - instead he asks the slave to calculate the new surface area if the dimensions are doubled. The slave replies quickly that of course it is common sense that the area will also double. Then Socrates says lets test your hypothesis experimentally at which stage the slave boy quickly sees his mistake and goes on to suggest an alternate hypothesis for Socrates.

Nothing can ever be known for certain - nothing at all. Nothing can be known ever at all except through at least one of the senses. Our senses deceive us more often than they inform us - so we have a duty to throw away all thoughts and theories that cannot thoroughly be supported by hard solid evidence.

[nevgee]

Just to add to yours and Gary's comments...

John Locke's Tabula Rasa http://en.wikipedia.org/wiki/Tabula_rasa

David Hume's "Impressions versus Ideas" http://en.wikipedia.org/wiki/David_Hume

Man can predict nothing about the natural world by merely rational means. Empiricism wins every time.

The rationalists say that the sun orbits the earth, that heavy stones fall faster than light stones, that the planets have to orbit in perfect circles, that if you fire one electron at a time at a double split you will have no interference patterns etc etc. But the empiricists find, when they test these thesis experimentally, that the arguments and evidence always point to something quite clearly the opposite of common sense.

Two of Socrates dialogues called Meno and Theaetatus are devoted to the theory of knowledge (Epistemology)

http://www.sacred-texts.com/cla/plato/meno.htm
http://www.sacred-texts.com/cla/plato/theaetet.htm

In the Meno Socrates explains that people are able to work many things out for themselves but only if they experiment and never if they just sits and thinks alone. He gives the example of a square having it's sides or peripheral dimensions being doubled - he is explaining to a slave boy how it works but not by telling the slave - instead he asks the slave to calculate the new surface area if the dimensions are doubled. The slave replies quickly that of course it is common sense that the area will also double. Then Socrates says lets test your hypothesis experimentally at which stage the slave boy quickly sees his mistake and goes on to suggest an alternate hypothesis for Socrates.

Nothing can ever be known for certain - nothing at all. Nothing can be known ever at all except through at least one of the senses. Our senses deceive us more often than they inform us - so we have a duty to throw away all thoughts and theories that cannot thoroughly be supported by hard solid evidence.

Empirically, I recon that was a sort of an affirming comment

[DTLarca]

Empirically, I reckon that was a sort of an affirming comment

Indeed, each concept (universal) must be founded upon an already agreed, by empirical means, concept. No causal concepts can be known a priori.

Each concept (principle) must be presented in a form tech's are familiar with.

[Aik]

Empirically, I recon that was a sort of an affirming comment

May be you want to process theory with some formulas...
http://www.refrigeration-engineer.co...ad.php?t=25601

[desA]

The shape of the fabric of space-time & its effect on RHVAC systems, would be of interest. You may wish to cover that topic in your latter articles - as required.

Of practical interest:
1. 2nd law of thermodynamics;
2. Various refrigeration cycles & associated log(p)-h, T-s diagrams etc.;
3. Use of Coolpack & other process simulation tools.

[desA]

Use the same theory as used for water pipelines. It's generally well covered in hydraulics theory literature at most technical colleges, or universities.

Nice idea, by-the-way. Would have suspected that the height & diameter of the device would be pretty important, though.

[DTLarca]

The shape of the fabric of space-time & its effect on RHVAC systems, would be of interest. You may wish to cover that topic in your latter articles - as required.

Of practical interest:
1. 2nd law of thermodynamics;
2. Various refrigeration cycles & associated log(p)-h, T-s diagrams etc.;
3. Use of Coolpack & other process simulation tools.

Oh yes - maybe not so much from coolpack, not sure yet, but there are so many "but why?" questions that are asked by students when it comes to the likes of PH charts - so the articles will be looking at many of those.

Use the same theory as used for water pipelines. It's generally well covered in hydraulics theory literature at most technical colleges, or universities.

Nice idea, by-the-way. Would have suspected that the height & diameter of the device would be pretty important, though.

Height and diameter? Surely not - Pascals Barrel comes to mind

[desA]

Height and diameter? Surely not - Pascals Barrel comes to mind

You may want to elaborate further.

There is a difference between steady, or quasi-steady processes, & time-variant processes. Water hammer is a wave phenomenon & is therefore time-variant.

Management methods for each may be different, hence the diameter/height discussion. This can interrupt wave timing...

[DTLarca]

You may want to elaborate further.

There is a difference between steady, or quasi-steady processes, & time-variant processes. Water hammer is a wave phenomenon & is therefore time-variant.

Management methods for each may be different, hence the diameter/height discussion. This can interrupt wave timing...

I was being a little pedantic.

The diameter would not matter and nor would the length though only so long as you have sufficient trapped vapour volume in the vertical stub. But the stub could be say 3/8" on a 1-1/8" liquid line so long as its height creates sufficient compressible vapour. So its the volume of the stub and its ability to retain vapour that matters only.

The Tee'd stub, for instance, would be of no use if it was orientated downward from the pipe.

The liquid should be flowing from where above it there is vapour - for this reason we do not need to worry about the sound-wave properties causing impulse damage back up stream at the other end.

[desA]

I was being a little pedantic.

The diameter would not matter and nor would the length though only so long as you have sufficient trapped vapour volume in the vertical stub. But the stub could be say 3/8" on a 1-1/8" liquid line so long as its height creates sufficient compressible vapour. So its the volume of the stub and its ability to retain vapour that matters only.

The Tee'd stub, for instance, would be of no use if it was orientated downward from the pipe.

The liquid should be flowing from where above it there is vapour - for this reason we do not need to worry about the sound-wave properties causing impulse damage back up stream at the other end.

I would respectfully disagree.

There will be two potential mechanisms at work here:
1. Physical compression of a vapour located towards top of vertical tube (interesting for a RHVAC circuit);
2. Tube length tuned to disrupt water-hammer frequency. (Wave phenomenon, remember).

[Aik]

Use the same theory as used for water pipelines. It's generally well covered in hydraulics theory literature at most technical colleges, or universities.

About theory I have the same opinion...

Nice idea, by-the-way. Would have suspected that the height & diameter of the device would be pretty important, though.

I have some interesting information:
-height of Tee is about 3-5 diameters of tube.
- distance between solenoid and Tee is about 5-7 diameters of tube.
Also I suppose that tube plug on Tee must be spherical...
It's data without theory, I prefer understand in detail...

[mad fridgie]

When doing this type of article/training you need to start at the very beginning with each level reinforcing the previous level.
Examples; Already you are talking about P H diagrams, what is P or H, why do P and H change, then after clearly explaining apply to a common refrigeration (AC) system which is used all the way through.

[Peter_1]

I've written for school in Dutch the beginning of a manual/course starting from scratch.

I entirely explain the log p/h starting from water. Latent heat principle: how many heat there must be removed to freeze water, how many water must be removed to vaporize water....steady boiling and freezing temperature at at certain pressure.
Water boils at 100°C at 10313 Pa, at the Mount everest it boils at 80°C (forgot exact figures), in an old fashioned steampot on 2 bar at 120°C. These are figures mot understand and knows or have heard of.
Give them saturated tables of water and explain all the columns.
Explaining what saturated tables are.
Then give them empty log paper and they then have to make the 2 axis on it, P and h.
Then let them point 20 points out of the table and they then draw the 'bubble' on the log p/h.
Explaining the other way of visualizing the same tables in a log /h bubble.
Then make a cooling chamber with the water, with ice,.. the figures coming out of the book from Dossat.
The the switch to R134a and again making a cooling plant exactly the way Dossat is describing it. I like Roy's approach of this.
And so on.

[DTLarca]

I've written for school in Dutch the beginning of a manual/course starting from scratch.

I entirely explain the log p/h starting from water. Latent heat principle: how many heat there must be removed to freeze water, how many water must be removed to vaporize water....steady boiling and freezing temperature at at certain pressure.
Water boils at 100°C at 10313 Pa, at the Mount everest it boils at 80°C (forgot exact figures), in an old fashioned steampot on 2 bar at 120°C. These are figures mot understand and knows or have heard of.
Give them saturated tables of water and explain all the columns.
Explaining what saturated tables are.
Then give them empty log paper and they then have to make the 2 axis on it, P and h.
Then let them point 20 points out of the table and they then draw the 'bubble' on the log p/h.
Explaining the other way of visualizing the same tables in a log /h bubble.
Then make a cooling chamber with the water, with ice,.. the figures coming out of the book from Dossat.
The the switch to R134a and again making a cooling plant exactly the way Dossat is describing it. I like Roy's approach of this.
And so on.

Though as Mad Fridgie implies - we are already very advanced by the time we get to that level if our aim is to impart a true and full unforgettable understanding - we still then get questions such as "what is pressure?" and "why do we refer to pressure as energy?" And "if two different rigidly sealed containers each hold a different gas but each of equal volume and temperature do they have the same kJ as in the same kJ/m³ but not the same kJ/kg?" Or then "Why do different gases have different specific heat capacities but all have the same thermal coefficient of expansion?".

[mad fridgie]

Though as Mad Fridgie implies - we are already very advanced by the time we get to that level if our aim is to impart a true and full unforgettable understanding - we still then get questions such as "what is pressure?" and "why do we refer to pressure as energy?" And "if two different rigidly sealed containers each hold a different gas but each of equal volume and temperature do they have the same kJ as in the same kJ/m³ but not the same kJ/kg?" Or then "Why do different gases have different specific heat capacities but all have the same thermal coefficient of expansion?".

I think !!!!!!!!!!!?????? that you should undertake a sample, we can then look at your method or appraoch and comment on this side more, than the particular data. You use "note" statements to show common beliefs, or used terms,

[DTLarca]

I think !!!!!!!!!!!?????? that you should undertake a sample, we can then look at your method or appraoch and comment on this side more, than the particular data. You use "note" statements to show common beliefs, or used terms,

I have no doubts about my methods - they have been tried numerous times.

I'm wondering what particular topics are commonly misunderstood

[Gary]

Some things are highly likely. Some things are highly unlikely. And everything else is somewhere in between.

[nevgee]

Some things are highly likely. Some things are highly unlikely. And everything else is somewhere in between.

Be careful now Gary ... "Opinions" ( if they exist) are ( can be ) like blue touch paper .... Oops that may be an opinion ....

[DTLarca]

Be careful now Gary ... "Opinions" are like blue touch paper ....

Gary is pretty much right.

The situation is like this...
Facts can be true or false but arguments can never be true or false - arguments can only have degrees of success or failure but can never be proved right or wrong - only better or worse.

Arguments can never have proofs - only mathematics has proofs. Nothing can prove that the sun will for certain rise again tomorrow but we can prove that the angles in a triangle add up to 180°.

[nevgee]

Philosophically outlined . . .

Gary is pretty much right.

Facts can be true or false but arguments can never be true or false - arguments can only have degrees of success or failure but can never be proved right or wrong - only better or worse.

.

Empirically tested by Monkey Spanner's mate ...... with the conclusive retort "Ouch!"

I can see how the "Classics" can be applied now. . .I like this edification stuff. Real kool

[Brian_UK]

Facts can be true or false but arguments can never be true or false - <snip>

Sorry, wrong.

A false Fact is an oxymoron. Facts can only be true.

[DTLarca]

Sorry, wrong.

A false Fact is an oxymoron. Facts can only be true.

Yes, indeed, nicely spotted - very true when considered in that form

But what is meant is rather that propositions or assertions of a factual nature are either true or false.

"The light IS on" is an assertion proposing a matter of fact and thus can be either true or false.

"This light has always been on this time of the night when I walk past therefore it will be on again this time tomorrow night when I walk past" is not an assertion proposing a matter of fact but is rather an argument for which it just would not make any sense at all to say that it is either true or false but rather that it is relatively strong or weak.

[nevgee]

Well .... I was only playing .... however, I am aware the Greeks did their stuff I don't see how writing long comments on the classics and the methodologies applied thereto can be of any help in your quest.

I can see lots of "Tech" people doing a lot of yawning

[monkey spanners]

Friend of mine was teaching his apprentice basic physics, went a little like this....

"touch that pipe wayne"

wayne "OUCH!!"

"don't touch that pipe, its hot"

"touch that pipe wayne"

wayne "OUCH!! my fingers stuck!!!"

"thats frost wayne, don't touch that pipe"

Repeat for all the common hazards

[mikeref]

Monkey S, its human nature to have sticky fingers, i know what your saying but if Wayne were to learn everything by feel, he might be worse for wear. Take the poor old sparkie, he is forbidden to feel his way around an electrical circuit. As we cannot see electricity, we can only observe its effects,so to speak, but the newbe forgets this or does not believe his tutor and tests for himself. BAM!! I'm sure all of us have had a taste of the invisible force at one stage or another,, C'mon, fess up..mike.

[stufus]

Physics 101
"Magnetism, as you may recall from physics class, is a
powerful force that causes certain items to be
attracted to refrigerators

[desA]

The more you learn, the more you realize how little you know.

It takes a certain amount of learning to realize how ignorant you really are.

[Gary]

When you know all the answers, that means you don't know all the questions.

[Peter_1]

Well, well ,w ell, what a philosophic thread this has become.
But....nice to read.

[buddy]

Well, well ,w ell, what a philosophic thread this has become.
But....nice to read.

Dont forget Pragmatism.


Definition - The doctrine that practical consequences are the criteria of knowledge and meaning and value.

[DTLarca]

Dont forget Pragmatism.


Definition - The doctrine that practical consequences are the criteria of knowledge and meaning and value.

Pragmatism is one ism in answer to the problem of the seeming impossibility of acquiring certain knowledge. There are quite a number of ism's offered in answer. But all have both Pro's and Con's and to me the best seems to be Coherentism operating under the roof of contextualism.

http://en.wikipedia.org/wiki/Epistemology

[Gary]

If the splendours of the universe implies a superior creator, then that creator must necessarily have a superior creator, which in turn implies the creator's creator's creator, which in turn implies... etc... etc... etc... ad infinitum.

[desA]

We digress. Apologies to Marc.

[Gary]

If we are to say that the wonders of the universe are evidence of a creator, then we must say the the wonders of that creator are evidence of the creator's creator and so on...

Any evidence of a creator must necessarily be evidence of a creator's creator.

Or we must say that the wonders of the universe are not evidence of a creator. There is no evidence of a creator.

[rooboy]

Gday Fellas

Haven't posted much over the past few years. Read quite often with interest though.

Much sources of wonderful knowledge on here I have to say.

This is a ripper of a thread.

I had no idea us fridgies were so intelligent.

Maybe we could get this thread published in some plumbing and trade mags - just to mess with their heads

How did believing in God stop us from getting to the moon in 400BC ? Bit confused

Rooboy

[nevgee]

Gday Fellas

Haven't posted much over the past few years. Read quite often with interest though.

Much sources of wonderful knowledge on here I have to say.

This is a ripper of a thread.

I had no idea us fridgies were so intelligent.

Maybe we could get this thread published in some plumbing and trade mags - just to mess with their heads

How did believing in God stop us from getting to the moon in 400BC ? Bit confused

Rooboy

Right on dude .... you must be a mystic as well, along with everyone else ....

[desA]

If we all lived in Flatland (2D), we'd find it difficult to understand the real world (3D, or more?)...

[Gary]

Which proves what?

[desA]

Which proves what?

A bit like the painting trying to figure out what makes the artist tick.

[lawrence1]

Is this post going somewhere?

[DTLarca]

Testing testing testing

[DTLarca]

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