Car AC theory question

You're right. sorry.

because that's what it is, technically speaking. it's not convection in the traditional sense - it's forced transfer of a medium typically characterized by its mass. you've heard of air conditioners rated by their tonnage haven't you?

technically, it's not convection because that is what occurs unaided.

further reading:

WTF? That's got nothing to do with "mass transfer," which is a term used for other processes. I looked it up because I never heard the term used when talking about heat transfer. You won't find mass transfer conflated with heat transfer anywhere. Analogies only.

Kiss my ass with your condescending bullshit. . There's forced convection and natural convection. I was a trained Navy boilerman for

4 years, further studied heat exchange while in the Merchant Marine, worked in the power generating plants at U.S. Steel, had a stationary engineers license, and worked on plenty of car cooling systems. Nobody but you ever used the term "mass transfer" to describe a simple car cooling system heat exchange process. Only you. The term "mass transfer" is mostly used in chemical engineering. According to Wiki, "The driving force for mass transfer is typically a difference in chemical potential." Heat exchange is driven by temperature differences. You can study the details if you like. I'm done caring now.

why are you on a "tech" forum if you're not interested in using technical language? to put this another way, if people use language that you don't understand, why is it their problem not yours?

!!!

???

no, science only.

it's not condescending, it's helpful to people on a "tech" forum with an interest in understanding what they don't know.

i don't know where you got that little nugget - you don't cite a link - but there's no "chemical" potential here.

i do like. that's why i have studied them. why someone who doesn't and hasn't thinks they're better informed is the confusing bit.

pretzel logic given that you took the trouble to tell everybody what you think.

It's to do with emissivity. Read this.

Mass is not being transfered across the system boundary. Only heat. Yes, water flows in the engine cooling system and air flows through the radiator, but no water is transfered into the air and vice-versa.

Yes, we've not only heard of it, but actually understand it. It has nothing to do with mass transfer. A ton in HVAC terms is the amount of energy it takes to transform a ton of ice at 32F into water. Again, no mass is transfered, it just melts.

That's just wrong.

You use Amazon as a reference for physics and engineering?

That's for sure!

that's deliberate obfuscation. air [mass] is transferred within the greater body of itself. that's why "mass transfer" is used to describe the process which for free bodies is otherwise known as "convection" or forced systems, "advection".

!!!

look up the definition of "convection".

ah, so you're not serious. should have guessed.

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It's not obfuscation, it's basic physics.

 air [mass] is transferred within the

BS. Convection is convection whether it's natural or forced. An example of natural convection is hot air rising above an electric stove burner. An example of forced convection is the air flowing through the car radiator. If we're all wrong, then maybe you can explain all the "convection ovens" being sold and used. I have two here in the house. Both have fans. When you select convection heating, the fans turn on to circulate air within the oven cavity. That is how a convection oven works. Very basic.

If you have some point, !!! doesn't make it. I would note that you accused me of obfuscation. YOU asserting that "tons" in an HVAC context has something to do with mass transfer, that it proves your point, now that's obfuscation. Tons in that context is a measure of heat energy, nothing more. I hope you accept that now.

I have, perhaps you should too. Here, it could not be spelled out any clearer:

"Convection can be "forced" by movement of a fluid by means other than buoyancy forces (for example, a water pump in an automobile engine). In some cases, natural buoyancy forces alone are entirely responsible for fluid motion when the fluid is heated, and this process is called "natural convection." An example is the draft in a chimney or around any fire. In natural convection, an increase in temperature produces a reduction in density, which causes fluid motion due to pressures and forces when fluids of different densities are affected by gravity (or any g-force). "

It's particularly interesting that as an example, they actually use an auto cooling system. That should remove any doubt.

That link is to a book being sold on Amazon. It's a college engineering text book on heat and mass transfer. So, what on earth are you implying that picture of the book proves? That's a scientific reference? A book cover? Good grief.

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Not, hardly. Read the introductory chapter of the granddaddy of all transport phenomena texts, Bird, Stewart, and Lightfoot. It's preview is available at

The first few paragraphs of Chap 0 and the table of processes on p. 4 (Table 0-2.1) (and where they're covered in the book) is sufficient.

This is a dual-loop, closed system forced convection heat transfer problem. No mass transfer in the analytic meaning thereof is occurring.

um, i'm not referring to the "picture" but the contents. but you'd recognize that if you weren't contriving to be so disingenuous.

no, it's suggested reading.

are you for real? do you understand what you're reading? if you think that contradicts a single thing i said, you have a serious comprehension problem.

comprehension problem. there is one closed loop on an automotive engine coolant system. the other is wide freakin' open.

There is also the fact you may not want to see the bright aluminum through the front grill. Not so common these days, but sometimes you can see right in. Same with intercoolers.

Greg

te:

Do you still deny that convection is the primary energy transfer mechanism in a car radiator?

Do you still deny that convection can only exist if it's natural convection? If the answer to the above is yes, please explain:

A - Convection ovens, which use a FAN . I have two here so I know they exist.

B- Why numerous references, some of which have been cited, talk about natural and forced convecton. I have yet to see your reference that says convection can only be natural, ie without a fan or pump.

C- Why engineers treat air to water heat exchangers using CONVECTION, not mass transfer

And citing a book cover on Amazon is not a scientific reference.....

rote:

These are misnomers. The terms have come into use through attempts by salespeople to differentiate between normal and fan ovens.

The correct term would be "forced air circulation ovens" Commercial ovens are identified as such.

circulation.html

Without a fan, the correct term is "passive/natural air circulation".

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Convection is the concerted, collective movement of ensembles of molecules within fluids (e.g., liquids, gases) and rheids.

The term convection may have slightly different but related usages in different scientific or engineering contexts or applications. The broader sense is in fluid mechanics, where convection refers to the motion of fluid regardless of cause.[2][3] However in thermodynamics "convection" often refers specifically to heat transfer by convection. [4]

Additionally, convection includes fluid movement both by bulk motion (advection) and by the motion of individual particles (diffusion). However in some cases, convection is taken to mean only advective phenomena. For instance, in the transport equation, which describes a number of different transport phenomena, terms are separated into "convective" and "diffusive" effects, with "convective" meaning purely advective in context.

Forced convection: In forced convection, also called heat advection, fluid movement results from external surface forces such as a fan or pump. Forced convection is typically used to increase the rate of heat exchange.

Moron.

such.http://www.powdercoating.romerpp.pl/kategoria/3_50_84/Oven_with_force... >>

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Let me take a shot at in a different way. If you have a gas/liquid the density of the g/l is determined by the size of the molecules. It seems to me that adding energy to a molecule would would increase its size and make it less dense than the surround molecules in your g/l. When there is gravity, the lighter molecules would tend to migrate to the top of a container and if collected and cooled to a temperature below that of your existing g/l, those cooled molecules would have less energy thus less density than the g/l and would tend to migrate toward the bottom of your container. If you are a PhD and this is wrong thinking don't howl at me because it's a SWAG made from observation and could be totally wrong and too simplistic. ^_^

TDD

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Yes, that's the essence of the idea of how fluids move via natural convection. Except that it's not the size of the molecules that changes, it's the spacing between them. The more energy they have, the more they are bouncing around, the more space between them.

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I see you snipped the bit we are talking about.

Shitfer brains.

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Exactly correct Duf.