IR Condenser Heating.

[wwest]

[wwest]

"Sensor" is a mostly empty r-134a canister.

The sensor was charged to 97 PSI from the high side fitting of the LS400 in 84.7dF garage.

Charge level was verified via having stabilize in 91dF OAT environment, low side guage went to 105 PSI with a minute or so and remained at level.

Fired up the '88 911, 92 octane, drove it "hard" for about 5 miles.

Parked the car in the shade, idling (~800 RPM) inserted contact thermometer in the rear lid condenser fins to monitor OAT during the test, 91dF throughout the test. A/C was never turned on at any time.

Placed the canister on the lip and brace inside the rear of the driver's side rear wheelwell.

(Tried to measure the converter temperature [Craftsman 50455] several times during the test and it "pegged" out each time.

Low side guage pegged at the limit with seconds so I opened the high side guage.

I had a reading of 120 PSI within 30 seconds.

Sustained at that level for more than 2 minutes.

Removed the HOT canister and gave it a light coat of flat black paint.

Paint dried quickly.

Returned the canister to the inside wheelwell position.

Now got 130 PSI within 20-30 seconds, sustained.
Craftsman still pegged out.

Switched off the ignition, removed canister to allow it to equalize at OAT, 91dF.

Retreated inside (central A/C) for iced tea and cool off.

When I returned several minutes later the "sensor" reading was 105 PSI.

But a BIG surprise awaited.

Remember that the 911's A/C was never turned on.

When I went to remove the contact thermometer it was indicating....

Wait for it....

[wwest]

That's equivalent to 386 PSI high side pressure.

Anyone know for sure what the high pressure does upon firing up the A/C with the entire rear lid condenser already at 181dF, 386 PSI..??

I was to chicken...

[wwest]

Craftsman 50455 maximum temperature reading is 500dF.

The R-134a canister had just been used to top off the central A/C, no air was introduced.

[SilberUrS6]

Originally Posted by wwest

That's equivalent to 386 PSI high side pressure.

Anyone know for sure what the high pressure does upon firing up the A/C with the entire rear lid condenser already at 181dF, 386 PSI..??

I was to chicken...

Where do you get the idea that 181*F is 386psi? With the system off, the pressure equalizes around the entire system. Unless you have the gauges attached, your temperature reading doesn't equal any kind of pressure.

Hook up the gauges and prove it. You can't, because the TVX isn't closed, and never will be. The whole system is pressure relief. In addition, I don't think you calculated the pressure correctly. I'll have to check with my own calculation, but a delta of 90*F isn't really all that much in a P-V-T calculation.

[SilberUrS6]

Originally Posted by wwest

Low side guage pegged at the limit with seconds so I opened the high side guage.

I had a reading of 120 PSI within 30 seconds.

Sustained at that level for more than 2 minutes.

Removed the HOT canister and gave it a light coat of flat black paint.

Paint dried quickly.

Returned the canister to the inside wheelwell position.

Now got 130 PSI within 20-30 seconds, sustained.
Craftsman still pegged out.

Switched off the ignition, removed canister to allow it to equalize at OAT, 91dF.

When I returned several minutes later the "sensor" reading was 105 PSI.

So, in a very small, closed system, you got a pressure increase of 30 or so psi. Call it 35%. I notice that your test sensor, unlike an actual condenser, has a lot of surface area perpendicular to the radiant body. In addition, your sensor has no cooling airflow, also unlike a condenser (conductive thermal transfer of heat is much more efficient than radiant transfer.) So, because your experiment design sucks in approximating a fender condenser, your experiment is pretty terrible in telling us much except that you don't know how to design an experiment.

[Bob Kontak]

Originally Posted by SilberUrS6

So, because your experiment design sucks in approximating a fender condenser, your experiment is pretty terrible in telling us much except that you don't know how to design an experiment.

Right or wrong he tried something. Let's assume flawed for a scientific study. That's what science is known for. Hypothesis, attempt to prove, get you ass kicked. Tighten up the experiment.

A better way?

[Bob Kontak]

Originally Posted by wwest

Incorrect response. Ask for assistance and input.

[SilberUrS6]

Originally Posted by Bob Kontak

Right or wrong he tried something. Let's assume flawed for a scientific study. That's what science is known for. Hypothesis, attempt to prove, get you ass kicked. Tighten up the experiment.

A better way?

No, what he has proved is that there is radiant heat from the exhaust that added some small amount of delta T to a small, closed system. Really? No schitt? No fscking way, stop the presses.

It doesn't address, at all, the thing he is trying to prove. He is making the suggestion that somehow, the proximity of a condenser to a radiant heat source makes that condenser somehow less efficient. OK, let's allow for the absolute statement. In the absolute, the system would perform better by not being next to a radiant heat source. Ahhh, but that doesn't really address the overall questions of the quantity of performance increase. That's the really sticky part. Absolutes are fine for a moral argument, but this is a discussion of science and engineering. See, Bob, I could have proven the same thing Willard did by heating a mostly empty can of refrigerant up by taking it out of my cabinet at 90*F and placing it inside my car at 160*F. What have I proven, exactly? And what does it have to do with 911 AC?

I have done the radiant heat calculation, using the distance from the catcon to the nears part of the condenser, using the flat surface area of the entire condenser, rather than the actual surface area (look at it, and you'll see mostly air when you look at the front or rear of a heat exchanger), and using mass transfer (air/aluminum) vs radiant transfer (assuming an emissivity of 0.25 for non-polished aluminum, way above the published number) and found a shocking result. Well, not shocking to me, because I understand physics and math. The ambient air temperature is so much more a factor in the efficiency of the system that the very small (but still not zero) effects from radiant heat transfer come close to not actually mattering at all. In fact, my major concern with the design of behind-the-wheel condensers is the debris and water spray they are subjected to from the tire. the exhaust system isn't a factor at all, and if you ran the car super hard, or shielded the condenser completely from the catcon, you wouldn't be able to measure the difference in the cabin. That's how truly small it is.

[Bob Kontak]

Originally Posted by SilberUrS6

The ambient air temperature is so much more a factor in the efficiency of the system that the very small (but still not zero) effects from radiant heat transfer come close to not actually mattering at all.

I trust what you are saying.

I can't do the calcs because of my skill set limitations (I still have the ice cream spoon sticks from first grade for reference).

Tell a layman in layman's terms why it does not matter that the cat is radiating several hundred degrees o' heat but does not interfere much with condenser efficiency a foot or so (less) away.

Why is ambient so much more of a factor? Once the car is moving, though, I have no questions.

Not trying to undermine anything. Just asking.

Also, if I understand, other folks probably will as well.

[SilberUrS6]

Because, primarily, if the differences between the efficiency of radiative heat transfer, and mass heat transfer. So, in the condenser system of which we speak, the working fluid (R134a) heats the aluminum of the condenser as it is compressed and turned into a liquid. This is mass transfer, via conduction. That means, the molecules actually touch one another - R134a/aluminum. Energy is transferred, because the working fluid molecules are quite warm, and the aluminum is not. The heat moves by conduction through the aluminum to the outside, where a different fluid is cooling the condenser. The fluid is gaseous air, moved by a fan. The air is cooler than the aluminum, so the molecules of air carry away the heat whenever they touch the aluminum. Again, this is conduction, the most efficient method of energy transfer. Compare this to radiative energy transfer. The energy density function is a reciprocal cube function, that is, the energy being transmitted is reduced be a factor of some number over the third power of the distance. So, if a heat source was one inch away from my finger, I would feel some form of heat on my finger. If I moved my finger out to two inches away, I would feel heat at about eight times less intensity, that is two cubed, or eight. Since that number is in the denominator, well, you see. That's why you could melt lead on the surface of Mercury without any heat source other than the sun, but feel perfectly comfortable on earth with the sun shining directly on you. And why you would freeze to death on Mars if you wore the same clothes. The heat source is the same, but the radiative transfer really drops off quickly with distance.

At the distance of the catcon to the condenser, you could hold your hand up to a running car's catcon and feel warmth. In fact, it might even be hot. But not uncomfortably so. And here's the kicker - your skin's emissivity is about 0.97 - an almost perfect heat absorber. The perfect heat absorber would have an emissivity of 1.00. Non-polished aluminum has an emissivity of about 0.1 to 0.2. IOW, it would absorb about a fifth (at best) the amount of energy your hand would. Radiative heat transfer is a terrible way to heat anything. That is why most houses have forced air heating and cooling systems. That's conductive and convective transfer, which are much more efficient than radiative, even when the subjects are near perfect heat absorbers.

The real experiment is an easy one. And familiar to anyone who has ever boiled pasta on the stove. So, you have your pasta boiling, and you see that if you don't do something in the next five seconds, the water will boil over out of the pan. A gas range user might immediately turn the gas way down or off - essentially removing the heat source, right? Well, what about an electric stove? It doesn't turn off right away like gas, so you have to do something else. Lifting the pot even just a little bit off the burner will make the water stop boiling. Why? Because before, the pot and water were being heated by conduction. Direct contact of all the materials involved, and direct, molecular transfer of heat. Lift the pot off, and now the heating of the pot (and water) is being done radiatively. And the pot will convectively (mass transfer, again) cool faster than the burner can replace the energy, even though the burner might be at red heat - 2000*Kelvin or so. Way hotter than any catcon. Radiative heat transfer really is a very poor way to heat anything, which is why the effect is so small when we are talking about this condenser/exhaust heat transfer system.

[Bob Kontak]

Originally Posted by SilberUrS6

Radiative heat transfer really is a very poor way to heat anything, which is why the effect is so small when we are talking about this condenser/exhaust heat transfer system.

Originally Posted by SilberUrS6

Again, this is conduction, the most efficient method of energy transfer.

Thank you. Nice write up.

[tirwin]

Bob,

If I may paraphrase was Eric so eloquently stated.

[Bob Kontak]

Originally Posted by Bob Kontak

Thank you. Nice write up.

Wow - even reads better without beer.

[wwest]

Originally Posted by Bob Kontak

Incorrect response. Ask for assistance and input.

Just stated facts without drawing conclusions, no assistance or input required.

[SilberUrS6]

Originally Posted by wwest

Just stated facts without drawing conclusions, no assistance or input required.

Did the conclusion really need to be stated outright? OK, I will do so, but it seems pretty cruel.

On these two issues, you are totally and completely full of schitt. Your experiments suck, and your conclusions don't follow from the data. Even your hypotheses are poor, and your experiments do not address the questions posed in these hypotheses. None of this matters at all, because the real reason that you do any of this is to try and discredit Charlie Griffiths. And this is why you'll never succeed. It is because you start with this overarching framework, and try and fit data to this goal. You might try and bluff people by using big words you learned at Google U., but you can't bluff me. Willard, I actually understand this stuff. Not only that, but I understand the science behind it. In addition, I understand how the scientific method works. Finally, I understand logic in the rhetorical sense, and can communicate effectively through writing (well, mostly. I have failed more than a few times). These are all things you lack, and in some cases, lack entirely.

You have offered 911 AC folks a couple of things: comedy in your verbal pratfalls. I doubt that's intended, however. But in a material sense, your warning to add a high pressure switch is a very good one. It helps save expensive components from damage, and is a good suggestion.

[SilberUrS6]

Originally Posted by Bob Kontak

Wow - even reads better without beer.

Thanks. Does it show that I love science?

[wwest]

Why the focus on conductive heat and not also calculate the effects of radiant heating of the hundreds of square inches of condenser tubing/fins...??

Our sun's radiation does not heat our atmosphere directly because our atmosphere (much like the refrigerant gas in the condenser) is to "transparent" for the radiant heat passing through to be effective. The sun's radiation heats the "opaque" earth's surface wherein CONDUCTIVE heat transfer takes over to heat our atmosphere.

So the question becomes...

How effective is the HOT (150dF) refrigerant gas-to-metal fins-to-atmosphere (91dF) CONDUCTIVE heat transfer vs the RADIATIVE heat transfer of the HOT(900dF) catalytic converter-to-cool(130dF) "opaque" condenser?

So we're not discussing the highly efficient CONDUCTIVE heat transfer of a solid metal pan bottom in actual contact with the solid heating element of an electric stove.

The discussion involves the CONDUCTIVE efficiency of a gas-to-metal-to-gas transfer of heat, in the factual case a "D" of only 59dF.

To be fair... COMPRESSED refrigerant gas, more gas to metal "interface". But on the other hand "thicker" gas means less transparency to RADIANT heating. Provided the fins of the condenser are wrinkled/rippled to create turbulence in the fan forced airflow, a better metal-to-air "interface".

So, not exactly a simple gas-to-metal-to-gas heat transfer equation.

[wwest]

Originally Posted by SilberUrS6

Where do you get the idea that 181*F is 386psi? With the system off, the pressure equalizes around the entire system. Unless you have the gauges attached, your temperature reading doesn't equal any kind of pressure.

Hook up the gauges and prove it. You can't, because the TVX isn't closed, and never will be. The whole system is pressure relief. In addition, I don't think you calculated the pressure correctly. I'll have to check with my own calculation, but a delta of 90*F isn't really all that much in a P-V-T calculation.

181dF is the EQUIVALENT of 386 PSI, or vice versa.

Note: The A/C was NEVER in operation prior to, during, nor after the experiment was completed.

LQQK before you JUMP!

[SilberUrS6]

Originally Posted by wwest

So, not exactly a simple gas-to-metal-to-gas heat transfer equation.

Your attempt at obfuscation notwithstanding, yes, it is really that simple.

The major driver of heat exchanger operation is working fluid-exchanger-cooling fluid conduction. Period.