irlandes: Newton’s law of cooling DOES result in a curve. Because the rate of cooling is proportional to the temp diff, as the diff decreases the rate of cooling decreases, and therefore the rate of temp change decreases.
This gets into differential equations, but the result is an exponential curve. I’ll try to draw one and get back to you.
here is an example of Newton’s law for cooling, starting at a 100º temp difference and cooling at an initial rate of 10º/min
Great observations, Oblivion. Pretty much what I thought. Which does explain away the concept that the relatively low temps in the summer, compared to motor temps, shouldn’t make that much difference.
And, Bill, yes, that curve is exactly what we observed with our thermocouples in the environmental chambers. And, so, yes, I need a good dictionary. Hee, hee.
In December 1995, I was in my house in Mexico City, and one day fell on my face. I was in a coma for 6 days in Hospital ABC (American British Cowdray) one of the best hospitals in Mexico. This is where the Old Money goes! You see uniformed chauffeurs standing beside Mercedes Benz limos in the parking lot. My SIL, a nurse, nearly fainted when she saw the bill, but in comparison to the US, it was nothing.
Though they didn’t know it was encephalitis, the MRI did show brain swelling so they did the right thing without the correct diagnosis. We went to a neurologist in our State University, who put it together with an interview. They had told me about him back at ABC; he was world famous and the ABC neurologist had attended one of his seminars in Mexico City.
When I got back to the States, I developed a pulmonary embolism from being in a coma for 6 days (though they did put the special sox on me) and spent another 5 days in the US hospital. Then, I had to go every day for a blood test for the coumadin.
it was running about 20 below during that period. We had a new garage, no insulation, just a shell, but a very good shell. When I went out in the morning to go to the lab, the temperature in the garage would be close to zero. With the hot car put in the night before (I was not allowed to go to work but I could take my wife to the mall, heh, heh.) that is all the colder it got in there. And, the thermometer inside the car was at least 10 degrees, or close to 20.
That to me demonstrated the curve. The inside of the garage cooled down fast to the low single digits, then cooled only very slowly. And, inside the car, it cooled down fast to maybe 20 degrees, then very slowly, so the car was actually comfortable when I got in it.
I guessed if I had something perishable inside a container in the car, it would not have frozen in that short time, but it was only a guess.
“amount of heat transferred is directly proportional to the temperature difference”
“But, no, not directly proportional to the temperature difference. It is on a curve.”
Directly proportional = linear relationship.
A non-linear relationship can still be proportional, as long as there’s no inflection point in the curve (like reaching a peak then falling).
I hope our moderator will tolerate a quick description of the environmental chambers I mentioned, and their use. Military avionics needs to be able to function anywhere they can start the engines. That means North Pole; South Pole; even Fort Leonard Wood, heh, heh. On the hot side, Saudi Arabia and more.
So, we had to cycle the boxes from say +70 C. to -60 C. all depending upon the aircraft specs. Cars have tiny compressors. Ours weighed hundreds of pounds and ran on 440V. To even rebuild one cost a minor fortune.
Specs on a box might say run down to -50 C, cooling at 4 degrees a minute; hold for perhaps 4 hours, testing basic operation once every day at that temp. Then, run up to +70 C. for 4 hours, at the rate of 4 degrees per minute with power on all the way. And, test once a day at that temp. Except on weekends. Test on Friday, then on Monday at hot and cold.
The compressors might be capable of changing temperature much faster than 4 degrees a minute. But, too fast a change could damage the equipment so the controller limited it to the specified amount.
Total run typically 96 hours, after a complete test first.
If a module failed during the 96 hours, or during final test after the temp cycle, the run had to be partially repeated, based on gov’t requirements.
This hot and cold cycling also eliminated infant mortality on the chips (integrated circuits.) Chips have millions, even billions of junctions, and any weak junction is likely to break during cycling. Though I think later, for consumer electronics, such as car stereos and what not, they simply put the bare IC’s in a tray and cycled them without power. In 2015, I have no idea what current procedures may be.
The refrigeration guy was one of those rare world class people. He knew his equipment as few ever do. He taught me to observe carefully the Rustrak[tm] temperature recorder and let him know if it wasn’t correct. As a result I made half of the service calls in our department which had a large number of chambers.
He would come out and I’d show him, “Look here on the chart, this little glitch right here during the cold transition isn’t normal.” He’d look and think a minute, and then happily say, “Yes, I know what can cause that.” And, he’d run back for a relay and it would be fixed.
Later, I transferred to another department and immediately started making half the service calls in the new department. Some people started criticizing me for making so many service calls. He told them, “YOU LEAVE HIM ALONE! When he calls me out, I need to change a twenty dollar relay. When the other men call me out, I have to change an entire compressor because they didn’t spot the relay problem like he does. In years of this, I have never had to change a compressor on one of his chambers.”
Can you imagine what a great automotive mechanic someone like that might be? Although I think we have a couple here of that quality, to be totally honest. Y’all know every well whom I mean.
This is what was happening in my work when I learned high-rel maintenance. High rel means if you know about when any part of an airplane (or car) will most likely start to fail, statistically, you just replace it at that time so you never see a failure.
The most common such item on a car is the battery. A lot of people replace them at about 5 years even if it tests okay, because you know it won’t be long.
High rel isn’t important if you live a mile or two from AutoZone etcetera, For me, it’s awfully important, because it is at least two hours to a Toyota dealer, or any other place where I can buy many Toyota parts, such as Auto Zone in Tehuacan. And, some parts will be very high priced here, or even need to be air freighted in.
I am going to try to legally import my 2002 Sienna next year. When I go back to Texas, I plan to have the remaining O sensors replaced. Some people go a long ways on a sensor, but in my own limited experience they start to fail somewhere around 100,000 miles.
They do have smog verification here. And, last year it leaked out that the government ordered a certain percentage to fail verification, EVEN IF THEY DON’T FAIL. How do you fix failed smog when it isn’t failed? I suppose with a large bill? Anyway, I need maximum health sensors. So, horribly expensive sensors it is.
I have always felt my work on electronics helped me troubleshoot cars, and myself as well. The background information you need for each field is different. Knowing how TACAN works certainly doesn’t help directly diagnose insecticide food poisoning as such. But, the concepts of diagnostics is the same in all three fields.
The neatest thing I encountered was when I got my first OBD II car. I was leery of the system, until i learned it’s almost the same as military avionics Self-test. As soon as I realized this, I knew I could deal with OBD-II very well. And, so it has been.
And, in both cases, the codes don’t tell you exactly what the problem is. But, they do lead you to the area of the failure. For example, the local garbage pickup truck has a -30 degree coolant temperature reading. that would not be hard to find the problem, most likely the sensor itself, or the wiring to it.
And, the problem with the synchronization of crankshaft to valve train, how many mechanics would spot that problem, ever, without OBD-II? Several here might think of it, but I sure doubt most mechanics I would take my person car to, would ever find it.