Noob question, 12v fan on multiple 9v batt

MisterBill2

Joined Jan 23, 2018
8,420
So, in this case what does AC actually mean? We know it's not an air CONDITIONER, it would just be a fan. But what sort of fan? And what does AC stand for? Acceptable Cretin? As in Fool and his money?
In that instance AC probably means "Actually Cheapo", or more likely "Amazingly Cheap".

And now I am wondering why a 2 year old is wearing a crash helmet.
 

Tonyr1084

Joined Sep 24, 2015
5,860
AH! Evaporative cooling. I have that on my roof. Works great in low humidity conditions. But when humidity is up - it doesn't work so well. Poorly when humidity is high.
 

MisterBill2

Joined Jan 23, 2018
8,420
OK, now we know that "AC" means Air Cooling in this instance. But if it does not remove heat by transporting it away, lie standard refrigeration systems, it transfers the heat energy into warm water vapr by evaporation. So the claim about reducing humidity is a LIE, plain and simple. But even with no description that should be obvious, because to remove heat energy it must be moved to someplace else..

IN THIS CASE IT IS AN EFFORT TO MISLEAD PEOPLE!
 
Last edited:

ThePanMan

Joined Mar 13, 2020
62
Moving air strips away the heat. That's what wind chill is all about. It can be 33˚F outside with a wind chill of 25˚F. That's because whatever boundary layer of body heat you have gets stripped away. And if you're wet and the air is dry - it'll be even worse.

If outside temperature is above normal body heat then blowing wind will only feel like fiery razorblades. I've been there too. That's why heat index is another one of those "Feels Like" numbers.

We can probably come up with a whole bunch of other terms for AC, like Active cooling, which a fan is doing exactly that. However, when we hear "AC" we automatically think of Air Conditioning - another phrase for refrigeration. It actively pumps the heat out of a given space.
 

AnalogKid

Joined Aug 1, 2013
9,162
AH! Evaporative cooling.
It isn't evaporation, it's conduction. Or convection, depending on how semantically picky you want to be.

Tap water is colder than skin temperature, and probably colder than room temperature if the water has been running for a while. The term "Air Conditioning" might be entirely correct: When you blow warm air across cold water, heat is transferred to the water. It isn't evaporative cooling, it's just cooling. Granted, the evaporator coil inside a forced-air HVAC system is a lot colder than tap water, but the mechanism is the same - thermal transfer through direct contact.

ak
 
Last edited:

crutschow

Joined Mar 14, 2008
26,974
It isn't evaporation, it's conduction.
Not so for the typical swamp cooler on the roof or in a window of a house (and likely for the "AC" unit in discussion).
If you look inside you will see that a swamp cooler blows the air through a mat saturated with water.
There is a small pump that recirculates the water from the base of the cooler to the mat to keep it saturated.
I's the evaporation of that water with its high heat of vaporization the cools the air.
The water temperature has only a slight effect on the temperature of the air after it's gone through the mat, and the cooler will work well even if the water temperature is equal to the outside air.
 

ThePanMan

Joined Mar 13, 2020
62
What I know about evaporative cooling is that it takes energy to convert water into humidity. And no, the two are not the same. The simple part is the fact that as temperature goes up, humidity goes down and vice versa. That relationship is quite linear and it works well. Consider the weather in Phoenix, Arizona, on a sunny summer afternoon. It may be 110°F, but, as they say, "It’s a dry heat". There is almost no moisture in the air when the temperature is that hot - often it is less than 10 per cent humidity. As a result, evaporative cooling works great in the desert.

Water evaporating from your wet cool cell pads has a cooling effect on the hot air passing through the cool cell inlets. This is the complicated part of the relationship between temperature and humidity. To evaporate water, heat (energy) is required. The heat comes from whatever object the water is in contact with as it evaporates; in our cool cell situation, that object is the hot outside air itself as it passes through the wet pads. As heat is removed from the air, the temperature of that air is decreased but the heat remains in the air, in another form.

Water evaporating from your wet cool cell pads has a cooling effect on the hot air passing through the cool cell inlets. This is the complicated part of the relationship between temperature and humidity. To evaporate water, heat (energy) is required. The heat comes from whatever object the water is in contact with as it evaporates; in our cool cell situation, that object is the hot outside air itself as it passes through the wet pads. As heat is removed from the air, the temperature of that air is decreased but the heat remains in the air, in another form.

To learn more about this; here's my source:
https://thepoultrysite.com/articles/evaporative-cooling-systems-how-and-why-they-work
 

djsfantasi

Joined Apr 11, 2010
7,622
But if you’re not in the desert, I disagree with your statements. 100° in Boston feels a lot hotter than 100° in Phoenix. It’s not the heat, it’s the humidity.
 

MisterBill2

Joined Jan 23, 2018
8,420
There are other parts of the world, and even here in the USA, where it can be 95 degrees with the humidity almost 100%. So sweating does no good at all. Just a few dozen miles south of the Port of New Orleans I have experienced that. Incredible heat and very high humidity. Water will not evaporate because the air is already saturated. Also in jungles in another part of the world, a bit south of the equator and a bit west of China. But in my recollection the cooking humid heat was the very best part of being there. Enough on that topic.
Evaporative cooling only works well if you have an adequate supply of dry air.
 

ThePanMan

Joined Mar 13, 2020
62
When you blow warm air across cold water, heat is transferred to the water. It isn't evaporative cooling, it's just cooling.
What about human sweat? That's a temperature of 98.6˚F. What about when the air temperature is 90˚ and you're sweating? Doesn't sweating and the evaporation of said sweat cool you off? Can't say water temperature has all to do with it. Water temperature may actually have very little to do with it. It's the evaporative process that is responsible for the cooling effect.
 

ThePanMan

Joined Mar 13, 2020
62
But if you’re not in the desert, I disagree with your statements. 100° in Boston feels a lot hotter than 100° in Phoenix. It’s not the heat, it’s the humidity.
Swamp coolers are hardly available in places like Boston whereas there is high demand for them in Phoenix. When humidity is up swampers are less effective.

Wasn't this thread about putting fans and batteries on top of a 2 yr old's head? How is it devolving into an argument about swamp cooling and air conditioning; and other definitions of "AC"?
 

Tonyr1084

Joined Sep 24, 2015
5,860
PanMan has a very good point. The thread has wandered so far away that the original query is totally abandoned. And nothing useful has been mentioned.
Thanks for pointing that out. Yes, it has wandered. Thanks for the morning laugh.

Thread topic: Battery powered helmet fan. How to accomplish this? Honestly, I haven't an answer. Had plenty of cautions. Suggested a backpack with batteries; but kids and wires don't do well together. There are chances of breaking the wire. There's also the possibility of accidental strangulation. So battery packs are out. NASCAR helmets with hoses hooked up to blowers was mentioned. But the kid will probably get beat up for looking like a geek. I guess the best advice is to let the kid get used to the helmet. It protects his brain.
 

MisterBill2

Joined Jan 23, 2018
8,420
I was wondering about the purpose of the helmet from the start. None of the infants in my extended family have had helmets at age 2, that I can recall. Wearing the helmet on a powered riding toy is different, but a 2 year old is not ready for that.
Of course, there have been perforated helmets available for many years.
 

Tonyr1084

Joined Sep 24, 2015
5,860
When I grew up - I never had a helmet. Rode bikes, mini-bikes, skateboards (no elbow pads either), motorcycles, go-carts, all kinds of powered stuff. Never hit my head once. However, there's still no apparent explanation for my brain-damage.
 

MisterBill2

Joined Jan 23, 2018
8,420
When I grew up - I never had a helmet. Rode bikes, mini-bikes, skateboards (no elbow pads either), motorcycles, go-carts, all kinds of powered stuff. Never hit my head once. However, there's still no apparent explanation for my brain-damage.
I HAVE had a few concussions from things other people did. Some intentionally delivered and some accidentally happening. Mostly in situations where one would not normally be wearing any protection. And most of them when I was an adult, not a kid. There are some rather nasty folks around, and a few rather careless ones as well.
The perforated helmets for kids seem to have a fair amount of ventilation, but they don't do much to keep the sun off. So I am wondering what a two year old does that requires a helmet. All of the two year old kids that I know seem to be quite well supervised so that they do not get into situations needing a helmet.
 
Top