Thermodynamics!

OK - just how does this thing work?



The shade is obviously blocking sunlight from coming through that windshield.

But for keeping that car's interior cooler, is the reflective surface any more effective than a non-reflective surface? Would a similar shaped piece of cardboard accomplish the same thing ("shading" the interior)?

I guess what I'm getting at is, the shade prevents the sun from hitting the seats, etc. But the windshield glass heats up, with or without the shade. So wouldn't the hot windshield transfer heat into the air of the interior by conduction and convection?



T.

Forget that Tom.... Get one of *THESE*

I use one of those (the shiny thing inside the windshield) frequently (when I'm in CA) and can vouch that it does work. Significant reduction both in air temperature inside the car, but especially in surface temperature. Without it, I can barely touch the steering wheel, even with a leather cover on it.

Yes, the reflective surface works much better. The light (radiation) is the major energy source, only a tiny fraction of it is converted to heat by the glass. (There's even a law about that in CA, but I don't recall the number offhand. Has to be less than 5% or something like that.) The reflective shade actually makes the glass hotter (because most of the light goes through it twice) but there is still an overall reduction in heat to the interior because most of the light gets sent back outside the car. Light that isn't reflected (like on a sheet of cardboard or your car's interior) gets 100% converted to heat.

Technically, even cardboard reflects some light, otherwise you couldn't see it. You could get some relief by sticking a sheet of cardboard behind the windshield. But the shiny mylar coating reflects more of it.

Yes, some conduction and convection from the hot glass. Again it's smaller.

Gliderman8 said:

Forget that Tom.... Get one of *THESE*

Click to expand...

That would work real fine in our New Mexico winds!

Surely anything is better than a black interior absorbing energy.

The tent looks fun, but I would think a blanket would be easier.

My son says most folks at his base in Kuwait use them on the 1 window they have in there rooms to block the the sunlight/heat

Elliot, I'm gonna get 1 of those for when the heavens start raining bricks on us

DNK said:

Elliot, I'm gonna get 1 of those for when the heavens start raining bricks on us

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It’s good for falling coconuts too.

Edit: delete

Dark surfaces reflect light as infrared. Glass does a lousy job of transmitting infrared, this equals heat trapped inside the car. Silver / bright surface reflects more of the light back out - less heat.

Windshield reflectors are effective at reducing internal
temps.

Was going to post the joke about the final exam "is **** exothermic" and answer involved freshman Marie Joe Poloski saying she would sleep with student when he'll freezes over, since this hasn't happened etc. But link didn't work.

Shame. That was a good one, worth seeing again.

The physics was discussed in this thread: https://www.britishcarforum.com/bcf/showthread.php?113189-Garage-roof-insulation

TR3driver said:

Technically, even cardboard reflects some light, otherwise you couldn't see it.

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Good thing too, imagine the UPS driver trying to deliver your package if the back of the truck was just an inky black hole...

One of the mysteries in all this: there are several references to "the shiny side should be down", due to its lower emissivity. See PC's reference:

https://www.dulley.com/docs/f411.htm

But the windshield shades have the shiny side up toward the sun.

hmmm

Not to steal Elliott's thread but this has to do with Hydrodynamics
See, kind of similar !

I call this Overboard Outboard

Overboard schmoverboard.

I call it "tail heavy".

harumph

NutmegCT said:

harumph

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No, I believe they're Yamahas

Don, i'll see your 270 hp and raise you 1,130 hp.

Boat seen at dock in Key West, FL. i can't impagin the need for that much motor on a boat that size.

Tried to make it bigger and failed.

Bob McElwee said:

Don, i'll see your 270 hp and raise you 1,130 hp.

Boat seen at dock in Key West, FL. i can't impagin the need for that much motor on a boat that size.

Tried to make it bigger and failed.

Click to expand...

Thats for when you want to get to that favorite fishing spot really fast!