I disagree.
There has to be a definitive answer to this question other than opinion based upon anecdotal observations.
Surely there is a ? “mass/temperature” formula? that accounts for airflow of a deviant temperature across a given body…
There are a set of formulas that could be derived. Once we know airflow patterns, heat output, shape of car seat, outside air temp, how well the car is insulated, and a hundred other factors.
The one guy who used to be a car design engineer has left us. He might have been able to give us which parameters probably really mattered and which ones probably had trivial influence. Then once you WAGged all the inputs, we could compute a sum-of-WAGs output for you. For what little that’d be worth.
I understand this is frustrating. The tradeoffs are not obvious and simple and there are several significant unknown variables. So we (or at least I) cannot simply say a priori that one choice is obviously better than another.
I have a suggestion. On your next pizza run, buy two pizzas. Put one on the floor and one on the seat. Measure their temps when you get home. Also measure the temps before you leave the store. After 5 pizza runs I bet you have enough data for a reliable conclusion. Which may be that there is no significant difference. Or may be that the results are not repeatable at all.
The best part about this experiment is a) you don’t need to apply for a grant and b) you get extra pizza out of the deal.
Good luck and please report your findings here. We’re (or at least I’m) actually interested to know the answer.
Was trying to illustrate a concept by utilizing a familiar real life experience .Despite the effort to frame things as such, my analogy apparently failed to connect…Was not looking for a way to keep pizza hot per se but rather the conditions that causes it to cool down .
Pizza was never the issue.
Sorry for wasting your time
It will remain hotter on the floor because in this scenario the floor is warmer than the seat. At worst case it will be as warm as floor temp. Which is marginally higher than the seat, all other factors being equal .
And it keeps the pizza flat, which matters to the end user.
Pizza’s the only reason I clicked on this thread. For your purpose, you might as well heat up two bricks in your oven, take them to the bathroom, put one on the toilet seat and the other on the floor; blasting the latter with a hairdryer for 15 minutes.
Still air acts as an insulator. The thermal conductivity of solid surfaces in contact with the pizza (major ones here being the bottom of the pizza box, the seat, and the floor) will be the primary variables. The insulated delivery bags are designed around this idea, and have reflective material to help keep the heat in.
If I’m understanding your hypothetical correctly, your question is which position, floor with forced hot air vs seat with chilly ambient temperature, would cause the greater temperature drop from the initial from-the-oven temperature, over a timespan of 15 minutes.
On the seat, you have still-ish air around the box providing some insulation, but contact patches between the bottom of the box and the seat will transfer heat away until the seat warms up to match the box temperature.
On the floor, what the forced air is actually doing is keeping the lid at 115°, transferring away any heat that has made it through the lid. You would have the benefit of a relatively warmer floor, though.
In conclusion, this has been an intriguing thought experiment, and in my opinion, the seat might be the better choice due to the insulating properties of (relatively) still air, if the main goal is to lessen the heat loss.
Things to consider:
The pizza construction - some ingredients will hold temperature longer, oils may saturate the box affecting heat conductivity etc
If the pizza did not come in a box then the floor is likely a better bet… best of luck to you in that scenario 
This.
The tradeoff - still air insulating the pizza, forced air carrying away the heat of the pizza but still 115°. The pizza is of course, initially much hotter than 115°F.
My wild-ass-guess is that forced air is not a good idea, even if it is fairly warm.
The tradeoff - cold seat, possibly warm floor.
I would think if you don’t have an insulated pizza bag (I happen to have one) the next best thing is to lift the pizza box off the seat (or floor) to minimize conduction loss. Take off your damn gloves and put them under the box to lift the pizza off the seat or floor. Presumably your gloves are a bit warm and less contact area than the alternative. Also, you may have a floor liner with thin rubber ridges to limit box contact, or double carpet mat to help insulate the bottom of the box on the floor.
Debatable - depends how insulated from the outside the floor is. And how long it stays warm when cold air is rushing under the car, and a cardboard box is blocking hot air from above; and the latent heat of the floor. All the more reason to put your gloves under the box.
Short answer - forced air is faster at cooling the object than still air. Conduction from the bottom is your biggest problem.
The hot pizza is sitting on the bottom of the box, the top of inside the box has its own still air gap insulation layer, so conduction is a worse loss than convection. insulate the bottom of the box, with an air gap. Preferably still air. A cold seat - the cold does not rise, so a half inch of separation will keep the bottom of the box warm better than anything.
As the OP is trying to look just at the difference between a colder still air and warmer forced air, I think that it would be better to assume a spherical cow super special insulating material between the box and whatever it rests on to [magically?] eliminate conduction through the bottom of the box. That way only the heat from convection can be examined.
Actually not. Heat loss through air isn’t a trivial thing to calculate for most people. Thermodynamic engineers may disagree, but it’s much more difficult than things such as falling objects, if I recall from my physics for engineering series.
Here is a question I found online being asked by a physics student.
That actually is a much easier problem than the one you posed because with pizza boxes, there is air convection within the box as well, rather than directly being exposed to the outside air.
As one person answered on for this question, h, the convective heat transfer coefficient needs to be obtained empirically.
In short, you aren’t going to find simple answers.
There is also the sogginess that has to be considered. Pizza that is kept warm in an enclosed space too long usually has a less crisp crust, this may be a factor that is important to you. We sometimes let it cool then pop in in a preheated oven when we get back. This is rare as we have excellent pizza 3 minutes away though they close on Tuesdays which substantially increases pizza travel time if we were so inclined.
I was going to say that it occurred to me that it wasn’t the temperature of the pizza itself that was relevant, but the temperature of the outside of the box, which would probably favor putting it near the vent. I was going to say that, but…
In that case, no answer is possible until we know what the actual situation is. It’s a complicated enough problem that it’ll depend on all sorts of subtle factors, and you won’t get the same subtle factors present in a pizza and in whatever it is you’re actually asking about. Just for a sampling: Is the thing you’re actually asking about in a partially-insulating container, like the pizza? Is the thing you’re actually asking about moist and shedding water vapor? Is the thing you’re actually asking about going on for pizza-pickup-like timescales? Is the relative amount of change of temperature of the environment the same for your actual thing as for pizza? Is the convective fluid actually air, or some other gas, or possibly even a liquid?
It’d probably be easiest just to tell us the actual question.
I think this is getting at the cheese and sausage of the matter. But I still think the physics minded of this board can better explain to the rest of us the likely relative contribution of the major sources of heat transfer, even without exact numbers.
My ignorant WAG, to be sliced apart by those who know more, is that with reasonable assumptions it isn’t close: the seat is going result in a warmer pizza.
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In the hypothetical conduction is a major contributor. Most car seats are designed to be poor conductors of heat. The floor not so much so.
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The efficiency of convection as a means of heat transfer is a big deal, likely, for any reasonable value of h, swamping the fact that the initial air surrounding the box is colder than the air coming out of the vent.
On the other hand, pizza boxes are flat, but neither car floors nor seats are. A pizza box sitting on either is mostly just going to make contact along parts of the edge of the box. So you’d get radiation and convection between the box and the floor-or-seat, and then conduction through the floor-or-seat.
At least, for the pizza situation. We don’t know if that’s applicable for the actual situation.
Very good point. Still then the bottom of the box is in the case of the box on the floor not exposed to the blowing less cold air and the air it is in contact with is next to a better heat conductor which in turn is in contact with the outside. While the seat box air under the box once warmed is likely to stay warm.
Any way it seems that @ZurBob’s hope to keep it simple still leaves a problem too complex to solve without details.
I am however surprised that the experts here are not confident that the convection is a bigger deal to heat transfer than initial surrounding air temperature over a wide variety of reasonable assumptions and starting conditions.
No measured results to report but when running out for carry-out pizza I have gotten into the practice of turning on the passenger seat warmer on the drive there and then putting the pizza box on the seat for the drive home. Does it make a difference? I have no idea.
It seems like one way to resolve this question practically, without need for advanced calculations, would be to physically measure the temperature of the top of the box when left in still air. Then, independently, measure the temperature of the air stream. If the top of the box (left in still air) never exceeds the temperature of the air stream (that is, if it is always colder than the air stream) then it would seem placing it in the air stream and getting the convective heat transfer acting on the top of the box would actually keep it warmer.
If, however, the air stream is at some point at a lower temperature than the top of the box in still air, then I strongly suspect there would be intervals where being placed in the air stream would draw off heat faster (because convection tends to be more effective for heart transfer than conduction through a given medium, although at what point the trade off between a higher delta T versus a higher mass flow rate would trade off would be specific to the materials involved).
Point being, (1) as noted, the air in the box is still, and (2) there is no contact between the top of the box and the pizza. So… you really don’t have to worry about the heat difference between the pizza and the air stream so much as you have to worry about the difference between the top of the box (the one thing exposed to the air stream) and the air stream itself.
Does anyone know the proper formula for “wind chill” calculations? That would be relevant here, how heat loss is affected by the speed of the air over the object losing heat. Ignoring cpld seat/cold floor issues, the real question is - does a cardboard box lose heat by convection (i.e. conduction to the surrounding air which then rises to remove itself for more cold air) faster through still air that is cool, or through warmer air moving faster?
The heat loss is -elementary - supposedly proportional to the difference between the two surfaces, box and air. It’s the air speed for the one case that makes the calculation complex.
Wind chill calculators do not work for temperatures above 50 deg. F. Why is there no wind chill at 50 degrees?
There’s no wind chill when temperatures are above 50 degrees as the layer of heat surrounding the body is hard to remove with such mild air.Jan 11, 2022
[
Science of Wind Chill | WeatherBug
https://www.weatherbug.com › news › Science-of-Wind-…
](Science of Wind Chill | WeatherBug)
Another consideration is whether any of the box other than what is in direct contact with the pizza is mathematically relevant for the 15 minute drive home.
How long does a boxed 325° pizza take to cool to 115° in still air? From the pizza’s perspective, there is very little air convection inside the box in either the seat or floor positions.
Having read the first half of the responses, I will be my normal contrarian self and say on the seat in still air.
My half-baked reasoning (heh) is a combination that the hot air blowing will still cool the pizza and the fact that if it is -10 degrees F in MN and completely still air I can actually stomach it naked for a bit.
Not that I ever did that. noooo. Who would do such a thing?
You’ve misinterpreted my comment, perhaps due to my poor choice of words and lousy sentence structure. My comments were indeed intended to be about the thermodynamics
of pizza delivery. No undisclosed agenda here.