# Tag Info

## Hot answers tagged convection

65

The reason is because the heat loss occurs mostly in the windows and the fenestration. The idea is that you would like the incoming air to be heated up. Also, it creates an air curtain that prevents more heat from being lost through these exposed areas. Finally, it makes the temperature of the room more or less uniform. If the heaters were placed at the ...

51

Partly practical, the wall under the windows isn't useful for anything else. We had a house where the heaters were placed in the middle of the only empty walls, so nowhere you could put furniture, bookcases, etc. Before double glazing there would be a draft from the windows so the idea was to heat this incoming air by having a radiator immediately below the ...

47

Since this is a physics forum I assume the OP is interested in a quantitative answer in terms of the efficiency of the system and how it differs based on the relative positioning of heat sources and heat sinks. The math required to analyzed such a system is too much for me to manage right now, but I believe the following principles apply and are objectively ...

29

Although it looks like the wood of the matchstick is burning, this isn't the case. Combustion is a gas phase reaction, and what actually happens is that the heat of the flame heats the wood and decomposes it so it gives off various flammable gases. These then react with oxygen to give the flame. So sustaining a flame requires that the burning material be ...

12

To pretty much everything you stated in your question, "no". That convection requires a medium is not the main difference, it is simply the most obvious aspect of what is a fundamentally different mechanism for transfering energy. Convection is the transfer of energy by movement of a medium, whereas radiation is the transfer of energy by, well, thermal ...

11

Convection is the collective motion of particles in a fluid and actually encompasses both diffusion and advection. Advection is the motion of particles along the bulk flow Diffusion is the net movement of particles from high concentration to low concentration We typically describe the above two using the partial differential equations: \begin{align} \...

10

I will try to explain in simple words. Every body which has a temperature above 0 Kelvin gives out (ie. radiates) some heat in the form of waves. (So, even we radiate!) Of course, the amount of this radiation depends on the temperature, so the more the temperature of the body, the more heat it gives out. Now, since this heat energy travels in the form of ...

9

You've actually identified a key area of ongoing research known as the coronal heating problem. First, let's get one thing out of the way. You ask: Or is there a type of matter with thermal conductive properties that could accomplish this? There can be no such material. Any material that passively diffuses heat from a cooler region to a warmer one ...

8

Convection is the movement of a fluid, typically in response to heat. Advection is the movement of some material dissolved or suspended in the fluid. So if you have pure water and you heat it you will get convection of the water. You can't have advection because there is nothing dissolved or suspended in the fluid to advect. If you have silt suspended in ...

8

As described in the other answers, putting the radiators (or hot air vents in a forced-air system) under the windows offsets the greater heat loss of the windows, but there is another reason. As room air flows over the surface of a window, it will lose heat to the window (and the outside). This can cause moisture in the air to condense out onto the window. ...

7

As Programmer mentions, by putting the radiator in front of the area most prone to heat loss and ingress of cold air, you are effectively screening off the room from cold air. However, there is also the fact that radiators are often quite a bit hotter than other heat sources such as forced air. Therefore it makes sense to put it in the coldest part of the ...

7

Your body removes heat by coating the skin with a thin layer of moisture (sweat). As this layer evaporates, the heat of vaporization comes from you and you feel cooler. A breeze speeds the movement of the vapor away from your skin, and therefore speeds the evaporation. This is why very hot, very humid days are so oppressive.

5

By conductor of heat, do you mean that it is bad at transferring heat via conduction? Or that it is just bad at transferring heat? First, a picture of the molecular structure of an oil: Conduction Oil is a liquid. Heat transfer by conduction requires strong bonds between the molecules, so that a vibration(heat) travels down the line. With liquids, this ...

5

I don't know a good answer to your first question (I'd be interested in a good text for that myself), but I can answer the second. It's easier to explain if we temporarily imagine $\phi$ represents the concentration of some dye made up of little particles suspended in the fluid. The convective term (aka advective term) is transport of $\phi$ due to the ...

5

This is covered in the standard convection-diffusion type of equation: $$\frac{\partial C}{\partial t} + \vec{u} \cdot \nabla C= D \nabla^2 C$$ Where $C$ is the smoke concentration, and $D$ is the diffusion coefficient of smoke. While the air may be stagnant initially, it will come to move due to buoyancy effects, thus giving some non-zero air velocity $\... 5 If you want to dry your hands completely, you need to turn them over and over anyways. But the best approach would be if you have your palms facing up/down (can't tell which of these diagrams it is). You need to maximise the surface area of the exposed part, as heat you receive will be$\propto (surface\space area)\times(time)\times\cos(angle\space of\...

5

In general, yes the updrafts also occur in warm dry air, as a result of heating on the ground which produces hyrdostatic instability in the atmosphere. As the updrafts go higher, they cool adiabatically and may, if they go high enough and if there is enough moisture in the air, cool enough to condense water vapor and form clouds. However there can also be ...

5

This is called an air curtain or air door and it actually keeps flying insects from being able to enter the store. It also helps trap the colder air inside. Edit: see the link for how it works.

5

Let's assume that the inner pots are suspended within the containing pots, so that heat can only be transferred to them through the water in the containing pot, and that they are all open above so that steam/water vapour can escape equally well from all of them. The water in the outermost pot cannot exceed the boiling point, so it can only heat the outer ...

4

KamLAND Borexino has set moderately strict limits of the total power of a central geo-reactor. See for instance Geo-neutrino: Experiments (pdf link) a talk by one of my colleagues. (Jalena notes that Borexino's limit is the strongest one going, but KamLAND was the leader for a while.) The upper extreme of these limits is less than half the total geological ...

4

I have a master's degree in meteorology so I think I can clear this up for you! This is simply ground clutter. You will see this sort of thing happening on evenings where the relative humidity is very high, more so when the mixing ratio is high also. The radar beam can actually start to interact with water droplets in the air when your humidity values ...

4

Let $\mathbf v(\mathbf x,t)$ denote the velocity of the fluid at position $\mathbf x$ and time $t$. Suppose that we imagine traveling on a path $\mathbf x(t)$ through the fluid, then we can ask ourselves If we travel along the curve $\mathbf x(t)$ through the fluid, then what will be the rate of change of the flow velocity of each point in the fluid ...

4

Most shopping malls have this kind of air door that blast you with high velocity air flow when you enter. As you might have noticed, shopping malls are always the cleanest places of them all. And I am not just talking about cleanliness of the floor area but the entire atmosphere in a mall. The reason they keep it clean is obvious. The method which they use ...

4

As the hot air goes up and the cold air goes down, the radiator is located where there is a better circulation, i.e. even though the window is double glazed, there will always be cold air entering the division by the material itself. So the cold will push the hot air inside the room. Another explanation can be the fact that external walls can have thermal ...

4

I think I'm in a bit over my head, but I don't think it's convection. The Corona, because of the sun's high gravity, thins out very quickly. http://sunearthday.gsfc.nasa.gov/2008/TTT/58_hotcorona.php from the article: It would be like standing in your kitchen far away from the open oven, but feeling temperatures almost 100 times higher than ...

4

Three processes are involved: Conduction: Heat flows from the object to its environment. Removal rate of heat from the interface further away from the object is proportional to the coefficient of conductivity (0.024 for air, 205 for aluminum -see http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html). Convection: The interface between the object ...

3

Semi-macroscopic view: The key word for understanding this problem is buoyancy. Buoyancy is the result of different pressures. Since the warm air is less dense than the cold one, there are less hits to the (imaginary) balloon of warmer particles from inside than from outside, so there is net pressure toward inside. However, since this pressure difference ...

3

The molecules are all moving, quite rapidly, all the time, and constantly colliding against each other. The warmer ones are moving even more rapidly, thus "winning out" in their collisions with the cooler ones, pushing them away. (That's what lower density is.) Then if there's some gravity field pulling all of them downwards against a surface (they're not ...

3

I'm sure it depends on the mug and the temperature of the coffee, but most of the time I bet that evaporative cooling from the top is the dominant source of heat loss. That's just based on experience--like it stays hot much longer when you cover the top, and much shorter when you blow on the top. I also think that it cools at a similar rate in my ceramic mug ...

3

No proposed urban rainfall effect is dominant enough to cause that picture. But limited radar range, with radars being located in larger cities would easily explain it. The urban rainfall enhancement effect would have to be pretty extreme for it to be otherwise.

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