# Tag Info

50

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 this exposed areas. The final reason is to make the temperature of the room more or less uniform. If the heaters were placed at ...

47

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 ...

36

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 ...

12

"Total energy of the Earth" is somewhat of an odd concept, but there's no reason we can't really entertain it. It brings up some genuinely difficult questions. The right way to approach this is to define the system correctly and then identify forms of energy content and flows. Things to "count" in the Earth's energy: Heat content Nuclear energy ...

10

If the metal pan was cool then you would expect to see water droplets staying in the same place once any original movement had dissipated. You would have a combination of cohesive forces within each water droplet and adhesive forces between the water and metal surfaces. With the metal having a temperature well above the boiling point of water, the water ...

7

You are right. The thermal equilibrium will eventually be reached. In this process, heat is transferred from the water to the thermometer. This increases the temperature of the thermometer and decreases the temperature of the water until they are equal. However, generally, the amount of water is large so that the heat it loses is too small to significantly ...

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 question seems to be about human body heat rather than other human activities that contribute to global warming. Humans body heat doesn't actually add any energy to the whole-Earth system (see below) but for a moment, I will assume that it does. Instead of looking at the mean temperature of humans, it's easier to look at the amount of energy our ...

6

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. ...

6

The heat generated from the Earth's core is about 4x10^13 W while the Sun provides about 1.7x10^17W so although the Earth's core is slowly cooling this has very little effect on the Earth's temperature. The Earth is in equilibrium between the energy received from the sun and the energy it emits into space. If the amount received changes, then temperature of ...

5

You seem to have overcomplicated this question quite a bit, you don't need to go further than the theory of relativity to find the answer. Heat is simply chaotic movement on the molecular and submolecular level, and as relativity dictate that any object moving relative to an observer will to that observer appear to have greater mass with greater relative ...

4

You are spot on, although the typical volume of the measuring fluid inside the thermometer tube is truly tiny and thus has an extremely small total heat capacity compared with the thing whose temperature is being measured. Your thoughts correspond to the following diagram: and you are to find the equilibrium temperature of the system. It would be ...

4

This device looks like a inherently bad idea safety-wise, for the reason you found. I don't know what exactly is inside the handle, but you have to assume all it is doing is connecting wall power to a resistive heating element. I imagine the outside of the heating element is intended to be insulated from everything else. (By the way, this has nothing at ...

4

If your box (at 0-20°C) starts out hotter than the environment (at -60°C) then your best strategy is to prevent any heat flowing out of the box into the environment i.e. insulate the box. Using foil will reduce radiative energy transfer, however in most cases the cooling is dominated by convection rather than radiation and foil is a rather good conductor of ...

4

"Burn" and "melt" are completely different things. "Burning" is a chemical reaction, usually with the oxygen in the air (or any oxidant, really). In organic burning, like the cake you suggested, the carbon compounds react with atmospheric oxygen, producing carbon dioxide, water (vapour) and (sometimes) an ashy residue. "Melting", on the other hand, is a ...

4

Let a quantum system with Hilbert space $\mathcal H$ and hamiltonian $H$ be given. If the system is in equilibrium with a heat bath at temperature $T$, then the system is in a so-called mixed state and is modeled by a linear operator on $\mathcal H$ instead of as a vector in $\mathcal H$. This operator is called the density matrix (or density operator). ...

4

It seems you're coming at entropy from a thermodynamics standpoint. This is completely consistent with (and, at the macro scale, equivalent to) the statistical derivation of entropy, but you might find the statistical version more intuitive, if the thermodynamic version is causing you issues. I warn you, statistical physics is both math-heavy and takes some ...

4

Assuming the cooling system is just a radiator, water and a pump then you can't cool the fluid below the ambient temperature of the radiator. A refrigerator manages this by compressing the fluid in the cooling circuit, extracting the excess heat and then expanding it to make it colder. If your system uses a phase change, a compressible fluid or a peltier ...

3

The answer is that a decrease in temperature does decrease the mass, though in most cases that change is exceedingly small. Temperature is a macroscopic phenomenon, so you can't really talk about the temperature of a single string or an atom. However consider the following analogy: If you have an isolated string (or atom) in some excited state, then to ...

3

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 ...

3

If you look at the first law of thermodynamics, $$dU=\delta Q-\delta W=TdS - pdV$$ then consider a reversible processes ($dU=0$), then we get $$TdS=pdV$$ Then using the ideal gas law, $pV=nRT$, we find $$dS \sim \frac{dV}{V}$$ The volume considered would be the volume of the system (e.g., a gas), with its infinitesimal increase(decrease) signified by ...

3

Dehumidifiers work by first cooling the air, then heating it back again. The cooler air can hold less moisture, so the cool air dumps much of its moisture load. This separates the incoming moist air into two streams, dry air and liquid water. The heat output of the heat engine that makes the cold temperature is used to warm the cooled air again. Actually ...

3

From the article you cited: A fan draws in humid air and carries it through a refrigerated evaporator. Evaporator is just a heat exchanger in which the working fluid (refrigerant, inside the tubes) evaporates. It accomplishes this by sucking out the heat from the air flowing through. This is the rectangular portion on the right side of the apparatus ...

3

Transfer of heat from one source to another can be very efficient. In fact, the first law of thermodynamics says that the internal energy of a system can be transferred as heat of there is no work done through compression, expansion etc. For example, electric heaters can deliver close 99% of the heat energy to their surrounding with minimal loss from ...

3

An electric heater that has "mechanical inefficiencies" as Programmer mentioned will nonetheless ultimately lead to near 100% conversion because things like expansion of wires, creaking sounds etc., will be absorbed by the surroundings and turned into heat, especially in a well-insulated house. I justify leaving the bathroom CFL light on in the winter (it ...

3

Can a laser be used to heat metal's to the point they glow red? Yes How much heat can a laser generate? How big can it be? What laser are you talking about? How are laser cutters able to cut metal very easily? Now that is a good question. Some laser cutters will melt the object they are cutting to cut them. More sophisticated laser cutters, ...

2

You're on the right track. Your statement can be true in special cases. More generally, the entropy is defined by the Boltzmann-headstone-equation you write down if $\Omega$ is the number of different detailed states (called the "microstates" or "compatible microcomplexions" in the thermodynamicist's jargon) that (i) the state could be in if (ii) its ...

2

I think you have a misunderstanding of the technical terms vapor pressure, boiling and partial pressure. Vapor pressure or better equilibrium vapor pressure is the pressure at which an equilibrium is reached between evaporation and condensation at the liquid surface. Usually it is a function of liquid temperature. E.g. water has a vapor pressure of about ...

2

The molten tin won't cool evenly because the cooling is at the surface of the container it's in. Your solidifcation will start at the outside and crystals will grow inwards. You will get a temperature gradient in your tin. This effect is more marked with faster cooling, so keeping the cooling rate as slow as possible will give you a sharper liquid to solid ...

2

From a measurement point of view, it might happen that by cooling too fast you don't see the transition. Another element could be that you cool down to a quenched state which is not the solidification you are hoping but more like into a glass state.

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