New answers tagged

2

Hence, I wonder why one would preferably use materials with a negative temperature coefficient? Most metals will have a positive temperature coefficient. Platinum, for example, is commonly used as a temperature sensor and the Pt100 has 100 Ω at 0°C and about 138 Ω at 100°C. Isn't it, that, the higher the resistance, the more warmth will be generated? So ...


2

(I am putting this forward as a opinion to be validated by others more knowledgeable than myself). I am not certain that the resistance will have the effect the original OP expected. i.e. I assume that the author was thinking of the formula: $$P = I^2 R$$ However, this is a derivation of the more basic $P=VI$, and in an alternative form: $$P=\frac{V^2}{R}$$ ...


2

Copper sheet with an absorbing and poor emitting coating is available which is easy to solder copper pipe to the untreated reverse side. Guess why many flat plate collectors are made like this… As for spacing you can get full details from Duffie & Beckmann Solar Thermal Engineering (can’t remember exact title, but it is a really good book) but panels I ...


0

I'm surprised nobody has mentioned infrared radiation. Supposedly somebody has invented a paint that reflects so much energy that the self-radiation of its surface is greater than the incoming radiation, and it cools down below ambient temperature. https://www.purdue.edu/newsroom/releases/2021/Q2/the-whitest-paint-is-here-and-its-the-coolest.-literally..html


0

The paper you linked states clearly that this is a steady state investigation of natural circulation of water near density extremes (density inversion), so as @Tiger Guy said in the comments, the heat in (heater) must equal the heat out (cooler).


4

Thermal Environmental Engineering 3rd Edition by Kuehn, Ramsey & Threlkeld (1998), Pearson.


0

I have a water cooled air conditioner. It takes cool water in and returns hot water to the floor drain, cooling the room next door.


1

If you are looking just for heat flux (aka heat flux density, heat-flow density or heat flow rate intensity) and you know that the heat rate is 128 W, then the heat flux is just: $$\phi_q = \frac{\dot{q}}{A}$$ where: $\phi_q$ is the heat flux $\dot{q}$: the heat rate in W ${A}$ the surface area.


5

Since the amount of energy per unit volume required to evaporate (or boil, depending on your desire for speed) the water is a constant, the only things to control are, roughly: efficiency of heat transfer from the propane burner head into the water insulating the "boiler" so that the energy does not leave the water other than via evaporation. ...


2

... some examples from real life ... A simple heat exchanger. The fluid travels in a tube carrying enthalpy content along the length of the tube. Heat flows radially outward. Your blood vessels. Enthalpy flows along the vessel. Heat leaves outward from the vessels. Certain types of ice-making machines. Water flows over a cold plate. Heat is extracted into ...


4

You can model heat conduction in two dimensions when there is no heat flux in the third dimension. (Sorry if that sounds trite, but IMO that part of the question is so trivial it shouldn't be necessary for anyone to ask it on an engineering forum!) An example would be heat flow in an electrical conductor that is heated by an electric current, where the heat ...


2

You can either: strive to have the temperature inside lower than outside and use AC to achieve that. In that case you want your windows to be closed and the walls to be insulated as much as possible. To maintain low temperature inside you need an AC unit capable to dump the 3kW of heat generated by the devices, as well as any extra heat coming inside from ...


2

Answers to some of your queries: I bought this in a hardware store a few months ago and tried to use it in my car bc my AC would take 20 mins to cool the interior (98' F weather). Your car AC is faulty. The air was sortof cool but it seemed like it wasn't any cooler than what I had in my car and it said it works better when you freeze some of the ...


-2

Heat's gotta go somewhere? One idea would be to deposit underground in geothermal coils.........


2

Theoretically? Sure. From a practical standpoint? No. At least, it's pretty hard to see that working in any feasible way. Regardless of what you do with the waste heat, you would need an inexhaustible supply of fresh air to cool the hot refrigerant. So the question is what to do with that hot air. As someone suggested, you could cool that with, say, ...


3

Edit 1 based on the current version of the question "Where can heat be vented from an air conditioner that isn't outside, in the attic, or into the ground?" Answer: It is possible to put the heat into something like a large water tank. The problem is that you have to take the heat out of the water tank eventually. This is the heat battery ...


3

When situated in the old industrial building, once we had a "cooling system" that was simply sucking in the air through the hole in the floor from the accessible there labyrinth of the industrial underground tunnels. I do not know how productive this would be in a large scale but worked well enough for a small server room, using electricity only to ...


4

Heat can be converted to electricity only according to the second law of thermodynamics: you need in this case a hot reservoir and a cold reservoir. The heat engine takes heat from the hot reservoir and puts it into the cold reservoir. That's the way all heat-based electricity generation works. In gas-fired generation, the hot reservoir is very hot (it's ...


8

Surprised they haven’t been mentioned yet because they seem to be all the rage in the spammy ads you see on a lot of sites, but depending (very heavily) on the general atmospheric conditions, an evaporative cooler (sometimes called a swamp cooler) might work. Evaporative cooling in general is based around the idea of latent heat of vaporization. In short, ...


8

Nobody specifically mentioned geothermal yet but this is exactly the principal used here. Rather than exchanging heat with the outdoor air, heat is exchanged with the ground a meter or two below the surface. I suppose one could make the argument that this is still "outside" but the heat does not make it to the atmosphere and if you have a heating/...


10

Use a (largish) water tank. I've never seen a water tank used as a heat sink for an air conditioner, but they were used for stationary engines some time ago. Typical air conditioners can produce about 2 kW of heat. If that heat is released in a 500 litter water tank: $$\frac {2 kW}{500 kg}\cdot\frac{1 kJ/s}{1 kW}\cdot\frac{0.24 kJ}{1 kcal}\cdot\frac{0.24 K\...


14

The possibilities of transforming heat into any other form of energy are limited by the second law of thermodynamics. Essentially, you cannot simultaneously lower the entropy in a closed system (e.g your house) by transforming heat into a different form of energy, and transferring heat from a colder object to a hotter one requires work, so that more heat is ...


Top 50 recent answers are included