38
votes
Accepted
Windmills in empty fields. Why no trees?
Trees increase the turbulence of the air that reaches the turbines. That creates all sorts of uneven, rapidly-shifting loads on the blades and structure. That increases the maintenance costs, ...
- 3,721
35
votes
How do heat pumps output more heat kW than the electrical kW used to run the heat pump?
In the traditional efficiency equation the power input is the power to run the compressor motor and the power output is how much mechanical power that motor is producing. In that case efficiency is ...
- 4,897
20
votes
Why does temperature not increase by putting more logs into the fire
Adding more fuel doesn't permit an arbitrarily high combustion temperature because of an unavoidable intrinsic limitation: The reaction has to heat its products. (In the case of wood, this is mostly ...
- 1,407
15
votes
Can aluminium foil be a thermal insulator?
If furnished in a thin, polished sheet, aluminum will reflect infrared radiation, as for instance in a so-called "space blanket" which consists of a thin sheet of plastic on which a thin and ...
- 13.5k
14
votes
Is there a way to make an air conditioner without venting heat outdoors?
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 ...
- 394
14
votes
How do heat pumps output more heat kW than the electrical kW used to run the heat pump?
A heat pump takes heat energy from one side, compresses it a bit (to get to a usable temperature) and transports it to another side.
So you are more or less “stealing” energy from the outside of the ...
- 318
12
votes
Accepted
How does a microbolometer (IR camera) work?
There are a lot of questions in your question, and it should probably be broken up into multiple different questions. I don't want to wait until that happens though so I'll address the ones that I ...
- 6,386
12
votes
Is there a way to make an air conditioner without venting heat outdoors?
Watercooled , if you don't count sewer as "outdoors".
- 6,057
11
votes
Do magnetic fields applied to a fuel line have an effect on heat output?
If you can replicate what you report above under controlled conditions then you can retire for life next year. Really.
The overwhelming opinion by all reputable test houses or suitably competent ...
- 3,844
11
votes
Can solar panels absorb heat for energy?
Yes, there are indeed combined PV-T (photovoltaic-thermal) hybrid panels that turn some of the incident light into electricity, and have a circulating fluid and heat exchanger to put some of the heat ...
- 3,721
10
votes
How can one calculate the change in heat energy when the specific heat varies with temperature?
In a similar vein to my answer about calculating the lever force in a continuous situation; you need to use integration.
You start by taking the standard heat law that you are familiar with
$$
\...
- 6,386
10
votes
Modeling Transient Heat Transfer between two 1-D materials
I am guessing, you are solving the following system:
$$\partial_t T = \alpha_i \partial_x^2 T$$
with $\alpha_i=\kappa_i/\rho_i c_{p,i}$ for material $i$, subject to the conditions:
$$T\left(x,0\...
- 167
10
votes
Is there a way to make an air conditioner without venting heat outdoors?
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 ...
- 427
10
votes
How do heat pumps output more heat kW than the electrical kW used to run the heat pump?
Heat pumps (commonly) use vapor compression cycles (the following is a short summary of a longer article in tlk-energy.de).
To understand this process, you only need the following three key physical ...
- 24k
9
votes
Why does temperature not increase by putting more logs into the fire
I agree with Chemodynamics, and I will try to add a different perspective (or maybe two).
The fire process is a process where you add a fuel (i.e. energy in the system), and that fuel is gradually ...
- 24k
9
votes
Accepted
Can aluminium foil be a thermal insulator?
It really depends on what you are trying to do with it. And thermal "conductors" and "insulators" are not a hard and fast distinction in properties like electric conductors or ...
- 501
8
votes
What is the Best Heat Resistant Translucent Material?
Illuminate the room indirectly via dichroic reflectors at 45 degrees to each transparent wall. These will reflect light at 90 degrees (i.e. into the room) but allow the heat to pass straight through.
...
- 1,610
8
votes
Is there a way to make an air conditioner without venting heat outdoors?
This question reminds of the concept of a heat bank, a form of heating I experienced in the 1970s. The type of heat bank I am familiar with consisted of a metal box which contained an electric ...
- 9,517
8
votes
Is there a way to make an air conditioner without venting heat outdoors?
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 ...
- 201
8
votes
Is there a way to make an air conditioner without venting heat outdoors?
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 ...
7
votes
Accepted
Heating the air in a small box
A simple approach would be to just consider the heat added.
The specific heat equation gives the temperature change due to heating as
$$Q=mc\Delta T$$ where $Q$ is heat added, $m$ is mass. $c$ is ...
- 1,035
7
votes
Accepted
Can an isothermal process also be adiabatic?
If a process is both isothermal and adiabatic, it is implied that the work done on the system is being stored somewhere other than the internal energy of the working fluid. (Or conversely, if the ...
- 3,034
7
votes
Accepted
Heat pipes vs fluid cooling
Heat pipes are very useful when you have limited space to work with or you want an entirely sealed and self contained unit.
An interesting example of this is that heat pipes are used to cool the ...
- 15.1k
7
votes
Accepted
Radiators in series or parallel?
The efficiency of any radiator (heat exchanger) is a function of the temperature difference between the two fluids in question. All else being equal, a heat exchanger with a greater temperature ...
- 6,844
7
votes
Windmills in empty fields. Why no trees?
There is a non-engineering reason as well: the people most open to placing turbines on their land are farmers who are interested in the extra income.
Turbines are not (yet) placed near built-up areas,...
- 187
7
votes
Accepted
Why is it more common to use ceiling fans instead of air pumps?
Mainly cost difference.
And also, a fan is sufficient for the job. The problem being solved is thermal stratification. That's caused by a lack of vertical mixing; the warm air rises to the top, the ...
- 3,721
7
votes
Accepted
Why are home geothermal systems usable anywhere in the U.S. but industrial geothermal plants limited in geographical use?
Because they're two completely different systems that have, in some circles, accidentally been given the same names.
The things that are sometimes (particularly in the USA) called home geothermal ...
- 3,721
7
votes
Accepted
In a diesel engine, does more heat leave the engine through the tailpipe or the radiator?
They are very nearly equal for typical four-stroke non-turbo diesels under load. A turbo diesel under load should have slightly more radiator loss than exhaust loss.
At the bottom is a link to the ...
- 4,159
7
votes
Is there a way to make an air conditioner without venting heat outdoors?
There are phase change materials (Similar to the cold pack for injuries) that at some point in time was the all the rage. Basically what they did was storing and releasing heat energy. However, they ...
- 24k
6
votes
Convective fix for air conditioning dilemma?
Those two holes by themselves will have little effect. The pressure difference between the two ends of the holes will be so small that only a little air will flow.
If you want to go thru all this ...
- 11.3k
Only top scored, non community-wiki answers of a minimum length are eligible