27
votes
Why does moving air feel cold?
There are a couple reasons. First of all, it's important to note that the sensation of warmth or coolness is only indirectly related to temperature. The receptors in your skin that deal with ...
- 3,211
14
votes
Accepted
How do train tracks handle really cold weather?
Precipitation
Snow
Snow can be a problem for running trains, but it really doesn't affect the rail/ballast. Just like on highways, the snow needs to be moved away, but it doesn't have many other ...
- 10.7k
14
votes
Steel expanding in a tight space
The cylinder would expand until constrained by the cylindrical hole. After that it depends on the relative strengths. If the block has thin walls it may be stretched by the expanding cylinder and ...
- 10.3k
6
votes
Accepted
Steel expanding in a tight space
Assuming your hypotethical question as what it would be for a difference of 200 degrees celsius and assuming the hole as rigid.
The volumetric expansion index of steel is
$$ \text{ $9*10^{-6}$ - per 1°...
- 22.1k
5
votes
Why does moving air feel cold?
The air feeling cold is really your skin being cooled by forced convection and evaporation of sweat.
With no air movement a boundary layer of hotter air forms over the skin and so because of the ...
- 151
5
votes
Easily compute a good approximation of heat conductivity of cooled semi-vacuum (water vapor + air)
In the molecular flow region of pressure, the thermal conductivity of an ideal, monatomic gas is obtained by this equation.
$$
k = \frac{1}{\pi^{3/2} d^2}\sqrt{k_B^3T/m}
$$
where $d$ is the ...
- 2,878
5
votes
Hack a kitchen freezer for lower temperature
No. The minimum temperature is set by the characteristics of the refrigerant. You could conceivably use a refrigerant with the characteristics you want, governed by a new thermostat setting, but I ...
- 6,544
4
votes
Accepted
Having three heaters on single PCB
Increasing the insulation between the heat sources there is quite difficult.
Instead, you can sink the heat away:
Add a full copper fill on the backside of the PCB and connect that into a heat sink ...
- 1,943
4
votes
Accepted
What's the difference between aircon modes Auto, Sun, Snowflake?
The sun is heating mode. When the room temperature reaches the set temperature, the air conditioner stops operating until the temperature falls below the set temperature and the starts operating again....
- 9,642
4
votes
High Fan Speed Not Cooling As Expected (PWM, Arduino)
Most likely the fan is getting into the stall regime and the flow then drops or the exhaust port is causing a pressure drop that the fan cannot overcome after a given speed.
- 15.5k
3
votes
Accepted
How large of an area of the earth's surface would we need to cover in mirrors to negate global warming?
The idea is not new, but using mirrors on the Earth's surface is a particularly inefficient way to go about it.
A Lagrange-point sunshade is actually much more practical, and the thermal analysis has ...
- 6,874
3
votes
Got to pour outdoor concrete next week, but forecast is cold. What are my options?
The absolutely critical factor is that the concrete does not cool to 0C before it has developed enough strength to resist the expansion if any free water in the mix freezes. If it does freeze before ...
- 12.5k
3
votes
At what cold ambient air temperature will power lines fail?
Here are some pylons in Norilsk, Northern Siberia, where temperatures get down towards -50°C
(source)
It's all a question of design and engineering: pylon spacing, the range of max and min ...
- 3,751
3
votes
Having three heaters on single PCB
Well, air has worse thermal conductivity than practically any solid, so chances are that a hole will decrease the heat transmission. There are however solids with thermal conductivity very close to ...
- 453
3
votes
Affixing a thermocouple to a surface
A little late to the game.
A method recommended in B&W's Steam, Its Generation and Use, is to drill small, closely set holes in the metal substrate, insert the individual wires into the holes, ...
- 171
3
votes
Accepted
Prolong frozen ground conditions (to trick fruit trees into flowering later)
Delaying flowering would definitely be a better solution than attempting to save the flowers after the fact. Its definitely going to take some experimentation and hypothesis testing to determine what ...
- 7,904
3
votes
Accepted
Store seeds at 1°C
The temperature control in a fridge is pretty crude. The evaporator is in the freezer and the compressor is controlled with an electric thermostat. The fridge portion however relies on convection from ...
- 7,904
3
votes
What does "+- %/K" mean?
Yes, this is the percentage change per kelvin.
Most engineers work in kelvin as some formulae need the absolute temperature such as when calculating the total internal energy, but we sometimes don’t ...
- 15.5k
3
votes
Ventilation setup high sleeper night cooling
I would recommend a modification Phil's answer: airflow is almost always better when the fan is exhausting to the outside - fans don't "like" back pressure and work most efficiently when dumping to an ...
- 4,199
3
votes
Can a chain of nested thermal heat pumps be used to to gain thermal energy out of the environment?
Did you ever get a real answer to your question? I have been considering this question for years and I have no real answer. Many responses I see show me that people are a bit confused as to what you ...
- 39
3
votes
Accepted
How do I determine the temperature inside a transformer vault?
Assumptions
Assume steady state and neglect all radiation terms. Assume the surroundings to the concrete wall is an infinite heat sink at a fixed (constant) temperature). Finally, neglect the heat ...
- 2,878
3
votes
Accepted
How does indoor temperature factor in when determining ideal relative humidity in a home?
In the world of heating/ventilating/air conditioning engineering (a.k.a. "HVAC") there is a number called the comfort index (which you can search on) which takes both humidity and temperature into ...
- 14.3k
3
votes
Accepted
What's the thermal bounds of a typical computer case fan?
The steam pressure in the boiler will be greater than atmospheric, so the steam temperature will be above 100C. A typical ready-built boiler boiler for steam powered models (sold with a pressure test ...
- 12.5k
3
votes
How to increase temperature in a wooden box up to 350 degrees F?
Do you know the burning temperature of the wood you intend to use? According to a quick search on the 'net, you're in trouble at about 450° F. Extended temperature at that level will ignite the wood.
...
- 6,940
3
votes
At which temperature and humidity should outside air be drawn inside?
Adding airflow will almost always decrease the humidity. If you pull in air at 70%rh/65f and inside the greenhouse this air is warmed to 85f, the effective RH of that air is now only 16%, since the ...
- 1,901
3
votes
Accepted
How can I trust a K-type thermocouple purchased from a no-name company?
Go to Omega.com to learn all you want to know about thermocouples (TC). I'll give you here a few basics, directed at your questions.
TC science is well understood and standardardized. Every type TC ...
- 417
3
votes
Accepted
Why materials with preferably a negative temperature coefficient for heating elements?
(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 ...
- 24.3k
3
votes
Why materials with preferably a negative temperature coefficient for heating elements?
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 ...
- 10.3k
3
votes
Why materials with preferably a negative temperature coefficient for heating elements?
It really depends. If you have multiple heating elements (or areas within a single element), in parallel, they will end up at slightly different temperatures. If the application is temperature limited,...
- 1,387
3
votes
Accepted
Up to what temperature, can titanium be safely used?
The titanium melting temperature is close to 1670 deg C.
However most titanium alloys have a maximum service temperature of 600 deg C.
In any case, purchasing and manufacturing cost would be ...
- 24.3k
Only top scored, non community-wiki answers of a minimum length are eligible