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 ...
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  • 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 ...
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  • 10.7k
12 votes
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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 ...
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6 votes
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How do I determine the thermal resistance of a metal box?

This will depend very much on the heat flow around the enclosure. There is a thing called the H factor which describes the heat transport properties between a surface and a fluid. The value of H ...
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  • 466
5 votes
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How can I calculate the temperature rise of a circuit board for a given power dissipation and area?

Assumptions: The copper side with the traces is modeled as a sheet of copper rather than traces. The body is thin enough that thermal conductivity within the body is unimportant, and the entire ...
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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 ...
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  • 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 ...
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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 ...
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  • 4,820
4 votes

How can I calculate the temperature rise of a circuit board for a given power dissipation and area?

Base on a quick calculation using online max current calculator for trace width properties, I believe your traces are undersized for 20A of current. Strip line current calculations (Internal Traces) ...
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4 votes
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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 ...
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  • 1,835
4 votes
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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....
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  • 9,527
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.
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  • 14.1k
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 ...
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  • 413
3 votes

How to extract a building's heat isolation and thermal inertia based on temperature curves?

Yes, there are at least two ways to do it. Static, deterministic analysis One is to look at total energy in over a long time period, such that the internal temperature is the same at the start and the ...
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  • 3,701
3 votes

Should the temperature of a heated metal cone decrease in a plastic enclosure?

For plastic thermoforming, or heating behavior, this kind of behavior would be expected. Quite simply, when you form the plastic you typically heat up the plastic rather than the metal. Say you ...
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  • 5,323
3 votes
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Why do heating elements have lower rated temperatures in vacuums?

One reason is because in vacuum there is no convection to help remove the heat. All heat loss from the element is either by radiation, or via conduction thru the supports and wires. Technically this ...
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  • 11.3k
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 ...
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  • 3,701
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, ...
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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 ...
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  • 12.5k
3 votes
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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 ...
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  • 7,489
3 votes
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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 ...
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  • 7,489
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 ...
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  • 14.1k
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 ...
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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 ...
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3 votes
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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 ...
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3 votes
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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 ...
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3 votes
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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 ...
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  • 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. ...
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  • 6,337
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 ...
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  • 1,608
3 votes
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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 ...
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