# Tag Info

27

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 temperature are mainly sensitive to heat transfer and changes in temperature, not so much absolute temperature values. For example, here's an interesting excerpt from ...

13

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 effects. Trains are used to plow through small amounts (Wikipedia): and large amounts (Wikipedia): Ice Ice could cause more of an issue due to adding thickness to ...

12

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 know the answers to. How is heat converted to an electrical signal (current or voltage)? A microbolometer is just a special case of a bolometer which ...

6

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 varies with surface properties and flow. So to do your calculation you need a few different assumptions. Let's simplify. 1) the air in the box is uniformly heated ...

5

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 smaller temperature difference the rate of heat loss decreases. Moving air over the skin disrupts this boundary later allowing unheated air to be in contact with the ...

5

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 device is considered to be at a uniform temperature. Only the two broad surfaces contribute to the heat loss, the sides are neglected. The surroundings, including ...

5

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 collision or molecular diameter and m is the molar mass divided by Avogadro's number. It is independent of pressure. Approximations have been derived for non-monatomic ...

5

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 suspect that it will require a redesign of the refrigeration system.

4

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) for 50 mil 4 oz copper is Max Current: 3.76 amps Trace Temperature: 35.0 °C Resistance: 0.0000640 ohms Voltage Drop: 0.000241 volts Power Dissipation: 0....

4

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 that is kept cool externally. Add copper rectangles between the separate heating elements. Connect the rectangles to back side with plenty of vias. This should ...

4

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. When in heating mode, the air conditioner does not cool. This setting is used during cold weather periods, such as in winter. The snowflake is cooling mode. ...

3

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 that of air, so if that board was made (on purpose) from one of those... you won't see much improvement for your hassle. And since you mentioned fiberglass while ...

3

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 end. And if you take the time period to be long enough (30 days or more, for many buildings), then any changes in heat content of the thermal mass will be ...

3

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 were working with LDPE, which is the only plastic I can think of that even changes shape at those temperatures. Each material has a heat capacity - 452 J/kg K ...

3

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 only means lower maximum heater power, but that may be dumbed down to temperature. Another reason is due to evaporation of the heating element. At high ...

3

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 ambient temperatures, and the range of currents carried on the cables - there will be whole design manuals that cover this, so a full answer would be way too long ...

3

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 setting, most likely you will have to remove all of it and start again. At 5C, concrete should develop enough strength to resist freezing after about 48 hours, ...

3

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 the freezer. The temperature control from the fridge is sometimes nothing more than a slider that establishes how quickly the convected air moves. There are ...

3

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 bother such as when dealing with temperature difference, but it was good practice when we were taught it so we continue to use K...

3

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 open area. So, use a fan in the window to push air out, and fill the rest of the window with an inlet duct which is routed up to your loft. This way, there'...

3

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 transfer that occurs at the corners of the concrete box (set the internal and external areas of the box to be equal as far as heat transfer is concerned). ...

3

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 account to determine where most humans would feel comfortable. This will tell you the range of optimum humidity percentages to shoot for at a given temperature ...

3

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 certificate!) would have a maximum working pressure of 4 or 5 bar, which would give steam temperatures around 150C. Many common plastics will start to soften at ...

3

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. Your insulation should be inside your enclosure and the enclosure should be non-combustible. A hot air gun blowing into a well insulated enclosure will likely ...

3

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 water capacity of the air increases massively with temperature. That changes your problem a bit. Basically you will have to balance how dry you want it in the ...

3

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 is made with it's own precise metal alloy and all TC of the same type will output a voltage uniquely related to the temperature of the TC junction, within ...

2

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, and peen them in place. This avoids the issues others have raised of welding affecting the properties. It provides intimate contact with the measured surface. ...

2

For an easily removable option you can use Kapton tape. It is heat resistant and works well for holding a thermocouple temporarily in place. I also wrap the wires in Kapton for electrical isolation.

2

I ended up finding a solution that works (haven't tried the cements suggested by others yet). The trick was to use a spot welder rather than a tig welder. With the correct power settings, that stuck the TC to the surface without damaging either component. It's not exceptionally strong (I used very fine TC wires), but it should result in conditions that ...

2

To borrow from a certain Brit physician, "I think it's a bit more complicated than that." For example, you could build/buy a double-walled box with a vacuum between the layers. That's esssentially what a thermos bottle is; there are varieties of drinkware that are built this way. But if you were to build a double-walled glass enclosure that's not ...

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