For Questions That Don't Merit Their Own Thread

[p1t1o]

15 minutes ago, 0111narwhalz said:

But if one were to build a new heat pump, one would be able to build it to a certain mass and/or power. Your argument appears to invalidate rocket engines' N/kg because you can't stick a quarter of an engine on a ship. Besides, if you put enough units on, their specific power becomes a useful quantity.

I just need a ballpark answer.

Im not making an argument? Im saying you can assign a W/kg value to a heat pump, but the value will only be relevant for that heat pump, same with the rocket values for N/kg.

[peadar1987]

5 hours ago, 0111narwhalz said:

The reason there's a mass there is for the mass of the heat pump. Per kilogram of apparatus, how much heat can be pumped up a gradient of a given temperature?

 

 

Ah right, no idea. Any thermodynamic systems I've worked on are firmly attached to the ground, so mass is right down the list of parameters I'd be optimising.

[StrandedonEarth]

It's all a matter of design requirements, really. How far are you pumping the heat? That adds piping mass. Are there any price or power restrictions? Peltier plates can probably move quite a few kW/kg, but iirc they are expensive. They are also power hungry which turns into additional heat. 

https://en.m.wikipedia.org/wiki/Thermoelectric_cooling

[peadar1987]

So just after a quick google:

4.5kW_th, 42kg:

http://www.aircon247.com/p/8849588/Toshiba-compressor-ACC-kw-btu-portable-air-conditioning-unit-.html?gclid=CMqnwYXdxtMCFVUz0wodIKIGoA

 

4.4kW_th, 29kg:

http://www.appliancesdirect.co.uk/p/p15hp/electriq-p15hp?refsource=Apadwords&gclid=CMPW8rzdxtMCFVEW0wodphoA1Q

 

2kW_th, 22kg:

http://www.appliancesdirect.co.uk/p/ac9000e/electriq-ac9000e-air-conditioner?refsource=Apadwords&gclid=CMGP4L7dxtMCFYoaGwod1o8A7g

 

4.1kW_th, 35kg:

https://www.toyotomiusa.com/factoryOutletStore/index.php?route=product/product&product_id=133

 

These are portable heat pumps so will be designed to be relatively lightweight, but mass won't have been the #1 optimisation criterion. Specific powers are about 100-150W/kg, so I'm guessing if mass was a major issue you could probably design one with a specific power of 200-250W/kg.

Again, for your temperature question, it's not something that would really come up. The temperature is a design parameter, and there's no real reason to compare systems that produce a different temperature output, you will always just go with the one that produces the minimum temperature that satisfies the design brief.

[0111narwhalz]

How best might I deposit eight to thirty Joules of energy onto a dark-colored object about .2 degrees wide?

[peadar1987]

6 hours ago, 0111narwhalz said:

How best might I deposit eight to thirty Joules of energy onto a dark-colored object about .2 degrees wide?

Hammer?!

Although i you want to game the question, the easiest way would be to move it to somewhere warmer than it is now and leave it there for a while.

[Green Baron]

Best is qualitative. And energy comes in different forms. I assume said thing is a real world thing and in reach ?

e-pot: put something on it (assuming thing is under the influence of a gravitational field).

e-kin: drop it (from a certain height in a certain gr. field).

Calories: see above, light a fire under it.

cold deformation: see above :-)

 

Concerning "best", i too find the hammer idea most appealing. It sounds like a solution.

:-)

 

[StrandedonEarth]

Laser

[p1t1o]

On 5/1/2017 at 3:15 AM, 0111narwhalz said:

How best might I deposit eight to thirty Joules of energy onto a dark-colored object about .2 degrees wide?

Is it large and far away, or small and close?

[0111narwhalz]

Small and close.

[peadar1987]

And what type of energy are you trying to deliver to it? Kinetic? Thermal? Potential? Does it matter if the object is destroyed in the process? What is its mass? What material is it made of? Are you working to a tight timescale, or have you got as long as you need?

[p1t1o]

I'd go for a magnifying glass and a radiant heat source, like the sun or a light bulb.

[Kerwood Floyd]

On 4/30/2017 at 9:15 PM, 0111narwhalz said:

How best might I deposit eight to thirty Joules of energy onto a dark-colored object about .2 degrees wide?

I think there might be some misunderstanding here. "eight to thirty" seems to me like a pretty unlikely range. Do you actually mean between 8 and 30 joules, or do you mean 8³⁰ or 8 x 10³⁰?

[0111narwhalz]

8 and 30.

[Kerwood Floyd]

3 minutes ago, 0111narwhalz said:

8 and 30.

OK, thanks.

[Green Baron]

That is a medium hammer on a small nailhead. 0.2° is too small for a fingernail, so it luckily hit. A fly swatter wouldn't deliver 8 joules (though i sometimes would like to !). A 30gram arrow from a strong bow can have 100 Joules, but if you don't tear it all the way ... I bet you wouldn't hit a 0.2° target :-)

Still looking for a solution ?

 

[p1t1o]

This is a pretty cryptic one XD

What is he doing? Manually soldering new components onto a microchip? Fighting a war with ants?

[munlander1]

Light always travels the speed of light, no matter what. The reason why it appears to be traveling slower in glass, for example is because it is bouncing off the glass molecules, correct?

[sevenperforce]

14 minutes ago, munlander1 said:

Light always travels the speed of light, no matter what. The reason why it appears to be traveling slower in glass, for example is because it is bouncing off the glass molecules, correct?

Technically, it is being absorbed and re-emitted by the glass molecules. But yes, you're right. Light travels at the speed of causality in spacetime; it cannot exist at a speed slower than that.

[munlander1]

Just now, sevenperforce said:

Technically, it is being absorbed and re-emitted by the glass molecules. But yes, you're right. Light travels at the speed of causality in spacetime; it cannot exist at a speed slower than that.

I was told during class they slowed down. When I asked about it, I was told the light physically slowed down. Thank you

[sevenperforce]

13 minutes ago, munlander1 said:

I was told during class they slowed down. When I asked about it, I was told the light physically slowed down. Thank you

The actual interaction is a little more than just absorption and re-emission by a single molecule. Transparent materials are a matrix of chemical bonds which have a collective wavefunction interaction with objects like photons. What happens is that the incident photon induces an excitation in that matrix, called a phonon. Although the phonon is a transient excitation, it is an excitation within that medium, which means it has relativistic mass. Objects with mass cannot travel at the speed of light, and so the phonon travels slower until it reaches the other side, and the phonon collapses and an identical photon is emitted.

This can be modeled as sequential absorption and re-emission by each molecule in turn, but that interpretation misses the quantum wavefunction nature of the molecular matrix.

[munlander1]

@sevenperforce the photons themselves are not traveling slower though... so I am correct.?

[sevenperforce]

20 minutes ago, munlander1 said:

@sevenperforce the photons themselves are not traveling slower though... so I am correct.?

The photons are converted into excitations, which travel through the medium slower than light and are then re-emitted as photons again on the other side.

[0111narwhalz]

10 hours ago, munlander1 said:

the photons themselves are not traveling slower though... so I am correct.?

You are correct, yes. They are turned into something else which is slower.

[p1t1o]

10 hours ago, munlander1 said:

@sevenperforce the photons themselves are not traveling slower though... so I am correct.?

"Photons themselves" is a troublesome concept when looking very closely, they aren't really little physical particles, they just behave that way under various circumstances.