I How Long Does It Take to Melt a 12.5 kg Gold Bar at 3000°C?

[john56789]

TL;DR Summary

time to melt gold

how long does it take a 12.5 kg gold bar to melting at 3000 degree C°?

Why does the water coming out of the waterjet slow down after a while?

 

[Baluncore]

Welcome to PF.

It depends on which way you aim the jet.
If you aim it downwards the water speeds up.
If you aim it upwards the water slows down, stops, then falls back on itself, as it accelerates downwards.
If you aim the jet sideways, it will gradually break up and form lumps of water due to surface tension. The lumps may look like they are going slower, but they are actually going faster because they are also falling due to gravity.
Maybe you could rephrase your question.

 

[john56789]

thanks and my first question?

 

[Baluncore]

how long does it take a 12.5 kg gold bar to melting at 3000 degree C°?

Not very long. But it does depend on the shape of the bar.

 

[russ_watters]

Melting rate is not a function of temperature per se, it is a function of heat transfer rate. The question is not answerable as stated.

 

[Melbourne Guy]

thanks and my first question?

Your question is pretty vague, @john56789, and PF is dedicated to scientific accuracy, so it helps to add details to your scenario when asking questions.

Anyway, pure 24 karat gold melts at 1,064 °C at normal pressure conditions, I'll assume that to start. But how is your 3,000 degree C applied? By a blow torch? Over a hob? In an oven? Induction heating?

Why pick 3,000 degrees, by the way, that's above its vaporisation point, so you're actually going to boil your gold.

But to answer your question, check out:

https://www.superbmelt.com/integrated-gold-melting-pot/​

This company's kit can melt just under 10kg of 24 karat gold in four minutes, so your amount would be around four and a half minutes.

 

[berkeman]

Thread closed temporarily for Moderation...

Thread re-opened after restoring both questions that the OP asked.

 

[john56789]

Your question is pretty vague, @john56789, and PF is dedicated to scientific accuracy, so it helps to add details to your scenario when asking questions.

Anyway, pure 24 karat gold melts at 1,064 °C at normal pressure conditions, I'll assume that to start. But how is your 3,000 degree C applied? By a blow torch? Over a hob? In an oven? Induction heating?

Why pick 3,000 degrees, by the way, that's above its vaporisation point, so you're actually going to boil your gold.

But to answer your question, check out:

https://www.superbmelt.com/integrated-gold-melting-pot/​

This company's kit can melt just under 10kg of 24 karat gold in four minutes, so your amount would be around four and a half minutes.

that melt by big electric arc.
and 3000 for fast melting.
how can i melt this gold bar in the fastest way?

 

[jbriggs444]

Why does the water coming out of the waterjet slow down after a while?

Interpreting this question as applied to a garden hose plus nozzle...

If you kink the hose near the nozzle and suddenly release it, the water will start with a fast/energetic stream and then slow down to whatever the faucet allows. That is because the first bit of water has the full pressure from the water company. The bits thereafter have the pressure reduction due to viscosity at the faucet, in the hose and upstream in the supply lines.

If you squirt the water in the air, the stream will not form a parabolic arch. The far side of the arch will have (typically) broken into droplets and will be moving more slowly and falling more steeply than the near side rises. That is air resistance in action. If the nozzle is adjusted to produce a fine mist, the deceleration may be immediate and dramatic.

 

[Hornbein]

If you squirt the water in the air, the stream will not form a parabolic arch. The far side of the arch will have (typically) broken into droplets and will be moving more slowly and falling more steeply than the near side rises.

In my years as a kid messing with hoses I'd say the stream typically stays together due to surface tension.

I once observed a shower nozzle. The water coming out expanded for a while then came back together due to surface tension, forming a footballoid shape.

 

[john56789]

What if I create a vacuum and destroy the air resistance?

 

[jbriggs444]

In my years as a kid messing with hoses I'd say the stream typically stays together due to surface tension.

Love it. Kids are experimentalists at heart.

Surface tension acts to disrupt the stream into droplets. It is a lower energy configuration that way. One can observe this in the kitchen or bathroom sink. A slow stream can be solid at the top but will stretch and break as it falls.

With a garden hose with one's finger over the end, the break-up into droplets takes place rather rapidly. With no thumb over the end, it takes longer and produces larger drops but does still occur.

You also get break-up with a garden sprinkler where the stream is forced to stretch infinitely.

I once observed a shower nozzle. The water coming out expanded for a while then came back together due to surface tension, forming a footballoid shape.

Further downstream, that stream would break up longitudinally. It is an unstable equilibrium. The effect of surface tension is to narrow the narrow bits of the stream and to widen the wide bits until a series of globules results. All other things being equal, those globules will tend to relax into spheres.

Edit: found a name for the phenomenon: https://en.wikipedia.org/wiki/Plateau–Rayleigh_instability

 

[john56789]

jbriggs444
What if I create a vacuum and destroy the air resistance?

 

[jbriggs444]

What if I create a vacuum and destroy the air resistance?

I would expect a series of droplets in a parabolic arch with the droplets moving faster and faster as they drop.

Of course, the droplets may boil away. So you might want to use purified water to remove nucleation sites.

 

[john56789]

so by the create a vacuum not reduce the pressure of outed water?

 

[jbriggs444]

so by the create a vacuum not reduce the pressure of outed water?

I do not know what you are trying to ask.

 

[Melbourne Guy]

I do not know what you are trying to ask.

Nobody does, @jbriggs444, and the OP appears reluctant to elaborate. I've reported this thread, even though it was already closed for moderation, it has the hallmarks of a prank troll. 3,000 degrees is an arbritary temperature and will boil gold, not just melt it, and we don't even know whether the OP is asking for hypothetical answers or a specific engineering purpose.

It is frustrating, why are we wasting our time?

 

[Lnewqban]

The temperature should be the melting point for your type of gold.
You need a lot of heat, or heat combined with a magnetic field, according to this link:
https://www.newsweek.com/scientists-melt-gold-room-temperature-1226339

 

[berkeman]

Nobody does, @jbriggs444, and the OP appears reluctant to elaborate. I've reported this thread, even though it was already closed for moderation, it has the hallmarks of a prank troll. 3,000 degrees is an arbritary temperature and will boil gold, not just melt it, and we don't even know whether the OP is asking for hypothetical answers or a specific engineering purpose.

It is frustrating, why are we wasting our time?

Agreed. This thread is now locked.

Part of the problem is that the newbie OP asked two totally unrelated questions in his first post (and tried to delete one mid-stream), so the thread was basically doomed from the start. Add to that the lack of information from the OP, and, well, the lock.

@john56789 -- For future thread starts, please ask only one question per thread start, and please post links to the reading that you have been doing while trying to answer your own question. When you ask specific clarifying questions about things that you don't understand in your reading, that makes for much better thread starts than this one. Thank you.

And thank you to all of you for trying to help the OP, despite the obstacles in this thread.