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Watco (Industrial) (OP)
2 Apr 06 10:02
What is the best way to heat water fast, like in an instantaneous hot water heater, or a coffee pot?  Is it possible to run the water inside of copper tubing that has been heated like the heating element in a dishwasher or oven?
IRstuff (Aerospace)
2 Apr 06 13:33
Depends on what you think you're doing with the resultant hot water.  Your problem statement is insufficient to determine the proper solution.  


Montemayor (Chemical)
2 Apr 06 15:10

IRstuff is exactly correct.  We don't know a lot of things about what you ask.  For example, are you dealing with static water or steady-state water flow?  I can answer the basic question with the basic truth:

The fastest way to heat water is to sparge live steam directly into it.

However, this may not be acceptable to you.  Everything has a trade off and sparging has its own tradeoffs as well.  For all I know you may just be trying to warm up a cup of coffee.  Nevertheless, I believe my statement to be true.
Helpful Member!  MortenA (Petroleum)
2 Apr 06 15:32
A fast way would be by induction.

Best regards

Watco (Industrial) (OP)
2 Apr 06 16:14
Ok, I will try to restate the question.  Is it possible to heat water that has a constant flow rate through a metal tube that is an electrical heating element?
Watco (Industrial) (OP)
2 Apr 06 16:18
Hello MortenA,
How do you heat water with induction?  Or can you direct me to a source to learn more?
Thank you.
Watco (Industrial) (OP)
2 Apr 06 16:25
More information:

I am trying to heat water in a coffee pot, with electricity, however we want to have as low a temperature as possible at the heating element and still get the water to 180F or so.  We thought that running the cold water through the inside of a hollow heating element would work well.  Do you think this will work?  
MintJulep (Mechanical)
2 Apr 06 16:29
Yes, it seems like it would be possible to heat water that is flowing through a tube that also serves as the heating element.

It does not seem like that would be efficient or wise, because:

Only half of your heater element's surface area is contacting the water.  You could of course insulate the outside.

The water would be directly in contact with an electrically live surface.

The properties of materials that make good pipes make bad resistance heaters.
Watco (Industrial) (OP)
2 Apr 06 16:37
Hello MintJulep,

In direct contact with an electrically live surface?  I don't understand, then why can you touch an oven heating element without getting shocked?  Never mind the scorching burn.
keepinitcool (Mechanical)
2 Apr 06 16:57
I don't see how the metal tube would be the heating element?  From my point of view, the tube would be a water pipe, such as copper, which is covered by the resistive electrical heating element (electrically insulated from each other) which is then covered with insulation.
MintJulep (Mechanical)
2 Apr 06 18:19
Oven heating element, from the inside to the outside:

Wire:  Conducts electricity and gets hot, as dictated by Ohm's law.

Ceramic, glass or other refractory fill:  Selected to be an electrical insulator, but a good conductor of heat.

Outer metal sheath:  To provide stiffness and protect the other two components.
IRstuff (Aerospace)
2 Apr 06 19:07
Never mind the mumbo-jumbo about what you think is the solution.  Newton's law requires that you can a temperature delta to cause heating.  You have a finite amount of heat energy that must be transferred in a given time.  The lower the heater temperature, the longer the contact with the heater must be.  

You seem to be thinking that you have some sort of killer product, yet you've done nothing or know very little about the problem that you seem to claim to have a solution for.  

Or is this for school?


MintJulep (Mechanical)
2 Apr 06 20:58
To heat water to 180F you need a heater at 180F and an infinite heat transfer area.

Or, a hotter heater with somewhat less area.

That is probably covered in your textbook.
MortenA (Petroleum)
3 Apr 06 2:34
Mintjulep you crack me up smile

I think we are back to the basic question: Is it "like a coffee maker" - or are you trying to make a coffee maker?

What is the scale we talking about? A few cups a day or many m3?

Best regards

pmover (Mechanical)
3 Apr 06 11:10
stick the darn thing in a microwave . . . hopefully microwaveable material . . .  or simply put hot water in pot to begin with . . .

good luck!
freedomtech (Aerospace)
3 Apr 06 21:00
Watco is asking about the best way to heat water fast, specifically, heat approx 1.5 Liters to 90 deg C in approx 3 minutes with starting temp around 7 deg C worst case.  Ideally heat it without a tank.  Heat incoming water from inlet valve as needed until 1.5 Liters of heated water is reached.

IRstuff (Aerospace)
3 Apr 06 21:10
I would use a red-hot iron bar for that scenario, about 2 lbs would be about right.


MintJulep (Mechanical)
3 Apr 06 21:14


Ideally heat it without a tank.

and later...


until 1.5 Liters of heated water is reached

If you don't have a tank, where will 1.5 liters of hot water be kept?

Does it seem to anyone else that freedomtech and Watco must be lab partners?

Have you figured out how much energy you need to heat 1.5 l of water 83 degrees C yet?  That would be a good place to start.
MintJulep (Mechanical)
3 Apr 06 21:17

They've switch to Metric, so I think they would need about a kilogram of red hot iron, not 2 pounds.

However, I think it would make the coffee taste bad.
IRstuff (Aerospace)
3 Apr 06 21:37
That was an exercise left for the reader winky smile


Mattysdad (Chemical)
5 May 06 13:30
Insinkerator and hotshot make hot water dispensers for 180+°F...

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