what's the fastest method to heat water?

[olweiser]

thanks guys for all your help, much appreciated.

 

there is no plan B. I said before this is something I'd like answers to the theory before it's worth taking to the next level. It appears that as of today, this can't be practically achieved.

[CaptainPanic]

thanks guys for all your help, much appreciated.

 

there is no plan B. I said before this is something I'd like answers to the theory before it's worth taking to the next level. It appears that as of today, this can't be practically achieved.

 

It couldn't be practically achieved also before today

[insane_alien]

but there are other ways to do it. we'd be happy to help you design a heat exchanger capable of handling the load, but we will need more information.

[olweiser]

the method or device needed would need to be compact, perhaps I could start by having something fitted to the bib tap end with the hose attached to that. All the other info still stands: fast heat over fast flowing, narrow water usig self sustainable energy like the sun or the water itself....

 

sounds vague? that's because this is simply an idea in my head - like a flux capacitor! I fell off the toilet seat and hit my head.....

[insane_alien]

you could make it about the size of a garbage can. but you won't get compactness with rewnewable energy sources due to the power requirements.

 

unless you count biodiesel as a renewable source. because if you do then you can use the garbage can sized heater for it.

[GDG]

Perhaps this thread would do better in Chemistry or chemical engineering: does not appear to involve biochemistry or molecular biology...

[insane_alien]

actually it belongs in physics as there ain't anything chemical going on either. althogh it does overlap heavily with chemical engineering.

[jimmydasaint]

This is from a man who makes bookcases that Homer Simpson would laugh at, but... would it make sense to have a boiler or sealed lagged container as an intermediate which is heated by barbecue charcoal (readily available). Then the hosepipe is attached to the boiler and the flow rate can be adjusted, but bear in mind the problem of lost heat as the water starts to flow quickly.

[insane_alien]

well, yeah, combustion is the only practical way to get such a high power for a domestic scale device.

 

gas, oil charcoal, they'd all work. but unless you have a few tens of thousands of dollars/pounds/euros then you can't really get it done with solar or wind or that.

[gbg112]

There is one simple method which could heat water 1000's of time hotter 1000's of time quicker than anyother suggestion but it's not possable yet.

 

Putting it in the sun --(not including time it takes to get there)--.

[Mr Skeptic]

I don't think the sun fits on the tip of a hose.

[insane_alien]

no, and it would have to be pretty deep in the sun as te external temperature for the area required has to be 22000K as per captain panics calculations.

 

we can reach 22000K here on earth but not with something that'll fit on the end of a hose.

[CaptainPanic]

The main problem here isn't so much the delivery of 67 kW. Any medium sized boiler can do that... and industrial boilers can easily do many, many times more.

 

The problem is that all this heat has to go through an area of just 31 cm^2... which means that the heat flux is impossibly high.

 

Since we are not about to re-invent physics, I propose we look for an alternative design. But again, since our OP does not give any additional info, we cannot improve the design.

 

Perhaps we should (for once) end a thread with "it can't be done, we're sorry".

 

the problem is a practical one, not theoretical - as I explained before.

[Spyman]

I don't have any answer to the question in the OP, but calculations of 67 kW or 22 631º K sounds a "little" to high...

 

This electrical through-flow water heater is small, only uses 3.5 kW and is still able to increase the temperature of a water flow of 2 l/min by 20º C through a water inlet of 1/2": http://www.azp-brno.com/p10421/aum-6-with-through-flow-water-heater-clage-3-5-kw-230v-50hz.html

[CaptainPanic]

The 67kW is correct. The 22 631K is based on some assumptions, but they are "best case scenarios". I have provided the entire calculation. Please point out where it is wrong if you think it is.

 

1. The OP wants to heat 2 liters in 8 seconds, not in 1 minute.

2. He also wants to increase the temperature by 50ºC, not 20ºC.

60/8*50/20 = 18.75

 

Hey, that's a coincidence: 67 kW / 3.5kW = 19.1

It's no coincidence that the values 18.75 and 19.1 are almost the same. You're trying to use a machine that's severely underpowered for the task. About 19 times underpowered to be exact.

 

And the inlet isn't so much the problem. It's the surface area of the hosepipe (the outside) through which we have to transfer the heat. The heater you show probably has a pipe in it in the shape of a coil or something... not just 10 cm straight pipe (and that's it).

 

If you think the calculations are "a little high", then please show why, and don't just say it's wrong.

I think the data from you actually confirms that we're completely correct.

[Spyman]

Well, actually the OP want to increase the temp from about 6º C to 70º C, which means that the heater I linked is even more underpowered.

 

I did not say that the your calculations where wrong, what I meant was that it's possible to have a "small" heater in the end of the hose that can rise the temperature to practically needs without extrem power sources or solar surface temperatures.

 

Maybe I was wrong, but I made the assumption that the use of the device in the OP was to take a shower or clean your hands in a summer house or something similar.

[insane_alien]

well you need 67kW otherwise it won't get it hot enough, and you need the high temperatures(actually greater than the surface of the sun which is only an inadequate 6000K) to enable the heat to transfer through such a small area as proposed in the OP.

 

you can get this from a trashcan sized device easily.

 

if you had a workshop and were able to deal with very small pipework then you could probably get the device down to something the size of a 3 litre bottle of coke but it would be very very heavy, very intricate and very fragile. not to mention the extraordinary costs asociated with minaturization.

[Spyman]

you can get this from a trashcan sized device easily.

Thats more what I meant and I am sorry I missed your comment about this in your post #30.

 

The OP says:

the heating process would need to be done in the last 10cm or so.

Which I interpret as the device could be larger even if it only takes up about 10 cm of the hose lenght at the end, the transmission area for heating could then be made larger.

 

The OP also later says:

I would like it to get to around 70 degress or so.

I wonder why 70º C ? For normal practicall purposes, in a home, you don't need that hot water. And with lower temperature it's also easier both to make smaller and to heat.

 

[EDIT]

Could Legionellosis be the cause for the high temp, where I live a heat rise in the hot water heater once a month is recommended to prevent the growth of bacteria.

(It could also explain why the thread is in Biology instead of Physics or Engineering.)

 

"Legionellosis is an infectious disease caused by bacteria belonging to the genus Legionella. Over 90% of legionellosis cases are caused by Legionella pneumophila, a ubiquitous aquatic organism that thrives in temperatures between 25 and 45 °C (77 and 113 °F), with an optimum around 35 °C (95 °F)."

http://en.wikipedia.org/wiki/Legionellosis

Edited October 7, 2009 by Spyman
Adding Legionellosis question

[insane_alien]

Which I interpret as the device could be larger even if it only takes up about 10 cm of the hose lenght at the end, the transmission area for heating could then be made larger.

 

I realise thice coould be taken as necromancing, but i'm searchig for an old thread around the same age as this and i came across this.

 

the trashcan sized heat exchanger was so you would have a bigger area to transfer the heat. it has already been shown that to get the heat through 10cm of hose, the outside needs to be several times hotter than the surface of the sun which is problematic to say the least.