what's the fastest method to heat water?

[olweiser]

Would it be possible to heat cold running water without using gas or electric sources fast and to a high temp?

 

I want to heat cold water coming down a conventional hosepipe from the very 1st drop BUT the heating process would need to be done in the last 10cm or so.

 

Has anyone got any ideas on how this could be achieved?

[insane_alien]

microwave would do it unless you counted that as an electric source.

 

and how hot are you wanting?

[CaptainPanic]

How fast is the water running?

How warm does it have to be?

 

Depending on those two questions, and on the surface area of your 10 cm hose (what's the diameter), you can calculate how many watts of heat you have to deliver per surface area.

 

You're looking at a classic heat exchange problem here... and it can always be done. Whether it's practical is another issue.

 

You could for example put a second (wider) hose around it and fill that with hot water. That will heat the inner hose and therefore the water. Then you heat it with hot water (which itself was heated by electricity or gas).

 

You get better answers if you describe why you want it. That will limit us in our solutions.

 

Can you adapt those last 10 cm of hosepipe and make it wider for example? Or do you have to heat it through the plastic of the pipe?

[olweiser]

thanks guys,

 

the flow of water, in this example would be through a standard diameter hose, and the speed of a conventional 'house tap pressure.'

 

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

 

I would really like to entertain ideas that dont use gas or electric.

 

thoughts?

[insane_alien]

well, what is a 'standard diameter hose'? there are numerous diameters available. also tap pressure varies from location to location(even room to room).

 

also, i'm assuming you mean celsius with the temperature?

 

find the flowrate through the hose by timing how long it takes to fill up say a 2 litre bottle or something you know the volume of.

[olweiser]

the flow of water is 1cm is diameter, and can fill 2 litres in 8 seconds.

yes, in degrees.

 

 

does this help?

[insane_alien]

so you have 0.25 litres per second. and a surface area of ~31cm^2

 

what temperature does it start off at roughly?

 

and remember degrees by itself is a unit of angle, not temperature. i wouldn't go on about it but it can be confusing for people whos first language isn't english. try using *C its explicit and easily understandable.

[olweiser]

so sorry, I meant *C, (its been a really tough week!)

 

starting temp, I'd guess at around 6*C

[insane_alien]

thats going to be roughly 67kW you need.

 

you'll need more than 10cm of hose to do that. and what are you wanting to heat it up with if not electricity or gas?

 

is coal or oil a possibility?

[olweiser]

thats one of the main problems - I have no idea if it is in fact possible to generate that heat over that distance consistently without the use of gas or electric.

 

when I run a hose, or a tap in the summer it is warmer, we all know this. Is there something here that I could harness? natural heat sources, solar energy or something.

what about a mini turbine of some kind.

 

I don't have a background in science so I really have no idea.

[insane_alien]

none of those would be practical.

 

and getting 67kW out of your mains isn't hopeful either.

 

you're going to have to use some sort of combustion reaction to generate the heat. this means either coal, oil, gas or wood. and you'll definitely need more than 10cm of rubber hose to do it. a coil of copper pipe would be good.

[Mr Skeptic]

What do you need the hot water for?

[olweiser]

Copper pipe sounds more practical.

 

in fact, if the hose was a large piece of copper by design, what could be done here to heat the copper?

[StringJunky]

what about a Chimnea with copper pipe wrapped tightly around the 'chimney' part and a rubber hose from the feed attached,but not too close to melt it. The cleanest and hottest fuel is Anthracite nuggets..it's also the dearest.

 

http://www.castironchimineas.co.uk/

 

EDIT: Wrapping the pipe around is easier said than done but but this idea might get the 'ball rolling' for you.

Edited September 5, 2009 by StringJunky

[olweiser]

I was thinking of something more self sustainable? like using solar energy, or even the flowing water itself?

 

I realise this is a huge challenge, but worthy of more thought perhaps!

[iNow]

Sounds like you should try something like this then:

http://www.sunmaxxsolar.com/evacuated-tube-solar-collectors.php

[insane_alien]

that isn't going to do 0.25l/s from 6-70*C unless it is over 100m^2 though. probably close to 180-200m^2 and even then only when in direct nearly perpendicular sunlight.

 

not really something you can have in your back yard.

[StringJunky]

It might help us to visualise a solution better if you tell us what you need it for. What's the scenario?

[CaptainPanic]

I was thinking of something more self sustainable? like using solar energy, or even the flowing water itself?

 

I realise this is a huge challenge, but worthy of more thought perhaps!

 

Forget it.

As insane_alien already said: it'll be too big to use the sun. And the energy in the flow of the water itself wouldn't even heat it by 1 degree C.

 

You need 67 kW, and even in a best case scenario you need 30 m2 of heated area to get that from the sun. You might be able to concentrate that sunlight onto a very small surface (with shaped mirrors)...

 

But your next problem is that this small surface is 10 cm of hosepipe. If you plan to build 30 m2 (or better a lot more) mirrors or solar boiler, perhaps it's easier to simply expand the size of the hose and make life simpler.

 

So, since we mythbusted that you can heat up 0.25 liter/s of water in 10 cm plastic hosepipe using the sun, and we also mythbusted the idea of using that hosepipe - perhaps you might telling us what the whole thing is all about? Then we can help you properly. You might have noticed that there are plenty of people who are willing to help, and even to pick up a calculator and do (some of) the maths for you. Now it's time for you to help us.

 

Write a long post to explain what this is all about. Please

[iNow]

that isn't going to do 0.25l/s from 6-70*C unless it is over 100m^2 though. probably close to 180-200m^2 and even then only when in direct nearly perpendicular sunlight.

 

not really something you can have in your back yard.

 

Thanks, mate. I made the mistake of completely ignoring scale when I submitted that post.

[insane_alien]

well, the ones you linked to would be more than adequate for keeping an insulated tank of water hot.

 

so assuming that you don't need a constant flow of 0.25l/s for an extended period of time then you can do it in batches with those.

 

again, we'd need more information on the usage scenaro to know if this is appropriate though.

[olweiser]

sorry for the late reply.

 

All my questions are simply to find out if in fact it is possible to heat water under these conditions. If the 'theory' answer is yes, then I can take it more seriously and move to the next level of finding someone (perhaps someone here?) who I can work with to create this.

 

Is it, in fact scientifically possible to do this under these conditions?

[insane_alien]

well, theoretically you can put 67kW into 0.25l of water through ~30cm^2 of hose but it is impossible to do practically.

 

the energy requirements alone really are too big to do domestically, especially with renewable energy sources.

 

we need all the information you can give us about this before we can say if it is posible or not.

[Mr Skeptic]

From what it looks like, you'd want a solar based heater to heat a water tank. If you don't want your hose to get hot, wrap the hose in insulation rather than trying to get that much energy to the tip.

[CaptainPanic]

Correct me if I'm wrong, but it looks like olweiser doesn't want to say what he needs this heating system for. That's a pity... and this makes it really difficult to help. We already explained several times that what he wants is nearly impossible.

 

Anyway, let's crunch some numbers to show it again:

 

Let's just assume we're dealing with a very standard liquid-liquid heat exchanger for water (heated also with hot water). The typical heat transfer coefficient is 1000 W/m2K (see for example: Perry's Handbook 7th edition, 11-25).

 

We want to find out what temperature difference is needed to achieve 67 kW in 30 cm2 (or 0.003 m2).

 

Formula: [math]P = U\cdot{A\cdot{\Delta{T}}}[/math]

 

with:

[math]P[/math], power, in [math]W = J/s[/math]

[math]U[/math], heat transfer coefficient, in [math]W/m^2K[/math]

[math]A[/math], surface area, in [math]m^2[/math]

[math]\Delta{T}[/math], temperature difference, in [math]K[/math] (or Celsius - it's a temperature difference)

 

so: [math]\Delta{T} = \frac{P}{U\cdot{A}}[/math]

[math]\Delta{T} = \frac{67000}{1000\cdot{0.003}} = 22333 K[/math]

That means that your outside heating must be hotter than the surface of the sun...

(sun = 5,780 K (5,510 °C), and you need 22,631 K (22,358 °C))

 

And that's what insane_alien meant when he said:

well, theoretically you can put 67kW into 0.25l of water through ~30cm^2 of hose but it is impossible to do practically.

Stop looking for "someone (perhaps someone here?) who I can work with to create this", and start thinking about plan B.

Edited September 9, 2009 by CaptainPanic