Water heating using friction trhough a small tube

Why not crack a text book and find out? Or maybe do an experiment?

when water is pumped at high pressures it does get warmer from friction.

What you need to do is do a calculation based on the water viscosity and 1000 feet of 1 millimeter diameter strong pipe and you calculate the pump energy to get, say 10 gallons/minute throught that thin tube and you feed the output to the input of the pump. All the energy will end up as heat and the water will get hotter.

So a 1 HP pump = 550 foot pounds/second. ?? It may take 10 HP to get 10 gallons through that tiny tube in a minute at 15,000??? PSI.

So look it up, calculate iteratively, then repeat with changed parameters and make some charts.

There is also a lot of heat conversion from velocity, as in hydraulic systems. Desigh a nozzle such that your velocity through the nozzle is the same as the molecular speed for 100 C, but watch the wear on your nozzle.

Rich

"when water is pumped at high pressures it does get warmer from friction."

2LofT?

Won't it take more energy to run the pump than can be transferred to the water in one pass or more through the 1,000 ft. of 1mm i.d. pipe?

Efficiency wasn't a requirement. possibility was. Wind power conversion to pressure/volume may make it practical fpr spmeone. A hot bath at night after the lights go out might be just what the doctor ordered.

Most impossibilities are impossible, the rest are just harder to do.

Rich

Dont know if that is the question the poster is raising, but basically with the system you are suggesting, wouldnt he just be raising the temperature by using the pump energy. I would think he would be better off with a calrod heater due to higher efficiencies.

I think it is a very good question: how tight should the tube be? My impression is that water would stick to the tube walls, and thereafter, friction might not be playing such a big role in heating the water, at least not friction between the tube wall and the fluid, since contact would just be water through water. if pressure is very high, effects such as hydrodynamic lubrication might also play a role, but I suppose those would eventually break a tube, wouldn´t they?

Power used to force water thru a tube:

(P->Power, p->Pressure, V->Volume, v->Velocity, rho->specific mass, cp->specific heat)

P=F*v =p*A*v =p*dV/dt =p*dm/dt/rho

Power used to heat up the same amount of water:

P=dm/dt*cp*deltaTemp

Elimination of Power leads to:

p=cp*rho*deltaTemp

boiling water -> pressure of 3800bar!!!

My question is this: Is it possible to heat water to 100 C by pressuring it through a very tight tube. If so, how much pressure would be needed and how long a tube would I need?

My answer is no. There is a pressure/flow relationship that will give you 100 C initially at the pump outlet and the pressure may be 3800 bar. However, since you are adding no energy to the fluid stream after the pump, the water will be cooling for the length of the tube.

looking at that, I see that adding a longer tube will increase the resistance and add to pump power wasted. Thus your comment seems wrong. The water has friction losses all along the tube = heat produced.

eith enough worok the water can go far above 100C. At some point it will become high pressure steam and this has less friction, but it still has friction of a lower order even if you take the temparature above the critical point where all is steam

Inouk Here (the one who asked the question)

From what I'm understanding is that it is possible but this will require a lot of power and a very big compressor.

The reason I am asking this is that we are looking for an alternate solution to the actual hardware in an expresso coffee machine and I wanted to ask an open question to have different opinions on the subject. What we would like to do is to amke the machine smaller, less bulky...

thank you very much for your answers!

Inouk

"What we would like to do is to amke the machine smaller, less bulky..."

Had you stated the problem rather than ask about a suggested solution the answer would have been arrived at sooner.

An ELECTRIC HEATER ELEMENT would be the most compact, space saving, practical, and economic way to heat water (& make steam) for an espresso machine. Isn't that the way they are made now?

Are they built different where you are located?

Do nothing SIMPLY if a way can be found to make it Complex and Wonderful!

Hi, Inouk!

Water molecules are not practially compressible like air molecules. Hence, the velocity increase is less likely to create as much useable heat as if you simply ran a small fan to blow air through a Venturi tube with a narrowing in it to create a red hot section of pipe that heated up the water via a heat exchanger in the coffee machine. You could then also place the fluted end of the Venturi behind a frost screen inside a closed box (with a door) next to the coffee machine to make a fridge for the milk and cream. Run a very tiny tube around the frost screen from the heat exchanger to keep your fridge frost-free.

Place thermostatic controls in the fridge section to turn the fan on or off. The heat exchanger would save your coffee machine from melting when nobody's making coffee in it, but keep the coffee warm when the fridge was running.

Mark

looking at that, I see that adding a longer tube will increase the resistance and add to pump power wasted. Thus your comment seems wrong. The water has friction losses all along the tube = heat produced.

Aurizon, Thanks for calling me on that. I was in the frame of mind that the tubing is going to be a good heat sink. However, if you insulate the tubing and run the pump long enough, you will see a rise in water temperature down the tube.

Hi,

with a high power electrical heater you can put out 1KW heat at 1000°C surface temperature of a 2mm diameter insulated (magnesia) and shielded (inconel) heater.

It is recommended to use only 400W per meter but I tried and it worked.

Or with an isolation transformer you can use a bare heating element.

This together with a thin tube or a thin film of water so that there is not much conduction needed will give you fantastic heaters.

So stay electrical unless you have only charcoal or else.

Mechanical energy is better converted to heat by atrue shearing action: rotation of a cylindric rotor inside a cylindric tube (some cm long) with a small gap filled with water.

This was used in wind-generators to produce hot water: simple, effective and control is not difficult.

RHABE

"Mechanical energy is better converted to heat by atrue shearing action: rotation of a cylindric rotor inside a cylindric tube (some cm long) with a small gap filled with water."

How about a Tesla turbine with close clearances, lots of counter rotating disc area and a throttled outlet. Still not as good as a calrod of similar electric heater.

if you have free rotational energy you can make heat this way. Suggest you make the fluid more viscous than water and non boiling so no pressure builds up.

A lot of older street cars in Toronto used shorted turn energy from braking to heat the passenger areas. In those days they had no SS controller to back feed the HV DC bus.

this took the form of copper disks and strong permanent magnets. for slowing you used 1 setting, and it would slow you adequately and as you slowed that energy ran the heaters. In case of urgent need to stop, further travel on the brake engaged conventional air brakes. Careful drivers were able to make their brakes last for years before needing relining.

This devise uses a microwave to heat the water in the tubing and insulate for thermal decline, using clear tubing.

Look up the Prostetron. http://www.urologix.com/uro_Prostatron.html

Perfect example of a microwave thermal heat exchanger with a water cooled jacket to maintain optimum efficiency; all in a small tube.