Producing Heat with Pressure Drop

GA; I'm amazed how many overlook the loses of different systems. Your last paragraph can be extrapolated to the efficiency loses and augmented emissions caused by the use of electric vehicles.

Google "heat pump" - A 1kw compressor can deliver the same heat as a 3kw element.

Ah, c'mon Fredski, you're killing the fun of his truly reverse engineering, Rube Goldberg project. GA though.

Nonsense. Use whatever is to drive the "gear pump" to heat the fluid directly.

Why are you interested in using this particular method (about which you have uncertainties about the fundamentals) to produce heat?\

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What advantages do you hope to take advantage of by using this method?

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I'll try to be of some help with the question you asked, but if you could give us the specifics you are working with and what you are trying to achieve, comments will be far more helpful.

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The heat produced in the system you described isn't really due to a change in pressure (though a change in pressure can the driving force behind the process responsible for the conversion producing heat). This is apparent when considering adiabatic expansion of hydraulic fluid causing a reduction in pressure without a substantial addition of velocity to the bulk fluid. Because the compressibility of hydraulic fluid is low, the increase in volume is relatively small, the drop in pressure is relatively large, change in temperature will be relatively small.

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Heating in the system you describe is the result of conversion of pressure head to heat via acceleration and subsequent various flow losses.

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So to answer one of you original questions, a large change in pressure restricted by things like a convoluted path and narrow channels, would probably heat up more quickly, than a less restricted, higher flow, lower pressure drop set up.

Vortex tube. Mainly used for air has been shown to have some similar effects on fluids. If used you will need two reservoirs. Nothing can be connected to the outputs that would disrupt the motion of the fluid inside.

The OP must have a reason to do it this way, instead of the more logical and efficient ways suggested here.

I have used this method to heat up oil sometimes, when other methods were not available or capable, recirculating trough a pressure relief valve.

If it is adjustable, better.

Regarding flow/pressure, you need both.

If you have a big pressure drop but very little flow, you can reach undesirable hot peaks, and a less homogeneous temperature in the circuit.

An biger flow and little (initially) pressure drop, will keep the oil at more homogeneous temperature, allowing a better control.

Consider insulation for the circuit. It will save time and kw/h.

Even a bad insulation will be better than none at all, use what you have at hand.

Salu2 cordiales,

Abel

This said, it seems to me that

Just re-circulate the hydraulic fluid through the pump. The pump's shear and friction will heat the fluid without any other devices.

Or. #1 This makes the most sense.

Measure the max pressure from pump with blocked output.

Use adjustable pressure regulator set to half max pressure.

Adjust reg. up & down incrementally to find max heating.

Locate regulator just before water tank.

But still not optimal solution -

If you can eliminate hydraulic fluid would be good, pump water. But then filtration & corrosion could be a problem.

Good luck.

"Measure the max pressure from pump with blocked output."

It's a gear pump.

So it won't have a max pressure?

Not for long (at least not what it used to be...the new one will be much closer to the input pressure). Positive displacement pumps do not behave well when run with the output closed.

Many of the images when searching google images for "gear pump performance curve" show pressure at zero flow. It is only to establish what that pressure is, not to operate for any length of time at that pressure.

If you prefer to not do the closed output test, then set up as I previously described, then starting from low pressure gradually increase pressure. Plot water temp; it should show temp rise, then a plateau (or more of a hill), then water output temp begins to drop.

Bring pressure back to the top of the 'hill'.

Check every week for a month, then every month.

Also smaller pipes pump > regulator, larger after heat exchanger. Turbulence in smaller pipes may aid heating - unless too small

I am not a mechanical engineer, but know once thing for certain that expansion through orifice, that is sudden expansion, produces cooling not heating.

Heating will be only through adiabatic compression of Oil in compressor or transfer of friction heat from piston and cylinder to oil.

Further if you want to vaporise oil then when heated pressurised oil if expanded my evaporate in to hot vapour at atmospheric pressure, depending upon the boiling point vs vapour pressure of fluid in question and its latent heat.

Is stead of going through all difficult exercise, it shall be easier to heat up oil directly by using gas heater or electric heater or dielectric heater or microwave heating (dielectric or microwave heating will not create any hot spots, uniformly heat up oil without altering its properties or directly heat by one these means under vacuum if the application needs hot oil vapours and not liquid (say for food industry in case you want to fry potato chips with less oils for healthy junk food).

Difference between an Engineer and Scientist is that Engineer has to device methods and means with both economy of cost in manufacturing and operation of any equipment and plant.

As said I am not a Mechanical but electrical engineer - but being very senior in age (64 now) can take the liberty to give above example to young engineers. This idea of hot vapour oil for frying chips also came up as I was typing this message.

Best of luck

Ramesh Kapur

'....I am not a mechanical engineer, but know once thing for certain that expansion through orifice, that is sudden expansion, produces cooling not heating....'

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Double check what we feel certain we know can be a good exercise for people of any age.

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While what you stated would not seem to be contradicted in many circumstances, but closer inspection shows it is not without conditions/exceptions.

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A good example would be expansion of hydrogen or helium around STP. The expansion does not result in cooling, in fact it results in warming.

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Another thin to note is that the liquid oil is not going to experience a large change in volume.

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Also, if you are willing to allow heat as a result of the motion of the piston, why not allow for heat that results from the motion of the fluid.

Since no one answered your direct question, the equation for heat produced when pushing oil over a pressure drop is as follows:

Power (kW)= (change in PSI) x (US gallons per minute)/2298

So 1 gpm pushed over a 1000 psi pressure drop generates about 0.4 kW of heat.

As one poster pointed out, you need enough oil flow to absorb the heat generated so you don't overheat the oil, especially at the point where the pressure drop is happening.

Depending on how much heat you want, moving oil through a gear pump without any restrictions except for the piping will generate some heat but not very much in a hydraulic system. Depends on how much heat you need.

I've used the pressure drop method to warm long hydraulic lines in subzero temperatures but usually put the warming pressure drop valve on a PLC controller to limit its use...you can easily boil the oil in a hydraulic power unit without any automatic controllers watching the temperature.

The method of pressure drop is immaterial--anything that restricts the flow of oil from a higher pressure to a lower pressure will do. In hydraulic circuits, a pressure relief valve will work, a hand valve, a fixed orfice, anything. Also, in general, a higher flow with a lower pressure drop will damage your oil the least from localized heating at the pressure drop point, where the heat is generated.

Hope this helps,

Jon.

As someone else suggested, water might be a better medium than oil, cheaper components for the mechanical side as well.....its also easy to add inhibitors to stop corrosion....

The oil method will probably ruin the oil on a regular basis and reduce its lubrication qualities, causing damage to the pumps and the need for regular replacement.

But as none of us have been told the background to this question, we can only guess...OP WHY????

You seem to still be stuck on that 4 year old project.

liquid friction equation

I'd suggest going back to http://www.engineeringtoolbox.com/pumps-temperature-increase-d_313.html and reviewing that.

Deja view all over again.

is this working

Are you getting warm?

yes it is - didnt upload last comment

typing for second time

thanks sawmilleng for reply on restictors.

yes still stuck in four year old project to make hydropowered japanese bath

japanese baths are modelled on natural hot spring in that they have continuous feed and continuous overflow

in my design the overflow water will go into a plate heat exchanger heating the feed water. the feed water will then be heated further a second time by the oil in the hydropowered-gear-pump-pressure-drop-machines heat exchanger.

the bath will run continuously. the water in the bath is 42 C. the oil in the machine is no more than 70 C.

the bath is for remote locations were there are no mains electricity.

i chose this method because i thought once set up the machine will last a long time and require little maintenance - which could be carried out by unskilled persons.

i am not an engineer and appreciate all responses.

thanks

i want to build the machine from off the shelf industrial parts bought from ebay.

OK, now that you have stated the purpose of your project:

_ What are you going to use as prime mover for the Oil Pump?

Since no Electricity, then I assume it not to be an electric motor.

Therefore, if it is a diesel or similar engine, you are wasting energy because you are better off using the fuel directly to heat the water.

Then, if it is Wind or Water fall or (??) maybe you can make sense on the practicality when no other means are available.

Where are we now??

the prime mover is going to be a pelton turbine. it is hydro powered.

Well, This makes sense if you do not want to bother to convert the hydro-energy to electrical then to use a heating element.

You will need less equipment with your project, but the control will be more difficult to maintain any specific temperature, even though workable.

If you Insulate properly all the pipings and the pump, it will be relatively efficient given that the prime mover is a pelton turbine, driving your pump, which means hydro - to - mechanical - to - heat (less one more conversion ...)

In that case, one of these might be better - http://en.wikipedia.org/wiki/Hydraulic_ram no hydraulic oil, "A typical energy efficiency is 60%, but up to 80% is possible", only one moving part -

You'll likely be far better off using the pelton turbine to power a heat pump.

maitland - what is the distance between the Pelton and the hot spring?

There is a simpler method, which someone from CR4 mentioned some years ago of stirring or agitating water which heats the water up. They were using wind energy, you could use your Pelton directly, no conversion losses then.

I am sure that a suitably built 50 gallon oil drum would do just fine, you just need to have rotating and fixed vanes and to insulate it to retain the heat.

Nothing could be cheaper that you can attach to your water turbine.

I even found a web site that mentions how this heats water up, look at the 2nd and third posts here:-

http://fuelzilla.com/homepower/Using-wind-power-to-heat-the-barn-5412-.htm

I believe such systems were or are used in Scandinavia.....