Temperature change after compression
Temperature change after compression
(OP)
I'm looking for some help.
To calculate the temperature change of a fluid (water for example), when its pressurised to 345bar from atmosphere or 3bar maybe, and then what the temperature change would be when brought back to atmosphere again.
Pressure rise gradient for a closed valve condition for a reciprocating positive displacement pump. I'm assuming it'll be the same the gradient of the calculated pulsation frequency of the pump, but with some damping effect based on the bulk modulus, and volume/ length of pipe between the pump and the valve?
This is all to evaluate a pressure relief valves response to a change in pressure.
Any help much appreciated, as this is outside my field of knowledge. I'm learning but I'm kind of stuck right now.
To calculate the temperature change of a fluid (water for example), when its pressurised to 345bar from atmosphere or 3bar maybe, and then what the temperature change would be when brought back to atmosphere again.
Pressure rise gradient for a closed valve condition for a reciprocating positive displacement pump. I'm assuming it'll be the same the gradient of the calculated pulsation frequency of the pump, but with some damping effect based on the bulk modulus, and volume/ length of pipe between the pump and the valve?
This is all to evaluate a pressure relief valves response to a change in pressure.
Any help much appreciated, as this is outside my field of knowledge. I'm learning but I'm kind of stuck right now.





RE: Temperature change after compression
RE: Temperature change after compression
RE: Temperature change after compression
The only mechanism for a liquid to increase in temperature during pressure increases is mechanical heat transferred in from the pump or fluid friction. Both are generally negligible. Heat of compression is not a thing in liquids (even when you add enough pressure to reduce the volume measurably any heat of compression would be lost to the atmosphere).
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Temperature change after compression
RE: Temperature change after compression
I'll echo the previous posters. What you are experiencing is the heating of water due to friction, either within the pump or within the piping or the pressure regulating valve. In a relatively small volume test set up with water constantly flowing round a loop and little opportunity for it to cool down it can get really quite hot. However this is friction, not due to compression.
Remember any pump has a hydraulic efficiency of no better than 75% and probably less. Hence look at the electrical power of your pump, take 25 to 30% of it and that is the heat going into the water. This could easily be a few kW constantly. Then think about if you put a heating element of that power in your tank and it should then become a bit clearer to you.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Temperature change after compression
That only applies to the pump-end efficiency (I know you know that, but the "pump" in many people's minds is properly called the "pump skid" or "the pump and driver"). I have seen people try to dump the heat lost in the driver into the process fluid and get a wrong number.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Temperature change after compression
http://www.freecalc.com/ptemfram.htm
RE: Temperature change after compression
I was hoping for an example of how I might calculate the temp rise, but think I'm understanding its a lot more complex than I'd maybe given credit for
RE: Temperature change after compression
That's exactly what I was looking for, but wanted to try and understand the math behind it.
RE: Temperature change after compression
Hence start with electrical power in, loose some in the motor heat / efficiency (5-10%, some in the pump (varies depending on your pump type and size, but 10% looks typical) then what work the fluid does. If the flow velocity isn't big or distance not long, but you have a big pressure drop over a valve, then tat's where most of you potential energy "stored" in the high pressure fluid is released as heat, mainly into the fluid.
Those look mighty big pumps for a non cooled test loop....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Temperature change after compression
The calc online comes up with +37degC after 1hr at normal rates.
RE: Temperature change after compression
375 kW and only a 37 deg rise after 1 hour?? Volume must be pretty significant for that???
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Temperature change after compression
Fluid is water
Flow rate 450lpm
Pump Head 2750m
Pump Eff 95%
Tank volume 5000ltr
Recic rate 1hr
result +36.61 C
That's a typical example of a smaller pump test. However I've convinced them to use a 32m3 tank now, so approx. +5.7C in an hour which is much more manageable.
RE: Temperature change after compression
Hope you now understand the theory a bit better.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Temperature change after compression
RE: Temperature change after compression
RE: Temperature change after compression
Some assumptions:
Your pump is set up with inlet at a nominal pressure (0-2 barg), your pump is flowing at the head you gave. This pressure is then dissapeted through a control valve (choke valve?) back ont pot he tank from which it came essentially at 0 barg.
This is then an energy equation. For all intents and purpose's the energy imparted into the fluid by the pump (shaft power) is then dissipated by friction (heat) in a small loop, mainly by friction inside the control valve resulting in increased temperature of the water. Assume no heat loss to the outside.
Shaft power = Q x H x density x g / (3.6 x 10^6 x eff (0.x) ) Units are m3/hr, m, kg/m3, 9.81 = KW
Heating of water - Specific heat of water is 4.186 kJ/kg/K.
So for you case, to raise 32,000 litres = 32,000kg of water 1 deg C needs 133,952 kJ.
Shaft power for your pump = 27 x 2750 x 1000 x 9.81 / (3,600,000 x 0.95) = 212.98 kW = kJ/sec.
So number of seconds to raise your water 1 deg C = 133952/213 = 628 seconds = 10.48 minutes. Hence rise in one hour = 60/10.48 = 5.72 C
Life is not as precise as this and some energy will dissipate not directly into the water, your pump may not run exactly as you want or be as efficient, but you should only get a temperature rise between 5 and 7 degrees C with that amount of water.
If you need any back up for the formulae or numbers just google it.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Temperature change after compression
RE: Temperature change after compression
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.