Looped fluid system

[ymehdi]

I have a system which heats a fluid while in a constant flow in a loop

how would i calculate the energy used to heat the fluid in the looped system to the temperature set and the time to reach it
sorry if i put it in the wrong forum

thank you

 

[itsmoked]

This would be way too hard to do for the lousy result you'd get. The way to do this is empirically. Monitor the power consumption on the actual loop.

Does this loop exist?

If you're trying to come up with a heater size for this existing loop you can use the pump power against the temperature rise of the media circulating in the loop to estimate the power needed to get to a higher temperature.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ymehdi]

the process is a project of mine, im heating objects with oil which is going through a heating unit. however rather then having a tank i have the circuit closed so its using the same oil. i was just wondering if i can calculate the energy used to heat the oil which is in constant flow in the looped circuit and the time it takes to heat up to set temperature

 

[LittleInch]

Yes you can.

Find the heat capacity of the fluid, the mass of the fluid and how fast you want the temperature to rise.

Allow a certain maount for heat loss of the loop, unless its very well insulated.

for a closed loop you can probably forget the power put into the system by the pump.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[itsmoked]

I was envisioning a facility loop not a small test loop. I agree with LI in this case.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[crshears]

Ah! The Disappearing Thread poster tries again!

Thank you for more properly spelling out your requirements.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[LittleInch]

Just be careful that you have some sort of pressure control / accumulator otherwise a true closed system will increase in pressure a LOT as you heat it up.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ymehdi]

Ok

Im using heat transfer oil so as i raise in temperature more the specific heat capacity also goes up

for example from the data sheet at 100 degrees Celsius:
the density of the oil is 811 kg/m 3
the specific heat capacity is 2.173 kJ/kg*K
and the thermal conductivity is 0.128 W/m*K
from testing the heating unit say that it flow at 49 L/min at 100 degrees Celsius

and also at 300 degrees Celsius
the density of the oil is 681 kg/m 3
the specific heat capacity is 2.902 kJ/kg*K
and the thermal conductivity is 0.114 W/m*K

Also from testing the heating unit say that it flow at 43.9 L/min at 300 degrees Celsius

if this helps more ?

 

[LittleInch]

What are you trying to find?

Energy or heater power??

You need total mass for both.

You need time from one temperature to another for power

~you can probably average the heat capacity between your two end points.

This will only be an approximate figure as you don't say what sort of heat losses are happening

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ymehdi]

I'm trying to find the following:
how much energy is used to heat the oil
how long the oil can hold heat for
how long it'll take theoretically for the oil to heat up to temperature
and how long it'll take the oil to heat up 2 tools made of mild steel weighing around 90kg each

the loop contains 18L of oil if this is what is meant by mass ??
and the heating unit is 24kw and running around 2.5 bar

Thanks for the help

 

[LittleInch]

Then you seem to have all the information available to do the calculations other than how much heat the system looses.

18litres is a vlume, but you know the density so you can work out mass ?(kg)

That's a pretty big heater for only 18 litres of oil. I suspect the surface temperature of your heater might be an issue and you could "cook" the oil unless you're flowing really fast through the heater elements.

Either that or the heater elements will burn out because they will get too hot.

Heat up time I get is about 5 minutes from 100C to 300C. In theory.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ymehdi]

ok thank you
the oil is flowing through fast so the oil isnt being cooked and elements wont burn
please can you comment the equations that need to be used as that would be a big help thanks as i dont understand where i can find them or if they are even the correct ones

 

[3DDave]

https://ocw.mit.edu/courses/mechanical-engineering/2-051-introduction-to-heat-transfer-fall-2015/

Heat Transfer: Introduction to Heat Transfer (1 of 26) by CPPMechEngTutorials

https://www.youtube.com/watch?v=TWTQx3W-2k8