Heat developed in circulating fluid
Heat developed in circulating fluid
(OP)
Hi guys,
I have a vessel with say 100m3 of water at room temp. I have to keep it recirculating with a centrifugal pump of 1MW capacity. I am concerned abt the temp rise of the fluid. The temp rise is only due to the friction losses, rite?
So, i should calculate as follows:
Electrical power (1MW)=mass flow rate x pressure developed + friction loss (f).
Now, f/(mass flow rate x specific heat) should be the rise in temperature, rite?
Is it the correct way or am i wrong, please advise.
Thanks in advance.
I have a vessel with say 100m3 of water at room temp. I have to keep it recirculating with a centrifugal pump of 1MW capacity. I am concerned abt the temp rise of the fluid. The temp rise is only due to the friction losses, rite?
So, i should calculate as follows:
Electrical power (1MW)=mass flow rate x pressure developed + friction loss (f).
Now, f/(mass flow rate x specific heat) should be the rise in temperature, rite?
Is it the correct way or am i wrong, please advise.
Thanks in advance.





RE: Heat developed in circulating fluid
RE: Heat developed in circulating fluid
Typically, the temperature rise across a pump is based on the pump's inefficiency. That energy goes into heating the liquid and generally results in a fairly small temperature rise except for high head, low efficiency pumps. The equations will be in any pump book.
However, if you are essentially pumping in a loop, you first put the energy into the fluid due to the pump's inefficiency. The remaining energy goes into velocity and head energy which in this case, is just recirculated to the suction tank. Since you have to have conservation of energy, your frictional losses also show up as heat.
As an example, I have a hot tub at home with about a 5 Hp motor. During the summer, I can't run the circulation pump constantly as the hot tub reaches the high temperature trip and shuts down.
RE: Heat developed in circulating fluid
This will solve the problem.
RE: Heat developed in circulating fluid
Sum dQ = Sum dW.
That is, "when a system undergoes a thermodynanic cycle the net heat supplied to a system from its surrondings is equal to the net work done by the system on its surrondings." Also, any energy input into a system that is not converted to work by the system is converted to heat.
So in a pump recirc. system, every watt of energy that is supplied to a system that is not utilised as work will be converted to heat. A general rule of thumb for these types of systems is:
1Kwh = 3600 Kj (this assumes no work is done on the environment)
Hope this helps.
saxon
RE: Heat developed in circulating fluid
RE: Heat developed in circulating fluid
I unfortunately have a similar case but with an insulated vessel containing hexene. Due to a change in process we have long periods where we need to kick back 99% of our pump flow back into this vessel. After about a day the temperature accumulates around 15degC, where it has reached an equilibrium of heat loss through piping/vessel and heat gain through pump. This may become unacceptable in summer so I've got to come up with a (inexpensive) solution before then! We can't afford to install a cooler!
RE: Heat developed in circulating fluid
This will help you calculate the heat duty. Then you have to do heat transfer calculations if you want to know the temperature rise in your tank versus time.