Watts needed to heat a water circulating system.

[JWS7]

Watts needed to heat a water circulating system.

I am trying to heat a closed recirculating fluid system from room temp to 194F, in less than an hour.

Currently with 2800 Watts into the 5 gallon tank of deionized water, the system peeks at 180F after three hours with the water flowing.
I’m sure the problem is the heat loss into the room. We keep adding insulation, but aren’t getting closer to the solution.

How can we calculate the watts need to do the job?
The system material is 316SS, I can estimate the mass of the piping system, surface areas etc.
Tank vented, Pressure after pump 12 psi; flow 6 gpm;

Any help would really be appreciated.

Thanks, JWS7

 

[JWS7]

OK. I appreciate the knowledge and talent here, and your help. The system has other features, but I didn’t want to complicate the original question. I have a non-disclosure agreement with the customer, so I was trying to be a little vague. Sorry. I could show you photos and schematics, but then, you know what would have to happen... Basically, there are actually two tanks, one at 86F and one at 194F. There are 1 1/2" ball valves to select the supply and return plumbing to one tank or the other, depending upon the test cycle. Also the pressure has two different requirements, so I have selectable pressure relief valves, with the 1 1/2" SS ball valve to shut of the lower pressure choice again depending upon the cycle. Also the plumbing has tees for pressure gages, and tees for temperature gages at certain locations. These all add mass and surface area to the system.
The performance issue I am addressing here is getting to the required temperature using the hotter tank. I was asked the distance between components, and the physical distance might be close, but the feet of tube (or pipe) the water travels to get there, I called the tube-feet. Sorry for the confusion.
In the end, if I could understand the formulas you are using to estimate these Watts, I could try to better estimate the variables to narrow down the answer. Thanks, JWS7

 

[ione]

It seems IRstuff and I are tuned on the same wavelength, but frankly I still have difficulties to figuring out your scenario.
If I’m not mistaken (but probably I am), you take water at 194 F from a tank to heat up water stored in another tank at 80 F. Water from the second tank (the colder) is then circulated back to the hotter and so on.

An enthalpy balance is required:

Mh*cp*Th + Mc*cp*Tc = Mtot*cp*Te

Where:
Mh = mass of water stored in the hotter tank
Mc = mass of water stored in the colder tank
Mtot = total mass of water (Mh + Mc)
cp = water specific heat
Th = hotter tank temperature
Tc = colder tank temperature
Te = equilibrium temperature (unknown to be computed)

It is understood that without keeping on heating the equilibrium temperature Te will always be lower than Th=194 F

You have now to evaluate power required to heat up the whole water mass Mh from Te temperature to Ttarget target temperature (this also involves another parameter, time t required to complete the heating process).
You have then to consider power required to heat up pipes, fittings and valves:

Msteel *Cpsteel *(Ttarget – Te)

You have then to add wattage to compensate heat loss through the system (you can consider 6 W/m^2/°C for heat transfer coefficient).

 

[zekeman]

jws7,

You can't come here asking for free advice and not give us a clear picture of the system you have.Worse than that ,you have wasted all of our time trying to help you with this "nondislosure" problem And to ask for equations is simply over the top. How can we give you equations? You haven't given us a straight problem.

It's like asking a doctor to diagnose a problem without giving him any symptoms.

I strongly suggest you bring in an engineer to unravel this problem and mercifully end this dialogue.

I think the administrator should close this thread out.

 

[willard3]

Beating a dead horse it seems...........

Get an Engineer familiar with fluids and thermodynamics. This is a lot more complicated than you think it is.

 

[JWS7]

Sorry Zekeman. I thought that my original question was straight forward. The extra tank is bypassed during the cycle in question, so I didn’t think it needed to be mentioned. I am trying to heat the test valve, not the 2nd tank of water.
I suppose you are right. We will just end this inquiry. Sorry, but I do appreciate your efforts. JWS7