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Old Apr 29th 2015, 10:08 AM   #1
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Industrial water heating / heat loss

Intro -

I am not a college student, and I have almost zero physics / thermodynamics knowledge. I am looking for a solution to a work problem, and if that isn't something I should ask about here, please let me know and I will apologize and figure something else out.

My employer has designed and manufactured a system to heat water. The application for this is to transfer water from a source to a storage tank, circulate the water through my heating system and back into the storage tank, then transfer to a job site. As I transfer out of my storage tank, I will be replenishing with water from the source, and continuing to circulate.

My source water is (e.g.) 40F and it needs to arrive at the job site at or around 80F. I know I only need to pass any water through my heating unit once to achieve the ΔT. I figured that volumetric flow x required ΔT x water density x specific heat = energy required in BTU/hr, and I know the horsepower of my heating unit is above that.


Q1 - I am not 100% sure how long it will take to heat my storage unit. At first I thought it would just be storage volume / flow rate = time to heat. But there will be some heat transfer when the hot water returning to the storage tank mixes with the cold water inside. How can I calculate what this will be, and ideally how long it will take to achieve my ΔT?

Q2 - Secondly, I will be constantly pumping hot water out of the storage tank, pumping in cold water at the same rate, and circulating water through my heating system. There are a lot of variables here and I am having a really (F*****!) hard time figuring out what the temperature curve over time will be for my storage tank - i.e. once I reach my ΔT, will I be able to maintain it, or will my storage tank temperature drop too rapidly?

I had thought that if I use the following equation:

((mass left in tank after transfer out / original mass in storage tank) * heated water temperature) + ((mass of cold water added to tank / original mass in storage tank) * cold water temperature)

- that I would figure out the temperature in the storage tank. But this only works for a finite amount of water - what if I am transferring constantly? Should I enter different amounts into that formula and record results to plot a graph?

Q3 - One last option I have is to blend hot and cold water on the way to my job site - I can send ~50% (or any amount) of cold water directly from my source to meet up with the hot water coming out of my storage unit. Would this help maintain temperature in my storage tank - given that there is less cold water going into the tank, and less hot water coming out?

A pretty simplistic diagram of the intended setup is attached. I included actual volumes and transfer rates on the image but I'd rather figure things out for variable numbers.
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Industrial water heating / heat loss-so-far.png  
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Old Apr 30th 2015, 04:31 PM   #2
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I think that you need to split the problem into two separate stages.
1) heat the storage tank to the required temperature,
2) only start pumping to the site when the required temperature has been reached.

You have worked out that your heating unit is powerful enough to heat the volume per minute of the required flow rate,
so as long as you have the tank up to temperature before you start delivering hot water, you should be able to maintain the temperature in the tank.

I think that the key issue might be the control system,
Don't turn on the pumps until the temperature is hot enough,
and have a thermostat to turn down the heating when the temperature is too hot.

As long as you don't need to control the temperature within very tight limits,
and as long as your heating unit is (more than) powerful enough for the required flow rate,
I think this should work.
You have GOT to Laugh !
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Old Oct 31st 2015, 04:49 AM   #3
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Regarding Industrial water heating/heat loss

I am fully agree with the idea of MBW. Still if you are facing any technical issue , it will be better for you to take the advice of technical professional dealing with the subject.
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