How pressure changes with time(solar water system)?

[zhangw2008]

Hi, this is my first thread. I need some help with my project.
The situation is as follows:
There is a leak of glycol from heating coil into the solar storage tank.The heating coil ruptures because the circulating pump stops. The whole system goes to stagnation.The high temperature and high pressure causes the crack.

The glycol loop has a expansion tank connected on it. When the leak occurs, the pressure in glycol loop was 87 psi. While the pressure in storage tank was 40psi which is connected to the water main. I know that the flow will stop if two pressure become the same.

How should I calculate the time it takes arriving to steady state(same pressure in the glycol loop and storage tank)?
Is it possible to know how pressure in glycol loop decreases with time?

Thank you for any hints.

 

[BigInch]

You'll have to relate these pressures to temperature gains and losses in each fluid, then assume the gas pressure in the expansion tanks take the same temperature as the fluid which causes a change in pressure. The heating and cooling rates depend on the solar energy flux that is heating the glycol, so it will be slower to heat in the morning than at noon and slower to cool at noon than in the morning or evening. The water heating will depend on how much glycol is flowing by and the heat it is transfering into the water tank and how hot that glycol is at any time. The heating and cooling rates can be calculated, if you know the solar heat flux and surface area exposed to the sun, the exchanger efficiency coefficients, the (pump) flowrate of the glycol moving between the solar collector and the volume of water in the water tank.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[Zapster]

A review of your fluid-mechanics and heat/mass-transfer college course work should answer your questions.

Do you have listed BFP (backflow preventers) between the water main and glycol tank?

Do you have PSVs (pressure safety valve) in the system to prevent the over pressure of system components and piping?

Is your pump a positive displacement pump?

Are there check valves in the system?

Can you provide a schematic of your design?

 

[zhangw2008]

Thank you for your replies.

There is no BFP between the water main and the water storage tank.The objective of this project is to see if a BFP is necessary by calculating how much of glycol will flow back into the water main without a BFP.If the concentration of glycol in the water main is higher than the health standard, a BFP must be installed.

We assume the pump stops and suddenly there is a crack on the coil due to stagnation. The glycol starts to flow into the water tank after cracking. This system do have a pressure relief valve which is set to 87psi. We also assume the crack occurs right before the PRV takes action.

 

[jte]

zhangw2008-

I've seen a few senior projects similar to your project. Check with your professors to see if they can help you set up the problem. Don't forget - its not just about flow, diffusion is also at work...

jt