Enclosed hypercaric test vessel, chiller problem
Enclosed hypercaric test vessel, chiller problem
(OP)
I am performing a preliminary thermal design for a test vessel.
The test vessel is required to have (sea)water maintained at 35°F. The test pieces will be suspended in this vessel to study the effect of long term exposure on coatings. The test pieces will be maintained at an elevated temperature ~300°F. Maintaining the seawater around this test piece at 35°F will give rise to a heat load of approximately 50,000 W.
There will be chiller-coiled tubing system with 30% glycol solution as the working fluid to take the heat away from the test vessel.
I have written down the equations for natural convection heat transfer from the test piece to the seawater. And, also calculated the OHTC (U) for the chiller tubing immersed in the seawater.
Assumed inlet temperature of chilled fluid to be 25°F and the exit temperature to be 50°F.
Also, the heat balance for the chiller fluid is set up.
My problem is that I cannot determine a good way to tie up the heat load to the heat being transferred away by the chilled fluid. The interaction between the ambient seawater and the chiller tubing is very complex involving natural convection, tubing geometry, and variable temperature differences.
This case is not a textbook heat exchanger so I cannot plug the traditional heat exchanger equations. Additionally, the seawater will be pressurized to around 8000 psi, so the chiller tubing cannot exceed 1" OD in size because of collapse loading concerns. This will constrain the maximum flow rate through the chiller tubing.
Can anyone guide me with the way to proceed? I need to determine amount of heat chiller-tubing system will take away and if I can even maintain the temperature of seawater at 35°F.
The test vessel is required to have (sea)water maintained at 35°F. The test pieces will be suspended in this vessel to study the effect of long term exposure on coatings. The test pieces will be maintained at an elevated temperature ~300°F. Maintaining the seawater around this test piece at 35°F will give rise to a heat load of approximately 50,000 W.
There will be chiller-coiled tubing system with 30% glycol solution as the working fluid to take the heat away from the test vessel.
I have written down the equations for natural convection heat transfer from the test piece to the seawater. And, also calculated the OHTC (U) for the chiller tubing immersed in the seawater.
Assumed inlet temperature of chilled fluid to be 25°F and the exit temperature to be 50°F.
Also, the heat balance for the chiller fluid is set up.
My problem is that I cannot determine a good way to tie up the heat load to the heat being transferred away by the chilled fluid. The interaction between the ambient seawater and the chiller tubing is very complex involving natural convection, tubing geometry, and variable temperature differences.
This case is not a textbook heat exchanger so I cannot plug the traditional heat exchanger equations. Additionally, the seawater will be pressurized to around 8000 psi, so the chiller tubing cannot exceed 1" OD in size because of collapse loading concerns. This will constrain the maximum flow rate through the chiller tubing.
Can anyone guide me with the way to proceed? I need to determine amount of heat chiller-tubing system will take away and if I can even maintain the temperature of seawater at 35°F.





RE: Enclosed hypercaric test vessel, chiller problem
That's just not going to happen unless you allow significant stratification of the seawater.
RE: Enclosed hypercaric test vessel, chiller problem
Say, the exit temperature is changed to 34°F. How should I proceed in that case?
RE: Enclosed hypercaric test vessel, chiller problem
Q = rho V Cp dT
Q is 50,000W (or 170,610 BTU/hr)
rho is about 66.8 lb/ft3 at that temperature
Cp is about .9 with the necessary glycol mix
and dT is 9°F (25 in, 34 out)
So you need 39 gpm of 25°F water. You might want to bump that up to a capacity of 60 gpm or something considering surface fouling, esp. with sea water.
RE: Enclosed hypercaric test vessel, chiller problem
The largest chiller tubing I can install is 1" OD x 0.7" ID. Will that be able to flow at 39 (or 60) GPM?
RE: Enclosed hypercaric test vessel, chiller problem
Alternative is a higher delta T, but it would be difficult to have cooler entering water.
Possibly a liquid N2 application?
RE: Enclosed hypercaric test vessel, chiller problem
Also, I have abandoned the idea of bent tubing in favor of fabricated 1.5" or 2" pipe.