Heat exchanger configuration leading to temperature cross??

[Iradah]

Hello all,

I have a question regarding lube oil heat exchanger designed for us by one of the companies.
we noticed after commissioning the system that the hot oil is not getting cooled. we think that there is no enough cooling water flow into the heat exchanger and working on increasing it. however, it was observed that the change in water temperature is very small, we think that if there is a small flow of cooling water into the heat exchanger, then the outlet temperature of water should be much higher than the inlet which is not the case. Does this suggest that there is a blockage inside the exchangers and there is no water flow inside the exchangers and that is why a very small temperature difference is observed between the inlet and outlet?
Another big concern I have is the configuration of the exchanger, it is shell and tube with the inlet and outlet of the shell on the top of the shell, inlet on right side and outlet on left side. the tubes are two passes with inlet and outlet nozzles above each other at the left side of the exchanger, the inlet is the top nozzle and the outlet is the bottom nozzle.

Please advise if you think that this configuration can lead to temperature cross or diminish the temperature driving force.

Thank you.

 

[gerhardl]

It seems likely that 'something' is wrong, and as you state probably something blocking the circulation. Is this forced (pumped) or natural circulation? You will have to check 'everything' from correct mounted unit and conections, pumps working properly and giving correct flow, valves correctly mounted (no checkvalves mounted wrong way), pipes and valves open ( no twist or foreign objects inside pipes blocking). Lube oil for what? Any particles that could gather in pockets or dry to blocking? Lubeoil to cold (viscosity wrong for design) etc. etc.

 

[Compositepro]

It is also possible that the cooling water flow and oil flow are relatively high and that the exchanger area is relatively low so you will not see a large change in temperature of the water or the oil. This may be intentional design. You want the lube oil to be warm, just not too hot.

 

[racookpe1978]

New construction?

Look for "real flow" - blockage, bad valve, bad controller lineup, construction debris, blind flange left in a spool ...... Anything can stop flow - and unless you've boroscoped all of your pipelines as each is turned over, its very, very easy to leave garbage inside what you think is a clean system.

 

[Iradah]

Thanks all, We have checked the whole system and there is no blockage, We just believe that there is no enough water flow because the flow has another easy way, but my question is can the configuration lead to poor heat transfer? as the flow is first counter current and then co current? (heat exchanger is shell and tube with the inlet and outlet of the shell on the top of the shell, inlet on right side and outlet on left side. the tubes are two passes with inlet and outlet nozzles above each other at the left side of the exchanger, the inlet is the top nozzle and the outlet is the bottom nozzle).

 

[MintJulep]

Consider that if there is NO FLOW at all then the water temperature will tend towards being equal to the oil temperature. No temperature difference = no heat transfer.

Could your "very small" indicated difference in inlet and outlet water temperature be attributed to instrumentation variability?

 

[crshears]

If the closure 'lid' on the end of the cooling water box has a septum [divider] in it and someone installs the head with the incorrect orientation, the cooling water could be bypassing the tubes instead of actually flowing through them [you would not think this could ever happen, but I actually encountered it once].

CR