Air Cooler UA when it rains
Air Cooler UA when it rains
(OP)
Hi,
I have an air cooled heat exchanger that is partially condensing a water/gylcol mixture. We have concerns that, when it rains, the partial condenser will turn into a total condenser and as such will reduce the pressure in the overheads line.
Basically, the exchanger will change from being a standard air cooler to being a wet surface air cooler (ie. an evaporative air cooler).
We are going to simulate this effect (using Hysys.Plant) however I need to know how much the UA will increase when it rains.
Noraml U value is 31.0W/m2°C with a finned area of 436.6m2.
Thanks for your help,
Paul
I have an air cooled heat exchanger that is partially condensing a water/gylcol mixture. We have concerns that, when it rains, the partial condenser will turn into a total condenser and as such will reduce the pressure in the overheads line.
Basically, the exchanger will change from being a standard air cooler to being a wet surface air cooler (ie. an evaporative air cooler).
We are going to simulate this effect (using Hysys.Plant) however I need to know how much the UA will increase when it rains.
Noraml U value is 31.0W/m2°C with a finned area of 436.6m2.
Thanks for your help,
Paul





RE: Air Cooler UA when it rains
I agree the UA will change ,due an a change in the U value
which is approximately of 1/U = 1/hi +1/ho + t/k
hi = tubes-inside heat transfer coefficient
ho = tubes-outside heat transfer coefficient
t = tube wall thickness, k= tube metal thermal coductivity
And the main cause for the increase is the variation in (ho)
the main change,on a rainy day will be an increase in (ho) wich will improve the U value ,causing more vapors to condense.
A common practice by the industry,to overcome excessive condensation,is to have a bypass line with a pressure control valve (PCV) ,that is actuated by a Pressure Controller(PC) on the reflux drum..the valve can be sized to pass up to (20%) of the main flow to the condenser
Hysis dynamic simulation will give you the solution,provided you give it the appropriate input data.
Regards,
Whylie
RE: Air Cooler UA when it rains
RE: Air Cooler UA when it rains