Rating of Wet surface Air cooler

[avkale]

We have existing Wet surface air cooler but the calculations for the same are not available.
I am analysing to check wther the same exchanger can be used for higher heat load. The heat load is increased due to increase in preocess stream feed temperature. I need to keep the process stream outlet temperature same as before to keep same load on downstream hydrator.
Are there any methods for rating available? Can simulator be used for this purpose.
Breif description of Wet Surface air cooler.
The precess stream is in tubes. Water is sprayed on Tubes. The Air and water flows co currently as crossflow over the tubes. When air and water reaches basin the Air path is changed by 90 Degress. Induced fan removes the Air.
Therefore Air at ambient temperature ( Ranging 45 Deg in Summer to say 15 deg winter)mixes with water at Wet bulb temperature. Water picks up the heat from the process fliud flowing tubes. Air provides turbulance. The water evaporates into air and finally reaches the basin at wet bulb temperature. Therefore it is combination of Air cooler and cooling tower.

 

[rmw]

What is your current approach to ambient temperature with this cooler?

rmw

 

[avkale]

The current process Gas temperature inlet/ outlet temperature is 42.8/ 29.4 deg C
The wet bulb temperature of water leaving the basin is 22.8 deg C.
Aitr inlet is 45 deg C
The approach Process Gas outlet- water outlet is 29.4-22.8=6.6 deg C

Regards,

 

[rmw]

The WSAC Mfg'r advertises 5.55C as their best approach to wet bulb. Therefore it would seem like you still have room for some more heat load before you reach that limit.

Cooling towers with the best technology can get to 3.88C of wet bulb. Frankly, I don't see why the WSAC Mfg'r doesn't use some cooling tower fill below the tube bundle (and before the 90 degree air turn) to get a closer approach to wet bulb, but that doesn't help you.

rmw

 

[willard3]

If the unit is still made, the mfg can model it for you.....contact them.

 

[avkale]

Thanks for the suggestion. I am making contact with equipment vendor. But I want to understand how do we represnt this senario mathamatically. The hot air based on Ambient condition comes in contact with spray water which is falling on tubes. As Air passes down with water it gets humidified and cooled. Then both contribute to the cooling of process gas( Which is flowing through tubes). The water which is sprayed on tubes is actualling making a film around the tubes and cooling the tubes. As the heat is taken from Process gas by water, Air cools this water. By the time water reaches the basin is again cooled to wet bulb temperature. The complete mechanism is quite exiting and possible errors in design calculations will have large impact on operation. Can someone help??

 

[rmw]

Your explanation gives me a headache, not that it might not be right.

The process gas cooling comes from sensible heat transfer from the water flowing over the tube surface separating the water from the process. Since the theory is that the tube surface is constantly wetted, there should be no sensible heat transfer from the air.

In that process (not to be confused with your process process) the water gains heat. The air flowing down with the water is heated by the water through both evaporation and some sensible heat transfer if the water becomes hotter than the air. In the process of giving off its latent heat to evaporation, and the sensible heat transfer to the air, the water cools.

The heated and moist air is evacuated from the unit by the fans carrying the process heat rejection away.

rmw