Dear All,

I want to design Evaporative system/water showering system to lower the temperature of intake air for air cooled heat exchanger. I want to calculate quantity of water required to lower the temperature of air from 47C to 34C. Please suggest if I can perform this on Hysys. Or please refer any literature for designing. Also attaching the sketch.

Thanks in Advance.

Looks like a bad idea to me.

Bobby

It is not uncommon for people to spray firewater onto air coolers during high ambient temperatures to assist in cooling.  However, this is unwise to do for very long.  There are a number of concerns:

• Any dissolved solids in the water will deposit on the tube bundle or fan blades.  This can cause balancing problems for the fans and foul the fintubes, further reducing heat transfer.
• Moisture on a steel will cause corrosion.  Moisture and oxygen will corrode carbon steel, and if there are any chlorides in the water it will corrode stainless steel.  
• The mass/heat transfer will be too slow inside the plenum of the air cooler.  You cannot balance the water spray rates exactly (100% evaporation) which means water would be impacting the fans.  They were NOT designed for this and will be damaged.
• In order to work out the temperature drop, need air data - is 34C the wet bulb temperature?  If so, then you need 100% saturation of the air.  This might be achieved in a COOLING TOWER.

Like Mr. Strain, I would NOT attempt this.

haseeb2212:

You would be very wise to heed what Bobby Strain and Tech Bard have advised.  I add to this thread because of personal and negative results experienced in my early years as an engineer.

I was operating a gas plant, 2 years out of college, when a new, “cost effective” cooling process was introduced by corporate process engineers to one of the plants I was managing.  This was what was then called a “trombone” design for gas cooling.  A stream of hot, saturated CO₂ was to be cooled with water sprayed on top of vertical oriented pipe “hair pins” ( 3” pipes in zig-zag configuration using 180 degree returns.  We were using “clean” well water as the spray source.  In less than 2 weeks I had to shut down the entire processing plant to literally chisel out the various layers of calcined solids deposited on the pipes.  I took torch in hand and cut out the entire piping assembly, designed my own shell and tube exchanger and resumed operations after approximately a month of down time.  I’ll never forget this disaster and prime example of naive engineering design.  Unless you are talking about double- or triple-distilled water, all water is contaminated with some degree of solutes.  Water is the universal solvent and it should be respected as such.

Your idea of a water spray is valid from a thermodynamic point of view, taking advantage of evaporating water causing a cooling effect - much like human sweat.  But like human sweat, the evaporation always leaves behind contaminants and is not a very practical application in industry.  With human sweat one can bathe; in an industrial environment, it can cause hell.

Dear Bobby, Bard & Montemayor:

Thank you for your experienced inputs. I will review this again and will move to some alternative design.

Hi,

The question I want to ask is why do you want to cool the Air from 47 degC to 34 degC.

Maybe you should think of installing a water cooled heat exchanger at the upstream or the downstream of the air cooler.

Regards