Cooling tower design

[Salah 1]

Hi guys:
I was looking to find thermodynamic or aerodynamic section to put my threat in which is :
As i understand water cooling towers work on evaporation cooling principle, with the water temp drop depending on initial water temp and air initial temp and humidity or (wet bulb temp)!
now if my goal is to cool water down to as much as possible ,does any of the following seem practical:
Heating the upcoming air befor intering the tower
Reducing air humidity using baking soda or table salt or paper cellulose fiber befor intering the tower
The air in my area is at temp 23 at midday with humid about 18%,which gives me about 10 temp drop only..
Thank you.

 

[IRstuff]

Hi guys:
I was looking to find thermodynamic or aerodynamic section to put my threat in which is :
As i understand water cooling towers work on evaporation cooling principle, with the water temp drop depending on initial water temp and air initial temp and humidity or (wet bulb temp)!
now if my goal is to cool water down to as much as possible ,does any of the following seem practical:
1. Heating the upcoming air befor intering the tower
2. Reducing air humidity using baking soda or table salt or paper cellulose fiber befor intering the tower
3. The air in my area is at temp 23 at midday with humid about 18%,which gives me about 10 temp drop only..
Thank you.

The forum you're looking for is Heat Transfer & Thermodynamics engineering but refrain from double posting, although it's unclear whether you can delete your thread here and repost there.

In any case,
1. That's the opposite of what I think you want, which is to cool the water; making the air hotter reduces the temperature difference between the air and the water, which reduces the heat transfer
2. This is a continuous process, presumably, and you'd need truckloads of any of the stuff mentioned to do a dehumidification. While dehumidification is probably desirable, you're already at 18%, so it's not low hanging fruit.
3. Short of cooling the incoming air, the only viable measures would be more air flow and more surface area for the air to flow over. The heat transferred is a function of something like k * area * deltaT, where k is the heat transfer coefficient that is dependent on thermal conductivity, etc., but also dependent on the moving air mass over the heat exchanger.

Ultimately, you can think of what you have as an oversized swamp cooler.

 

[LittleInch]

If you're at 18% humidity you could install an evaporative cooler in front of your cooling tower but you would need a unit which exhausts the warm humid air separately.

And you need a supply of water.

 

[Salah 1]

Thank you guys.
By air heating I assumed the air humidity will drop which as I think is good for evaporation cooling which aims in my case to get max water temp drop.....
As for using some materials. As air moisture absorpers as you mentioned it will not be that easy with already low air humidity...
Thank you very much..

 

[georgeverghese]

You cannot expect better than a 3-4degC temp approach at the cold end of the cooling tower. So at 23degC air temp, cold water exit temp cannot be better than 26degC or so no matter how much countercurrent flow air you pull in with those ID fans. What is the exit cold water temp you are getting now ?

 

[Salah 1]

You cannot expect better than a 3-4degC temp approach at the cold end of the cooling tower. So at 23degC air temp, cold water exit temp cannot be better than 26degC or so no matter how much countercurrent flow air you pull in with those ID fans. What is the exit cold water temp you are getting now ?

A week ago , i got water temp drop of 10 celsius at 1:00 p.m (ambient air temp about 24 celsius,humidity 16 ,final water temp about 14 celsius) simply by putting a water bowl in the home surface with wind air passing through without any insulation..
That is why I expected more temp drop with cooling tower having much higher surface area, with much higher air flow.

 

[LittleInch]

Different things going on.

A cooling tower is counter flow so the warmer drier air starts at the bottom and then gets (cooler?) but more humid as it rises against the flow of water coming the other way.

So there is no way your water at the bottom of the tower is going to be colder than the air coming the other way or it will start to cool the air.

What you're describing is an evaporative cooler. whilst this could work I would ask how much water and how long did it take to cool your bowl of water?

 

[EdStainless]

In your example of 24C temp and 16%RH your wet bulb temperature would be 11C.
Reaching 14C is a lot closer than I would expect in a cooling tower.
The size and style of the tower matter, as does the fill material.
You can consult the Cooling Tower Institute for some information.
One caution, the last time that I looked a small fraction of all cooling towers were actually performance tested.
And of those tested less than 50% achieved their design performance.

 

[Salah 1]

Different things going on.

A cooling tower is counter flow so the warmer drier air starts at the bottom and then gets (cooler?) but more humid as it rises against the flow of water coming the other way.

So there is no way your water at the bottom of the tower is going to be colder than the air coming the other way or it will start to cool the air.

What you're describing is an evaporative cooler. whilst this could work I would ask how much water and how long did it take to cool your bowl of water?

 

[Salah 1]

Different things going on.

A cooling tower is counter flow so the warmer drier air starts at the bottom and then gets (cooler?) but more humid as it rises against the flow of water coming the other way.

So there is no way your water at the bottom of the tower is going to be colder than the air coming the other way or it will start to cool the air.

What you're describing is an evaporative cooler. whilst this could work I would ask how much water and how long did it take to cool your bowl of water?

You are right ,I assume in case of cooling tower the outlet air from top shoud be more humid and cooler than inlet air from below..
I have not checked yet what air outlet temp because my goal is to cool water no matter what happens to the air...
That is why we feel cold breezes of air coming from far (where it is raining) to our area where ( no rain )with air temp around us is above 22 celsius the reason I guess evaporative cooling takes place where the rain is and the coming wind air is cold enough to feel something is wrong..
Now for the water bowl test : I got as I said final water temp of 14 celsius without any insulation
Ambient air about 24 celsius
Hum about 16...
This was about a week ago..
This week the temp during the day might still around 24 from 10 am up to 15 pm, but the humidity got higher today it is about 26 because the winter in the horizon and while temperature might not change alot but humidity is going up ..

 

[Salah 1]

Different things going on.

A cooling tower is counter flow so the warmer drier air starts at the bottom and then gets (cooler?) but more humid as it rises against the flow of water coming the other way.

So there is no way your water at the bottom of the tower is going to be colder than the air coming the other way or it will start to cool the air.

What you're describing is an evaporative cooler. whilst this could work I would ask how much water and how long did it take to cool your bowl of water?

Thank you guys for your interaction, I really appreciate it..

 

[Salah 1]

Different things going on.

A cooling tower is counter flow so the warmer drier air starts at the bottom and then gets (cooler?) but more humid as it rises against the flow of water coming the other way.

So there is no way your water at the bottom of the tower is going to be colder than the air coming the other way or it will start to cool the air.

What you're describing is an evaporative cooler. whilst this could work I would ask how much water and how long did it take to cool your bowl of water?

For those information about how much water in the bowl and what time required! The water bowl is small enough about 12 cm diameter from bottom and about 15 cm from above with water thickness about 3-4 cm .
For the time I need to check it but sure more than 3 hours..

 

[georgeverghese]

Error in my last post - I meant approach to wet bulb temp would be no less than 3-4degC. This is what you've got now - with RH =18%, wet bulb temp of 10-11degC, exit water temp 13degC

 

[pierreick]

Hi,
Probably good to read.
Pierre