3 replies to this topic

[Anthony429]

My company is trying to improve the cooling capacity of their lagoon, which is situated at the base of a hill. The water current dumps directly from a clarifier at the top of the hill into the lagoon from three large pipes. I had the idea to use the currently unused pressure head in a series of nozzles to spray the water out into the lagoon, thereby increasing the contact surface area of the water to the air. As the cost for this would be relatively low (piping and nozzles) with little to no maintenance costs, my manager liked the idea. However, he wants an estimation of what kind of cooling this should provide. This involves the modeling of water droplets through air in roughly 2-D, and is not a simple problem. I was wondering, as I am fresh out of college, if anyone who has more experience in this area can either direct me to a source (website or book) that would be able to answer my questions, or provide some general equations to approximate the expected cooling amount. The important numbers for the time of year when we would really need the cooling are as follows:

Ambient Air Temp: 85 degrees F
Relative Humidity: 50%
Pressure: Sea Level
Avg wind speed: 6 mph
Initial water temp: 100 degrees F
Droplet time in air: 2 seconds
Droplet size: ??? 150 um sound reasonable?

Let me know if there is more key information I need to provide. Thanks,

Anthony

[ankur2061]

My company is trying to improve the cooling capacity of their lagoon, which is situated at the base of a hill. The water current dumps directly from a clarifier at the top of the hill into the lagoon from three large pipes. I had the idea to use the currently unused pressure head in a series of nozzles to spray the water out into the lagoon, thereby increasing the contact surface area of the water to the air. As the cost for this would be relatively low (piping and nozzles) with little to no maintenance costs, my manager liked the idea. However, he wants an estimation of what kind of cooling this should provide. This involves the modeling of water droplets through air in roughly 2-D, and is not a simple problem. I was wondering, as I am fresh out of college, if anyone who has more experience in this area can either direct me to a source (website or book) that would be able to answer my questions, or provide some general equations to approximate the expected cooling amount. The important numbers for the time of year when we would really need the cooling are as follows:

Ambient Air Temp: 85 degrees F
Relative Humidity: 50%
Pressure: Sea Level
Avg wind speed: 6 mph
Initial water temp: 100 degrees F
Droplet time in air: 2 seconds
Droplet size: ??? 150 um sound reasonable?

Let me know if there is more key information I need to provide. Thanks,

Anthony

Anthony,

If you are a chemical engineer just out of college then surely you would be familiar with Perry's Chemical Engineering Handbook. In Perry, the chapter about 'Evaporative Cooling' has a section on 'Spray Ponds'. Go through it & I am sure it will help you to understand the concept of spraying for cooling. Happy reading.

Regards,
Ankur.

[Anthony429]

Ankur,

First off, thank you for your reply. Unfortunately, I have consulted Perry's already, which is always a good place to start :-P. The only one I have is from 1950, and the spray pond section covers less than half a page. There are some correlations I could make to a cooling tower and use the time in air for each droplet to determine a 'height' to reach a final temperature, but this answer is separate from droplet size, assumes 1-D droplet movement, a consistent air flow direction, and is more a function of film cooling. It would be in the ballpark, but I was wondering if there was perhaps something more accurate. Or do you think that this would yield an answer that would be accurate enough for what someone can expect in industry?

Anthony

[ankur2061]

Ankur,

First off, thank you for your reply. Unfortunately, I have consulted Perry's already, which is always a good place to start :-P. The only one I have is from 1950, and the spray pond section covers less than half a page. There are some correlations I could make to a cooling tower and use the time in air for each droplet to determine a 'height' to reach a final temperature, but this answer is separate from droplet size, assumes 1-D droplet movement, a consistent air flow direction, and is more a function of film cooling. It would be in the ballpark, but I was wondering if there was perhaps something more accurate. Or do you think that this would yield an answer that would be accurate enough for what someone can expect in industry?

Anthony

Anthony.

Do yourself a favor & get hold of the 7th or 8th edition of Perry. So much has changed since 1950.

Although I am not an expert on spray ponds & have never done or encountered any 2-D modelling, I still know that the guidelines as given in Perry (refer Table 12-3, 7th edition) should help in getting some preliminary sizing numbers.

SPX cooling technologies (formerly Marley Company) are pioneers in the field of evaporative cooling. They designed the very first cooling towers for the CPI. They are also active in spray ponds & you might want to talk to their local representative in your area & get some answers on the subject.

Hope this helps.

Regards,
Ankur.