Ammonia Evaporative Condenser HELP URGENT

[jaypz36]

Hi! I am a 3rd year mechanical engineering student in the philippines. i have a design project on Ammonia Evaporative Condenser. Here are the given values for my design project.

1000 TR
water/air 30 degrees celcius, 70 % relative humidity
with refrigerant ammonia(NH3) 98 degrees celcius


i have little knowledge about condenser, and i have checked on books, and have found formulas for this type of condenser. the problem is, how do i start? what should i solve first? thank you very much. i hope someone could help.

[mad fridgie]

Is the NH3 98C a typing mistake?

[jaypz36]

Is the NH3 98C a typing mistake?

sorry mate. it should be 48C.

[jaypz36]

is the 48C the condensing temperature? how about the 30C is it the wet bulb temperature?

[mad fridgie]

1 calculaute total heat of rejection (THOR)
2 Calculate water that needs to be vaporized to meet THOR
3 Decide the split of air in and air out of the condensor.
4 calculate the thermal properties of the air to achieve the above (air flow)
5 calculate surface area of heat transfer tubes.
6 calculate falling water volume to achieve above. (pump size)
7 calculate air velocities to ensure minimum carry over (physical size of the unit)
8 design water distribution/ heat configuration.
9 allow for removal TDS and carry over for make up system.
This should be enough for a project

[Brian_UK]

Why do all students have URGENT questions ?

Answers on a postcard to .......

[US Iceman]

48C condensing on an evaporative condenser???

That example is insane and not at all practical. No one should contemplate using that high of a condensing temperature. First off the condensing pressure will be very high for ammonia. Second, the suspended solids will stick to the metal very quickly even with excellent water treatment in place.

This serves no purpose other than an exercise in solving a questionable application.

I realize this may be a homework problem, but please, do not think this is a typical operating condition. It's not!

[Magoo]

You and me US Iceman

[Magoo]

Brian - UK.
It always urgent due to completing projects that the student is cramming for.
Bare in mind that these same individuals will be specifying system designs and equipment sooner than latter down the track some where.
Then we all endure there folly and ignorance. Remember there disclaimer on the bottom of each spec., page.
I want a job like that, expensive but if it doesn't work don't ring me!!

[US Iceman]

Bare in mind that these same individuals will be specifying system designs and equipment sooner than latter down the track some where.

That's what gets me so excited when I see questions like this. They are some academic exercise that is founded on some aspect of working theory but not at all based on practical applications. Seeing something like this from a professor lends some credence to suitability by the untrained and might suggest a starting point for actual designs.

If the student has to guess about applications because a professor suggested something unwise, how will anyone be better equipped to do designs?

This is no way to teach new students....

[Grizzly]

Second, the suspended solids will stick to the metal very quickly even with excellent water treatment in place.

Hi Iceman.

I find the above interesting!
As I stated recently in another post.
I am seeing the results of this very issue, out in the field.
Where more and more "clients" are converting simple drain down head cooling.
Using a water pump and the Evaporative Tower sump water.
Resulting in heavy deposits being left in the colling jackets.
I believe it is the phosphates that are coming out of suspension.

Call me cynical but the contamination seems proportional.
To whether the chemicals are paid for by the Customer or the chemical company!

Could you elaborate a little more?
At what sort of temperature do you envisage the "splitting of the chemicals?
Cheers Grizzly

[US Iceman]

Hi Grizzled one.

First issue: I'm not a water treatment specialists.

It is mt understanding the water temperature and TDS content are based on something called the Langelier Index. Further info below in links...

http://corrosion-doctors.org/Cooling...-Langelier.htm

http://www.arvanitakis.com/galeries/langelier_index.htm

As the metal surface temperatures increase there is a greater likelihood that minerals will precipitate out and stick. This is further exacerbated by higher water temperatures also as it allows the minerals to gain a higher solubility in the water.

The stuff sticking to heads is probably calcium and magnesium carbonates (I think that's right). Since the heads are a lot hotter than anything else it really wants to stick there.

Water treatment is supposed to allow higher cycles of concentration so that the blow down is reduced. If something goes wrong you have a lot of junk in the water that wants to stick to the hot metals.

What I have always used as a general rule is to keep the cycles of concentration below 3 and the water temperature well below 90°F (32.2°C). That low of a water temperature should not be an issue since it is largely predicated on the entering wet bulb temperature of the air.

I have maintained throughout the years that water treatment is bit like black magic and voodoo!.

[Magoo]

US Iceman.
Some how this forum has to short-cut the system and get to the so called Professors of our industry, start going forward with training and educating the next generation of design and specifying professional engineers. From my point of veiw, part of their "education " should be a pair of over-alls and a set of tools and apply their training in the feild of hard knocks.
Do you read any of the garbage published by these professors, they have never left the office. Absolute theory and no-practicul crap.

[US Iceman]

US Iceman.
Some how this forum has to short-cut the system and get to the so called Professors of our industry, start going forward with training and educating the next generation of design and specifying professional engineers. From my point of veiw, part of their "education " should be a pair of over-alls and a set of tools and apply their training in the feild of hard knocks.
Do you read any of the garbage published by these professors, they have never left the office. Absolute theory and no-practicul crap.

No argument form me on any of those points. They probably don't have time to get their hands dirty.

[Magoo]

US Iceman.
Yes they are all too busy pontificating their pet subjects on ashtray,( aka ashrea) and giving seminar speals for their own salary gain all around the globe.
You and I live with their folly, current speal is the plonkers in suits that rock up to clients and sell their services to save power costs. What really annoys me is they listen to them and pay truck loads of money for the con.
My response for a plant that is operating efficiently given the age, to save save power costs, "turn everything off " , screw quality, save money, money , money !!!.

[Gary]

No argument form me on any of those points. They probably don't have time to get their hands dirty.

Yep... we live in a world run by smoke and mirrors... where image trumps substance... where everyone wants to know, but nobody wants to learn... where everyone wants to be there, but nobody wants to get there.

[Frickman]

Man yall are brutal!!!l LOL, but I agree totally. I am a degreed engineer and argue with engineers every day because they do not get in the field. I recentaly had and engineer at a company want to put a high stage screw compressor using ammonia on their main head pressure of 170psig. so therefor their suction pressure for the compressor would be the system head pressure. LOL I asked him if he was somking crack. Then asked him if he remembered the hendinberg!

[US Iceman]

I recentaly had and engineer at a company want to put a high stage screw compressor using ammonia on their main head pressure of 170psig. so therefor their suction pressure for the compressor would be the system head pressure. LOL I asked him if he was somking crack. Then asked him if he remembered the hendinberg!

Not brutal, just brutally honest!

On the quote above, it's not entirely wrong. What you describe is a staged heat pump. The ability to do this is limited by the heat pump compressor design and operating envelop for the compressor.

Sabroe did this with some special recip. compressors. And yeah, the discharge on the heat pump compressor gets sorta' hot!

[sterl]

Actually Frickman: A circuit utilizing ammonia condensers as heat pump suction and appropriate compressors, etc. is operating today retrofitted to a plant Frick built with Delta Streams (Check that one in the archives...) in 1966. Retro HP arrangement uses transcritical 2-component and blanketed gas and R-502 compressors....

See also district heating arrrangement presentation by Star plus Vilter, March 2009 IIAR conference.