Change in oxygen concentration in water with temperature

[kmlucy]

Hi all,

I have a vessel, in which a fixed volume of water is in equilibrium with 10% oxygen gas. 10% oxygen and balance nitrogen gas is continuously pumped in to the vessel.
I am interested in knowing what will be the effect on oxygen concentration if the temperature of the water is raised from 20 C to 40 C.
I know that solubility of oxygen decreases with increase in temperature.
Let's suppose that solubility decreases by 20% when water is heated from 20 c to 40 c, will the concentration of the oxygen in water decrease by 20% as well?
what equations should i use to calculate the change in oxygen concentration in water with change in temperature?

Thanks

 

[siretb]

HI

use Henry's law p=H x (for x<<1)
be careful of units used
p is the Partial pressure of oxygen

x(weight fraction)
log10(x) =-1074.05 +29325/T°K +428.99 log10(T) -0.0326T 273<T<348
for 1 atmosphere of O2 (pO2=1 atm)
if you have only 10%, you'll get one tenth as per Henry's law.

the above formula gives 47 mg/l p=1 atm so 10% would be 4.7 mg/l 20°C and 3.3 mg/l at 40°C

Hope this helps

 

[ione]

http://www.engineeringtoolbox.com/air-solubility-water-d_639.html

Please consider pressure and water salinity will play a role as well.

 

[zdas04]

Henry's law has a reasonably consistent change with pressure, but the change with temperature is much more complex. I looked into this a couple of years ago and found that researchers could not agree on the direction of the change with temperature, let alone the magnitude. There are probably 50 learned papers on the interwebz (mostly PhD theses) describing experiments and conclusions, but zero agreement. Some say that temperature effects are insignificant. Some say that solubility will increase with increasing temperature. Some say that solubility will decrease with increasing temperature. Some say that the effect varies for different gases.

Most of them provide a complex empirical equation (no two are similar) to predict the magnitude. My conclusion for my project was that the magnitude of the change in solubility with temperature was indeterminate.

David

 

[ione]

I can agree on the fact there is an incertitude in the magnitude of the change in solubility with temperature, but I certainly disregard those studies which say that solubility will increase with increasing temperature. Amongst the boiler feedwater treatments it is well established the use of dearators which basically rely on the fact dissolved gases (oxygen and carbon dioxide) decrease their solubility in water as temperature increases.

 

[zdas04]

Since they only publish doctoral theses when they have been successfully defended, there are a number of review comittees in the world that don't accept your "well established" observations.

I don't have a dog in this hunt. The project I was working on when I did my desktop research is long over. I found most of the papers I read to be at least plausible.

David

 

[ione]

It's a sad day for the dearators manufacturers!

 

[zdas04]

Don't know about that. Some of thoes papers were written in the 1980's, so their impact is probably diluted by 30 years of being ignored. Equipment manufacturers are much like chemical salesmen--the only objective fact is next quarter's profit.

David

 

[rmw]

Having spent most of my career involved in the ramifications of the soluability of dissolved gases (principally air) in power plant water - BFW and condensate, cooling water, etc with respect to the detrimental results thereof: corrosion, etc., I find some of what is said above laughable. Deaerator manufacturers are still safe even if their salesmen are scum.

Sorry but I didn't believe a lot of what was said to me by PHD's in University (based experience already gained while working my way through an engineering education) and I haven't changed that outlook. Most of them just need to get their hands dirty. I think most of the basic science on the soluability of gases in water was settled long before the Internet was invented by Al Gore. We can continue to quibble on the exact numbers, however since it is difficult to quantify.

Those who have to get the oxygen out or pay the price for the consequences have no dispute with Henry's Law.

I likewise did some research on Henry's Law with respect to air dissolved in water (especially under pressure) about 2 years ago and observed that oxygen is more soluable in water than Nitrogen, so the ratio of 21/79% O2/N2 in air respectively in water does not result in a 21/79% dissolved ratio in water but I don't remember what the final number is - it isn't too greatly different, but guaranteed not 21/79% and I am too lazy to walk across the house to my work computer and look it up.

To the OP, Google "Henry's Law" and start reading and you can get your homework assignment done.

rmw

 

[25362]

It has been shown that thermal pollution of lakes and rivers, by a temperature increase of a few degrees, with the consequent reduced oxygen solubility, can harm fish and may affect the ecosystem composition.

 

[ione]

http://www.nist.gov/data/PDFfiles/jpcrd219.pdf

 

[rmw]

25362,

It has been shown that mother nature by heating up the rivers and lakes in the summer time can kill fish and affect the ecosystem composition.

Fish kills in the deep south of the USA where I have lived most of my life are a ho-hum event. Sad to see such beauties floating belly up and in such numbers, but hey, that's life.

rmw

 

[unclesyd]

Checkout the two links below. The USGS link has calculator that covers temperature to 40C, while the second is a table that goes to 50C.

http://water.usgs.gov/software/DOTABLES/

http://www.insiteig.com/pdfs/solubility-of-oxygen-in-water.pdf

 

[rmw]

Unclesyd

I didn't open the first one, but I recognize it a site I have used in my day job.

I've seen the second one, but since my need didn't involve salt water I didn't dwell on it.

rmw