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TDS - Density relationships


thassell
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Hi Tom,

 

I have been questioned on the relationship between calculated TDS and Density outputs in SpecE8 and was wondering if you might be able to provide some insight.

 

Two water compositions, with very different TDS (confirmed by field EC measurements) had very similar density.

 

SpecE8_output_SE_run4: TDS 1.0 mg/L Density 1.018 g/cm3 T = 18 deg C

SpecE8_output_SE_run16: TDS 34561 mg/L Density 1.017 g/cm3 T = 18.5 deg C

 

I noticed that an automatic density calculation is based on chlorinity and temperature. For both of these anaylses, Chlorinity is 0.00 molal. I can't see where or how chlorinity is caluclated or input.

 

Could you please give me a few ideas?

 

Cheers

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I noticed that an automatic density calculation is based on chlorinity and temperature. For both of these anaylses, Chlorinity is 0.00 molal. I can't see where or how chlorinity is caluclated or input.

 

Could you please give me a few ideas?

 

Cheers

 

Hi:

 

I'm going to post a brief response, which is not yet a direct answer to your question- I am in the process of locating the reference that describes the relationship between chlorinity, temperature and fluid density.

 

Below is the notation from the v8 GWB Reference Manual regarding the density command:

 

density.jpg

 

I'll follow this up with more detail about the actual calculations used.

 

Regards,

 

Tom

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Hi Tracey:

 

The attached PDF describes in detail how fluid density is derived from salinity and temperature.

 

Let me know if you have any further questions.

 

Regards,

 

Tom

 

Thanks Tom,

 

I can see how density would be calculated. What I can't seem to work our is why Chlorinity is reading as 0.00 molal. The second sample:

 

SpecE8_output_SE_run16: TDS 34561 mg/L Density 1.017 g/cm3 T = 18.5 deg C

 

has a composition similar to that of seawater i.e. NaCl dominated (which has an average chlorinity of 0.058 mol/kg - Stumm and Morgan). Does GWB calculate this automatically, and if so is there a command to run it. It seems as if the density of two samples I quoted as an example in the first post has been calculated based on a variable temperature only.

 

If you can help me that would be great.

 

Cheers

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Thanks Tom,

 

I can see how density would be calculated. What I can't seem to work our is why Chlorinity is reading as 0.00 molal. The second sample:

 

SpecE8_output_SE_run16: TDS 34561 mg/L Density 1.017 g/cm3 T = 18.5 deg C

 

has a composition similar to that of seawater i.e. NaCl dominated (which has an average chlorinity of 0.058 mol/kg - Stumm and Morgan). Does GWB calculate this automatically, and if so is there a command to run it. It seems as if the density of two samples I quoted as an example in the first post has been calculated based on a variable temperature only.

 

If you can help me that would be great.

 

Cheers

Hi:

 

Would you mind sending me the actual SpecE8 script?

 

If confidential, simply email it to me at gwb@rockware.com

 

Regards,

 

Tom Meuzelaar

RockWare,Inc.

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  • 2 weeks later...
Hi:

 

Would you mind sending me the actual SpecE8 script?

 

If confidential, simply email it to me at gwb@rockware.com

 

Regards,

 

Tom Meuzelaar

RockWare,Inc.

 

Thanks for sending me your script.

 

It turns out that the issue is that GWB does not calculate chlorinity when the phreeqc, wateq4f and minteq datasets are used, because of slight formatting differences.

 

There is a simple work-around- in the element list for either of the 3 databases, change the entry for chlorine from:

 

Cl			  (Cl)		  mole wt.=   35.4530

 

to:

 

Chlorine			  (Cl)		  mole wt.=   35.4530

 

You can use the default database (thermo.dat) for reference, since it has the correct formatting.

 

We'll address this issue formally in the upcoming patch 8.0.2.

 

Apologies for the inconvenience,

 

Tom Meuzelaar

RockWare, Inc.

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