Dear All ,
Kindly i have a question , and i am a little bit confused about H2s Calculations in sewer gems.
First Of all i have seen this article and it understand it well :
Modeling septicity / hydrogen sulfide (H2S) .
In this article i understand that SewerGems uses Pomeroy Parkhurst Equation to predict H2S formation
Then i want to verify if that formula is really used inside the Sewer-gems . what i did is make a simple model consist of 1 line only and compare the result from sewer-gems with result from excel sheet using Pomeroy Parkhurst Equation .
Result from model is shown below and data from model is shown below
The Sewergem model based on the above data give me a H2s result = 0.16487 mg/l
using excel sheet and applying Pomeroy Parkhurst Equation on the above data that i get from sewer gems , then unforuntly i did not get the same result !!!?
is there is some thing wrong inside sewer-gems programming , is sewer gems does not use the same formula or did i make a mistake ?
this is the result from the excel sheet i get H2S = 0.1114 mg/l
Sewergems model is here
H2s Model.rar
Hello Khalid,
The equation used by SewerGEMS is as below;
The above equation is the Pomeroy-Parkhurst equation in English units..
The equation you have shown seems to be in SI units. In SewerGEMS, the English units are used and the output is converted to SI units. This could be happening in your case.
Please check your model for the formula given above. You can also find it in the help section of SewerGEMS under Theory > Hydrogen Sulfide Modeling.
Hope this helps.
Regards,
Yashodhan Joshi
First of all , thank you for your continues efforts and for your time Yashodhan ,
in my opinion it is not an English or SI unit issue , i have already checked this before asked this question . the output in both equation is a concentration which is [mg/l] the factor 3.28 and 2.1 is used in English equation to convert the meter to feet . and after checking i found that the English formula give the same result for SI formula
i have post this question after too many trials trying to know what is the correct formula that SewerGems is using to predict the H2S , i know that theory > hydrogen sulfide in help section stated that this formula but when applying this formula on excel the same result is not achieved !! ,
All variables in equation such as : hydraulic radius , velocity , detention time , etc . is extracted through SewerGems Flex Tables .
Noting that i always verify each result from SewerGems using excel formulas and always there are match between result is happened, unfortunately H2S analysis take from me so much time in order to verify the result .
I think if a quick clarifying example with numbers is carried out by one of Bentley's Seniors or technical support member showing the application with number in H2S equation this will be an appreciated and grateful step from all Bentley community .
Bentley Communities is renowned by its full engaged technical supporter and its friendly interaction between it member .
Regards
Make sure that the precision for the values taken from the flextables are relatively high. I would suggest using a precision of 6 places after the decimal place. This will limit any issues caused by rounding errors.
It might be useful to see a copy of the your model and Excel files.
Scott
it is not an rounding errors issue i have already used 6 precision
Can you provide your model files and spreadsheet to us? This link has the steps to do this.