The image above represents water activity. To calculate water activity, two essential parameters are needed, and these parameters are the Partial Pressure of Water (Pw) and Equilibrium Vapour Pressure of Water at the Same Temperature (V.P.w).
The formula for calculating water activity:
aw = Pw/V.P.w
Where:
aw = Water Activity | Drying
Pw = Partial Pressure of Water
V.P.w = Equilibrium Vapour Pressure of Water at Same Temperature
Let’s solve an example;
Find the water activity when the partial pressure of water is 22 and the equilibrium vapour pressure of water at same temperature is 28.
This implies that;
Pw = Partial Pressure of Water = 22
V.P.w = Equilibrium Vapour Pressure of Water at Same Temperature = 28
aw = Pw/V.P.w
So, aw = 22/28
aw = 0.78
Therefore, the water activity is 0.78.
Calculating the Partial Pressure of Water when the Water Activity and the Equilibrium Vapour Pressure of Water at the Same Temperature is Given
Pw = aw x V.P.w
Where;
Pw = Partial Pressure of Water
aw = Water Activity | Drying
V.P.w = Equilibrium Vapour Pressure of Water at Same Temperature
Let’s solve an example;
Find the partial pressure of water when the water activity is 24 and the equilibrium vapour pressure of water at same temperature is 14.
This implies that;
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aw = Water Activity | Drying = 24
V.P.w = Equilibrium Vapour Pressure of Water at Same Temperature = 14
So, Pw = aw x V.P.w
Pw = 24 x 14
Pw = 336
Therefore, the partial pressure of water is 336.
Read more:Â How to Calculate and Solve for Entropy of Water | Enthalpy
Calculating the Equilibrium Vapour Pressure of Water at the Same Temperature when the Water Activity and the Partial Pressure of Water are Given
V.P.w = Pw / aw
Where;
V.P.w = Equilibrium Vapour Pressure of Water at Same Temperature
aw = Water Activity | Drying
Pw = Partial Pressure of Water
Let’s solve an example;
Find the equilibrium vapour pressure of water at the same temperature when the water activity is 10 and the partial pressure of water is 30.
This implies that;
aw = Water Activity | Drying = 10
Pw = Partial Pressure of Water = 30
V.P.w = Pw / aw
Then, V.P.w = 30 / 10
V.P.w = 3
Therefore, the equilibrium vapour pressure of water at the same temperature is 3.
How to Calculate Water Activity Using Nickzom Calculator
Nickzom Calculator – The Calculator Encyclopedia is capable of calculating the water activity.
To get the answer and workings of the water activity, use the Nickzom Calculator – The Calculator Encyclopedia. First, you need to obtain the app.
You can get this app via any of these means:
Web – https://www.nickzom.org/calculator-plus
To get access to the professional version via the web, you need to register and subscribe for NGN 2,000 per annum to have utter access to all functionalities.
You can also try the demo version via https://www.nickzom.org/calculator
Android (Paid) – https://play.google.com/store/apps/details?id=org.nickzom.nickzomcalculator
Android (Free) – https://play.google.com/store/apps/details?id=com.nickzom.nickzomcalculator
Apple (Paid) – https://itunes.apple.com/us/app/nickzom-calculator/id1331162702?mt=8
Once, you have obtained the calculator encyclopedia app, proceed to the Calculator Map, then click on Materials and Metallurgical under Engineering.
Now, Click on Ball Mill Sizing under Materials and Metallurgical
Now, Click on Water Activity under Ball Mill Sizing
The screenshot below displays the page or activity to enter your values, to get the answer for the water activity according to the respective parameters which is the Partial Pressure of Water (Pw) and Equilibrium Vapour Pressure of Water at Same Temperature (V.P.w).
Now, enter the value appropriately and accordingly for the parameter as required by the Partial Pressure of Water (Pw) is 22 and Equilibrium Vapour Pressure of Water at Same Temperature (V.P.w) is 28.
Finally, Click on Calculate
As you can see from the screenshot above, Nickzom Calculator– The Calculator Encyclopedia solves for the water activity and presents the formula, workings and steps too.
