Endress+Hauser NXA820 - Page 56

Calculations Tankvision
56 Endress+Hauser
Thermal expansion coefficient(s)
In the previous equations we have used two thermal expansion coefficients:
• α
1
= Linear thermal expansion coefficient
• α
S
= Area or surface thermal expansion coefficient
The first one represents the linear thermal expansion of the material of which the tank shell
is made. The second factor represents the squared or area thermal expansion coefficient.
It is of paramount importance that the factor used is in the correct engineering units, i.e. as
fraction per °C or fraction per °F.
The method for this calculation depends on what equation is to be emulated:
• In case of equation CTSh (3) = 1 + 2 * α * δT + α
2
* δT
2
In this case "α
S
" can be derived from "α
1
" by squaring, i.e. "a_tec" = "1_tec"
• In case of equation CTSh (4) = 1 + 2 * α * δT
In this case "α
S
" should be set to zero.
• For spherical and horizontal cylindrical tanks "α
S
" should be set to zero.
Please also make sure that the exponent value is considered when entering the value in
Tankvision.
For example if "α
1
" is set to be equal to "1.6 10^-5", while as engineering units shown is "10E-
7/°C", the "α
1
" value to be entered is "160".