Tangential method

Basically it is only possible to determine a wall thickness change in penetration direction from a density variation of a radiographic film. No absolute wall thickness values can be obtained in this way contrary to the tangential method. 

Tangential method for finding optimum time for maximum amount of heat transfer in evaporator with scale formation. 

Figure 5.15 Amount of portlandite measured by TGA (filled circles tangential method) and as free lime (empty circles measured according to Franke [1941]) CH dry = CH wet normalised to dry weight (diamonds), i.e. to the weight at 6S0°C. The relative measurement error of 5% to 10% is indicated by the dotted lines. (Data from Lothenbach, B., and F. Winnefeld, Cement and Concrete Research, 36(2), 209-226, 2006.)...

In literature, generally either the so-called stepwise or the tangential method is used to quantify portlandite. Figure 5.16 shows the effect of the stepwise and tangential methods on the quantification of portlandite in a... 

The tangential method assumes that the weight change due to the presence of C-S-H or other hydrates observed before and after the peak will continue (linearly) in the portlandite region. Such a correction results in the quantification of the portlandite weight loss only and is equivalent to... 

Figure 5.17 Amount of portlandite determined in a hydrated cement (blend of 50 wt.% Portland cement, 20% slag, 25% fly ash and 5% limestone [Scholer et al. 2015] hydrated for 196 days) and in the hydrated cement after the addition of 14 wt.% of portlandite tangential method (5.5 + 14 wt.%) and stepwise method (6.3 + 16.6 wt.%).

For the quantification of portlandite the tangential method is suggested, as discussed in Section 5.4. 

Tangential method is to directly take the tangent at the contact point after digitization of the drop profile. This method is a curve-fitting method and may have large errors due to disturbance in the drop shape caused by dust particles or contaminants or surface irregularities. 

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