Question: Plot 3d problem


I have a problem. I want to make plot 3d for pressure drop in diffuser by posuille formula,

plot3d(∫_0^l▒〖(128∙1.2∙〖10〗^(-3)∙〖10〗^(-14))/(π∙〖(d+2∙x∙tan⁡〖θ)〗〗^4 )  dx,d=0.1∙〖10〗^(-6)..1.5∙〖10〗^(-6),l=5∙〖10〗^(-6)..50∙〖10〗^(-6),axes=box,font=[TIMES,ROMAN,13])〗

but with increasing of "l"(length of channel) graph shows wrong pressure drop. Normally with i increasing of "L" we should have more pressure drop because of power of denominator( power 4) and inside of that parenthesis we have "L" too.  I think that something is wrong but I do not know what. In denomination, 0.176 is tangent of 10 degree, when we put tangent zero or zero instead of 0.176 the graph shows real shape and it is normal regarding fluid mechanics, but for tangent 10(= 0.176) or tangent 5 (= 0.0875) the graph is not OK, why I do not know? even you use plot 3d without integral the graphs are not normal because for that condition we have decreasing of pressure drop for increasing of L which is totally wrong.

When I get that integral(only integral not plot, the result is OK by increasing of "L" for integral (L=10, L=20,L=40) we have more pressure drop which is OK even for tangent 10 degree or 5 degree but when we try to get plot for some ranges we have problem. I wanted to use the plot to reduce time of integral taking to make table (simple plot instead of a lot of numbers in table).






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