I am designing a Fixed type HEx i.e Fixed tubesheet,tubesheet type-b.(ASME UHX)
In calculation, the value of "Diameter of Channel Gasket Load Reaction" 'ac' is shown as zero.what may be the reason behind it?The extract is shown below:

...Compute the Ratio [Rhoc]:
= ac / ao = 0.0000 / 195.7000 = 0.000000