3D cfd mesh

You not 'convert' 2D mesh into 3D mesh. But you can fill a closed 2D mesh with 3D elements (tet4, tet10).

Before filling, check if your 2D mesh was closed by using: Tool => edges => find edges. If you found nothing, your 2D mesh is closed and you can do next step to fill with TET.

i used tet10 for cfd 3D tetramesh 

i check edges it show no free edges.

i got another error 

<?xml version="1.0" encoding="UTF-8"?>

So check 'failed elems' to understand the issue.

HOW TO CHECK IT 

When you see the message '71 failed elems saved', do 'F5', select type 'Element' and 'retrieve', 'reverse', 'mask'. You have only failed elements on screen.

thank you 

but i have another doubt 

volume analyzer found one disjoint element 

what it mean its an error or any other can explain