meshing for dual cell heat exchanger
 

i am designing a heat exchanger. a helical coil is inside a cylinder. water at different temp. will flow in the helical coil and cylinder so heat transfer will take place. i want to use dual cell heat exchanger. it is necessary to get the overlapping mesh of helical coil wall surface. the helical coil surface mesh should be common for heat transfer. how to get that one. iam getting mesh for both part without overlapping..ansys 13. how to overlap in ansys 13.
my e mail is sandeepsethi910@gmail.com. please help it is my final year project.please help.. i want the overlap mesh .the helical surface will overlap ..the cells of helical coil surface should be common for both helical and cylinder