how to get the nodes spacing near the interface
 

I need to compile a udf compute the mass transfer between two phases which includes equaction:m_lg=D*dY/dz. where "Y" is the mass fraction,"z"is the coordinate on the vertical direction of the interface. Now my question is how to get the coordination of the interface and its adjacent node.Anyone could help me? Thanks !

Re: how to get the nodes spacing near the interfac
 

here is my UDF.there is something wrong.It shows "c_thread is unceclared" .pls help me: #include "udf.h" DEFINE_MASS_TRANSFER(vapourvapour,c,t,from_phase,f rom_index,to_phase,to_index) { real x[ND_ND]; real y1,z1; Thread *t; cell_t c; Domain *domain; domain=Get_Domain(4); Thread *c_thread=THREAD_SUB_THREAD(t,to_index); int i=2; thread_loop_c(c_thread,domain) { begin_c_loop (c,c_thread) { C_CENTROID(x,c,c_thread); y1=x[1]; z1=C_YI_M1(c,c_thread,i); } end_c_loop(c,c_thread) } return z1; }