[alnossory]

Hi
I have a case where the flow passes through an extremely hot pipe, and by the time the pipe is cooled by the fluid until it reaches the fluid temperature. There is no heat applied on the pipe's surface. In this case three different types of boiling are expected: film boiling, transition boiling and nucleate boiling and I need to model this case by modifying the the below UDF that provides in the Ansys UDF manual. This UDF calculates the Nu and heat transfer coefficient (h) for the nucleate boiling.
I need to add If statements to this UDF which allow me to add the other two boiling types.
Boiling types depend on the temperature difference between the wall pipe (Tw) and the fluid domain (Tf) where:

if Tw-Tf<30 then nucleate boiling occur
if 30<Tw-Tf<120 then transition boiling occur
if Tw-Tf>120 then film boiling occur
I already have the Nu and h of each boiling type

I there and one can help me to modify this UDF or have any other solution.



#include "udf.h"
#define PR_NUMBER(cp,mu,k) ((cp)*(mu)/(k))
#define IP_HEAT_COEFF(vof,k,nu,d) ((vof)*6.*(k)*(Nu)/(d)/(d))
static real heat_ranz_marshall(cell_t c, Thread *ti, Thread *tj)
{
real h;
real d = C_PHASE_DIAMETER(c,tj);
real k = C_K_L(c,ti);
real NV_VEC(v), vel, Re, Pr, Nu;
NV_DD(v,=,C_U(c,tj),C_V(c,tj),C_W(c,tj),-,C_U(c,ti),C_V(c,ti),C_W(c,ti));
vel = NV_MAG(v);
Re = RE_NUMBER(C_R(c,ti),vel,d,C_MU_L(c,ti));
Pr = PR_NUMBER (C_CP(c,ti),C_MU_L(c,ti),k);
Nu = 2. + 0.6*sqrt(Re)*pow(Pr,1./3.);
[/COLOR][/COLOR][/COLOR]h = IP_HEAT_COEFF(C_VOF(c,tj),k,Nu,d);
return h;
}
DEFINE_EXCHANGE_PROPERTY(heat_udf, c, t, i, j)
{
Thread *ti = THREAD_SUB_THREAD(t,i);
Thread *tj = THREAD_SUB_THREAD(t,j);
real val;
val = heat_ranz_marshall(c,ti, tj);
return val;
}