[vikku]

I am solving the fluid flow around a uniformly volumetric charge solid cylinder. For this, I solve Poisson's equation [ 0=(∇^2 𝜀_𝑟 &#120593+𝜌_𝑣/𝜀_0 ]. I defined one user-defined scalar transport equation and it has diffusion term ( (∇^2 𝜀_𝑟 &#120593and source term(𝜌_𝑣/𝜀_0). For source term, I have written UDF as:
#include "udf.h"
#define sigma 90e-6 /* Sigma is volumetric charge */
#define e0 8.854e-12 /* permittivity of free space */
DEFINE_SOURCE (electric_potential, c,t,ds,eqn)
{
real source;
source = (sigma/(e0));
ds[eqn] = 0;
return source;
}

Here, 𝜀_𝑟 is a diffusivity and its value is 1.5 but it is dimensionless. My confusion is in material properties' diffusivity show unit (kg/ms). Therefore how can I balance the unit of diffusion term and source term? Can you give me any idea such that I solve this correctly? Is my written UDF correct or wrong if it is incorrect please guide me in writing the correct UDF for the source term.