HOL // Mass balance
 

in PHOENICS documentation at http://www.cham.co.uk/phoenics/d_pol...ecs/hollec.htm

Mass balance definition

INOU: sum of inflows of liquid to the cell column minus the sum of outflows of liquid from the cell column. The inflows and outflows are computed from the volumetric flows obtained as convective fluxes, multiplied by the upwind values of VFOL*RHOL.

Can some one explain to me why and how the inflows and outflows are computed from the volumetric flows obtained as convective fluxes, multiplied by the upwind values of VFOL*RHOL ?

Thanks.