I am using HETVAL subroutine to simulate the latent heat released due to phase change during solidification. There are two parameters to be defined inside HETVAL: FLUX(1) and FLUX(2). It is clear what FLUX(1) means physically. But I couldn't figure out if FLUX(2) has any physical significance.

1. If I set FLUX(2) = 0, does it have any influence on the physics of the problem? 
EDIT: For my application, this has to be non-zero.

2. Where do FLUX(1) and FLUX(2) fit in the discretized system of equations for a coupled temperature-displacement problem?

Any kind of help would be appreciated. Abaqus documentation didn't help much.