# Diffusion term, convective term and time double derivative

1. Apr 17, 2012

$_{}$Dear Fellows,
I am just using a Green Naghdi heat transport equation which is represented as,

ρ$\times$C$\times$T''+aT_0$\times$U'_i,i=K$\times$T'_i,i+K*$\times$T_i,i

where (')=derivative with respect to time
(,i)= derivative with respect to space.

I am being informed that
U_i,i= is a convetive term
U_i,ii= diffusive term

I am very confused in this concept of diffusivity and convetion and specially T'' what it is representing????????????

Why diffusive term is represented by double derivative and single refered to convetion of heat ????????????