jmc

Distributing and combining like terms, we have $a(2a+b)-2a^2+ab=2a^2+ab-2a^2+ab=2ab$. Now $a$ and $b$ are different prime numbers greater than 2, so $2ab=2^1\cdot a^1\cdot b^1$ has $(1+1)(1+1)(1+1)=\boxed{8}$ divisors.