An evaporator has $R-410A$ at $-15C$ and a quality of $70\%$ flowing in$.$ The exit flow is saturated vapor at $-15C.$

a$)$ Consider the heating to be a reversible process and find the specific heat transfer from the entropy equation.

b$)$ If the heat source was at $-5C$ and the inlet and outlet streams still have the same properties as in Part a$),$ calculate the specific entropy generation.