Actually in this case, Q_dot is "rate" of heat transfer, and q_dot is rate of heat transfer on a per mass basis. Basically just heat transfer divided by mass, with units of kj/kg in the metric system.
Q with dot is in KJ/s or KW it means that it is the heat added or removed per unit time, while the small q is in KJ/KG, it is the heat per mass of the system
