A deaeration device for deaerating coolant fluid flow in a recirculation cooling system, where the recirculation cooling system includes a cooling fluid reservoir adapted to receive the deaeration device submerged within cooling fluid therein, includes an elongated deaeration tube including a fluid outlet and a deaerating skimming shaped slot for skimming air bubbles and cooling fluid from cooling fluid flow flowing through the deaeration tube, and including a fluid inlet for allowing the same amount of fluid that is skimmed off and removed through the top fluid outlet to re-enter the deaeration tube to maintain mass balance in the cooling fluid flow.