A reservoir tank which includes: a container for storing fluid therein, having an inlet through which the fluid flows into the container and an outlet through which the fluid flows out of the container; and a duct provided inside the container, which is connected to the inlet of the container and has a first opening open inside the container. The first opening is located above the outlet of the container and below a surface of the fluid in the container.
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.