In natural convection, the denser portions of the fluid move downward because of the greater force of gravity, as compared with the force on the less dense.

Heat Rejection and Cooling topics include: Heat rejection, engine heat transfer and cooling systems, liquid cooling systems and air cooled systems. Heat rejection is the process of transferring heat energy from a cool side to a warm side, plus the work done by the compressor. A cooling system transfers energy from a cool side to a warm side, along with the power needed to transfer the energy.  Heat rejection can be achieved in several ways, including: Air cooled: Air passes over a coil or channel containing fluid, transferring heat from the coil to the air. Water cooled: A spray system... Show more

Heat Rejection and Cooling topics include: Heat rejection, engine heat transfer and cooling systems, liquid cooling systems and air cooled systems.

Heat rejection is the process of transferring heat energy from a cool side to a warm side, plus the work done by the compressor. A cooling system transfers energy from a cool side to a warm side, along with the power needed to transfer the energy. 

Heat rejection can be achieved in several ways, including:
Air cooled: Air passes over a coil or channel containing fluid, transferring heat from the coil to the air.
Water cooled: A spray system passes water over coils or fill media to reject heat to the atmosphere through evaporation.
Evaporative condenser: Water is sprayed over tubing in which refrigerant condenses. Airflow across the tubing evaporates some of the water, causing the water and the tubes to be cooled.
Cooling tower: The type of heat rejection in a cooling tower is called "evaporative" because it allows a small amount of the water to evaporate into a moving air stream. This evaporation cools the rest of the water stream. 

Heat rejection can also be achieved through mechanical or natural ventilation to reject excess heat to the outside

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