Improved structures of cooling systems that may be used in air conditioning or refrigeration are described. To achieve a high efficiency in converting cooling effect from one or more cooling units, antifreeze liquid used to absorb the cooling effect is forced to pass through a box or container made out of graphite or thermally conductive metal or alloy holding a sponge-like structure or foam, also made out of graphite or thermally conductive metal or alloy, where the foam including open cells provides maximum surface contact with the liquid. Further the liquid is sprayed or vaporized onto the foam and passes through the foam by gravity or pressure. The cooled liquid is exited from the container for use in air conditioning or refrigeration.