in simplest form, a condenser can consist of a single tube of glass or metal, where the flow of outside air produces the cooling. in a further simple form, condensers consist of concentric glass tubes, with the tube through which the hot gases begin to pass running the length of the apparatus. the second tube defines an outer chamber through which air, water, or other cooling fluids can pass to reduce the temperature of the gasses to afford the condensation; hence, the outer tube (or, as designs become more complex, outer cooling chamber) has an inlet and an outlet to allow the cooling fluid to enter and exit.