Abstract: The transfer elements of a heat and humidity exchanger are made by forming the transfer elements in the desired configuration and of a non-hygroscopic metal such as aluminum, and treating the surfaces to produce an integral hygroscopic layer thereof. This is done by oxidizing the surface of the metal to form an oxide layer, which itself is hygroscopic, and preferably enhancing the hygroscopic properties by subsequent impregnation of the oxide with a hygroscopic material such as lithium chloride. According to one form of the method, the oxidizing layer is produced by immersing the transfer elements, in a bath such as a warm aqueous solution of sodium hydroxide, or sodium carbonate, followed by heating in humid air; in a second form of the method, the oxide layer is produced by heating in humid air, or in a water, without preliminary alkaline treatment; in a third form of the method, the oxide layer is formed in a water bath containing an oxidizing agent such as trietanolamin or hydrogen peroxide.

Abstract: The transfer elements of the rotor of a regenerative heat and humidity exchanger are made of a non-hygroscopic material, such as aluminum, the surface of which is treated to form a hygroscopic layer thereon. This provides the benefits in humidity transfer previously obtained with all-hygroscopic transfer elements such as paper, cardboard or asbestos, without the danger of fire in the use of paper or cardboard or the danger to health in the use of asbestos. Preferably the transfer element is of metal on which a hygroscopic surface layer is formed by oxidizing the surface by pickling and/or heat treatment, and preferably the oxide layer is impregnated with a substance, e.g. lithium chloride, to render it more hygroscopic. Preferably also, the layer is made more porous by acid treatment prior to oxide formation, and acid treatment may be used after the pickling process to arrest the pickling reaction promptly.

Abstract: A surface layer is formed on transfer elements of the rotor of a humidity and heat exchanger rotor, the layer not only being hygroscopic to provide the desired humidity transfer, but also serving as a bonding agent or cement for holding the transfer elements together in the desired rotor configuration. A preferred layer uses as a bonding agent a solution of cellulose acetate or nitrate in acetone, and with lithium chloride dissolved therein to produce the hygroscopic effect.

Abstract: A method of operating recuperative heat exchange means in the supply and exhaust ducts of a ventilation installation exposed to sub-freezing atmospheric condition so that the heat exchanger in the exhaust duct is allowed to ice up and is periodically defrosted. The method operates to control the temperature in the spent-air heat exchanger in various ways, including raising the input temperature of the the exchange medium to reduce the cooling effect on the spent air, or by reducing the flow of heat exchange medium to achieve the same result.

Abstract: A contact body comprising a sheet of material adapted to be positioned upright on edge within a cooling tower along with a plurality of similar bodies. Water is caused to flow downwardly upon the surfaces of said body, in the preferred embodiment countercurrent to the flow of air through the tower. A fine surface structure on the body consists of corrugations or folds disposed at an angle to the vertical between 65.degree. and 88.degree.. The corrugations have a wave length below 12 mm and an amplitude between 1 and 5 mm. The corrugations are arranged in fields whose angles of inclination alternate successively between positive and negative inclination. The fields may range between 20 and 50 mm and alternate along the vertical extent of the body. They may also alternate along the horizontal extent of the body. Integral spacer elements are pressed out of the body to position adjacent vertical bodies in spaced, generally parallel arrangement.