Abstract: The invention relates to a passive radiant cooler (1) having a substrate and a layer structure which is applied to the substrate (2) and comprises the at least one reflection layer (3) and at least one emission layer (4), the emission layer (4) comprising an at least partially crosslinked polymer and/or a ceramic material derived from this polymer which are produced in order to form the emission layer (4) from at least one crosslinkable, silicon-based prepolymer, the prepolymer being composed of at least one type of monomer unit according to formula (I).

Abstract: A heat exchanger includes ribs mounted transversely of the axis of the tube and uniformly spaced therealong. Each rib includes a plate with corrugations oriented along the flow of the fluid washing the tube. The ribs adjoin one another, their corrugations having lateral slits, the wall portions between these slits being offset relative to one another to provide passages for the flow of the fluid.Owing to this structure the thickness of the boundary layer at each one of said portions is reduced, and the effectiveness of heat exchange is stepped up. Furthermore, a heat exchanger with the disclosed ribs is considerably more compact and needs less metal for its construction, as compared with known heat exchangers.