Apparatus that primarily includes a narrow tube, through which a gas, preferably air, is forced to flow at a substantially high axial velocity. The gas, which must accelerate to reach that velocity and consequently becomes substantially cooler than the environment, then dissipates heat, through the wall of the tube from whatever is in thermal communication with that wall and thus refrigerates it. The gas does not undergo a change of phase. Preferably the tube forms the middle segment of a continuous tri-segment duct, through which the gas flows the other two segments have each a tapered passageway, whose diameter varies between that of the tube and a considerably larger diameter at the corresponding end of the duct.
