7 complete uniform circulation of refrigerant and complete evaporation of the carbon dioxide snow is assured by the fans 76 the carbon dioxide thereupon extracts heat from the articles moving through the chamber in the direction 18 and in so doing is converted completely into refrigerant gas this gas together with mixed snow particles prior to complete sublimation is circulated through the conveyor and the articles thereon and around the sides 77 as previously described the deflectors 48 that are closest to the opposite ends of the chamber are angled to project this spray away from the adjacent ends as indicated by the arrows in fig2 this further provides that all of the particles of carbon dioxide are converted to the gas finally this gas is drawn from each end 15 and 16 of the chamber 19 by gas collectors 78 and forced to the exterior by blowers 81 exhausting through exhaust pipes 82 as can be seen from the above description the apparatus of this invention provides an effective refrigeration structure of very simple design that uses readily available and relatively inexpensive liquid carbon dioxide as the cryogen or refrigerant no complex seals are required and the nozzles and their deflector plates not only prevent the carbon dioxide or similar cryogen setting up to a solid within the valve body but also provides good distribution of the solid as well as the gaseous cryogen across the conveyor and throughout the interior of the tunnel the valves do not clog up with.