A refrigeration duct system configured for use in a transportation vehicle having a cargo space and a refrigerator unit, the cargo space having a ceiling and cargo doors at a rear end thereof. The refrigeration duct system includes an elongated refrigeration duct disposed adjacent to the ceiling of the cargo space having a proximal end and a distal end, the refrigeration duct including a plurality of cold air outlets arranged along the length of the duct in which each of the cold air outlets has a downstream edge transverse to the refrigeration duct. The duct also includes a plurality of curved flaps operably connected respectively to at least some of the plurality of cold air outlets at the downstream edge of the cold air outlets in which the curved flaps are configured to direct cold air from the refrigerator unit in a downward direction.