An air flow apparatus (10; 110) having at least one array of air channels (18; 118), an air duct (20; 120) covering the array of air channels (18; 118) and being connected to the air channels, and a fan (34; 134) arranged at the air duct (20; 120) for generating an air flow through the array of air channels (18; 118), wherein the air flow apparatus further includes a cleaning device for the array of air channels (18; 118), arranged inside the air duct (20; 120), the cleaning device comprising: a nozzle bar (42; 142) extending in front of the array of air channels (18; 118); and a nozzle manifold (46; 146) including a plurality of nozzles (48; 148) arranged along the nozzle bar (42; 142) and directed towards the array of air channels (18; 118), wherein the nozzle bar (42; 142) is mounted to the air flow apparatus (10; 110) to be movable across at least a section of the array of air channels (18; 118), wherein the cleaning device further comprises: at least one rail arranged on the array of air channels ; and a trolley carrying the nozzle bar and movable along the rail in a front and rear direction of the trolley , wherein the trolley is configured for moving on a top side of the rail , wherein the nozzle bar extends to opposite sides of the trolley in a transverse direction of the trolley , wherein the trolley comprises a motor and at least one driving wheel for moving the trolley along the rail , wherein the trolley has at least one wheel (66; 68) and/or at least one slider that engages a bearing surface of the rail against lifting the trolley from the rail . a nozzle bar (42; 142) extending in front of the array of air channels (18; 118); and a nozzle manifold (46; 146) including a plurality of nozzles (48; 148) arranged along the nozzle bar (42; 142) and directed towards the array of air channels (18; 118), wherein the nozzle bar (42; 142) is mounted to the air flow apparatus (10; 110) to be movable across at least a section of the array of air channels (18; 118), wherein the cleaning device further comprises: at least one rail arranged on the array of air channels ; and a trolley carrying the nozzle bar and movable along the rail in a front and rear direction of the trolley , wherein the trolley is configured for moving on a top side of the rail , wherein the nozzle bar extends to opposite sides of the trolley in a transverse direction of the trolley , wherein the trolley comprises a motor and at least one driving wheel for moving the trolley along the rail , wherein the trolley has at least one wheel (66; 68) and/or at least one slider that engages a bearing surface of the rail against lifting the trolley from the rail . at least one rail arranged on the array of air channels ; and a trolley carrying the nozzle bar and movable along the rail in a front and rear direction of the trolley , wherein the trolley is configured for moving on a top side of the rail , wherein the nozzle bar extends to opposite sides of the trolley in a transverse direction of the trolley , wherein the trolley comprises a motor and at least one driving wheel for moving the trolley along the rail , wherein the trolley has at least one wheel (66; 68) and/or at least one slider that engages a bearing surface of the rail against lifting the trolley from the rail . <EOS>