Effect of side gaps on hot flow field inside a vertical channel was studied by an experiment of fire whirl in a vertical channel with the dimension 32 cm×32 cm×200 cm.Changes of hot flow field in the channel were obtained by changing fires and obstructing 5 cm at the bottom of gaps with wideth of vent 3.0 cm or 3.5 cm.From the experiment results

it can be concluded that the obstruction affected the combustion and hot fluid field.It blocked cold air flow into the channel and the fire was weakened.Then the duration of combustion became longer and the flame height was reduced.The effect became weaker with the oil pan becoming larger.Temperature at the axes and bottom of the channel became lower when the bottom of gaps was obstructed.The largest effect occurred at about 50 cm above the floor.Above 150 cm the effect was almost canceled.The ratio of averaged flame height to the diameter of fuel pool H/Φ was 1.732.The effect on the ratio was negligible whether the bottom areas of the side gaps were blocked.