Experimental study on the thermal flow characteristics of a columnar sodium fire affected by a small amount of fire extinguishing powder in a cylindrical confined space

•Some liquid sodium separates from the columnar sodium mainstream.•The longitudinal temperature can be described by a two-region model.•Spraying fire extinguishing powder may disturb the flow field.•The reignition hazard should be given sufficient attention. Liquid sodium, as a special form of metal has unique combustion characteristics and is difficult to extinguish quickly. To obtain a deeper understanding of the combustion and suppression characteristics of a columnar sodium fire affected by fire extinguishing powder in a confined space, investigative experiments were conducted in a cylindrical test chamber. The temperature of the space and the bottom surface were measured and analysed, and the effects on the suppression of combustion and the spatial heat flow field when different amounts of Class D fire extinguishing powder were sprayed into the space in the early and late combustion stages were compared. A local high temperature easily formed near the columnar sodium flow zone, because the sodium is more likely to adhere to the sensor at that measurement point. For a space heat flow field formed by a sodium fire in a confined space, the lateral temperature distribution at each height of the space is approximately linear. The overall temperature distribution at the upper space is relatively uniform, and the temperature near the fire source in the lower part of the space varies exponentially along the height. Compared with the spraying of fire extinguishing powder in the late stage of a sodium fire, spraying at the initial stage is more effective in suppressing the combustion of liquid sodium, the flow of liquid sodium and the disturbance of the space heat flow field. Further, the reignition hazard that may occur when spraying fire extinguishing powder to suppress a sodium fire should be given sufficient attention.