Frictional resistance characteristics of heat-moisture-oxygen co-conveying pipelines under low-pressure drying conditions

The special climatic conditions of the Qinghai-Xizang Plateau, which are low-pressure, oxygen-deficient and dry, make the need for humidification and oxygenation in buildings, while the existing studies have not considered the effects of changes in the air components due to low-pressure and humidification and oxygenation on the frictional resistance characteristics of pipelines. In this paper, the effects of atmospheric pressure, inlet velocity, wet oxygen concentration, pipeline diameter, wall roughness and other factors on the frictional resistance are studied in a straight pipeline transporting heat, moisture and oxygen. The results show that when the pipeline only supplies heat, the frictional resistance per unit pipeline length at an altitude of 5 kilometers is about 62% of that at normal pressure. When the heat, moisture and oxygen are transported together, the increase of the oxygen concentration can increase the frictional resistance per unit pipeline length by about 8.4%, while increasing relative humidity has little effect on the frictional resistance per unit pipeline length, which only reduces 2%. The frictional resistance per unit pipeline length increases with the increase of inlet velocity, and can increase by about 16 times at most. When the wall roughness is small (K=0.03-0.20 mm), the resistance in the hydraulic smooth zone does not change with the increase of roughness. When entering the mixed friction zone (K>0.40 mm), the resistance begins to increase with the increase of roughness, and the maximum increase can be about 45%. Finally, the recommended values of frictional resistance of the heat-moisture-oxygen co-conveying pipeline under different working conditions are given under low-pressure conditions.