Low-speed gas flow subchoking phenomenon in a long-constant-area microchannel

The study on gas flow characteristics in a long-constant-area microchannel in mixed Knudsen-number-regime flows has not only theoretical meaning, but also important application in controlling outer-space aerocrafts. Flow characteristics were studied based on the experiment and approximate theoretical analysis. The inlet pressure was 130, 250, and 320 kPa, and the outlet pressure ranged from 9 to 100 kPa. Five pressure measuring points were distributed along the microchannel, and the temperature sensors were located at the inlet and outlet. The pressure distribution and the volume flow rate of air were measured experimentally. An approximate theoretical model based on Poiseuille flow was applied. Experimental investigations with the long-constant-area microchannel indicate that the mass flow rate through the microchannel changes little as the inlet-to-outlet pressure ratio reaches some critical pressure ratio. The phenomenon is defined as subchoking, and the corresponding pressure ratio is defined as the subchoking critical pressure ratio. The phenomenon of subchoking is caused by the surface effects. Moreover, the effects of the ratio of surface to volume on the critical pressure ratio are studied.