This paper describes the results of methodical investigations of the effect of the Pitot tube on measurements of gas-dynamic parameters of supersonic axisymmetric underexpanded real and model microjets. Particular attention is paid to distortions of Pitot pressure variations on the jet axis associated with the wave structure of the jet and to distortions of the supersonic core length. In experiments with model jets escaping from nozzles with diameters ranging from 0.52 to 1.06 mm into the low-pressure chamber, the measurements are performed by the Pitot tubes 0.05 to 2 mm in diameter. The results are analyzed together with the earlier obtained data for real microjets escaping from nozzles with diameters ranging from 10 to 340 µm where the parameters of real microjets were determined by the Pitot microtube 12 µm in diameter. Interaction of the Pitot tube with an unsteady jet in the laminar-turbulent transition region is investigated; the influence of this interaction on Pitot pressure measurements is determined, and a physical interpretation of this phenomenon is provided.

The gasdynamic structure of supersonic underexpanded nitrogen microjets emitted from supersonic nozzles with diameters of 10–340 μm has been studied. Data on the mean wave-structure cell length in the initial region and the length of the supersonic region have been obtained. The relative length of the supersonic region significantly increases when the nozzle diameter is reduced below about 20 μm. The results of measurements are compared to available published data for gas macro- and microjets.

Experimental data used to determine the friction factor in microchannels are presented. Glass microchannels with a circular cross section, diameters of 34.5, 33.6, and 24.5 μm, and different lengths are studied in the experiments. Pure deionized degassed water is used as a working fluid. The range of the Reynolds numbers is 13 ⩽ Re ⩽ 330. A method of two channels is used to calculate the friction factor. The results obtained are in good agreement with theoretical predictions for the case of a developed laminar flow in circular channels, but the use of the method of two channels has some constraints.