Flow Characteristics of Transition Region between Laminar and Turbulent Gas Flows through Micro-Tubes

Abstract

Flow characteristics in the transition region between laminar andturbulent gas flows through micro-tubes were experimentally investigated.The experiments were performed for nitrogen gas flowing through two stainless steel micro-tubes of D= 124and 162mand two fused silica micro-tubes of D = 100and 151 m. The Mach numbers and gas bulk temperaturesat the inlet and locations neartheexit were also obtained by measuring stagnation temperatures, stagnation pressures, pressures at locations near exit and mass flow rates. The average Fanning friction factors also were obtained. The mass flow rate levels off in the transition flow region for micro-tubes as thestagnation pressure increases.The Mach number increases with an increasing Reynolds number in the laminar flow region. However Mach number decreases when Reynolds number goes higher in the transition flow region since the mass flow rate stays nearly constant with an increase of the stagnation pressurein the transition flow region.On the other hand,the bulk temperature increasesin the transition flow region.This was validated by measuring wall temperature of micro-tubes whose outerwalls are thermally insulated.The decrease in Mach number and the increase in the bulk temperatures in the transition flow region are the dominant scaling effect for the smallest diameter micro-tubes