FRICTION CHARACTERISTICS OF WATER, R-134a, AND AIR IN SMALL TUBES

Abstract

This manuscript provides a systematic test of friction characteristic for air, water, and liquid refrigerant R-134a in 10 tubes with inside diameters from 0.173 to 4.01 mm. The test results show that the conventional minor losses correlations for large tubes may be adequately used to estimate the related inlet, exit and acceleration components for water, refrigerant, and low-speed air flow in microtubes. For high-speed air flow, however, the flow Mach number is too high to be treated as incompressible flow. The conventional minor losses correlations may not be accurate for this condition. The laminar-turbulent transition Reynolds number varies from 1,200 to 3,800 and increases with decreasing tube diameters. The test friction factors for water and refrigerant R-134a agree very well with the conventional Blasius (f = 0.079Re d −0.25) and Poiseuille (f = 16/Re d ) equations in turbulent and laminar flow regime; however, for air flow in small tube at high Reynolds conditions, the flow is entered into the high subsonic flow regime. The Blasius equations developed for the incompressible flow will no longer be appropriate for friction factor prediction.