Measurement of Adiabatic Single and Two-Phase Pressure Drop Behavior of R134a in MicroChannel Tube

摘要

Brazed aluminum beat exchanger constructions using flat multiport tubes on the refrigerant side and louver fins on the air-side, commonly referred to as the microchannel heat exchangers (MCHX), are becoming increasingly attractive in residential and commercial HVAC applications due to superior performance and lower cost. With the advent of newer and environmentally friendly low-GWP refrigerants there is renewed interest in improving understanding of the transport phenomenon in mini/ micro geometries as applicable to the MCHX condenser and evaporators. In particular the hydraulic performance of the microchannel tubes is important for low and medium pressure refrigerants. This study investigated the two-phase pressure drop characteristics in a conventional multiport microchannel tube using R-134a as the working refrigerant. The main objective is to quantify the two-phase flow pressure drop characteristics and compare the measurements with existing correlations from the literature to assess the predictive capabilities. The extruded 25 port microchannel tube was nominally 32mm (1.26in) wide and 2mm (0.079in) thick with an average hydraulic diameter of 1.1 mm (0.04 3 in). Although some of the existing studies reported the early flow transition at the Reynolds number of less than 1000, it was not found in the single-phase flow pressure drop tests. The conventional theory predicted the friction factor trends reasonably well for laminar and the turbulent regime. The two-phase flow pressure drop tests were conducted over a range of vapor quality from 0.2 to 0.9 nominally and mass flux of 75 to 500 kg/m~2-s (55302-368677 lb/ft2-hr). As expected the two-phase flow pressure drop increased with increasing quality and increasing mass flux. The measured two-phase adiabatic pressure drop were compared to seven different correlations from the literature for a comparative study.