Coiled flow inverter is an innovative device, which works on the principle of complete flow inversion and centrifugal force. It was fabricated by introducing 90 degrees bends in helical coils. It has two-fold advantage of intensifying the convective transfer processes (i.e. increase heat and mass transfer coefficients) and also provide increased transfer area per unit volume of space. It is very compact in size as compared to straight tubes and straight helix. Hence, it is a step towards process intensification. An experimental study was conducted for estimating the gas void fraction and flow patterns for gas-liquid two-phase flowing through this device. The coils were prepared using transparent PVC tubing of 0.005-0.015 m internal diameter with coil diameter varying from 0.08 to 0.2 m. A wide range of gas and liquid flow rates, 8.33 x 10(-5) to 0.001 and 3.33 x 10(-6) to 0.001 m(3) A respectively were investigated. Sixteen coiled flow inverters of different geometric configurations were tested. Various flow patterns observed were stratified, slug, plug, wavy and chum flow. An empirical correlation for void fraction for laminar, transition and turbulent regimes were developed. Data from 7582 gas-liquid flow experiments in coiled flow inverter have been processed for power law and composite power law friction factor correlations to flow regime determination. Separate power law correlations for laminar and turbulent flows were obtained for all flow regimes in the database and also for different flow patterns. The results were compared with Lockhart-Martinelli correlation and Hughmark's correlation. (c) 2007 Published by Elsevier B.V.