Experimental characterization of gas-liquid flows in splitting distributor for parallel microchannels Appurva Tiwari 1 , Apoorva Maheshwari 2 , V. M. Rajesh 3 * 1,2,3 Shiv Nadar University, Uttar Pradesh, India, 201314 *Corresponding author: vm.rajesh@snu.edu.in Highlights  Splitting distributor was designed to ensure the flow uniformity in parallel channels.  Effect of Qkerosene on bubble/slug splitting mechanism, relative lengths of bubbles/slugs in parallel channels were studied.  Uniform relative lengths of bubble/slugs were observed in all blocks for Ca ranges 0.0041- 0.0071. 1. Introduction Microreactors technology have evolved rapidly over the past two decades with extensive application in chemical synthesis [1]. A diversity of experimental studies of gas-liquid flows in microchannels have also been performed to understand the flow physics (formation dynamics of bubble/slugs and flow regimes). However, most of the reported study are restricted to single microchannel [2]. In spite of key advantages of improved control over reaction and high surface area to volume ratio (5000-50000 m 2 /m 3 ), increasing the throughput pretence a serious challenge for microreactors. The scale up of microreactor processes is highly desired to make micro-reaction technology applicable to industrial production which is done by numbering up single micro channels [3]. Recently, a new numbering up approach of designing a splitting distributor has evolved [4,5] in which a single microchannel is fabricated on a plate through etching and branched into multiple microchannels to form a tree like structure. Although, it is an effective scaling route to increase throughput but the application of parallel microchannels pose a challenge of maintaining a uniform fluid flow distribution in the microchannels. Current work reports experimental investigations of gas-liquid flow in parallel microchannel contactor that has been designed using splitting distributor. The main objectives of the present work are to study the effect of continuous phase flow rate (QKerosene = 3-16 ml/min) on the flow regimes, formation dynamics, splitting mechanisms of air bubbles/slugs and relative slug/bubble lengths while keeping a constant flow rate of dispersed phase (Qair= 3 ml/min). The primary aim of this work is to achieve flow uniformity in all parallel channels through splitting distributors in terms of relative lengths of bubbles/slugs (Lslug/bubble/Wchannel) in all blocks (see Figure 1) at different Ca (=0.0022 – 0.0071). 2. Methodology The test microchannel reactor was fabricated on a transparent polymethyl methacrylate (PMMA) sheet using laser machining as shown in Figure. 1, wherein, the reduction in width of the successive blocks is by a factor of 2  (where =0.5) for ensuring constant Lslug/bubble/Wchannel ratio in all the blocks. The depth of channels in all the blocks was 1 mm. At the 1 st T-junction, air was injected perpendicular to the T-junction whereas, liquid (kerosene) was pumped through the main inlet. The gas flow rates were measured and controlled by using mass flow controllers (Bronkhorst, Germany). Liquid was pumped using a continuous push-pull type syringe pump (Coleparmer, USA) ranging from 3-16 ml/min. A high speed digital camera was used to visualize and record the flow behavior and distribution within the microchannels. The images were recorded at a speed of 1000 frames/second. A fiber optic quad white Sugar CUBE LED light source was used to illuminate the system. The formation and splitting frequency as well as the relative slug lengths were measured for ten successive bubbles/slugs and the mean values were used for further analysis. The analysis