For chemical reactions, which require residence times of several hours, enhanced heat transfer, or narrow residence time distribution (RTD), good radial mixing combined with poor axial mixing in laminar flow regime has long been desired by industry and R&D. The main goal of this work is to obtain the narrowest RTD curve in a continuously operated reactor at Reynolds numbers smaller than 100. By using a stepwise method the most promising reactor type was chosen to meet the requirements. Design parameters of this reactor, the coiled flow inverter (CFI), were characterized and their effects on RTD were experimentally investigated. Design of CFI includes several straight helix modules, where the tubular reactor is coiled around a coil tube. After each straight helix module, the coil direction is changed by a 90 degrees-bend. As a starting point for designing a CFI reactor for specific applications, the "best performance" design space diagram was investigated. Regarding narrowing RTD, the diagram gives the user the design space for the CFI reactor, which leads to the best performance. The most significant design parameter regarding a narrow RTD was experimentally determined as number of bends. By using a CFI design consisting of 27 bends at volume flow rate of 3 mL/min, which corresponds to Reynolds number of 24 and mean residence time of 2.6 h, a Bodenstein number over 500 was achieved. Beside its narrow RTD behavior, CFI is a compact and cost-efficient reactor concept, which is flexible to scale-up and implement for different processes, even for single-use applications. (c) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.