chemical engineering research and design 9 5 ( 2 0 1 5 ) 22–33 Contents lists available at ScienceDirect Chemical Engineering Research and Design journal h om epage: www.elsevier.com/locate/cherd Narrow residence time distribution in tubular reactor concept for Reynolds number range of 10–100 Stephan Klutz a,*,1 , Safa Kutup Kurt b,1 , Martin Lobedann a , Norbert Kockmann b a Invite GmbH, Chempark Leverkusen, Building W32, 51373 Leverkusen, Germany b TU Dortmund University, BCI, Equipment Design, 44227 Dortmund, Germany a r t i c l e i n f o Article history: Received 25 August 2014 Received in revised form 5 December 2014 Accepted 3 January 2015 Available online 13 January 2015 Keywords: Tubular reactor Laminar flow Continuous flow process Residence time distribution Mixing Coiled flow inverter design a b s t r a c t For chemical reactions, which require residence times of several hours, enhanced heat trans- fer, 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 reac- tor is coiled around a coil tube. After each straight helix module, the coil direction is changed by a 90 ◦ -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 perfor- mance. 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. © 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction In chemical industry many processes are driven in continuous operation mode because a continuously operated process may serve for constant product quality, better process control and higher production rates compared to batch operation mode. In the case of continuous operation mode, most reaction systems require efficient heat transfer and a narrow residence time distribution (RTD) to achieve the desired reaction rates, yield, ∗ Corresponding author. Tel.: +49 21431203103. E-mail address: klutz@invite-research.com (S. Klutz). 1 Both authors contributed equally to this article. selectivity, and product quality. Especially for kinetically con- trolled reaction systems, where side reactions or consecutive reactions may take place, a narrow RTD is essential. Conse- quently, good radial mixing combined with poor axial mixing is desired within the continuously operated reaction system because improper mixing can result in low product quality (Vashisth and Nigam, 2008). Within this work, the combina- tion of good radial mixing and poor axial mixing is defined as effective mixing for an easier speech. http://dx.doi.org/10.1016/j.cherd.2015.01.003 0263-8762/© 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.