Numerical study of flow mixing and heat transfer in helical pipes, coiled flow inverters and a novel coiled configuration

Experimental study of the two-phase flow distribution in helical-structured vertical headers

A vertical header is a crucial component of a microchannel heat exchanger that facilitates the distribution of the two phases of the refrigerant into horizontally aligned channels. Ensuring an even distribution of the refrigerant into the channels is imperative for achieving the designed optimal performance. Previous studies have indicated that the distribution characteristics of the vertical header are contingent upon the mass flow rate and geometric properties of the header. This study aims to investigate the distribution characteristics of two-phase flow resulting from structural modifications in the header, specifically by implementing a vertical header with a helical structure. Hence, an experimental device simulating a microchannel heat exchanger found in a commercial air conditioning system was employed. The distribution characteristics of the vertically oriented header with a helical structure were measured by varying the inlet conditions (mass flow rate: 50-100 kg h-1; vapor quality: 0.1-0.2). The measured distribution characteristics were compared with those obtained from a conventional straight vertical header possessing the same cross-sectional properties. The experimental findings demonstrated that the helical structure induced a distinctive flow pattern and facilitated the mixing of the two phases. Furthermore, this helical structure exhibited reduced inertial forces compared to the simple vertical header, leading to improved distribution performance.

Engineering advancements in microfluidic systems for enhanced mixing at low Reynolds numbers

Mixing within micro- and millichannels is a pivotal element across various applications, ranging from chemical synthesis to biomedical diagnostics and environmental monitoring. The inherent low Reynolds number flow in these channels often results in a parabolic velocity profile, leading to a broad residence time distribution. Achieving efficient mixing at such small scales presents unique challenges and opportunities. This review encompasses various techniques and strategies to evaluate and enhance mixing efficiency in these confined environments. It explores the significance of mixing in micro- and millichannels, highlighting its relevance for enhanced reaction kinetics, homogeneity in mixed fluids, and analytical accuracy. We discuss various mixing methodologies that have been employed to get a narrower residence time distribution. The role of channel geometry, flow conditions, and mixing mechanisms in influencing the mixing performance are also discussed. Various emerging technologies and advancements in microfluidic devices and tools specifically designed to enhance mixing efficiency are highlighted. We emphasize the potential applications of micro- and millichannels in fields of nanoparticle synthesis, which can be utilized for biological applications. Additionally, the prospects of machine learning and artificial intelligence are offered toward incorporating better mixing to achieve precise control over nanoparticle synthesis, ultimately enhancing the potential for applications in these miniature fluidic systems.

Open-source multi-purpose sensor for measurements in continuous capillary flow

Abstract

Limited applicability and scarce availability of analytical equipment for micro- and millifluidic applications, which are of high interest in research and development, complicate process development, control, and monitoring. The low-cost sensor presented in this work is a modular, fast, non-invasive, multi-purpose, and easy to apply solution for detecting phase changes and concentrations of optically absorbing substances in single and multi-phase capillary flow. It aims at generating deeper insight into existing processes in fields of (bio-)chemical and reaction engineering. The scope of this work includes the application of the sensor to residence time measurements in a heat exchanger, a tubular reactor for concentration measurements, a tubular crystallizer for suspension detection, and a pipetting robot for flow automation purposes. In all presented applications either the level of automation has been increased or more information on the investigated system has been gained. Further applications are explained to be realized in the near future.

Article highlights

• An affordable multipurpose sensor for phase differentiation, concentration measurements, and process automation has been developed and characterized

• The sensor is easily modified and can be applied to various tubular reaction/process units for analytical and automation purposes

• Simple integration into existing process control systems is possible

Graphical abstract