Solid Circulating Velocity Measurement in a Liquid–Solid Micro-Circulating Fluidised Bed

Abstract

Liquid–solid circulating fluidised beds (CFB) possess many qualities which makes them useful for industrial operations where particle–liquid contact is vital, e.g., improved heat transfer performance, and consequent uniform temperature, limited back mixing, exceptional solid–liquid contact. Despite this, circulating fluidised beds have seen no application in the micro-technology context. Liquid–solid micro circulating fluidised bed (µCFBs), which basically involves micro-particles fluidisation in fluidised beds within the bed of cross-section or inner diameter at the millimetre scale, could find potential applications in the area of micro-process and microfluidics technology. From an engineering standpoint, it is vital to know the solid circulating velocity, since that dictates the bed capability and operability as processing equipment. Albeit there are several studies on solid circulating velocity measurement in CFBs, this article is introducing the first experimental study on solid circulating velocity measurement in a CFB at micro-scale. The experimental studies were done in a novel micro-CFB which was fabricated by micro milling machining 1 mm2 cross-section channels in Perspex and in a 4 mm2 cross-section micro-CFB made by additive manufacturing technology. Soda-lime glass and polymethyl methacrylate (PMMA) micro-particles were employed as solid materials and tap water as the liquid medium. The digital particle image velocimetry (PIV) method was used as a measurement technique to determine the particle velocity in the micro-CFB system and validated by the valve accumulation technique using a novel magnetic micro-valve. The measured critical transition velocity, Ucr, is comparable to the particle terminal velocity, i.e., the normalised transition velocity is approximately 1 in line with macroscopic systems results and our previous study using simple visual observation. As in macroscopic CFB systems, Ucr decreased with solid inventory (1–9%) and finally becomes stable when the solid inventory is high enough (10–25%) and it increases with a reduction in particle size and density.

Design and Investigation of a 3D-Printed Micro-Fluidized Bed

“…This again indicates the influence of wall effects and surface force of particles on solid fluidization. Compared to the fungal pellets, the higher theoretical and extrapolated Ut for particles fluidization was due to the higher density of printed particles, which could be explained from Stokes Law [19]. In addition, different from the dense and solid particles, pellet is actually a core of packed hyphae surrounded by the hairy region that contains the radially growing portion of the hyphae [70].…”

“…Initially, Potic et al [16] proposed the concept of MFB with an inner diameter (ID) of 1 mm. The asserted boundary for MFB witnessed a gradual increase from the submillimeter scale [17,18] to millimeter scale [19,20] and the current centimeter scale [21]. For instance, a fluidized bed reaction analyzer with a 2 cm ID developed by Xu and his colleagues for their thermochemical studies was regarded as micro-scale by them due to the distinguished reactor flow characteristics [22,23].…”

“…In recent years, the fabrication of MFB via 3D-printing techniques has become a hot topic, as the additive manufacturing produces highly complex and/or bespoke geometries in a much cheaper and faster way compared to the traditional workshops [32]. For instance, McDonough et al [33] used the stereolithography printing technique to fabricate a toroidal fluidized bed (50 mm ID), allowing to minimize the particle entrainment by the swirling fluidization, and do Nascimento et al [19] developed a liquid-solid micro-circulating fluidized bed of 2 × 2 mm 2 cross-sections by using digital light processing (Miicraft+ printer, Young Optics Europe GmbH, Jena, Germany) and stereolithography (Form2 printer, Formlabs GmbH, Berlin, Germany), which successfully reduced the circulating fluidized bed size to the micro-bed dimensions.…”

Characteristics of flow fields in the gas–liquid mini‐bubble columns with particle image velocimetry measurements

“…In the measurement methods of multiphase flow characteristics, laser‐based measurement technology has great potential. As a noninvasive visual experimental technology, particle image velocimetry has been widely used in velocity field measurement and structure display of multiphase flow, such as fluid mechanics, aerodynamics, hydraulic engineering, and other fields 26–28 . The classical PIV, consisting on two‐dimensional (2D) investigations of the velocity flow field, is typically referred to as two‐dimensional PIV (2D‐PIV).…”

“…As a noninvasive visual experimental technology, particle image velocimetry has been widely used in velocity field measurement and structure display of multiphase flow, such as fluid mechanics, aerodynamics, hydraulic engineering, and other fields. [26][27][28] The classical PIV, consisting on two-dimensional (2D) investigations of the velocity flow field, is typically referred to as two-dimensional PIV (2D-PIV). The 2D-PIV can measure the 2D velocity field in the flow field in real time, and has the characteristics of little influence of the flow field and high temporal and spatial resolution.…”