Contents lists available at ScienceDirect Chemical Engineering Science journal homepage: www.elsevier.com/locate/ces Dynamics of gas–liquid flow in a cylindrical bubble column: Comparison of electrical resistance tomography and voidage probe measurements Brajesh K. Singh, Abdul Quiyoom, Vivek V. Buwa ⁎ Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi 110016, India ARTICLE INFO Keywords: Electrical resistance tomography Voidage probe Dynamics Gas volume fraction Bubble column ABSTRACT Gas–liquid flow in bubble columns is inherently unsteady, and dynamics of such flow is known to influence local mixing, mass and heat transport and therefore, the performance of bubble column reactors. The present work is carried out to verify dynamics of gas–liquid flow measured using time-resolved Electrical Resistance Tomography (ERT) with the measurements performed using in-house developed voidage probes. Experiments were performed in a cylindrical bubble column under dilute to dense conditions (superficial gas velocity (U G ) in the range of 1–40 cm/s). The instantaneous and time-averaged gas volume fraction distribution was measured using the ERT and voidage probes for uniform and local spargers. The time-averaged gas volume fraction measured using both the techniques was found in a quantitative agreement for all U G and sparger configurations considered in the present work. The low-frequency oscillations ( < 1 Hz) generated by mean- dering motion of bubble plume and high-frequency oscillations (1–10 Hz) generated by bubble-scale processes, measured using the ERT and voidage probes were in a satisfactory agreement. The results reported in the present work will help to benchmark the ERT to infer the dynamics of gas–liquid flow and to validate the dynamic characteristics predicted using CFD models under dense flow conditions. 1. Introduction Several technologically important process equipment used in power generation, chemical and bio-chemical industries involve dense gas– liquid flows with or without phase change, for example, bubble columns, gas–liquid stirred vessels, boilers and other process equip- ment. For efficient design and scale-up of these reactors or process equipment, measurement of gas volume fraction distribution is im- portant in addition to other flow/process variables, especially under dense operating conditions that are relevant to the industry. Bubble column is one of the aforementioned process equipment that is used extensively as a contactor or a reactor due to several advantages e.g. high heat- and mass-transfer rates, low operating and maintenance costs. Gas–liquid flows in bubble columns are inherently unsteady in nature and dynamics of such flows is known to influence mixing, heat and mass transport performance of bubble columns. It is, therefore, important to characterize the dynamics of gas–liquid flow, particularly under dense flow conditions. Over last few decades, several intrusive (e.g. voidage probes (conductivity or resistivity probes), optical fiber probes etc. (Boyer et al., 2002; Buwa and Ranade, 2005; Cartellier and Barrau, 1998; Chabot et al., 1998; Chaumat et al., 2007; Magaud et al., 2001; Moujaes, 1990; Shiea et al., 2013)) and non-intrusive (e.g. γ-ray tomography, electrical resistance tomography (ERT), electrical impe- dance tomography (EIT), X-ray tomography etc. (Dickin and Wang, 1996; Roy et al., 1997; Warsito and Fan, 2001; Warsito et al., 2007; Young et al., 1991)) techniques have been developed and used for the measurement of gas volume fraction distribution in bubble columns. The intrusive techniques provide local/point measurements whereas non-intrusive techniques provide distribution over a cross-section with different spatial and time resolutions. The advantages and disadvan- tages of different intrusive and non-intrusive techniques and their applications to multiphase flows are discussed in detail in the review articles by Boyer et al. (2002); Chaouki et al. (1997) and Mudde (2010). While conventional X-ray tomography (except the recent develop- ments on ultrafast X-ray tomography) and γ-ray tomography provide time-averaged measurements, ERT is a non-intrusive technique that provides time-resolved measurements. Further, unlike safety and cost issues associated with X-ray or γ-ray tomography, ERT can be applied to laboratory- and to large-scale bubble columns easily for online measurements of gas volume fraction distribution. It measures the electrical conductivity of mixture by applying a voltage to the electrodes mounted on the column periphery and subsequently volume fraction of a phase, averaged over a certain volume, is calculated (Dickin and http://dx.doi.org/10.1016/j.ces.2016.10.006 Received 28 May 2016; Received in revised form 27 September 2016; Accepted 6 October 2016 ⁎ Corresponding author. E-mail address: vvbuwa@iitd.ac.in (V.V. Buwa). Chemical Engineering Science 158 (2017) 124–139 0009-2509/ © 2016 Elsevier Ltd. All rights reserved. Available online 07 October 2016 crossmark