Sensors and Actuators B 184 (2013) 100–105 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journal h om epage: www.elsevier.com/ locate/snb Modelling ultrasonic sensor for gas bubble profiles characterization of chemical column M.H.F. Rahiman a,∗ , R.A. Rahim b,1 , H.A. Rahim b,2 , N.M.N. Ayob b , E.J. Mohamad c,3 , Z. Zakaria a,4 a Tomography Imaging Research Group, School of Mechatronic Engineering, Universiti Malaysia Perlis, Pauh Putra Campus, 02600 Pauh, Perlis, Malaysia b Process Tomography and Instrumentation Research Group, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia c Department of Mechatronic and Robotic, Faculty of Electrical and Electronic Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia a r t i c l e i n f o Article history: Received 29 January 2013 Received in revised form 12 April 2013 Accepted 15 April 2013 Available online 23 April 2013 Keywords: Ultrasonic sensor Gas bubble Ultrasonic measurement Bubble column a b s t r a c t In this paper, we present a modelling and experimental work to characterize gas bubble profiles in chemical column using a pair of ultrasonic sensor. The gas bubble profiles from 2.90 mm to 7.50 mm diameter are of interest in this study. The modelling concerns ultrasonic investigation via transmission- mode technique. The modelling estimation was compared with the experimental data and the gas bubble profile characterizations from the chemical column were deduced. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Liquid/gas columns, also known as bubble columns, are widely used in chemical applications. According to Kantarci et al. [1], a bubble column belongs to a general class of multiphase reactors which consist of three main categories namely, the trickle bed reac- tor (fixed or packed bed), fluidized bed reactor, and the bubble column reactor. A bubble column reactor consists of a cylindrical vessel with a gas distributor at the bottom. The gas is sparged in the form of bubbles into either a liquid phase or a liquid–solid sus- pension [1]. The purpose of the column may be simply to mix the liquid phase. There are wide applications of bubble column such as in process bio-reaction, oxidation, hydrogenation, chlorination and alkylation [2]. Ultrasonic sensors have been successfully applied in flow mea- surement [3], non-destructive testing and it is widely used in medical imaging [4]. The method involves passing ultrasound energy through a fluid via transmitter and receiver sensors that are ∗ Corresponding author. Tel.: +60 4 9885166; fax: +60 4 9885167. E-mail addresses: hafiz@unimap.edu.my, hafizfr@ieee.org (M.H.F. Rahiman), ruzairi@fke.utm.my (R.A. Rahim), herlina@fke.utm.my (H.A. Rahim), normuzakkir@mail.com (N.M.N. Ayob), elmy@uthm.edu.my (E.J. Mohamad), zulkarnay@unimap.edu.my (Z. Zakaria). 1 Tel.: +60 7 5537801; fax: +60 7 5566177. 2 Tel.: +60 7 5535434. 3 Tel.: +60 7 4537502; fax: +60 7 4536060. 4 Tel.: +60 4 9885166; fax: +60 4 9885167. axially spaced along the liquid/gas column. The ultrasonic sensor can be clamped on the column wall so that it does not obstruct the flow. When the sensing area is obstructed by the gas component, the ultrasonic beam is scattered [5]. Thus, the sensing area could locate the gas distributions by measuring the ultrasonic attenuation at receiver channels [6]. This research focuses modelling ultrasonic sensor for charac- terization of gas bubble profiles in chemical column. This article begins with modelling the attenuation in the liquid column and it consists of three parts. It starts with a discussion on attenuation of ultrasonic energy due to absorption mechanism and an assumption was made at the end of the section. Next, the discussion continues with modelling attenuation at media interfaces on the experimen- tal column followed by scattering phenomenon. Finally, the linear model for ultrasonic sensor is estimated and compared with the experimental studies. 2. Attenuation in liquid column Attenuation is the loss of acoustic energy from a sound beam. In general, the sources of the attenuation can be very complex [7]. However, when an ultrasonic penetrates a medium, there are three main attenuation mechanisms [8] which will be discussed in the following section: (i) Absorption mechanisms that convert acoustic energy into thermal energy. 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.04.062