Research article Determination of minimum pressure drop at different plate spacings and air velocity in a wave-plate mist eliminator Sayed Abdolhossein Banitabaei, 1 Hassan Rahimzadeh 1 * † and Roohollah Rafee 1,2 1 Department ofMechanical Engineering, Amirkabir University of Technology, Tehran, Iran 2 Department of Mechanical Engineering, Semnan University, Semnan, Iran Received 9 August 2010; Revised 26 May 2011; Accepted 27 May 2011 ABSTRACT: In this article, the flow pressure drop across a wave-plate mist eliminator has been studied experimentally by changing both the air velocity and the plate spacing. The measured values for pressure losses have been compared with the results of the available formulas. Despite the literature, this study shows that by decreasing the plate spacing, the pressure loss will not remain constant. Results show that decreasing the plate spacing from 11.5 to 9.5 mm leads to a decrease in pressure loss. However, further decrease in spacing will result in an increased pressure loss. On the basis of dimensional analysis, a dimensionless variable is defined for spacing, and it is shown that the value of 0.24 for this variable gives the minimum pressure coefficient for all cases studied by current experimental setup.  2011 Curtin University of Technology and John Wiley & Sons, Ltd. KEYWORDS: wave-plate mist eliminators; experimental investigation; pressure drop; plate spacing INTRODUCTION Wave-plate mist eliminators are widely used to remove liquid droplets from gas streams in industrial pro- cesses. [1–3] This type of separator is used to pre- vent escaping of the droplets from cooling towers, to restrict pollutant emissions into the environment, to recover valuable liquid droplets dispersed throughout gas streams, to protect downstream equipment against corrosive liquid droplets and to increase purity of gases in transmission lines. In a wave-plate mist eliminator, the droplet-laden gas stream is forced to travel through a series of channels made from zigzag or sinusoidal plates. In contrast to the gas stream, the droplets cannot change their direction at the bends because of their inertia. Therefore, they impinge on plate walls and will be separated from the gas stream. Wave-plate mist eliminators are typically less efficient in removing very small droplets (d < 10 μm) compared to other types of separators such as cyclones; however, they usually have a low pressure drop and are able to collect up to 100% of droplets greater than 10–40 μm depending on their design parameters. [4] Wave-plate *Correspondence to : Hassan Rahimzadeh, Department of Mechani- cal Engineering, Amirkabir University of Technology, Tehran 15875- 4413, Iran. E-mail: rahimzad@aut.ac.ir † Current Address: School of Engineering Systems, Queensland University of Technology, Brisbane, Australia. mist eliminators are preferred in those applications where other types of separators such as wire mesh mist eliminators would rapidly be blocked. Moreover, this type of mist eliminator is used in mass flow rate of droplets up to one-tenth of the air flow rate, and their pressure drop and droplet removal efficiency are relatively independent from inlet mist loading. [5] Regarding the performance evaluation of a mist eliminator, two parameters are important: (1) pressure drop of the air flow across the mist eliminator and (2) droplet removal efficiency. The removal efficiency of an eliminator is defined by the following equation: η = ˙ m d,in −˙ m d,out ˙ m d,in , (1) where ˙ m d,in and ˙ m d,out are the total mass rate of water droplets at the inlet and outlet, respectively. [1] The pressure drop and droplet removal efficiency of an eliminator depend on its geometrical parameters. According to Fig. 1, the main features are the plate spacing (S ), bend angle (α) and the number of bends in each plate (n ). Verlaan has discussed how these parameters affect the performance of a mist eliminator. [6] He noted that decreasing the plate spacing (S ) will increase the droplet collection efficiency, but the gas pressure loss will remain constant. [6]  2011 Curtin University of Technology and John Wiley & Sons, Ltd. Curtin University is a trademark of Curtin University of Technology ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING Asia-Pac. J. Chem. Eng. 2012; 7: 590– Published online 15 July 2011 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/apj.611 597