## 1 Introduction  
Submicron-sized particles suspended in air (aerosols) are hazardous as they can cause more adverse effects compared to larger particles [1]. Therefore, studying pretreatment technologies for removing submicron-sized particles is important [2]. In a conventional electrostatic precipitator (ESP), all particles are first charged by unipolar ions and then moved toward the collecting electrodes. Agglomeration is an effective method to improve ESP collection efficiency, as smaller particles either are swept and scavenged by larger particles or form larger particles via agglomeration. Unipolar charged aerosol agglomeration induces charging with a single polarity, causing relative movement due to differences in particle size and mass. Several studies including [PERSON] et al. [3] and [PERSON] et al. [4] have investigated the effect of unipolar charged particle agglomeration. Bipolar charged aerosol agglomeration, another method of electric agglomeration, operates on the principle that half of the particles in an air flow are positively charged in a corona charger, while the other half are negatively charged in another corona charger. These oppositely charged particles enter the agglomerator together and oscillate in an alternating current (AC) electric field [5, 6]. Several studies have investigated the effect of bipolar charged particle agglomeration in an AC electric field, such as those by [PERSON] et al. [5], [PERSON] et al. [7], [PERSON] et al. [8], [PERSON] et al. [9], [PERSON] et al. [10], and [PERSON] et al. [11]. Recently, [PERSON] and [PERSON] [12] reported a 25-27% decrease in the mass concentration of NaCl aerosols (100 nm) by attaching them to Arizona test dust 4 particles (1 \(\mu\)m) flowing together with the NaCl particles when an alternating current (AC; 10 kV/cm, 60 Hz) was applied to the agglomerator (the face velocity was 0.1 m/s, resulting in a residence time of 3 s). This decrease was in good agreement with the one theoretically obtained from an agglomeration model. In the work of [PERSON] and [PERSON] [12], the concentration and size of NaCl after a certain period of time (3 s) were derived from the initial concentration and size. Aerodynamic agglomeration, also known as turbulent agglomeration, has been extensively studied to improve the removal of PM2.5 (particulate matter smaller than 2.5 \(\upmu\)m) suspended in gas. In the study by [PERSON] et al. [2], vortex generators were evenly arranged in an agglomeration chamber (face velocity = 15 m/s, residence time \(\approx\) 0.1 s, blue gas flow rate = 350 m\({}^{3}\)/h) installed at the inlet of an ESP. The number concentration of PM2.5 at the inlet of the agglomeration chamber was 1.93 \(\times\) 10\({}^{7}\) particles/cm\({}^{3}\), which decreased to 1.44 \(\times\) 10\({}^{7}\) particles/cm\({}^{3}\) at the outlet of the agglomeration chamber (25.4% decrease). [PERSON] et al. [13] studied aerodynamic agglomeration to promote the removal of PM10 aerosols. Their aerodynamic agglomerator had a square cross-section with eight pairs of vortex generators alternately arranged in two columns. The PM10 number concentration was approximately 9.08 \(\times\) 10\({}^{6}\) particles/cm\({}^{3}\) in the original blue gas, which reduced to 7.69 \(\times\) 10\({}^{6}\) particles/cm\({}^{3}\) after turbulent agglomeration (15.4% decrease). The gas velocity was 10 m/s and the gas flow rate was 300 m\({}^{3}\)/h (residence time \(\approx\) 0.3 s). [PERSON] et al. [14] installed two aerodynamic agglomerators (blue gas velocity = 15.2 m/s, gas flow rate = 350 m\({}^{3}\)/h, residence time \(\approx\) 0.18 s) in front of the electrostatic precipitator of a 330 MW PC-fired boiler. The PM2.5 and PM10 particles were swept and scavenged by 50-100 \(\upmu\)m particles, resulting in mass concentration decreases of 56.2% and 50.6% for PM2.5 and PM10 particles, respectively. [PERSON] et al. [15] investigated the structural characteristics of vortex generators affecting particle agglomeration. Triangular vortex generators were used for turbulent flow.