Research Note pubs.acs.org/IECR
Particle Image Velocimetry (PIV) Investigation of Flow Characteristics in Confined Impinging Jet Reactors Zhengming Gao, Jing Han, Yingdao Xu, Yuyun Bao, and Zhipeng Li* State Key Laboratory of Chemical Resource Engineering, School of Chemical Engineering, Beijing University of Chemical Technology, Mailbox 230, Beijing 100029, People’s Republic of China ABSTRACT: The flow characteristics in confined impinging jet reactors (CIJRs) were investigated, using particle image velocimetry. The effects of Reynolds number (Re), jet velocity ratio (u1/u2), jet diameter (d), and the factor L (defined as the distance between the axes of two jets and the top wall of the CIJR chamber) on the flow characteristics of CIJRs were discussed. The similarity of the turbulent flow in CIJRs was extended to the operating conditions with high Reynolds numbers, ranging from Re = 10 620 to Re = 21 210. The position of the stagnation point in CIJR is closely related to u1/u2, but independent of d. The decrease of the ratio of the factor L to impinging jet diameter (L/d) from 4 to 1.5 can increase the values of turbulent kinetic energy and intensify momentum transfer and mixing in the impinging region of CIJR. The present study shows that CIJRs are ideal reactors for rapid chemical reactions, and optimized parameters are helpful for the design and operation of such reactors.
1. INTRODUCTION Confined impinging jet reactors (CIJRs) are widely used in various process industries, such as absorption and desorption,1 drying,2 extraction,3 mixing,4−7 bioreaction,8 crystallization,9 and precipitation.10 The principle of CIJRs is to make at least two impinging jets collide with each other and intensify the momentum, heat, and mass transfer in the impinging region. Therefore, CIJRs offer many advantages for rapid chemical processes. In recent years, there has been a renewed interest in these devices, because they can achieve good mixing much faster than other reactors such as stirred tanks. Several mixing studies of CIJRs have been published over the past decades. Johnson and Prud’homme11 performed a micromixing study on a second-order parallel dimethoxypropane (DMP) reaction and discussed the effect of reactor geometry and operating conditions on the micromixing. Liu and Fox12 used a computational fluid dynamics (CFD) model for computational studies of micromixing with a DMP reaction in the CIJR with impinging diameters of 0.5 mm. Gavi et al.13 studied the mixing and reaction in CIJRs by means of CFD method. Siddiqui et al.14 investigated the energy dissipation rate and mixing efficiency of CIJRs with low Reynolds number (Re) values, using iodide−iodate reactions. A few studies have focused on the flow characteristics in CIJRs. Liu et al.15 employed microscopic particle image velocimetry (microPIV) techniques and CFD procedures to study a planar microscale CIJR with Re values in the range of 211−1003. Icardi et al.16 investigated the flow fields in a CIJR with four inlet flow rates, using microPIV and direct numerical simulation, presenting both the mean and the fluctuation velocity fields. However, the effect of geometric parameters and operating conditions, such as jet diameter, jet velocity ratio, and the distance between the axes of two jets and the top wall of CIJR chamber (L), on the flow characteristics of CIJRs has not been reported until the present work. Motivated by the great potential of CIJRs and the need for understanding the flow characteristics in CIJRs to promote beneficial applications, we determined (1) the mean velocity © 2013 American Chemical Society
and turbulent kinetic energy (TKE) distributions at high Reynolds numbers, (2) the relationship between the stagnation point and mean velocity ratio for impinging jets with different diameters, and (3) the effect of the factor L on TKE distribution.
2. EXPERIMENTAL SECTION 2.1. Experimental Setup. A schematic diagram of the experimental apparatus is shown in Figure 1. The apparatus
Figure 1. Experimental setup: (1) confined impinging jet reactor (CIJR), (2) storage tank, (3) rotameters, (4) centrifugal pumps, and (5) valves.
consists of five parts: (1) a CIJR made of copper and manufactured by using computer-controlled machine tools, (2) a storage tank made of acrylic for the circulation of deionized water, (3) two rotameters (LZB-15, Changzhou Qinfeng Flowmeter Corporation, China) to measure the flow rates of the two jets of Received: Revised: Accepted: Published: 11779
March 21, 2013 June 22, 2013 July 26, 2013 July 26, 2013 dx.doi.org/10.1021/ie400891u | Ind. Eng. Chem. Res. 2013, 52, 11779−11786
Industrial & Engineering Chemistry Research
Research Note
Figure 2. Dimensions and solid model of a CIJR (yellow: x−z plane; green: x−y plane).
Table 1. Operating Conditions for CIJRs Group 1 Group 2
Group 3
d1 (mm)
d2 (mm)
u1 (m/s)
u2 (m/s)
Re1
Re2
L (mm)
3 3 4 5 3
3 3 4 5 3
3.54−7.07 7.86 4.53 3.52 5.89
3.54−7.07 7.07−8.65 4.11−5.05 3.23−3.87 5.89
10 620−21 210 23 580 18 120 17 600 17 670
10 620−21 210 21 210−25 950 16 440−20 200 16 150−19 350 17 670
7.5 7.5 7.5 7.5 4.5−12
Figure 3. Instantaneous flow field on x−z plane of CIJR at Re = 21 210.
the particles were less than one-quarter of the sizes of the interrogation windows and the thickness of the lightsheet. Thus, Δt varied from 8 μs to 22 μs when the mean jet velocity was in the range of 8.65−3.23 m/s. The measured images were interrogated by 32 × 32 pixels windows with 50% overlap, and then instantaneous velocities were obtained by using a twoframe cross-correlation algorithm. The spatial resolution of the velocity vectors was ∼0.21 mm. The statistic independency was verified on the mean and fluctuating velocities, and the difference between the fluctuating velocities calculated from 200 and 300 pairs of images was
