Performance evaluation of venturi aeration system

The venturi aeration is an effective practice to increase the dissolved oxygen accessibility in the water bodies. This study aims to optimize the various geometrical parameters of the venturi aeration system. A non-dimensional technique was applied to find the optimum performance of various geometric parameters i.e. throat lengths (t_l), number of air holes (N), and converging and diverging angles (α and β). These experiments have been carried out using 1124 L capacity of tank having dimensions of 105 cm long, 105 cm wide and 102 cm deep. The experiments were conducted at a constant flow velocity of water (1.096 m/s) with varying throat length (t_l = 20–100 mm keeping 20 mm as interval between two consecutive length), number of air holes (N = 1–17 at an equal hole to hole distance of 5 mm between them), and converging and diverging angles (α and β = 10°, 15°, 20° and 25°). Multiple non-linear regression equations were also developed from the linear relation with the dependent variable (Non-dimensional form of standard aeration efficiency, NDSAE) and independent variables (t_l and N). With the geometrically optimized venturi aerator the optimum performance was found for t_l =100 mm, N = 17, and α and β = 15°. The maximum value of standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) obtained was 0.0216 kgO₂/h and 0.611 kgO₂/kWh respectively. From the non-dimensional study, it was found that the NDSAE is the function Reynolds number (Re) and Froude number (Fr). The simulation equations were developed on the basis of Re and Fr for NDSAE, and subjected to 7.378 × 10⁻⁶ < Re < 3.689 × 10^-5 and 0.163 < Fr < 0.817, respectively.     

一种新型管式曝气装置的设计与试验

随着水产养殖业逐渐向高密度、集约化方向的发展,为实现氧气(O_2)高效溶解、二氧化碳(CO_2)调控、流态改善等目的,急需研制新型高效曝气装置,开发高效节能的曝气技术。基于气水两相溶解的双膜理论和文丘里原理,设计开发了一种管式曝气装置,经初步试验获得了影响增氧性能的关键技术参数,并以此为基础对曝气装置进行优化设计,研究新型节能增氧技术。试验结果表明,管式曝气装置中影响曝气效果的因素有水面高程(Hw)、缩径(D_1/D_2)、旋混结构、进气口大小、进气量等。水面高程、缩径、进气口越大,进气量越充足,曝气装置的增氧效果越高;而额外增加延长结构和旋混结构后,曝气装置水头损失增大、进气量下降,从而导致增氧效果显著下降。该装置利用额外水流动力实现增氧,是一种高效、节能、经济的新型曝气装置,可为水产养殖提供一种新的增氧方法。     

Effects of different layouts of fine-pore aeration tubes on sewage collection and aeration in rectangular water tanks

Sewage collection and dissolved oxygen (DO) management have always been the focus of industrialized recirculating aquaculture. However, there are still no reports on how to achieve efficient sewage collection and increase DO in rectangular water tanks. In the present study, the performance of sewage collection and aeration in rectangular water tanks were compared among three fine-pore aeration tubes (disc-type diffuser, four corner-type diffuser and distribute-type diffuser) layouts at three airflow rates, 6, 18, and 30 m³/h. The results of computational fluid dynamics (CFD) modeling and bait collection tests revealed that sewage collection using the four corner-type diffuser was better than using the disc-type diffuser and the distribute-type diffuser. Using the four corner-type diffuser, a strip-shaped sewage collector could be set up at the bottom of the tank to collect sewage at an airflow rate of 18 m³/h and a disc-shaped sewage collector could be set up at the bottom of the tank to collect sewage at an air flow rate of 30 m³/h. In terms of aeration, volumetric oxygen transfer coefficient (K_La₂₀), standard oxygen transfer rate (SOTR), and standard oxygen transfer efficiency (SOTE) of the distribute-type diffuser were all the highest at the three airflow rates, followed by four corner-type diffuser, and finally the disc-type diffuser, indicating that the aeration performance in the distribute-type diffuser was optimal. However, there were no significant differences in K_La₂₀, SOTR, and SOTE between the four corner-type diffuser and the distribute-type diffuser at both 18 and 30 m³/h airflow rates. Therefore, four corner-type diffusers were the optimal choice for recirculating aquaculture, considering the sewage collection and aeration requirements. The results of the present offer novel insights on the application of CFD in recirculating aquaculture, in addition to basic data and theoretical guidance on how to achieve efficient sewage collection and aeration in recirculating aquaculture.