# Design and Application of New Aeration Device Based on Recirculating Aquaculture System
## 2 Materials and Methods
### Design and Parameter Selection  
#### 2.2.1 Key Structure of Microporous Aeration Component: Centrifugal Fan  
The centrifugal fan is the core component of the microporous aeration component driving water oxygenation. Two main aspects were considered in the calculation of its parameters. On one hand, the rated boost pressure of the fan has to be greater than the sum of the actual outlet aeration loss pressure and the water depth pressure, i.e., \(\Delta P\geq\Delta P_{1}\); on the other hand, the fan's outlet airflow rate has to satisfy the overall oxygen demand of the cultured fish and the other organisms in the water, i.e., \(q_{v}\geq q_{v_{2}}\). However, under actual use conditions, the outlet airflow (\(q_{v_{2}}\)) is affected by a variety of outdoor conditions, including temperature (\(T\)), relative humidity (\(d\)), air pressure, etc. ; thus, the outdoor test conditions need to be determined prior to calculating the outlet airflow. Figure 2: Specific structure of the NAD: (A) impeller aeration component; (B) microporous aeration component. (1) Load-bearing float; (2) feeder; (3) control box; (4) inclined plate adjusting rod; (5) centrifugal fan; (6) aeration pipeline; (7) water baffle plate; (8) aeration disc; (9) buoy; (10) bearing seat; (11) water-flow-generating impeller; (12) electric motor for component; (13) coupling; (14) impeller shaft; (15) bearing. This study was conducted in an environment with maximum temperature \(T\) = 20 \({}^{\circ}\)C and average relative humidity \(d\)= 80%. The RAS had tank area \(A\)= 110 m\({}^{2}\), a maximum fish load of 80 kg/m\({}^{2}\), average hourly oxygen consumption \(K_{1}\)= 39 \(\times\) 10\({}^{-4}\) kg/(h\(\cdot\)kW), and hourly ammonia discharge from the farmed fish \(K_{2}\)= 57 \(\times\) 10\({}^{-4}\) kg/(h\(\cdot\)kW). Based on work by [PERSON] et al. [6], the necessary theoretical air supply, \(q_{v_{1}}\)= 185.3 m\({}^{3}\)/h, was computed, and Equation (1) displays the actual output air volume of the aquaculture tank under standard conditions:  
\[q_{v_{2}}=q_{v_{1}}\frac{T_{2}P_{1}(1+d_{2})}{T_{1}P_{2}(1+d_{1})}=q_{v_{1}} \frac{T_{2}P_{1}(1+d_{2})}{T_{1}P_{2}} \tag{1}\]  
where \(q_{v_{1}}\) denotes the theoretical volume of gas required for the aquaculture tank; \(T_{1}\) and \(T_{2}\) denote the absolute temperature of the gas under standard and actual conditions, respectively (in K); \(P_{1}\) and \(P_{2}\) denote the inlet pressure of the blower under standard and actual conditions, respectively (in kPa); and \(d_{1}\) and \(d_{2}\) denote the air moisture content under standard (equal to 0.0073, generally negligible) and actual conditions, respectively (dimensionless). For the microporous aeration component in the form of the arrangement of the gas delivery pipe, the aeration diffuser determines the pressure loss of the device. The same kind of aeration diffuser as that in the study by [PERSON] [15] was used for the loss (\(P_{g}\)) in the fan distribution pipe in order to simplify the calculation. The parameters of the pipeline losses are included in Table 1, and the arrangement of eleven branch pipes. All pipelines were of tee type. With the aeration diffuser pressure loss, \(h_{0}\)= 1.5 kPa, one can compute the overall loss of the aeration pipeline, taking into account the resistance loss due to diffuser clogging. The pressure losses in the main pipe (\(h_{1}\)) and branch pipe (\(h_{2}\)) were estimated using the pressure loss calculation presented, as indicated in Equation (2):  
\[P_{g}=h_{0}+h_{1}+h_{2} \tag{2}\]  
where \(P_{g}\) denotes the total loss of the aeration pipeline (in kPa) and \(h_{0}\), \(h_{1}\), and \(h_{2}\) denote the pressure losses of the bottom aerators, main pipeline, and branch pipeline and along the course, respectively (in kPa).