# Design and Fabrication of a Novel Window-Type Convection Device
## 3 Discussion and Validation of Results
### Effects of Airfoil Camber and Outlet Slit Size on Air Entrainment Performance  
The flow velocity distributions generated by the NACA1412, NACA2412, and NACA4412 airfoils with various slit sizes were examined to investigate the effects of the airfoil camber and outlet slit size on the air entrainment performance of the convection device, as shown in Figure 10, which shows the simulation results of flow velocity distributions at the YZ cross-section of the center of the airflow multiplier. In Figure 10, the upper part is the indoor flow region, and the lower part is the outdoor flow region. The flow velocity is presented by color variation. Dark blue is the low-flow velocity, while light blue is the high velocity. In addition, the gray can be regarded as airflow multiplier and wall. Applying a constant slit size and increasing the airfoil camber enabled increasing the distribution of high-velocity airflow around the slit. Thus, increasing the airfoil  
Figure 8: Areas with boundary conditions (highlighted in blue) in the analysis model. (**a**) The runner inlet of the window-type convection device, (**b**) the flow-field inlet, (**c**) the flow-field outlet, and (**d**) the wall surface. camber can induce low pressure around the outlet slit, entraining outdoor air through the pressure difference. Figure 10: Flow velocity distributions, with fixed airfoil thickness and various airfoil cambers and outlet slit sizes. Figure 9: Relative positions of numerically measured planes in the analysis model. (**a**) 3D view, and (**b**) bottom view. The effects of airfoil camber and outlet slit size on air entrainment performance were quantified according to the mass flow rates on Planes S, M1, M2, and M3 observed using the three airfoils. At identical slit sizes, increasing the airfoil camber had a negligible effect on the mass flow rate on Plane S, although the mass flow rate increased notably when the slit was enlarged (Figure 11a). For example, with a slit of 1.5 mm, all airfoils demonstrated a mass flow rate of approximately 0.016 kg/s, which was three times that of the foils with a 0.3 mm slit. Accordingly, the slit size affected the mass flow rate more than the airfoil camber did. Figure 11b illustrates the effects of the airfoil camber on the mass flow rate on Plane M1 of three airfoils at various slit sizes, suggesting that the airfoil camber notably affected the mass flow rate. For example, the NACA4412 at slit sizes of 1.5, 1.2, 0.9, 0.6, and 0.3 mm attained mass flow rates 1.12, 1.09, 1.07, and 1.23 times higher than those of the NACA1412 at equivalent slit sizes, respectively. Thus, increasing the airfoil chamber can increase the mass flow rate on Plane M1, with a peak air entrainment performance at a slit size of 0.6-0.9 mm. Table 1 presents a summary of the airflow velocity and pressure induced on Plane M1 by all of the airfoils at various slit sizes, which determine the air entrainment performance of the convection device. As shown in Table 1, the higher the flow velocity on Plane M1, the lower its corresponding pressure (negative pressure). These corresponding flow pressure changes were due to changes in the velocity of flow passing the slit, indicating that negative pressure around the slit facilitates the convection device to draw more outdoor air. Figure 11c depicts the mass flow rate at the outlet of Plane M2, which was the sum of those on Planes S and M1, and whose airflow was comprised largely of entrained air. Finally, Figure 11d presents the mass flow rate on Plane M3, which exhibits similar changes to those shown in Figure 11c (namely, decreasing mass flow rate as the airfoil camber  
Figure 11: Mass flow rate (**a**) at the inlet of Plane S, (**b**) on Plane M1, (**c**) at the outlet of Plane M2, and (**d**) at the outlet of Plane M3 in relation to the slit sizes of the NAC1412, NACA2412, and NACA4412 airfoils. decreases); this panel also suggests that the mass flow rate on Plane M3 at a 1.2 mm slit was notably higher than at other slit sizes.