# Impact of Mesh Resolution and Temperature Effects in Jet Ejector CFD Calculations
## 2 Materials and Methods
### Jet Ejector  
As the geometry of the jet ejector plays an important role in determining its performance, this study focuses on a particular jet ejector designed throughout previous work and is intended to work in a jet ejector refrigeration cycle [18]. Figure 1 illustrates an exemplary geometry of the fixed jet ejector, while Table 1 summarizes the main geometric parameters of the considered ejector, which are schematically represented in the sketch in Figure 1.  
Figure 2 represents the axisymmetric shape of the analyzed jet ejector, designed for refrigeration applications. This ejector was designed to use the refrigerant fluid R1234 yf as the working fluid. Additionally, Table 2 shows the specific boundary conditions used for its design [18].  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**D\({}_{e,1}\) [mm]** & **D\({}_{e,2}\) [mm]** & **D\({}_{e,3}\) [mm]** & **D\({}_{e,4}\) [mm]** & **L\({}_{e,1}\) [mm]** & **L\({}_{e,2}\) [mm]** & **L\({}_{e,3}\) [mm]** & **L\({}_{e,4}\) [mm]** & **\(\alpha_{e,1}\) [\({}^{\circ}\)]** & **\(\alpha_{e,2}\) [\({}^{\circ}\)]** \\ \hline
15.194 & 2.252 & 3.1978 & 5.8862 & 11.01 & 4.4926 & 58.12 & 110.78 & 159.85 & 21.8 \\ \hline \end{tabular}
\end{table}
Table 1: The measured ejector’s dimensions, in regard to Figure 1.  
Figure 1: An illustrative drawing showing the location of individual dimensions.  
Figure 2: The actual geometry of the ejector, represented in 2D-axisymmetric shape, with the main variables noted.  
The working map used to define the jet eject's performance is usually represented by means of a group of characteristic curves, which represents the operating pressures expressed as pressure ratios (\(\tau_{sp}=p_{s}/p_{p}\) and \(\tau_{op}=p_{out}/p_{p}\)) together with the entrainment ratio of the mass flows (\(\omega=\hat{m}_{s}/\hat{m}_{p}\)). These dimensionless parameters are used to create a working map of the eject, which graphically and dimensionlessly represents the behavior of the device under different working conditions (see Figure 3).  
In Figure 3, the solid lines connect the points with the same \(\pi_{\text{sp}}\), represented on the \(\omega\) vs \(\pi_{\text{op}}\) graph. The specific position of these lines depends on the values of \(\pi_{\text{sp}}\), with higher or lower placements corresponding to its value. When operating a jet eject under constant inlet temperatures, varying the pressures alone produces predictable results, as observed in the performance maps. Specifically, the relationship between \(\omega\) and \(\pi_{\text{op}}\) follows a characteristic pattern. It typically begins with a horizontal linear segment (_critical zone_), when the two flows, primary and secondary flows, are blocked followed by a linear decline at a constant angle (_subcritical zone_). The dotted line connects the points of transitions from the critical to subcritical modes (_critical points_). For 3D representation, the plane connecting _critical points_ (*) draws the _best operation plane_, as at these points are where maximum entrainment ratios (\(\omega\)) are obtained together with maximum outlet pressure ratios (\(\pi_{\text{op}}\)). At the bottom of the figure, where the entrainment ratios become negative, the reversed secondary flow causes the eject to be inoperative (_backflow operation_).