Units: W_m in kg/h, P_m in bara.
This is the core engine where areas and velocities are calculated using the formulas from Section 2. Calculate sonic velocity (
Ad≈mm+msρmix⋅Vsoniccap A sub d is approximately equal to the fraction with numerator m sub m plus m sub s and denominator rho sub m i x end-sub center dot cap V sub s o n i c end-sub end-fraction Fixed Excel Setup Blueprint ejector design calculation xls fixed
Comprehensive Guide to Steam Jet Ejector Design Calculations
) will lead to 'choking' or 'backflow' in fixed-nozzle designs." Efficiency ( Units: W_m in kg/h, P_m in bara
In supersonic ejectors, "choking" can occur at the nozzle exit AND the mixing throat. A robust calculation sheet must check for Mach 1.0 at both locations. If the spreadsheet ignores choking at the secondary inlet, it will over-predict suction flow capacity.
In a fixed spreadsheet, avoid =ITERATION or circular references. Use these direct formulas. A robust calculation sheet must check for Mach 1
: $$A_t = \frac\dotm_mP_m \times \frac1C_d \times \sqrt \fracR T_mk \left( \frack+12 \right)^\frack+1k-1 $$ Excel Formula (assuming $R=8314/M_m$ and $C_d = 0.95$): =(B11/B2) * (1/0.95) * SQRT( ( (8314/B7)*B5 / B9 ) * ((B9+1)/2)^((B9+1)/(B9-1)) )
A higher compression ratio requires a tighter mixing throat to prevent backflow or "break" conditions, where the ejector fails to maintain vacuum.
The most critical dimensionless number in ejector design is the Area Ratio ($AR$). $$ AR = \frac\textArea of Mixing Throat\textArea of Nozzle Exit $$ This ratio dictates the operating curve of the ejector.