from manufacturer curves (like Graham or Croll-Reynolds) for a given absolute pressure, recalibrate your mixing chamber efficiency factor ( ηmixeta sub m i x end-sub ) downward. Summary of Design Variables
, where the geometry is optimized for a specific design point (MDP - Motive Design Pressure). It utilizes high-velocity steam (motive fluid) to entrain and compress a lower-pressure gas (suction fluid). 2. Input Parameters (Data Entry)
If you attempt to pull too much suction gas, the combined volume exceeds the physical limits of the fixed mixing throat diameter (
w=A⋅ErB⋅PeC⋅PcD⋅exp(E+F⋅ln(Pp))w equals cap A center dot cap E r to the cap B-th power center dot cap P sub e to the cap C-th power center dot cap P sub c to the cap D-th power center dot exp open paren cap E plus cap F center dot l n open paren cap P sub p close paren close paren Ppcap P sub p : Motive steam pressure. Pecap P sub e : Entrained vapor pressure. Pccap P sub c : Discharge pressure. : Expansion Ratio ( : Nozzle Throat ( D2cap D sub 2 ) : Based on motive mass flow and pressure. Mixing Chamber Diameter ( D5cap D sub 5 ) : Typically 8 to 14 times the needle/nozzle diameter. Diffuser Length ( XL6cap X cap L sub 6 ) : Sized to allow flow deceleration and pressure recovery. 🧪 Advanced Modeling (CFD & 1-D) ejector design calculation xls fixed
When using a calculation spreadsheet or manual method, the following parameters are critical: Entrainment Ratio ( The ratio of the mass flow rate of the secondary fluid ( ) to the mass flow rate of the primary fluid ( Compression Ratio ( cap C cap R The ratio of discharge pressure to suction pressure. Area Ratio ( cap A cap R
The fluid velocity in the diffuser throat is sonic. These units are sensitive to "off-design" conditions; increasing motive pressure may actually lower suction capacity.
While sophisticated CFD (Computational Fluid Dynamics) software exists, most daily engineering tasks are best handled by a . The benefits include: Speed: Instant results for "what-if" scenarios. from manufacturer curves (like Graham or Croll-Reynolds) for
The spreadsheet must contain a fixed internal lookup table for saturated steam, superheated steam, or ideal gas constants. Unlike dynamic databases, a fixed XLS uses embedded arrays covering 0 to 500°C and 0 to 100 bar. This allows the engineer to select a fluid by index number, preventing VLOOKUP errors.
While a fixed-method spreadsheet is excellent for preliminary design, it is important to recognize its limitations: The constants used (
Calculated based on the sonic velocity of the motive fluid at the throat. Diffuser Throat Diameter ( cap D sub d Pccap P sub c : Discharge pressure
Ejector design relies heavily on thermodynamics and fluid mechanics, specifically the conservation of mass, momentum, and energy. The process is divided into three functional zones:
Build verification checks directly into the sheet using conditional formatting (e.g., highlighting cells red if the calculated Mach number exceeds structural limits).
, specific constants (A through J) are used in empirical correlations to determine Non-Choked Flow: For compression ratios is less than 1.8 , a different set of constants is applied. Motive Mass Flow Rate: For a fixed nozzle, the mass flow rate (