Calculator Inputs
Example Data Table
| Fluid | Density (kg/m^3) | Flow (m3/h) | dP (bar) | Pump Eff (%) | Motor Eff (%) | Safety (%) | Recommended Motor (kW) |
|---|---|---|---|---|---|---|---|
| Liquid Nitrogen (LN2) | 808 | 10 | 5 | 60 | 90 | 15 | 2.96 |
Formula Used
- Flow conversion: Convert flow to m^3/s based on unit.
- Total differential pressure: dP_total = dP_input + rho * g * dz.
- Hydraulic power: P_hyd (W) = Q (m^3/s) * dP_total (Pa).
- Shaft power: P_shaft = P_hyd / eta_pump.
- Motor input: P_motor = P_shaft / eta_motor.
- Recommended motor size: P_design = P_motor * (1 + safety).
How to Use This Calculator
- Select the calculation method that matches your gauges or transmitters.
- Choose the fluid, then confirm or override the density value.
- Enter flow rate and pressure values in your preferred units.
- Add elevation change if the line rises or falls significantly.
- Set pump and motor efficiency from vendor data or nameplates.
- Use safety margin for startup loads, fouling, and uncertainty.
- Submit to view results above the form, then export CSV or PDF.
Why pump power matters on cryogenic worksites
Cryogenic transfer skids often run near tight margins because low temperatures increase brittleness risk and make shutdowns expensive. Correct power sizing keeps flow stable during commissioning, purge cycles, and controlled cooldown. Undersized motors can stall on startup, while oversized motors waste energy, raise inrush demands, and inflate cable and breaker selections.
Key inputs and typical ranges
Use measured flow and total differential pressure across the pump, including losses from valves, hoses, and vaporizers. For common services, density can range from about 450 kg/m^3 for LNG to roughly 1400 kg/m^3 for liquid argon. Practical pump efficiency often falls between 45% and 75%, and motor efficiency commonly ranges from 85% to 95% depending on frame size, VFD use, and loading.
Unit conversions and pressure methods
The calculator converts flow to m^3/s and pressure to pascals before computing power. If you have a single dP value from a transmitter, select the differential method. If you record suction and discharge pressures, select the two pressure method so the tool can compute dP consistently, clamp negative values, and highlight instrument or tap-line errors.
Interpreting results for motor selection
Hydraulic power represents ideal energy delivered to the fluid. Shaft power accounts for pump losses, and motor input accounts for electrical losses. Elevation change adds or subtracts static head using rho*g*dz, which can be significant on tank farms and elevated pipe racks. Apply a safety margin, typically 10% to 20%, to cover transient loads, minor fouling, valve throttling, and measurement uncertainty, supporting dependable starts and continuous duty.
Cost planning and reporting
Daily energy is calculated from motor input power and operating hours, then multiplied by your tariff for an operating-cost estimate. Use this figure to compare transfer durations, evaluate generator capacity, and justify efficiency upgrades. Export the CSV for tender worksheets and progress tracking, or generate a PDF report for method statements, QA records, and handover documentation for site teams.
FAQs
1) What does total dP include?
Total dP should represent the pressure rise the pump must deliver, including line friction, fittings, filters, control valves, and any equipment in the transfer path. Add static head from elevation change when pumping uphill.
2) Which pressure method should I choose?
Use differential pressure when you have a single transmitter reading across the pump. Use suction and discharge when separate gauges are logged. The tool subtracts suction from discharge and prevents negative dP.
3) How do I select density for cryogenic liquids?
Density varies with temperature and composition. Start with typical values from your supplier or datasheet, then override with site measurements if available. Small density changes usually shift power proportionally.
4) Why does elevation change affect power?
Elevation adds static head. A positive rise increases required pressure by rho*g*dz, increasing power. A negative drop reduces required pressure. Confirm sign conventions and units when field elevations are large.
5) What safety margin is reasonable?
For steady transfer, 10% to 20% is common. Increase margin when startup conditions are uncertain, valves may throttle heavily, or fouling is expected. Avoid excessive margin that drives oversizing and high inrush.
6) How should I use the cost estimate?
It is a planning figure based on input power, hours, and tariff. Use it to compare scenarios and support budgeting. For billing, apply utility demand charges, power factor, and actual runtime data.