Inputs
Example Data Table
| Scenario | Pin (kPa) | Pout (kPa) | L (m) | D (mm) | Elevation (m) | K total | Estimated flow (m³/h) | Velocity (m/s) |
|---|---|---|---|---|---|---|---|---|
| Truck-to-tank transfer | 350 | 200 | 150 | 150 | 0 | 3.0 | ≈ 100 | ≈ 1.6 |
| Uphill transfer, same line | 350 | 200 | 150 | 150 | 10 | 3.0 | Lower than baseline | Lower than baseline |
| Higher losses with more fittings | 350 | 200 | 150 | 150 | 0 | 8.0 | Lower than baseline | Lower than baseline |
Formula Used
1) Driving pressure balance
The calculator balances usable driving pressure against hydraulic losses: pipe friction + minor losses + valve losses.
ΔPdrive = (Pin − Pout) + ΔPpump − ρ g Δz
and a safety factor reduces usable driving pressure.
2) Darcy–Weisbach for pipe friction
ΔPpipe = (ρ v² / 2) · f · (L / D)
where v = Q / A.
3) Minor losses from fittings
ΔPminor = (ρ v² / 2) · K,
using either a manual K total, a fittings list, or both.
4) Friction factor
For laminar flow f = 64 / Re.
For turbulent flow the Swamee–Jain correlation is used:
f = 0.25 / [log10(ε/(3.7D) + 5.74/Re^0.9)]².
5) Optional valve loss from Cv
If a Cv is provided, valve drop is estimated using a common liquid relation,
then converted into SI pressure units and added to total losses.
How to Use This Calculator
- Choose a mode: compute flow from pressures, or compute required pressure for a target flow.
- Enter line length, inner diameter, elevation change, and LNG properties (density and viscosity).
- Add losses using a manual K, the fittings list, and optional valve Cv if applicable.
- Set a safety factor to reserve margin for uncertainty and operational variability.
- Press Calculate to see results above the form.
- Use consistent pressure basis (all gauge or all absolute).
- For cryogenic systems, verify allowable pressure ratings and insulation performance.
- Check that outlet pressure stays above process minimum to reduce flashing.
- Export CSV/PDF for shift handovers, QA, and commissioning packs.
Design Inputs That Drive LNG Transfer Capacity
Transfer capacity on construction sites is governed by available differential pressure and total hydraulic losses. This calculator combines pipe friction, fitting losses, optional valve restriction, and elevation effects to estimate achievable LNG flow. Typical temporary transfer packages use short to moderate hose or pipe runs, but fittings, quick-couplers, and control valves can dominate losses when diameters are small.
Pressure Margin and Elevation Effects
A positive elevation change increases static pressure demand by ρgΔz. For LNG near 450 kg/m³, a 10 m uphill transfer adds roughly 44 kPa of static requirement. Adding a safety factor reduces usable driving pressure to preserve operational margin for temperature swings, composition changes, and instrumentation uncertainty.
Pipe Friction, Roughness, and Reynolds Number
The Darcy–Weisbach method links friction loss to velocity squared, so small diameter reductions can sharply increase losses. The calculator estimates Reynolds number and selects a laminar or turbulent friction model. Rougher pipe or corrugated hose increases the friction factor and reduces flow for a fixed pressure drop, especially at higher velocities.
Minor Losses from Fittings and Valves
Minor losses are modeled with a summed K value. Elbows, tees, and valves add (ρv²/2)·K to the pressure drop. If a valve Cv is provided, the calculator adds an estimated valve ΔP based on flow and specific gravity. This helps compare throttled control strategies against full-open transfer scenarios.
Example Data for a Typical Transfer Line
Example: Pin 350 kPa, Pout 200 kPa, L 150 m, D 150 mm, elevation 0 m, ρ 450 kg/m³, μ 0.20 mPa·s, K total 3.0, safety factor 10%. The calculator will typically return a flow close to 100 m³/h with velocity near 1.6 m/s, depending on roughness and fitting selections.
| Input | Value | Unit | Notes |
|---|---|---|---|
| Driving ΔP (Pin−Pout) | 150 | kPa | Before safety factor |
| Pipe length | 150 | m | Straight length only |
| Inner diameter | 150 | mm | Use true ID for hoses |
| Minor loss K total | 3.0 | — | Fittings combined |
| Estimated flow | ≈ 100 | m³/h | Illustrative baseline |
FAQs
1) Should I enter gauge or absolute pressure?
Either is fine, but be consistent for inlet and outlet. If you use absolute pressure, keep all pressures absolute to avoid incorrect differential pressure and wrong flow results.
2) What density and viscosity should I use for LNG?
Use values from your supplier or process datasheet at operating temperature. LNG density often falls roughly 410–500 kg/m³, while viscosity is commonly near 0.1–0.3 mPa·s.
3) Why does flow drop sharply when diameter decreases?
Friction and minor losses scale with velocity squared. Smaller diameter increases velocity for the same flow, which raises losses rapidly and reduces achievable flow for a fixed pressure differential.
4) How do I account for many couplers and valves?
Use the fittings list and/or add a manual K total that represents couplers, strainers, and miscellaneous items. If a control valve dominates, consider entering its Cv to estimate its ΔP.
5) What does the safety factor do?
It reduces usable driving pressure to reserve margin for uncertainty. Higher safety factors lower predicted flow, helping you plan conservatively for field variability and non-ideal conditions.
6) What if the calculator shows negative usable driving pressure?
That indicates the available differential pressure cannot overcome static head plus losses. Reduce elevation demand, increase inlet pressure, add pump head, increase diameter, or lower target flow.
7) Are the results suitable for final cryogenic design?
This tool supports planning and comparison. Final design should verify allowable pressures, flashing margins, insulation performance, and vendor data for cryogenic valves and hoses.