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Capillary-Tube Pressure-Drop Screening Calculator — result sheet
Estimate single-phase frictional pressure drop, Reynolds number, velocity, and head loss in a small tube from flow, fluid properties, length, diameter, and roughness.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Area = πD²/4; velocity = mass flow ÷ (density × area); Reynolds number = ρvD/μ; friction factor = 64/Re for laminar flow or a Swamee–Jain estimate otherwise; Darcy–Weisbach pressure drop = f(L/D)(ρv²/2).
A capillary tube can have strong frictional losses, but a real refrigerant device may enter two-phase flow. This page therefore labels itself a single-phase screening model: it calculates velocity, Reynolds number, an explicit friction-factor branch, Darcy–Weisbach pressure drop, and equivalent head loss without pretending to select a working refrigeration component.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Mass flow rate — kg/s; minimum 1.0E-9; maximum 1000
- Fluid density — kg/m³; minimum 1.0E-6; maximum 20000
- Dynamic viscosity — Pa·s; minimum 1.0E-12; maximum 1000
- Tube length — m; minimum 1.0E-6; maximum 1000000
- Inner diameter — m; minimum 1.0E-9; maximum 100
- Absolute roughness — m; minimum 0; maximum 1
- Gravitational acceleration — m/s²; minimum 1.0E-6; maximum 100
Worked example
| Input | Value |
|---|---|
| Mass flow rate | 0.001 |
| Fluid density | 1100 |
| Dynamic viscosity | 0.0002 |
| Tube length | 1.5 |
| Inner diameter | 0.001 |
| Absolute roughness | 1.0E-6 |
| Gravitational acceleration | 9.80665 |
The scenario gives about 1.159 m/s mean velocity, Reynolds number 6,374, and a frictional pressure drop of roughly 39 kPa using the stated single-phase approximation.
Assumptions and limits
- The fluid is single phase with constant density and dynamic viscosity along the tube.
- The tube is circular and the entered diameter is the internal diameter.
- The pressure drop is frictional and fully developed; fittings, inlet effects, elevation, and heat exchange are omitted.
- Laminar flow uses 64/Re; higher-Re flow uses a Swamee–Jain estimate with relative roughness.
- The transitional range is reported as uncertain rather than being hidden.
- Real refrigerant capillary sizing needs thermodynamic state, flashing, oil, safety, and validated design data.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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