❄️ Refrigerant Capillary Tube Calculator
Enter your capillary tube’s inside diameter, length, pressure drop, and liquid refrigerant properties to get a simplified estimate of mass flow rate.
What This Calculator Does
This calculator gives a simplified estimate of refrigerant mass flow rate through a fixed-restriction capillary tube in a vapor-compression refrigeration system, based on the tube’s diameter, length, the pressure drop across it, and the liquid refrigerant’s properties.
The Formula
It models the liquid refrigerant as an incompressible fluid in laminar flow and applies the Hagen-Poiseuille equation, Q = (π × r⁴ × ΔP) ÷ (8 × μ × L), then converts volumetric flow to mass flow using ṁ = ρ × Q, where r is the tube’s inside radius, ΔP is the pressure drop, μ is the liquid’s dynamic viscosity, L is the tube length, and ρ is the liquid density.
- Important simplification: real capillary tubes typically have refrigerant flashing into a two-phase liquid-vapor mixture partway along their length, which this single-phase liquid model does not capture.
- This is best used as a rough, general educational estimate or a starting point for comparison; actual capillary tube selection is normally done from manufacturer performance data or ASHRAE capillary tube sizing charts/software.
This calculation uses the standard Hagen-Poiseuille laminar flow equation applied as a simplified idealization for general engineering education and planning purposes only.