Refrigerant Capillary Tube Calculator

Use our refrigerant capillary tube calculator to adjust your cooling device's current capillary tube system when changing tube size.

All-liquid mass flow10.9 kg/hour3.0278 g/s treating the refrigerant as an incompressible LIQUID the whole way. Real flow is substantially lower — see the limitation below

Flow velocity5.0197 m/s

Reynolds number26,771.5turbulent

Friction factor0.02474Blasius, 0.3164 Re^(−0.25)

Pressure drop required9.5 barfrom 12 bar condensing to 2.5 bar evaporating

Pressure gradient4.75 bar per metre

Flow at a 10% larger bore13.8328 kg/hour26.9% more. Flow goes roughly as bore to the power 2.5 but only as the inverse square root of length, so a small bore change swamps a large length change — which is why tubes are specified by bore and trimmed by length

THE LIMITATIONreal flow is two-phaserefrigerant FLASHES to vapour partway along the tube. The vapour accelerates, the mixture chokes, and actual mass flow is typically half to two-thirds of this all-liquid figure. Treat it as an upper bound and a starting point, never as a design value

Why capillary tubes at allno moving partsa fixed restriction cannot modulate with load the way a thermostatic expansion valve does, but it costs almost nothing and essentially never fails — which is the trade every domestic refrigerator makes

The formula

Δp = f(L/D)ρv²/2; ṁ = ρvA

A deliberately crude device

A capillary tube is a long narrow tube that drops refrigerant from condensing to evaporating pressure through friction alone. It has no moving parts, costs almost nothing, essentially never fails, and cannot adapt to changing load — which is exactly the trade every domestic refrigerator makes.

Bore dominates length

Mass flow goes roughly as the bore to the power two and a half, and only as the inverse square root of length. A ten percent change in bore therefore outweighs a large change in length, which is why tubes are selected by bore and then trimmed by length for fine adjustment.

The all-liquid figure is an upper bound

Real capillary flow is not single-phase. As the pressure falls the refrigerant begins to flash into vapour partway along the tube, the mixture accelerates sharply, and the flow chokes. Actual mass flow runs typically half to two-thirds of the all-liquid calculation. Use it to get within range, then size against manufacturer data — never as a design value.