# Internal Flow Calculator

Calculate fluid flow through a tube, including static, total, and wall fluid states, flow speed, wall flux, and heat transfer coefficient.

This model represents the quasi-1D state of a real fluid flowing through a duct. It is an extension on the quasi-1D real fluid external flow model, which itself is an extension of the static real fluid model. Nusselt number correlations are used to estimate wall temperature and heat transfer rate for circular duct cross-sections assuming non-participating fully-developed flow.

Key sub-models are the static fluid state Static , the total fluid state Total , and the wall fluid state Wall .

Press to see the model. Try your own inputs or the examples below. Refresh your browser to clear results.

## Static state, circular tube diameter, Reynolds number, roughness, and adiabatic

1. Choose Fluid = air and assert the static temperature T = 300  K  and pressure P = 1  bar.
2. Assert tube diameter Dh.mm = 1 and Reynolds number Re = 20000 (turbulent). The model infers the speed, mass flow rate, volumetric flow rate, and other properties of the fluid.
3. Also asserting that the tube is adiabatic qu = 0 and frictionless «ctrl+g»e/Dh = 0 , the model infers the temperature difference between the wall and bulk flow as well as other properties of the fluid at the wall Wall .

## Wall temperature and pressure, Reynolds number, Mach number, roughness, and static temperature

1. This example will mimic the fluid state at a point in the heat exchanger tube of a microwave thermal rocket. Choose Fluid = ammonia and assert the wall temperature Wall.T = 720 K  and wall pressure Wall.P = 10 bar.
2. Assert tube Reynolds number Re = 50000 (turbulent), Mach number M = 0.7 and friction «ctrl+g»e/Dh = 0.001 ⏎.
3. Assert the ammonia’s static temperature T = 415 K. The model infers the tube diameter and net useful heat flux at the tube wall.