From reading years ago I recall that there can be two types of flow through any conduit, laminar, and turbulent. The type of flow depends on diameter of conduit and the velocity of flow.
This predictable effect can also be used for cooling . I will have to find a source article I read that was directly about gasifier design parameters.
Edit: Found it!
Tubing diameters depend on the gas quantity, but also on the temperature. In most tubing, we want a laminar flow (< 5 m/s). In some tubing we need a turbulent flow(> 6 m/s). Unfortunately turbulence raises the pressure drop in the system and reduces the filling degree and with that, engine power output.
To determine the tubing diameter, we first calculate the gas flow in liters per second. “We had that number already?!” you will notice; indeed, the quantity of cold gas. But since the gas is hot, an increase of volume occurs. We recalculate this flow using a conversion in Kelvin. 0 degrees Celsius are 273 Kelvin. 350 degrees Celsius are 273 + 350 = 623 Kelvin. 18.4 [l/s] at 350 degrees becomes:
(623/273) x 18.4 = 42.0 [l/s]