A method of manufacturing a target reactor having a flow-channel system in which a plurality of reactants continuously flowing into said target reactor are mixed and interconvert to form a target volumetric flow-rate (f2) of a product continuously flowing out of said target reactor, wherein the smallest hydraulic diameter (dh2) of said target reactor is calculated based on the relationship d h ⁢ ⁢ 2 = d h ⁢ ⁢ 1 ⁡ ( f 2 f 1 ) 3 - n 7 - n in a turbulent or transitional turbulent flow, wherein n is a non-integer number with 1>n≧0, between the corresponding smallest hydraulic diameter (dh1) of a standard reactor having the same fluidic type of flow-channel system, f1 is a standard volumetric flow-rate of said standard reactor carrying out the same interconversion, and f2 is said target volumetric flow-rate.