Radiant tube burner, radiant tube, and method of designing radiant tube burner

A method of designing a radiant tube burner adapted to be inserted and installed in a tube having an oval-shaped opening cross section and which has a gas injection unit having a secondary combustion air nozzle injecting secondary combustion air arranged in a center portion and a plurality of primary combustion air nozzles injecting primary combustion air and a plurality of fuel gas nozzles injecting fuel gas arranged to surround the secondary combustion air nozzle, the method comprising:

• virtually dividing the opening cross section of the tube into four areas with two straight lines as boundaries, the two straight lines being obtained by tilting a minor axis of the oval, which is a shape of the opening cross section, by ±45° with a center of the oval as a center;
• and
• when a short diameter of the oval is defined as La and a long diameter orthogonal to the short combustion diameter is defined as Lb, setting an amount of the primary combustion air blown out from each of the primary combustion air nozzles such that a flow rate ratio (mt/mx) satisfies Equation (1),
• the flow rate ratio (mt/mx) being a ratio of a flow rate mt of the primary combustion air injected from the primary combustion air nozzles located in the areas containing the minor axis to a total air quantity mx of the primary combustion air injected from all of the primary combustion air nozzles,
• La2/(La2+Lb2)≤(mt/mx)<0.5 (1).