Computer Numerical Simulations of Gas-Fired Radiant Tubes

In gas-fired radiant tube heaters, the combustible gas is burned in the tube, and the generated heat is radiated to the heater. This method avoids the release of hazardous gases which harm the internal environment of the heater. Effectively storing and reusing heat energy has considerable economic and environmental benefits. To achieve these goals, a heat exchanger can be installed at the front end of the radiant tube to preheat fresh air with the enthalpy of the flue gas. However, most radiant tubes have low surface temperature uniformity. Thus, we designed double-P-type radiant tubes to increase the temperature uniformity by incorporating flame tubes. ANSYS/FLUENT was used to construct models for numerical simulations and identify the difference between the highest and lowest temperatures of the straight tube section. Six designs were investigated including 1) a baseline radiant tube and radiant tubes with 2) heat conduction bars on the straight tube section, 3) heat conduction bars on both the straight tube and branch tube sections, 4) flame tubes on the straight tube section, 5) both heat conduction bars and flame tubes on the straight tube section, and 6) both heat conduction bars and flame tubes on both the straight and branch tube sections. The radiant tube stress and deformation were simulated to identify the design with the lowest temperature difference and the effect of the temperature difference on radiant tube strain. The simulation results revealed that adding flame tubes significantly decreased the inner-wall temperature difference and was more effective than other designs. In addition, adding heat conduction bars in the outer wall effectively reduced the high-temperature zones of the tube wall. The results can be used as a reference for optimizing gas-fired radiant tubes. Furthermore, the proposed method improves the performance of radiant tubes and reduces their negative environmental effects. The design contributes to critical breakthroughs in sustainable energy use and environmental protection.