Fig. 1. Schematic diagram of fluid model of heated spiral tube

Fig. 2. Temperature distribution of spiral tube after heating for 1 000 s when Q is 2 L/min

Fig. 3. Temperature distribution of spiral tube after heating for 1 000 s when Q is 4 L/min

Fig. 4. Temperature distribution of spiral tube after heating for 1 000 s when Q is 6 L/min

Fig. 5. Temperature distribution of spiral tube after heating for 1 000 s when Q is 8 L/min

Fig. 6. Temperature distribution of spiral tube after heating for 1 000 s when Q is 10 L/min

Fig. 7. Temperature distribution of spiral tube after heating for 1 000 s when Q is 12 L/min

Fig. 8. Schematic diagram and image of backscattering measurement in absorption cavity of laser power meter

Fig. 9. Composition diagram of calibration system for laser energy meter

Fig. 10. Temperature variation of water inlet

Fig. 11. Temperature variation of water outlet

Fig. 12. Temperature differences between water outlet and water inlet

Fig. 13. Monitoring power curve

Fig. 14. Relative error of measurement at different water flow rates