Fig. 18 Finned tube experiment at feed water flow rate of 630 kg/h and fuel flow rate of 18.8 mN3/h
4.2.2 Temperature distribution in bank of fin pitch 5 mm tubes
Shown in Fig. 18 is the comparison of experimental result and one-dimensional prediction for the bank of fin pitch 5 mm tubes. The scattering of the gas temperature is also considered to be due to the wet thermocouples. The measured gas temperature with the dry thermocouple at the middle of bank agrees well with the predicted gas temperature. The general temperature profiles can be predicted well with the one-dimensional mass and heat balance calculation.
5. CONCLUSION
(1) Condensation heat transfer on horizontal spirally finned tubes of fin pitch 5 and 10 mm was investigated experimentally by using an actual flue gas from a natural gas boiler. The experiments were conducted at different steam mass concentrations of the flue gas and a wide range of tube wall temperature. The mass concentration was controlled with a steam injection into the flue gas. Fin efficiency at the condensation region was significantly lower than that at the dry region. The empirical correlation developed for a single-phase fluid was extrapolated to the condensation heat transfer region. The fin efficiency was evaluated with an equivalent heat transfer coefficient used as a first approximation. The heat and mass transfer behaviors on the spirally finned tube were well predicted with the analogy correlation based on the empirical correlation.
(2) Thermal-hydraulic behavior of the economizer for the latent heat recovery was investigated experimentally by using an actual flue gas from a propane gas fuel boiler. The above mentioned correlation was incorporated into the prediction code and verified with the experiments. The experimental results for the temperature distributions of water and flue gas in the test heat exchangers with bare and finned tubes agreed well with the prediction.
ACKNOWLEDGMENT
The authors appreciate the helpful supports by Miura Institute, Miura Industry Co. Ltd., The Japan Society of Industrial Machinery Manufacturers and NEDO (New Energy and Industrial Technology Development Organization of Japan).
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