Fin Heat Transfer Modeling and Its Impact on Predictions of Efficiency and Condensation in Gas-Fired Boilers

Abstract

In conventional and high-efficiency boilers it is important to understand where water from the products of combustion may condense onto the heat exchanger surface. The usual fin modeling approach is inadequate because it predicts no circumferential preference for condensation, whereas spatial effects have been observed. Two alternative approaches for modeling fin heat transfer are explored: one method is based on a generalization of observed trends in local convective heat transfer coefficients, and the other on a semiempirically motivated variation in convective flow temperature. Temperature distribution and fin efficiency predictions are compared to the conventional fin modeling approach. The alternative fin heat transfer models described in this study both predict more extensive condensation on the portion of the fin within the wake of the tube. Furthermore, both models predict fin efficiencies below those obtained using an assumption of constant heat transfer coefficient and convective temperature.