Fouling and thermal-hydraulic characteristics of aligned elliptical tube and honeycomb circular tube in flue gas heat exchangers

In this paper, aiming at resolving the contradictions of heat transfer enhancement, resistance reduction and soot-blowing effect of common heat transfer surfaces, aligned elliptical tube bundle (AETB) and honeycomb tube bundle (HCTB) were proposed for the high dust content conditions, and the fouling characteristics and thermal-hydraulic performance before and after fouling were investigated. Firstly, the thermal-hydraulic performance of aligned circular tube bundle (ACTB), AETB, conventional staggered circular tube bundle (SCTB) and HCTB in the clean state were compared, and advantages of AETB and HCTB were verified. Secondly, based on the ash fouling model and prediction method established by the author's group, fouling distribution and morphology of AETB and HCTB were obtained, and ash fouling and thermal-hydraulic characteristics were examined by parameterization. Finally, in the range of geometry parameters studied in this paper, the correlations of the asymptotic value of fouling thermal resistance R-f (*) in fouling state, Nusselt number Nu and friction factor f in clean state were developed. Results show that the relative deviations between the predicted results and the numerical values is within 4%, which indicates that the proposed correlation is of sufficient accuracy for engineering purposes, and can accurately predict the thermal-hydraulic characteristics of flue gas heat exchanger. The results of this paper can provide a reference for development and engineering application of the heat-transfer surface for the efficient recovery of industrial flue gas waste heat.