Numerical investigations on extraction effect for steam condensation in the presence of air

Abstract

Steam condensation containing air is a ubiquitous phenomenon in practical industrial applications. It has been extensively investigated through numerical analysis and experimental studies. The conclusion that the high concentration air layer is the primary thermal resistance of the condensation process is widely accepted. Therefore, thinning the high concentration air layer is the key to enhancing condensation performance. For this purpose, applying the extraction method to remove the high concentration air layer near the heat exchanger can potentially be a direct and effective way to enhance condensation performance. To evaluate the extraction effect, this work conducted numerical simulations for a single tube that added extractors at P = 0.3 MPa, △T = 15 °C, and ωa = 0.56. In the discussions, the condensation performance with various extraction structure parameters (e.g., extraction height Z, extraction distance △L, extractor diameter D, number of extractors n) were investigated. The results indicated that the extractor could greatly enhance the condensation performance. For the single extractor case, the extractor (Z = 0.75 m, D = 50 mm, △L = 5 mm) has the optimal enhancement effect, which can reach 42.4%. For the multi-extractor case, the enhancement effect is optimal (76.3%) when the number of extractors n is 11.