Please use this identifier to cite or link to this item: https://hdl.handle.net/10356/163479
Title: Theoretical study on forced convection filmwise condensation inside converging channels in the presence of a non-condensable gas
Authors: Liu, Pengfei
Ho, Jin Yao
Kandasamy, Ranjith
Wong, Teck Neng
Keywords: Engineering::Mechanical engineering
Issue Date: 2022
Source: Liu, P., Ho, J. Y., Kandasamy, R. & Wong, T. N. (2022). Theoretical study on forced convection filmwise condensation inside converging channels in the presence of a non-condensable gas. International Journal of Thermal Sciences, 181, 107775-. https://dx.doi.org/10.1016/j.ijthermalsci.2022.107775
Project: NRF-ubrk 2015ENC-GDCR01001-010
Journal: International Journal of Thermal Sciences
Abstract: In this paper, a theoretical study is performed on forced convection filmwise condensation inside a vertical converging channel in the presence of a non-condensable gas. Two solution schemes are developed with consideration of the turbulence effect in gas mixture and a laminar condensate film flow. Various heat transfer mechanisms are revealed by examining condensation heat transfer inside converging channels. In the present study, steam and air are taken as the vapor and non-condensable gas, respectively. It is found that the film velocity transits from a linear profile to a parabolic profile for a straight channel along the channel axial direction under the combined influence of gravitational force and interface shear stress. However, for a converging channel, the transition process from linear to parabolic velocity profiles is substantially delayed along the axial direction due to the enhanced interfacial shear stress in the latter condensing section. The film thickness decreases along the channel axial direction at the latter condensing section for both natural and forced convection condensation due to the substantially decreased local condensation rate and/or the enhanced interfacial shear stress in a converging channel. The combined influence of the curvature effect and enhanced interfacial shear stress leads the local heat transfer enhancement to increase substantially at the latter condensing region for forced convection condensation inside a converging channel. A uniform enhancement on the normalized local heat transfer coefficient in the inlet condensing section was found for both natural and forced convection condensation. However, the reduced condensation area has led the normalized local heat transfer coefficient to decrease substantially along the axial direction for converging channel as compared to straight channel in the case of natural convection condensation. Comparatively, the increased interfacial shear stress results in the normalized heat transfer coefficient along the entire channel to be enhanced. The average heat transfer coefficient increases as the converging angle or the Reynolds number increase. The turbulence effect can enhance the condensation heat transfer. However, the presence of air can cause a significant decrease in the condensation heat transfer. For the case of pure vapor condensation, the enhancement ratio increases as the Reynolds number increases. When the air is present in the system, an insufficient vapor supply is observed when the Reynolds number is low. Therefore, the enhancement ratio increases substantially as the converging angle increases. When the air mass fraction is high (W=0.4), the enhancement ratio appears to be insensitive to the Reynolds number in the laminar and turbulent regime, respectively. In addition, the enhancement ratio generally increases as the air mass fraction increases.
URI: https://hdl.handle.net/10356/163479
ISSN: 1290-0729
DOI: 10.1016/j.ijthermalsci.2022.107775
Rights: © 2022 Elsevier Masson SAS. All rights reserved.
Fulltext Permission: none
Fulltext Availability: No Fulltext
Appears in Collections:MAE Journal Articles

Page view(s)

18
Updated on Jan 30, 2023

Google ScholarTM

Check

Altmetric


Plumx

Items in DR-NTU are protected by copyright, with all rights reserved, unless otherwise indicated.