Modelling of evaporative falling-film heat transfer over a horizontal tube
File(s)
Accepted version
Author(s)
Type
Journal Article
Abstract
This article focuses on evaporative falling film heat transfer through numerical simulations. A two-dimensional symmetric liquid film flowing outside a single horizontal tube was simulated using the open-source CFD software OpenFOAM. The Tanasawa model was employed to consider mass transfer at the liquid–vapour interface, and the isoAdvector VOF method was used for interface tracking. The simulations explored the impact of film flow rate, tube surface heat flux, and tube diameter on the liquid film thickness and surface heat transfer coefficient. Additionally, the critical heat flux and operational limits were considered. The results demonstrate the accurate reproduction of evaporative falling film heat transfer performance by the present model. The film thickness exhibits a similar profile to adiabatic and sensible falling film heat transfer but provides smaller values. Similarly, the evaporative heat transfer coefficient exhibits significantly higher values and a gentle peripheral variation. The influence of heat flux on evaporative falling film heat transfer is contingent on the film flow rate; it can either enhance or weaken the process. Notably, a larger tube diameter negatively affects heat transfer, suppressing the impact of heat flux, and also increases the risk of liquid film dryout. For a given film flow rate, the average heat transfer coefficient increases initially, reaches a maximum value, and then decreases as the wall heat flux is increased. The peak heat flux, termed critical heat flux, increases with film flow rate but decreases with tube diameter. An operational limit exists where the heat flux is lower than the critical heat flux and the film flow rate is higher than the critical film flow rate; under these conditions, evaporative falling film heat transfer operates in a fully wetting status.
Date Issued
2024-10-15
Date Acceptance
2024-07-18
Citation
Applied Thermal Engineering, 2024, 255
ISSN
1359-4311
Publisher
Elsevier
Journal / Book Title
Applied Thermal Engineering
Volume
255
Copyright Statement
Copyright © 2024 Published by Elsevier Ltd. This is the author’s accepted manuscript made available under a CC-BY licence in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy)
License URL
Subjects
Computational phase change
CONDENSATION
Energy & Fuels
Engineering
Engineering, Mechanical
Evaporation
Evaporative heat transfer
Falling film
FLOW
LIQUID-FILMS
MASS
Mechanics
Numerical simulation
NUMERICAL-SIMULATION
Physical Sciences
Science & Technology
SURFACE
Technology
Thermodynamics
Publication Status
Published
Article Number
123997
Date Publish Online
2024-07-20