Experimental Investigation of Convective Flow Boiling in Concentric and Eccentric Annulus
Abstract
The convective boiling heat transfer of annular flow in concentric and eccentric annuli was investigated experimentally using a central heating rod in an unheated tube. Advanced measurement techniques—laser-induced fluorescence (LIF) and confocal chromatic sensor (CCS)—were applied to acquire the dynamics and instabilities of the liquid thin film on the tube. Boundary conditions included a heating rod heat flux (167–201 kW/m2) and mass flow rate (58–155 g/s); the annuli in which the flow occurred have a hydraulic diameter of 15.5 mm. Previous research on isothermal annular flow in bare tubes indicated that vapor superficial velocity is a primary factor that influences liquid film dynamics including base film thickness and wave amplitude. The liquid film thickness in eccentric geometry was found to be constant for liquid superficial velocities ranging from 0.15–0.34 m/s and vapor superficial velocities ranging from 6.5–13.2 m/s. The heat transfer coefficient ranged from 2.734– 4.279 kW/m2∙K and 2.063–3.096 kW/m2∙K for the concentric and eccentric geometries, respectively. The heat transfer coefficient showed an increasing trend with an increase in the liquid superficial velocity; a reverse trend was observed for the vapor superficial velocity. The boiling condition was assumed to be dry out when the measured heat transfer coefficient was exceptionally low (< ~2.0 kW/m2∙K).
A flow boiling computational fluid dynamics (CFD) simulation was performed using the volume of fluid (VOF) method. Phase change models such as the Lee, Sun, and Chen models were implemented in OpenFOAM and tested. The film thickness data obtained from the flow boiling simulation were compared with the experimental data to determine the mass transfer intensity (β_e) for the Lee model. The simulation result with β_e=0.3 showed the best match with the experimental result.
Subject
Two-phase flowFlow boiling
Annular flow
Concentric annuli
Eccentric annuli
Film dynamics
Bubble and droplet
CFD
VOF
Citation
Seo, Joseph (2021). Experimental Investigation of Convective Flow Boiling in Concentric and Eccentric Annulus. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /196108.