Keywords
Supercritical carbon dioxide (SCO$_2$), Heated turbulent buoyant jet, Particle Image Velocimetry (PIV), Real-gas biconjugate heat-transfer CFD, Turbomachinery thermal management, Momentum-buoyancy interaction
Subject Categories
Energy Systems | Heat Transfer, Combustion | Mechanical Engineering
Abstract
Supercritical carbon dioxide (SCO$_2$) has emerged as a promising working-heat transfer fluid for advanced Brayton cycles, gas turbines, and compact thermal management systems because of its high density, favorable compression characteristics, and potential for high cycle efficiency. However, the strong thermophysical property variations that occur near the critical and pseudocritical regions introduce challenges in predicting turbulent flow behavior, heat transfer, entrainment, and buoyancy effects. These challenges are particularly relevant when heated SCO$_2$ discharges into a surrounding SCO$_2$ environment, where the coupling between momentum, density variation, and thermal stratification can alter jet behavior in ways not captured by classical constant property jet theory.
This dissertation presents experimental and computational investigations of heated turbulent SCO$_2$ flow exiting a circular tube as a buoyant free jet into a quiescent and thermally conditioned high pressure environment. Experiments were conducted in a closed-loop SCO$_2$ facility at pressures up to 9 MPa with inlet temperatures up to 40$^\circ$C. The study combined thermal measurements, heat loss characterization, and particle image velocimetry to quantify near field velocity structure, jet development, turbulence behavior, and ambient interaction. Companion 3D biconjugate heat transfer simulations were performed in ANSYS Fluent using real gas thermophysical properties and validated against experimental wall temperature and velocity data.
The results show jet behavior is governed by the interaction of Reynolds number, heat addition, density gradients, buoyancy, and ambient thermal stratification. Increasing mass flow rate strengthened jet momentum and preserved the core region, while increased inlet temperature enhanced jet velocity but also amplified buoyancy and thermal interaction with the surroundings. Near field PIV resolved the initial shear layer development and velocity structure, while validated CFD extended the analysis downstream to interpret jet decay, spreading, wake formation, and recirculation. The findings provide new insight into heated SCO$_2$ jet physics and establish a validated framework relevant to SCO$_2$ turbomachinery, combustion-adjacent injection, thermal management, and advanced power cycle applications.
Completion Date
2026
Semester
Spring
Committee Chair
Jayanta Kapat
Degree
Doctor of Philosophy (Ph.D.)
College
College of Engineering and Computer Science
Department
Mechanical and Aerospace Engineering
Format
Document Type
Dissertation
Language
English
Release Date
8-15-2028
STARS Citation
Gabriel-Ohanu, Emmanuel C., "Thermal Fluid Characteristics And Performance Of Supercritical Carbon Dioxide (SCO2) Turbulent Buoyant Jets" (2026). Graduate Studies Theses and Dissertations 2026. 268.
https://stars.library.ucf.edu/gradstudies_etd_2026/268
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