Graduation date: 1995

Natural convection provides a means for circulating fluids without the use of pumps. This type of system is of great interest for a wide variety of applications, including solar heaters, process industry, and nuclear reactors. Natural convection will play a vital role in the area of passive safety and reliability, particularly for the development of Generation IV nuclear energy systems. This study mainly focuses on the linear stability analysis of asymmetrically heated/cooled natural convection loops with large temperature variations across the heated core. The study targets the Argonne Lead Loop Facility (ALLF), a concept for an experiment loop to support the development of the Secure Transportable Autonomous Reactor-Liquid Metal (STAR-LM) at Argonne National Laboratory, using lead-bismuth eutectic (LBE) as the primary reactor coolant. A one-dimensional linear stability analysis is performed and the Nyquist criterion is employed to find the linear stability boundary of both forward and backward circulations. It was found that the natural circulations could be linearly unstable in a high Reynolds number region. Increasing loop friction makes a forward circulation more stable, but destabilizes the corresponding backward circulation under the same heating/cooling conditions. The preliminary results suggest that as the Peclet number decreases, the forward circulation is prone to become unstable while the backward circulation is prone to remain stable. / Graduation date: 2003

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Described in this thesis is an investigation of the fully developed natural convection heat transfer in a vertical channel formed by two infinitely wide parallel plates maintained at a uniform wall temperature. Closed-form solutions for the velocity and temperature profiles are developed along with local and averaged Nusselt numbers. The local Nusselt number based on bulk temperature is found to be 3.77. This result is an analog corresponding to 7.60 for fully developed laminar forced convection in a parallel plate channel with uniform wall temperature boundary condition. The local Nusselt number based on the ambient temperature is deduced as a function of flowwise location. Results are compared with existing numerical and experimental data to find good agreement. / Graduation date: 1997

The problem of simple mathematical models of laminar natural convective flow within a long vertical parallel-plate channels and circular tubes kept at uniformly heated walls is revisited to seek a clear physical understanding of heat transfer mechanisms. A series solution method to analyze the fully developed flow and an integral solution method to analyze the developing flow are used. Chapters 3, 4, and 5 of this dissertation constitute a series of three-paper manuscripts for submission to archival journals. The channels and circular tubes considered here are assumed to be sufficiently long to yield a fully developed flow thermally as well as hydrodynamically before the exit is encountered. In such fully developed flow situation, the fluid mass flow rate naturally induced into the channel due to buoyancy is found to be a function of the wall heating condition. The predicted average Nusselt number as a function of GrPrD/L not only agrees with the existing literature but also is found to be in a functional form comparable to that proposed by Elenbaas (1942 a and b). Our results show that, in spite of being driven by buoyancy (rather than by a pump or a blower), the flow and heat transfer characteristics in the fully developed regime are essentially the same as those of fully developed laminar forced convection in which the flow is externally driven. This observation is confirmed to be valid also in the study (Chapter 5) of laminar natural convection in the developing (entrance) region within a long vertical parallel-plate channel and circular tube. The mass flow rate, which has to remain invariant with axial location even in the entry region, is determined by the flow in the fully developed region. This is the same mechanism involved in forced convection in which the fluid outside the developing boundary layers (i.e. the core flow) is forced to accelerate in the entrance region. The entrance length of channel natural convection is also discovered to be about the same as that in forced convection. / Graduation date: 2001

Graduation date: 1992

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 232-245.

The onset of laminar Rayleigh-Bénard convection is investigated for a low-Prandtl number liquid metal in a cylindrical container. All surfaces are considered to be solid and no-slip. Two cases are considered for the thermal boundary conditions at the side wall: conducting and insulated surfaces. A Chebyshev Galerkin spectral model is used to reduce the governing Boussinesq system to a first-order system of ordinary differential equations. A local stability analysis using the linearized system determines the first critical Rayleigh number. The results are compared with experimental data and a numerical study. / Master of Science

Graduation date: 1993

As the cost of variable renewable energy resources like wind and solar decline rapidly the major barrier to decarbonization of the electrical grid becomes that of energy storage. Current storage technologies are much too expensive to justify widespread adoption and it is unclear what type of technology is even capable of fulfilling this role. Flow batteries are an often proposed technological solution to this problem but they are plagued by high cost and reliability issues due to the expensive and complex balance of plant included in the system design. In this work a new design for a gravity driven flow battery is explored which is capable of drastically lowering the cost of flow batteries by removing the pumps and membranes and replacing their function with density stratification and flow driven by the density change of the electrode reactions. A design for a zinc-bromine battery which makes use of this free convection during operation is explored. The system is studied through construction of prototype cells, exploration of key design variables, and a techno-economic analysis of the technology is performed showing cost viability. The free convection phenomenon which underlies the battery operation is expanded upon by connecting non-dimensional correlations in heat transfer with electrochemical transport equations in order to create predictive understanding of flow behavior based on system composition. This correlative understanding is used to construct a model of a zinc-bromine gravity driven flow battery. This model shows results which align with experimental data and gives insight into the complex transport dynamics of the system.