Browsing by Subject "porous media"

Now showing 1 - 3 of 3
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    CFD Simulations and Thermal Design for Application to Compressed Air Energy Storage
    (2015-06) Zhang, Chao
    The present computational research focuses on fluid flow analysis and heat transfer enhancement in support of the design of a hydraulic Compressed Air Energy Storage (CAES) system. A CAES system compresses air to high pressure during high power generation periods, stores the compressed air, and expands it to generate power during high power demand periods. The main benefit of using CAES is that it overcomes the mismatch between power generation and power demand. An innovative liquid piston method is used in the present research, where liquid (water) is pumped into the lower section of a compression chamber, and the gas (air) is compressed by the rising liquid-gas interface. Important to the efficient operation of CAES is reducing the temperature rise during compression. The work input process for compressing the air requires two main steps. In the first step, compression work compresses the air to a high pressure. The air temperature rises during compression, and this leads to a second step, where the compressed air cools. In order to maintain the work potential, the pressure of the compressed air is maintained during cooling, volume decreases and cooling work is done. As a result, higher temperature rise during compression requires greater amount of total work input for a given amount of air and a given pressure ratio. For similar reasons, it is also desirable to reduce the temperature drop during expansion of compressed air. The use of a liquid piston offers opportunities to insert heat exchanger matrices into the compression chamber to improve heat transfer. Computational Fluid Dynamics (CFD) and design analyses on the heat exchangers are done in the present research. Two main types of heat exchangers, a commercially available, open-cell metal foam and an in-house designed interrupted plate matrix, are investigated, mainly through computational methods, and with experimental validations. CFD modeling of the liquid piston chamber inserted with exchanger matrices requires closure models that characterize the heat transfer and flow resistance characteristics of the heat exchanger elements. For the metal foam matrix, characterization is done by measuring the flow pressure drop and comparing existing heat transfer models to a liquid piston experiment. For the interrupted plate matrix, large numbers of CFD simulations on the unit cells of the exchanger and experiments are applied for developing correlations for these terms. Based on the unit cell simulations, models for three-dimensionally anisotropic heat transfer behavior of porous media have been developed. Using these models, 3-D global-scale CFD simulations of the liquid piston chamber have been done. As the liquid chamber represents an application of two-phase flow through porous media, the simulation combines a VOF (Volume of Fluid) method and a two-energy-equation modeling method for porous media. The choice of the interrupted plate matrix offers flexibility to vary the shape (e.g. plate height, thickness and separation distance) based on an optimum design to further improve CAES efficiency. Design sensitivity analyses typically require large numbers of computational runs and would demand extraordinary computational resources if combined with 2-D or 3-D CFD simulations. Developed in the present research is a simplified, one-dimensional (1-D) code that is much less computationally expensive, and preserves the main physics of the two-phase flow in porous media. The 1-D code is used for the design analysis of the heat exchanger shape distribution along the axial direction of the chamber. CFD Simulations have been done to also compare a no-insert chamber to chambers with exchanger inserts, for both compression and expansion processes. The expansion process allows the expanding compressed gas to push the liquid out of the chamber to generate power. It is shown that in both the compression and expansion processes, using a heat exchanger matrix in the liquid piston chamber can significantly reduce the rise or drop in gas temperature, thus reducing the losses. Using the CFD modeling tools, a design exploration is also done to investigate the effect of changing the profile of the chamber's cross sectional radius along the axial direction to design a gourd-like shaped chamber to agitate flow and enhance heat transfer.
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    An Evaluation of Perfusion in Human Body Thermal Modeling through the Integration of a Porous Media Model for Tissue
    (2023-02) Smith, Christopher
    Historically there has been one primary method for modeling the thermal condition of the human body. This method, referencing the bioheat equation, has been and is used widely across the medical device and human comfort industries. The present work leverages an alternate method to biological tissue modeling by using a porous media approach. In doing so, it provides a more physiologically and anatomically representative alternative to human body thermal modeling to contrast the computationally efficient, but low fidelity bioheat method. The present work shows the feasibility of using this porous media approach for high fidelity tissue modeling, allowing both researchers and designers to have an alternative modeling method to leverage – ensuring that they can choose a method best fit for their need.
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    Numerical Modeling And Optimization Of Thermofluid Systems: Heat Pumps, Turbocompressors, Porous Media
    (2020-03) Goldenberg, Vlad
    In this dissertation, three types of thermofluid systems: an air Brayton cycle heat pump, a centrifugal compressor stage, and a porous media heat pipe, are investigated. In each of the investigations, numerical modeling is used as the basis that underpins the analyses. Furthermore, the goal of each investigation is to develop a framework for the design and optimization of practical engineering systems. The parameterization of each system is explored and defined. A thermodynamic model of a recuperated air cycle heat pump is developed and used to parametrically study the effects of component performance, operating environment, and design parameters. A numerical optimization is conducted to maximize the heating COP of the air cycle heat pump while maintaining robust performance across a wide operating envelope. Comparison is made to a conventional vapor compression cycle heat pump. It is found that a judicious choice of pressure ratio and maximization of component performance enables a recuperated air cycle heat pump to be comparable in COP to a vapor cycle heat pump for high temperature ratio duty. The recommended pressure ratio is determined to be 1.4. Such a heat pump requires high performance compressor, expander, and heat exchangers. A novel method of the flow path synthesis of a centrifugal compressor stage is revealed. A preliminary design procedure that enables fast and efficient candidate designs is reported. Computational fluid dynamics in conjunction with optimization algorithms, surrogate modeling, and machine learning is used to analyze the fundamental fluid mechanics and to automatically optimize the designs. A single stage performance improvement of over 4% points of isentropic efficiency gain is demonstrated using numerical methods. The microstructure of a flat porous media heat pipe consisting of layers of wire mesh is characterized using numerical techniques. The analysis encompasses the characterizations of the flow-induced pressure drop and interfacial heat transfer for liquid and vapor water phases in a 16-gauge and 200-gauge wire mesh porous domain.