Browsing by Subject "Porous media"

Now showing 1 - 8 of 8
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    Analysis of generalized Forchheimer flows of compressible fluids in porous media
    (University of Minnesota. Institute for Mathematics and Its Applications, 2009-06) Aulisa, Eugenio; Bloshanskaya, Lidia; Hoang, Luan; Ibragimov, Akif
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    Compression/expansion within a cylindrical chamber: Application of a liquid piston and various porous inserts
    (2013-08) Yan, Bo
    Efficiency of high pressure air compressors/expanders is critically important to the economic viability of Compressed Air Energy storage (CAES) systems, where air is compressed to a high pressure, stored and expanded to output work when needed. Any rise in internal energy of air during compression is wasted as the compressed air cools back to ambient temperature. Similarly, a drop in temperature of the air during the expansion process would reduce the work output. Therefore, the amount of heat transfer between air and surrounding heat sink/source surfaces determines the compression/expansion efficiency. Slowing down the compression/expansion process would give more time for heat transfer, thus increasing the efficiency. However, it reduces the power of the compressor/expander which is undesirable for a CAES system. A porous medium inside the compression chamber and a liquid piston is an ideal candidate for effectively increasing the heat transfer area and, consequently, thermal efficiency of the compression/expansion process, without sacrificing power.The present study focuses on experimentally testing and evaluating the effectiveness of various types of porous media, including two types of metal foam and two types of plastic interrupted plates of different pore size and porosities inside of a liquid-piston compression/expansion chamber. The liquid piston compression system is a cylindrical cavity first filled with air. As water is pumped into the bottom of the cavity, the air inside is compressed. Flow meters and pressure transducers are used to measure the volume and pressure changes during compression. Porous inserts of various designs are placed inside the chamber to reduce the rise in temperature as the air is compressed and to reduce the temperature drop as the air is expanded. Compression and expansion efficiencies are investigated with and without the porous inserts. For the compression experiments, all the experiments are conducted with constant volume trajectories. However, in expansion experiments, the volume trajectories are determined by constant orifice opening area. The study shows that compression efficiency is increased from 77% without a porous insert to 94% with the best-performing, 40ppi metal foam insert at a compression ratio of 10 and compression time of 2s. Due to the significant amount of water trapping inside the metal foam, in the expansion tests, only interrupted plates are tested. The expansion efficiency is increased from 80% to 90% with the 2.5 mm characteristic size interrupted plate insert for expansion process at expansion ratio of 6 and expansion time of 2s. Normalized pressure volume trajectories and dimensionless temperature profiles are calculated and compared for different types of inserts. It is concluded that adding a porous insert into the air space of a liquid piston compressor/expander is an effective means of boosting heat transfer rate and increase compression/expansion efficiency. It is recommended that future work is needed to optimize the pore size and layout of the porous insert and to couple other heat transfer augmentation schemes, including spray cooling trajectory optimization and control. Meanwhile, in order to investigate the compression/expansion process at a higher pressure and wider pressure ratios, a high compression/expansion setup is designed and being fabricated in order to have a better control the pressure-volume trajectory, and improve ease of operation. Detailed design requirements, specifications, system schematic, 3-D models and drawings are presented and discussed.
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    Dynamics and stabilities of generalized Forchheimer flows with the flux boundary condition
    (University of Minnesota. Institute for Mathematics and Its Applications, 2011-02) Hoang, Luan; Ibragimov, Akif
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    Increasing efficiency and power density of a liquid piston air compressor / expander with porous media heat transfer elements
    (2014-12) Wieberdink, Jacob Henry
    In this thesis, a power dense and efficient air compressor/ expander is investigated experimentally. High power density and high efficiency are realized with a quasi-isothermal process, made possible by a liquid piston compressor/ expander and the addition of porous media heat transfer elements. Uniform and non-uniform distributions of porous media are considered and compared with a baseline case.Experiments are conducted using a 2.2 L displacement compressor/ expander. Air is compressed from 7 bar to 210 bar in compression tests and expanded from 210 bar to 7 bar in expansion tests. Baseline compression times vary from 2s to 400s and compression power density varies from 4 kW/m3 to 600 kW/m3. Baseline expansion times vary from 1s to 400s and expansion power density varies from 4 kW/m3 to 2 MW/m3. The baseline compression experiments covered. This study finds that as power density increases, efficiency decreases. At 90% efficiency, a moderate amount of porous media (uniform distribution of 76% porosity) improves compression power density by a factor of 10 and expansion efficiency by a factor of 17. Further improvements are possible with an optimized porous medium geometry.These results have implications for many applications where efficient gas compression/expansion is required including: compressed air for energy storage at scales that range from residential-scale to grid-scale, pneumatics, compressed industrial gasses, and compressed gaseous fuels like hydrogen and natural gas. Quasi-isothermal compression and expansion also enables the realization of thermodynamic cycles that require isothermal compression or expansion.
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    Natural convection in water-saturated metal foam with a superposed fluid layer.
    (2010-11) Wade, Aaron D.
    Experimental results are presented for steady state natural convection heat transfer in an enclosure with a horizontal layer of copper foam and an overlying water layer, heated from below. The foam was placed between two parallel plates in a cylindrical enclosure adjacent to either one or both boundaries. The cylindrical copper foam disks were manufactured by ERG Aerospace with 127 mm DIA, with porosity ranging from 0.88 to 0.92, and pore densities of 5 and 10 PPI. The effective thermal conductivity of the foam was measured by running experiments at pre-convection Rayleigh numbers. The permeability and drag coefficient of the foam were determined by measuring the pressure drop across foam samples in a separate facility. With foam on the hot boundary, natural convection heat transfer experiments are run for 5 and 10 PPI foam, Rayleigh numbers, based on the total height of the enclosure and the water properties, from 2 × 106 to 5 × 108, aspect ratios, H/D, from 0.1 to 0.8, and ratios of the total foam layer height to the total height of the apparatus, η = Hp/H, of 0.25, 0.5, and 0.75. With foam on both boundaries, experiments are run for 10 PPI foam, Rayleigh numbers from 1 × 107 to 3 × 108, aspect ratios from 0.3 to 0.8, and η of 0.5 and 0.75. Natural convection heat transfer experiments were also performed for water alone over the Rayleigh number range 9 × 105 ‒ 3 × 108 and for aspect ratios 0.2 to 0.8. Heat transfer results are presented as an enhancement factor, the ratio of heat transfer with foam to that of water alone at the same Rayleigh number. The results with foam on the hot boundary were not a function of η. 10 PPI foam on the hot boundary did not enhance heat transfer with an average enhancement factor of 0.98. 5 PPI foam on the hot boundary had an enhancement factor of 1.1. The increased enhancement of 5 PPI foam over 10 PPI foam is attributed to the greater permeability of the 5 PPI foam. With foam on both boundaries, enhancement tended to increase with Rayleigh number and is a function of η. For η = 0.5 enhancement ranged from 0.93 to 1.33. For η = 0.75 enhancement ranged from 1.1 to 1.29. For the same enclosure filled with copper foam (from Kathare et al. [13]), enhancement was not a strong function of Rayleigh number and ranged from 1.2 to 1.6, though enhancement was typically above 1.35. The decreased enhancement of a partially filled enclosure, compared to a fully filled enclosure, is attributed to a lack of direct conduction path from each boundary, significantly decreasing the apparent conductivity of the enclosure, and decreased advection as the convection cells do not fully penetrate the porous layer(s). Power law correlations relating the fluid Nusselt number to the fluid Rayleigh number were determined for the three foam cases. The data for foam on the hot boundary alone and on both boundaries were also successfully correlated using porous media variables where an apparent conductivity of the composite system, considering the foam and fluid layers in series, was used as the effective conductivity. The porous media Nusselt number is related to the porous media Rayleigh number and a modified porous media Prandtl number.
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    Particle image velocimetry data characterizing flow and turbulence fields at free-flow-porous media interface
    (2020-12-01) Kang, Peter K; Kim, Junsong; pkkang@umn.edu; Kang, Peter K
    The data includes two-dimensional (2D) instantaneous velocity fields and time-averaged 2D flow properties. We obtained the velocity data in an experimental flume, which is composed of an open channel and underlying porous media, at the St. Anthony Falls Laboratory, University of Minnesota using Particle Image Velocimetry (PIV). The PIV is a non-intrusive laser optical measurement technique, which measures flow at the high spatiotemporal resolution by estimating cross-correlations between laser-illuminated subsequent images recorded by a high-speed camera. We used the PIV-measured 2D flow fields to validate the results of numerical flow simulations based on Large Eddy Simulation. The main objective of this study is to investigate pore-scale flow effects on solute transport across open channel- porous media interfaces. The released data would also be useful to researchers who need to validate flow simulation results.
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    Stability of solutions to generalized Forchheimer equations of any degree
    (University of Minnesota. Institute for Mathematics and Its Applications, 2012-04) Hoang, Luan Thach; Ibragimov, Akif; Kieu, Thinh; Sobol, Zeev
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    Structural stability of generalized Forchheimer equations for compressible fluids in porous media
    (University of Minnesota. Institute for Mathematics and Its Applications, 2010-01) Hoang, Luan; Ibragimov, Akif