Showing papers by "Terrence W. Simon published in 2013"

Design of an interrupted-plate heat exchanger used in a liquid-piston compression chamber for compressed air energy storage

Abstract: In the Compressed Air Energy Storage (CAES) approach, air is compressed to high pressure, stored, and expanded to output work when needed. The temperature of air tends to rise during compression, and the rise in the air internal energy is wasted during the later storage period as the compressed air cools back to ambient temperature.The present study focuses on designing an interrupted-plate heat exchanger used in a liquid-piston compression chamber for CAES. The exchanger features layers of thin plates stacked in an interrupted pattern. Twenty-seven exchangers featuring different combinations of shape parameters are analyzed. The exchangers are modeled as porous media. As such, for each exchanger shape, a Representative Elementary Volume (REV), which represents a unit cell of the exchanger, is developed. The flow through the REV is simulated with periodic velocity and thermal boundary conditions, using the commercial CFD software ANSYS FLUENT. Simulations of the REVs for the various exchangers characterize the various shape parameter effects on values of pressure drop and heat transfer coefficient between solid surfaces and fluid. For an experimental validation of the numerical solution, two different exchanger models made by rapid prototyping, are tested for pressure drop and heat transfer. Good agreement is found between numerical and experimental results. Nusselt number vs. Reynolds number relations are developed on the basis of pore size and on hydraulic diameter.To analyze performance of exchangers with different shapes, a simplified zero-dimensional thermodynamic model for the compression chamber with the inserted heat exchange elements is developed. This model, valuable for system optimization and control simulations, is a set of ordinary differential equations. They are solved numerically for each exchanger insert shape to determine the geometries of best compression efficiency.Copyright © 2013 by ASME

Numerical Investigation of Metal-Foam Filled Liquid Piston Compressor Using a Two-Energy Equation Formulation Based on Experimentally Validated Models

Abstract: The present study presents CFD simulations of a liquid-piston compressor with metal foam inserts. The term “liquid-piston” implies that the compression of the gas is done with a rising liquid-gas interface created by pumping liquid into the lower section of the compression chamber. The liquid-piston compressor is an essential part of a Compressed Air Energy Storage (CAES) system. The reason for inserting metal foam in the compressor is to reduce the temperature rise of the gas during compression, since a higher temperature rise leads to more input work being converted into internal energy, which is wasted during the storage period as the compressed gas cools.Liquid, gas, and solid coexist in the compression chamber. The two-energy equation model is used; the energy equations of the fluid mixture and the solid are coupled through an interfacial heat transfer term. The fluid mixture, which includes both the gas phase and the liquid phase, is modeled using the Volume of Fluid (VOF) method. Commercial CFD software, ANSYS FLUENT, is used, by applying its default VOF code, with user-defined functions to incorporate the two-energy equation formulation for porous media.The CFD simulation requires modeling of a negative momentum source term (drag), and an interfacial heat transfer term. The first one is the pressure drop due to the metal foam, which is obtained from experimental measurements. To obtain the interfacial heat transfer term, a compression experiment is done, which provides instantaneous pressure and volume data. These data are compared to solutions of a zero-dimensional compression model based on different heat transfer correlations from published references. By this comparison, a heat transfer correlation which is most suitable for the present study is chosen for use in the CFD simulation.The CFD simulations investigate two types of metal foam inserts, two different layouts of the insert (partial vs. full), and two different liquid piston speeds. The results show the influence of the metal foam inserts on secondary flows and temperature distributions.© 2013 ASME

Optimization of the Axial Porosity Distribution of Porous Inserts in a Liquid-Piston Gas Compressor Using a One-Dimensional Formulation

Abstract: A One-Dimensional (One-D) numerical model to calculate transient temperature distributions in a liquid-piston compressor with porous inserts is presented. The liquid-piston compressor is used for Compressed Air Energy Storage (CAES), and the inserted porous media serve the purpose of reducing temperature rise during compression. The One-D model considers heat transfer by convection in both the fluids (gas and liquid) and convective heat exchange with the solid. The Volume of Fluid (VOF) method is used in the model to deal with the moving liquid-gas interface. Solutions of the One-D model are validated against full CFD solutions of the same problem but within a two-dimensional computation domain, and against another study given in the literature.The model is used to optimize the porosity distribution, in the axial direction, of the porous insert. The objective is to minimize the compression work input for a given piston speed and a given overall pressure compression ratio. The model equations are discretized and solved by a finite difference method. The optimization method is based on sensitivity calculations in an iterative procedure. The sensitivity is the partial derivative of compression work with respect to the porosity value at each optimization node. In each optimization round, the One-D model is solved as many times as there are optimization nodes, and each time the porosity value at a single optimization node is changed by a small amount. From these calculations, the sensitivity of changing the porosity distribution to the total work input (objective) is obtained. Based on this, the porosity distribution is updated in the direction that favors the objective. Then, the optimization procedure marches to the next round and the same calculations are completed iteratively until an optimum solution is reached. The optimization shows that porous media with high porosity should be used in the lower part of the chamber and porous media with low porosity should be used in the upper part of the chamber. An optimal distribution of porosity over the chamber is obtained.Copyright © 2013 by ASME

Heat transfer apparatus and method

Abstract: A method is provided for heat transfer from a surface to a fluid. The method includes directing a first fluid flow towards the surface in a first direction and directing a second fluid flow towards the surface in a second direction. The first and second fluid flows cooperate to cool the surface.

Heat Transfer Enhancement of a Heat Sink by Inclined Synthetic Jets for Electronics Cooling

Abstract: Rising thermal dissipation from modern electronics has increased the challenge of cooling using conventional heat sinks. In addition to fans and blowers, focus is turning to active cooling devices for augmenting performance. A piezoelectrically-actuated synthetic jet array is one under consideration. Synthetic jets are zero-net–mass-flow jets realized by a cavity with an oscillating diaphragm on one side and an orifice or multiple orifices on the other side. They generate highly unsteady jetting flows that can impinge upon heated surfaces and enhance cooling. However, the synthetic jet actuation components might interfere with other components of the electronics module, such as the fan, requiring a displacement of the cavity center from the jet array center. Herein, heat transfer enhancement by an inclined piezoelectrically-actuated synthetic jet arrangement in a heat sink for electronics cooling has been experimentally and numerically studied. A wedge-shaped platform is designed to introduce the jets with an inclined configuration into the finned channels of the heat sink. The unit is inclined to avoid interference with other components of the module. The penalty is described in terms of velocities of jets emerging from this wedge-shaped platform, compared to those from an aligned cavity-orifice design. Effects on heat transfer performance for the heat sink are documented. The jets are arranged as wall jets passing over heat sink fins. The experimental study is complemented with a numerical analysis of flow within the synthetic jet cavity. Optimization is done on the number of jets against the penalty on jet velocity for obtaining maximum cooling performance. The jets are driven by piezoelectric actuators operating at resonance frequencies of 700–800 Hz resulting in peak jet velocities of approximately 35m/s from 92, 0.9 mm × 0.9 mm orifices. The results give guidance to those who face a similar interference problem and are considering displacement of the synthetic jet assembly.Copyright © 2013 by ASME

Effects of Channel Aspect Ratio on Convective Heat Transfer in an Electronics Cooling Heat Sink Having Agitation and Fan-Induced Throughflow

Abstract: Fan-driven throughflow is frequently used for convective cooling of electronics. Channels with walls behaving like fins are common. In the present study, the flow inside the channels is agitated by means of translationally oscillating plates called agitators. Effectiveness of agitation by oscillating blades is found to be dependent on the channel width, a parameter studied herein. Heat sinks having narrower channels have a greater number of channels in total for the fixed size of heat sink and therefore greater heat transfer area than heat sinks with wider channels. Thus, with the same channel height, as the aspect ratio increases, channel width decreases, and it is found that opportunities for agitation are reduced and the generated turbulence is more strongly damped, thus reducing heat transfer coefficients. A study was carried out to find direction toward an optimal number of channels for a given heat sink using the agitation strategy. As part of the study, fluid damping and power consumption to drive the agitator assembly were addressed. The study was done numerically using ANSYS FLUENT on a representative single channel of the heat sink and the results were extended to the full size, multiple-channel heat sink system. Recommendations for moving toward an optimum geometry, based on thermal performance and agitator power are made.© 2013 ASME

Effects of Combustor Exit Temperature Profile on Adiabatic Effectiveness of Leakage Flow Film Cooling Over an Axisymmetric Endwall

Abstract: The effects of a representative combustor exit temperature profile on leakage flow film cooling effectiveness were experimentally documented. This was done in a stationary, linear blade row cascade with an axisymmetric blade platform of dolphin-nose-shape. Endwall adiabatic film cooling effectiveness distributions and near-endwall passage thermal fields are documented. Results from the case with a representative combustor exit temperature profile are compared to those with other combustor exit temperature profiles including a base case with a uniform temperature distribution. All cases were done in the same facility over a range of disk cavity leakage flow rates. This study quantifies the sensitivity of endwall film cooling due to coolant in the leakage flow and in the approach flow to the shape of the combustor exit temperature profile. The results indicate that leakage flow film cooling effectiveness is significantly lower with a well-mixed (uniform temperature) combustor exit temperature profile than in cases in which the combustor exit temperature distribution is strongly variable. That is, it is demonstrated that combustor cooling flow aids endwall protection considerably. It is also shown that leakage flow has only a mild influence over the endwall cooling that can be attributed to coolant in the approach flow.Copyright © 2013 by ASME

High pressure turbine rotor stage endwall cooling and passage thermal fields as affected by leakage flow and combustor liner coolant streams

Abstract: The effects of an engine-representative combustor exit temperature profile and different disc cavity leakage flow rates on endwall adiabatic effectiveness distributions and passage temperature fields in a high pressure turbine rotor stage of a gas turbine are experimentally documented. The measurements are made on a stationary linear blade row cascade with an axisymmetrically-contoured endwall of modern engine geometry and with engine-representative approach flow thermal and fluid mechanics characteristics. The measurements give insight into mixing of coolant emerging as leakage flow and combustor liner coolant mix with hot core gases ahead of the airfoil row. Reported results are thermal fields in the passage, adiabatic wall temperatures and adiabatic effectiveness values in using an engine-representative approach flow temperature profile and with approach flow temperature profiles with 1) no coolant in the approach flow (flat profile) and 2) coolant only within 10% of the span (approach flow profile with a thin thermal boundary layer).The results give insight into mixing between the leakage flow and the mainstream passage flow and its effects on endwall cooling. The results demonstrate that for the conditions studied; much of the endwall cooling is contributed by the coolant in the approach flow. This is an important result that has previously not been well documented.Copyright © 2013 by ASME

Spray-cooling for wind-based compressed air energy storage

Abstract: Energy systems can benefit from compact and efficient energy storage technologies. In particular, energy storage is well suited for off-shore wind turbines whose output energy variability is typically inconsistent with grid power demand. Furthermore, accommodating peak power generation can lead to over-sizing of electrical generator and transmission lines. It would be more efficient and economical if off-shore wind turbines could be sized for average power and could produce this power on a continuous basis. This would allow the traditional wind turbine generator and transmission lines can be replaced by a smaller, lower-cost, constant-speed generator and a transmission system sized for average power output. This study analyzes a compressor to build and maintain compressed air energy storage for a 35-MPa accumulator sized for a 5 MW off-shore wind turbine. The compressor employs a liquid piston for compression and water spray for heat transfer to achieve near isothermal behavior and efficiency. The overall compression is achieved in three stages with pressure ratios of 10:1, 7:1, and 5:1 under 1-Hz working frequency. The results indicate that droplet surface area plays a critical role in system performance and that high mass loading and small drops can increase overall system efficiency by as much as 50%, as compared to conventional air compressor systems.

Validation of Multi-Dimensional Stirling Engine Design Codes: Measurements in the 90-Degree Turn Test Section

Abstract: The work to be presented herein was motivated largely by a desire to improve the understanding of oscillatory fluid mechanics inside a Stirling engine. To this end, a CFD project was undertaken at Cleveland State University with the goal of accurately predicting the fluid dynamics within an engine or engine component. Along with the CFD efforts, a code validation project was undertaken at the University of Minnesota. The material covered herein consists of four main parts. In section 1, an experimental investigation of a small aspect ratio impinging jet is discussed. Included in this discussion is a description of the test facilities and instrumentation. A presentation of the collected data is given and comments are made. Next, in section 2, a parallel experimental investigation is presented in which the same geometry as that of section 1 is used, but the flow conditions are changed from steady unidirectional flow to sinusoidally oscillating flow. In section Two, collected data are presented and comments are made. In section 3, a comparison is made between the results of sections 1 and 2, namely, sinusoidally oscillating flow results are compared to steady, unidirectional flow results from the same geometry. Finally, in section 4, a comparison is made between experimentally collected data (the main subject of this work) and CFD generated results. Furthermore, in appendix A, an introductory description of the primary measurement tool used in the experimental process the hot wire anemometer is given for the unfamiliar. The anemometer calibration procedure is described in appendix B. A portfolio of data reduction and data processing codes is provided in appendix C and lastly, a DVD and a roadmap of its contents is provided in an appendix D. 1.0 Unidirectional Flow Investigations 1.1 Introduction This unidirectional experimental program was undertaken to complement an oscillatory flow investigation conducted at the University of Minnesota. The oscillatory investigation is discussed thoroughly in section 2. We defer the description of the motivation behind these experiments until the introduction of section 2. The work that is discussed in this thesis began (chronologically) with oscillatory flow visualization experiments. It was decided that it would be valuable and important to investigate the flow under unidirectional conditions in the same geometry as that of the oscillatory experiments. The thought was that the unidirectional case would be less complicated to model with a CFD program (a moving boundary would be replaced with a steady state boundary condition). Thus, a series of unidirectional experiments were carried out to capture the important features of the flow within the test section. The purpose of these experiments was to provide a data set for comparison to CFD generated velocity fields. Hot-wire anemometry data were taken and flow visualization was conducted as a standard for code validation. The flow geometry was simple, such that it could be easily gridded in a CFD program. However, the geometry provided separation and transition zones, shear layers and recirculation zones. These characteristics made the flow complex and challenging for CFD computation. We comment that the order of experiments that produced this report is as follows: experimental flow visualization under oscillatory flow conditions was carried out; this was followed by unidirectional flow visualization and hot wire anemometry; finally, oscillatory hot wire anemometry was conducted. We present the results out of chronological order for the following reason: the unidirectional results are easier