Norbert Müller

Preliminary Study of a Novel R718 Compression Refrigeration Cycle Using a Three-Port Condensing Wave Rotor

Using a novel 3-port condensing wave rotor enhancing the turbocompression in a R718 refrigeration cycle, which uses only water as a refrigerant, has been introduced. The wave-rotor implementation can increase efficiency and reduce size and cost of R718 units. The condensing wave rotor employs pressurized water to pressurize, desuperheat, and condense the refrigerant vapor—all in one dynamic process. The underlying phenomena of flash evaporation, shock wave compression, desuperheating, and condensation inside the wave rotor channels are described in a wave and phase-change diagram. The thermodynamic process is shown in pressure–enthalpy and temperature–entropy diagrams. A computer program based on a thermodynamic model was generated to evaluate the performance of R718 baseline and wave-rotor-enhanced cycles. The effect of some key parameters on the performance enhancement is demonstrated as an aid for optimization. A performance map summarizes the findings. It shows optimum wave rotor pressure ratio and maximum relative performance improvement of R718 cycles by using the 3-port condensing wave rotor. DOI: 10.1115/1.1850503

Gas dynamic design analyses of charging zone for reverse-flow pressure wave superchargers

The paper is focused on a comprehensive and systematic gas dynamic analysis of the high-pressure phase (charging zone) of pressure wave superchargers. The procedure is documented for a four-port reverse flow (RF) wave rotor, the typical configuration for engine wave superchargers, also named Comprex. A one-dimensional analytical gas dynamic model is employed to calculate flow characteristics inside the channels. Existing normal shock wave equations along with isentropic relations for expansion waves are used for calculations. Useful design parameters such as cycle timing and port widths are determined by formulating traveling times of the waves inside the channels. The gas dynamic study of the internal wave process demonstrates its fundamental dependence on the externally imposed compression ratio of the pressure wave supercharger.Copyright

NUMERICAL SIMULATION OF UNSTEADY- FLOW PROCESSES IN WAVE ROTORS

The wave rotor (pressure exchanger) is a device working based on a relatively simple idea of operation, but is challenging in its technical realization and difficult to simulate numerically. It has been common practice to create and use specialized codes for simulating the wave rotor operation. The current work presents an attempt of developing 2D and 3D models of radial and axial wave rotors using the commercial software package FLUENT. In this study geometrical models are used for the device casing and rotor cells. The application of carefully chosen initial and boundary conditions enabled the realization of relative motion of the rotor model. The vast information about the unsteady processes occurring during simulation are visualized. It occurs that such type of models are useful for the final test of devices, after the geometry was optimized by the use of specialized but much simpler 1D codes.

On the Realization of Filament Wound Composite Impeller for Water Refrigerant

In the present work, the concept of composite impeller through automatic filament winding manufacturing approach was realized. The advantage of using filament winding method to manufacture high performance and light-weight composite impellers is that the production can be rapid, inexpensive and utilize commercially available winding machines. This work focuses both on how to achieve the automation of the production process, as well as evaluate the composite impeller’s mechanical properties. For the automatic production process, a new filament winding facility for manufacturing fiber-reinforced composite impellers was developed. A kevlar/epoxy matrix was selected to manufacture the high strength-to-weight ratio composite material. In order to maintain the epoxy’s freshness, a two component syringe dispensing device was designed to control the dispensation of resin. The composite material’s properties were measured in order to ensure the impeller was able to withstand the large stresses incurred during the high speed rotation required to achieve large volume flows and a high compression ratio. With these properties, a 3D structural analysis using ANSYS was performed, which resulted in a maximum tip speed of 830m/s before the composite impeller’s failure. In terms of momentum change, this is a high tip speed needed to compress water vapor.Copyright

Simulation and Production of Wound Impellers

The wound composite impeller, developed at Michigan State University, is a new way of manufacturing turbomachine impellers with a wide range of potential applications, even including use in gas turbines. The production can be rapid, inexpensive, and utilize commercially available winding machines. This work focuses on the modeling of the Wound Impeller for computer simulation and optimization processes, and for automation of the production process.Copyright

Design of Composite Water Turbine in Free Stream Using CFD

The objective of this paper is to investigate the performance of composite material axial water turbines in a free stream using Fluent, a Finite Volume based commercial CFD package. Based on three dimensional numerical flow analysis and fluid-structure interaction, the flow characteristics of water turbines including a nozzle, impeller and diffuser are predicted. The extracted power coefficient is calculated for water turbines of different tip speed ratios in a free stream of water with inlet velocity of 2.5m/s. The extracted powers of one single turbine unit and an array with ten turbine units are analyzed and compared for different rotating speeds and water inlet velocities. The calculated results will provide a fundamental understanding of the impeller as a water turbine, and this design method is used to shorten the design process and improve the water turbine’s performance.Copyright

Numerical Analysis of the Wave Topping Unit for Small Turbojet

The paper is focused on the numerical analysis of a wave topping unit used in a small turbojet engine. The analysis focuses on a four-port reverse flow (RF) wave rotor. The special feature of the considered wave rotor is its very high rotational speed. The wave rotor is connected directly with the common shaft between compressor and turbine, thus, the effects of Coriolis accelerations become important. In this study, first a one-dimensional model is used to estimate geometry of the wave rotor and port timings. Then, multi-dimensional analysis models are employed to predict the different flow characteristics inside the wave rotor channels. Three-dimensional flow features that reduce machine performance and influence rotor blade and duct wall thermal loads are identified.Copyright

CFD Analysis of Composite Axial Water Turbine

This paper presents computational investigation of the flow in composite material axial water turbines using Finite Volume based commercial CFD package namely Fluent. Based on three dimensional numerical flow analysis and fluid-structure interaction, the flow characteristics of water turbines including nozzle, impeller and diffuser are predicted. Two particulare cases are studied and compared. The extract power of water turbine in different rotating speed and water inlet velocity are analyzed. The calculated results will provide a fundamental understanding of the impeller as water turbine, and this design method is used to shorten the design period and improve the water turbine’s performance.Copyright

Wave Rotor Design Procedure for Gas Turbine Enhancement

This paper presents an analytical design procedure for pressure wave machines, also known as wave rotors, to enhance gas turbines and internal combustion (IC) engines in a topping or bottoming cycle. The advantage of using a wave rotor for improving the performance of gas turbines or internal combustion engines is that it uses a pressure and enthalpy exchange process. Employing pressure or even shockwaves for the energy transfer, no mechanical parts like pistons or blades are necessary inside the chamber (channel) that houses the process, which increases the air pressure delivered to the combustor of a gas turbine or cylinder of an internal combustion (IC) engine. The wave rotor has found fair success in its application to IC engines. Research and development continues for both, applications in IC engines and its originally envisioned application in gas turbines. Here an analytical 1-D algebraic wave model is realized by utilizing shockwave theory and linear gas dynamic principles to model the process in a 4-port wave rotor, with five wave reflections in the low pressure part for better gas scavenging. Using this analytical model, a comprehensive design space has been investigated and documented in performance maps. From this, conclusions and recommendations are drawn for performance and geometry optimization. The analytical algorithm has been validated using a 1-D commercial code GT-POWER and 2-D CFD code FLUENT. While here the interest is mainly in steady state operation, the analytical algorithm also models transient processes.© 2008 ASME

Preliminary Design Considerations for Integrating a Composite Impeller in a Brushless Permanent Magnet Motor

Traditional turbomachine design is generally characterized by a shaft driven impeller that was created using common manufacturing processes. However, a cutting edge and innovative impeller design involves the manufacturing of the impeller on a winding machine. Through the use of such a machine, a lightweight and high-strength impeller with carbon fibers or other fibers can be prototyped quickly and easily while also produced in large quantities. The impeller will not only be a composite of multiple parts, but a single solid piece. One of the most interesting attributes of this impeller however, is the ability to integrate it as the rotor for a permanent magnet electric motor. Using the concepts of permanent magnet motor design, current can be applied to the housing of the impeller, which would generate forces that would serve the purpose of both rotating the impeller, and securing it into place. This has the advantage of eliminating most of the moving parts in a turbomachine design, but also creating a durable, lightweight and cheap design to prototype and reproduce. Another key advantage to this design is where the torque on the impeller is applied. Traditional turbomachines generally have the torque generated from forces applied from the shaft, which requires higher tangential forces and hence shear stresses due to a much smaller moment arm. But the integration of magnetics into the outer shroud of the impeller allows for the forces to be applied to the outer edge, which requires less force due to a much greater moment arm. Furthermore, this type of motor inherently allows for all of the electrical components to be outside of the fluid flow, which reduces the need for extensive sealing and insulation. In this paper, basic concepts behind the design of electric motors are outlined, as well as how they can be integrated with a rotor impeller, such that together they could act as a turbomachine.Copyright