Incorporating 3D Suction or Discharge Plenum Geometry into a 1D Compressor Simulation Program to Calculate Compressor Pulsations

A 3D calculated impedance transfer matrix method has been developed and demonstrated to provide accurate and efficient prediction of pressure pulsations in positive displacement compressors. The method is easily incorporated into 1D compressor simulation models, where a single impedance matrix, normalized to density and speed of sound, can be used to model all compressor running speeds and operating conditions. The general transfer matrix or “4 pole” method is documented by Bilal, et al (2010) where the hybrid approach used here is also introduced. More recent developments of this method are presented by Novak and Sauls (2012). This paper describes how the model has been integrated into a family of 1D thermodynamic simulation programs used for design and analysis of reciprocating, scroll and screw compressors. A review of how the model compares to test results for a twin screw refrigeration compressor is provided. In addition, we show one example of the type of design study that can be carried out using the 1D simulation with the hybrid model

Comparing FEM Transfer Matrix Simulated Compressor Plenum Pressure Pulsations to Measured Pressure Pulsations and to CFD Results

Improving efficiency of positive displacement compressors requires improving current computer compressor simulations to better model compressor behavior. This paper will specifically look at increasing fidelity of the 1D thermodynamic compressor simulation program by incorporating suction and discharge pulsations due to complex suction and discharge three dimensional (3D) plenum geometry. This method allows for quick pressure pulsation analysis and enables the design engineer to make changes early in the compressor development cycle. Finite Element Method (FEM) full harmonic analysis is used to calculate suction or discharge plenum’s impedance transfer functions in the frequency domain. The impedance transfer functions are normalized to the FEM conditions and normalized impedance transfer functions are used to model all compressor operating speeds and operating conditions. The normalized impedance transfer functions are independent of mass flow, compressor speed, valve dynamics, sonic velocity, refrigerant density, refrigerant, bore size and stroke size which allow the 1D compressor simulation program to change any of these variables without have to solve for a new FEM impedance transfer function. We have also worked on a new way to include damping and phase shift between mass flow and pressure pulsations that better agrees with experimental and Computational Fluid Dynamics (CFD) results. Since some of this method is novel or may extend beyond the limits of linear acoustic analysis, it requires good agreement to compressor test results and to CFD results. The main part of the paper will show good agreement between simulated pressure pulsations to suction and discharge test results in a reciprocating compressor. The paper will also show our latest improvements in pulsation modeling to obtain better agreement to CFD resultsthan the original comparison in Bilal et al (2010)

Growing the New American Economy: Public-private partnerships for the development of Transit Greenways

As the new Obama-Biden Administration begins to plan for the implementation of a stimulus plan to jump-start the economy and create new jobs by various tax cuts and spending programs, this panel of experts shows how a multimodal approach could enhance the infrastructure benefits expected from the infrastructure expenditures proposed. By proposing unique public-private partnerships in connection with new transit communities, immediate and long-term economic growth can be projected. Specific methods, applications and implications are presented and discussed, and a specific stimulus policy is recommended. Among the common themes that urban studies in America share, two are critically important. One is the need to return to denser urban planning, which contributes to economic development and commerce, while facilitating a high quality of life, social and economic integration, and environmental sensitivity. The second is the need to mitigate traffic congestion that has persisted even with the continuing expansion of the road network. Negative and destructive consequences from traffic congestion include: environmental and global weather consequences, public health threats, and productivity losses. By coordinating investments in mass transit with housing and mixed-use development at passenger rail station sites and transit stops, passenger rail and transit use will significantly increase. Only by providing for high quality pedestrian linkages to and within these new American transit communities and providing for enhanced opportunities for higher education and job training, will such communities substantially contribute in the near and long term to growth of the economy. Only with a proper concern for the impacts of such built environments, will the quality of life for residents and visitors be improved and sustainable natural environments preserved. Merely rebuilding aging bridges, rail beds, and creating new highways will not solve our mobility, energy, and economic problems. A change from past transportation and community planning is necessary and a new integration of policy, political, and implementation efforts must evolve. Public-private partnerships leverage public investment and allow market-based economics to support synergies of interest. Substantial public investments in infrastructure serve as the catalyst. By focusing on pedestrian urban mobility, education and a decision to build a globally competitive multimodal transportation system, we can move people to employment through investment in infrastructure, growth in the economy, and predictable improvements in the quality of life. The authors (26 individuals with expertise in community development, public finance, and public policy development) welcome opportunities to discuss these matters with national and state policy makers. The following article describes proposed tools for economic growth and the preferred community in the 21th Century and clearly defines these unique pedestrian-oriented, educationally enhanced transit communities. The Author Resumé Statements, Endnotes and Appendices are available from Tom Gustafson on request at: [email protected] or [email protected]