A transient fluid and thermodynamic model of a compressed air system

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University of Alabama Libraries

Air compressors are significant energy users in nearly every industrial facility. Air compressors have become a primary focus of industrial energy audits because they are vital for production processes but are very energy inefficient machines. Industrial energy auditors often perform a detailed energy analysis on a compressed air system using logged amperage data from the air compressors in the system. Most of the current air compressor simulation tools use logged power data to perform simulation according to an electrical analysis. These tools perform their analysis based on averaged power draws taken from the logged amperage data. The airflow demands of a compressed air system are then calculated based on the general shape of the performance profile. This static analysis of a compressed air system's operation invariably prompts an inquisitive auditor to dynamically model a compressed air system. While the current compressed air software tools are useful for modeling systems with an electrical analysis, a potential exists to develop a modeling tool with a sound physics and thermodynamics based approach. This thesis responds to the need for a transient thermodynamic compressed air system model. The central focus of the resulting investigation is the generation of a comprehensive compressed air model to be used in analyzing recorded airflow supply data from a rotary screw air compressor operating under three different capacity control methods. The rotary screw compressor is chosen as a focus of this work because of its dominance in the industrial air compressor market. System responses will be tracked for verification of the compressed air model. Several compressed air system examples will be evaluated to reflect compressor operation under adequate and inadequate storage. The main objective of this report is to: educate the reader on the performance of current rotary screw compressors, describe the generation of a transient thermodynamic compressed air model, analyze several different compressed air systems, and evaluate these compressed air systems through quantitative and qualitative comparisons.

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