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Theoretical and Experimental Analysis of Dynamic Characteristics in Linear Compressors
thesisposted on 05.03.2020 by Xinye Zhang
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
Linear compressor technology is characterized by the absence of a crank mechanism, which has gained increasing attention in vapor compression systems due to its compactness and lower friction losses in comparison to conventional reciprocating compressors. Limited work was found in the open literature related to the development and in-depth validation of a comprehensive linear compressor dynamic model that couples thermodynamic aspects with both mechanical and electrical sub-models. The current thesis presents a comprehensive and generalized simulation model that is used to simulate the dynamic performance of a linear compressor. The model is based on mass and energy balance equations applied to open control volumes. The overall model is composed of several sub-models including the piston dynamics, electrical motor, valve dynamics, and leakage flows. The thermodynamic model and the sub-models are integrated into a compressor overall energy balance that describes the different heat flows and losses. The linear compressor model is able to predict both transient and steady-state behaviors of the piston movement, internal pressure and temperatures as well as the overall performance. Moreover, the simulated compressor was characterized experimentally by using a hot-gas bypass test stand over its operating envelope and the experimental data (i.e., measured mass flow rate, motor power and overall isentropic efficiencies), was used to validate the developed linear compressor model. The validated model was then used to investigate and quantify major sources of losses, analyze the system vibration as well as eccentricity caused by the spring assembly. The validated comprehensive model is a powerful tool that can be used to improve the prototype linear compressor design as well as explore alternative designs.
In addition, the comprehensive compressor model has been exercised to design and 3-D print novel liner compressor component with the goal of evaluating their potential to approach an quasi-isothermal compression process.
The concept of design has been integrated into a refrigeration system and a system simulation model was developed and used to analyze the system performance and to assess its potential for approaching a quasi-isothermal compression process through the utilization of refrigerant economizing and regeneration technology. Moreover, the scalability analysis is conducted in terms of heat pump and air compression application, which provides a guidance to design a scale-up linear compressor as well as the selection of components.