Dynamic Modeling of Vapor Compression Cycle Systems

Dynamic Modeling of Vapor Compression Cycle Systems
Author: Eric S. Miller
Publisher:
Total Pages: 149
Release: 2012
Genre:
ISBN:
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Vapor compression cycles (VCS) based thermal management systems are being considered in modern aircraft where dynamic changes in heat loads are very common. Predicting dynamic behavior of vapor compression systems is critical to design, sizing, and control of aircraft thermal management systems. A novel Lagrangian method to model the dynamic behavior of vapor compression cycles is presented in this thesis. Fluid flowing through a vapor compression cycle is divided into a large number of material volumes (or mass elements). The mass contained in each element is fixed while the size of the material volume is allowed to change based on its density. At every time step, heat transfer to each mass element is determined and corresponding changes in the thermodynamic properties are evaluated. Each mass element is tracked as it moves through the evaporator, the compressor, the condenser, the expansion valve, and the piping connecting these components. This approach improves on previous models by accounting for spatial mass and enthalpy distribution, meaning that transport delays are reflected in the model result. The model predicts the transient variation during normal operation as well as start-up and shut-down modes. Model results were compared to experimental data at steady state. The model was then validated by comparing the predicted system behavior with experimental data. Results are presented and explained for three major operating condition variations : change in heat load, change in sink availability, and changes in system throttling via the expansion valve and compressor. The results depict extensive coupling of system parameters and significant response to exogenous inputs. The resulting model is modular, adaptable and runs cases faster than real time. Many opportunities exist for its utilization.

Dynamic Modeling and Cascaded Control for a Multi-Evaporator Supermarket Refrigeration System

Dynamic Modeling and Cascaded Control for a Multi-Evaporator Supermarket Refrigeration System
Author: Ankush Gupta
Publisher:
Total Pages:
Release: 2013
Genre:
ISBN:
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The survey from US Department of Energy showed that about one-third of energy consumption in US is due to air conditioning and refrigeration systems. This significant usage of electricity in the HVAC industry has prompted researchers to develop dynamic models for the HVAC components, which leads to implementation of better control and optimization techniques. In this research, efforts are made to model a multi-evaporator system. A novel dynamic modeling technique is proposed based on moving boundary method, which can be generalized for any number of evaporators in a vapor compression cycle. The models were validated experimentally on a commercial supermarket refrigeration unit. Simulation results showed that the models capture the major dynamics of the system in both the steady state and transient external disturbances. Furthermore the use of MEMS (microelectromechanical) based Silicon Expansion Valves (SEVs) have reportedly shown power savings as compared to the Thermal Expansion Valves (TEVs). Experimental tests were conducted on a supermarket refrigeration unit fitted with the MEMS valves to explain the cause of these potential energy savings. In this study an advanced cascaded control algorithm was also designed to control the MEMS valves. The performance of the cascaded control architecture was compared with the standard Thermal Expansion Valves (TEVs) and a commercially available Microstaq (MS) Superheat Controller (SHC). The results reveal that the significant efficiency gains derived on the SEVs are due to better superheat regulation, tighter superheat control and superior cooling effects in shorter time period which reduces the total run-time of the compressor. It was also observed that the duty cycle was least for the cascaded control algorithm. The reduction in duty cycle indicates early shut-off for the compressor resulting in maximum power savings for the cascaded control, followed by the Microstaq controller and then the Thermal Expansion Valves. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148111

Parameter Estimation and Dynamic State Observer Design for Vapor Compression Systems

Parameter Estimation and Dynamic State Observer Design for Vapor Compression Systems
Author: Travis D. Pruitt
Publisher:
Total Pages: 51
Release: 2019
Genre: Air conditioning
ISBN:
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"Between cooling our house, our workplace, and keeping our food cold both in home and commercially (among other uses), the vapor compression cycle (VCC) is a common method for removing heat from various environments and it accounts for a significant amount of the energy used throughout the world. Therefore, with an ever-growing demand for more efficient processes and reduced energy consumption, improving the ability to accurately model, predict the performance of, and control VCC systems is beneficial to society as whole. While there is much information available regarding the performance for some of the components found in VCC systems, much of the challenge associated with modelling the VCC lies within the complex behavior of the heat exchangers found within the system. Over the years, lumped parameter models have been developed for the VCC. However, many of these rely on simplified geometry (mainly a bare tube assumption), and neglect to capture the effect of the fins found throughout those heat exchangers. This thesis builds upon approaches used in the past by identifying effective heat transfer coefficients that capture this effect. Using this approach, a 2-ton residential air-conditioning unit was modelled, which was able to predict the heat removed by the VCC system within ±4% error when compared to published performance data from the manufacturer. Furthermore, these coefficients, along with the complete dynamic model, form the basis of a nonlinear state observer which can be used to further the ability to accurately predict and monitor system performance."--Boise State University ScholarWorks.

Encyclopedia Of Two-phase Heat Transfer And Flow Iii: Macro And Micro Flow Boiling And Numerical Modeling Fundamentals (A 4-volume Set)

Encyclopedia Of Two-phase Heat Transfer And Flow Iii: Macro And Micro Flow Boiling And Numerical Modeling Fundamentals (A 4-volume Set)
Author: John R Thome
Publisher: World Scientific
Total Pages: 1460
Release: 2018-03-13
Genre: Technology & Engineering
ISBN: 9813227427
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Set III of this encyclopedia is a new addition to the previous Sets I and II. It contains 26 invited chapters from international specialists on the topics of numerical modeling of two-phase flows and evaporation, fundamentals of evaporation and condensation in microchannels and macrochannels, development and testing of micro two-phase cooling systems for electronics, and various special topics (surface wetting effects, microfin tubes, two-phase flow vibration across tube bundles). The chapters are written both by renowned university researchers and by well-known engineers from leading corporate research laboratories. Numerous 'must read' chapters cover the fundamentals of research and engineering practice on boiling, condensation and two-phase flows, two-phase heat transfer equipment, electronics cooling systems, case studies and so forth. Set III constitutes a 'must have' reference together with Sets I and II for thermal engineering researchers and practitioners.

The Control Handbook (three volume set)

The Control Handbook (three volume set)
Author: William S. Levine
Publisher: CRC Press
Total Pages: 3526
Release: 2018-10-08
Genre: Technology & Engineering
ISBN: 1420073672
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At publication, The Control Handbook immediately became the definitive resource that engineers working with modern control systems required. Among its many accolades, that first edition was cited by the AAP as the Best Engineering Handbook of 1996. Now, 15 years later, William Levine has once again compiled the most comprehensive and authoritative resource on control engineering. He has fully reorganized the text to reflect the technical advances achieved since the last edition and has expanded its contents to include the multidisciplinary perspective that is making control engineering a critical component in so many fields. Now expanded from one to three volumes, The Control Handbook, Second Edition brilliantly organizes cutting-edge contributions from more than 200 leading experts representing every corner of the globe. They cover everything from basic closed-loop systems to multi-agent adaptive systems and from the control of electric motors to the control of complex networks. Progressively organized, the three volume set includes: Control System Fundamentals Control System Applications Control System Advanced Methods Any practicing engineer, student, or researcher working in fields as diverse as electronics, aeronautics, or biomedicine will find this handbook to be a time-saving resource filled with invaluable formulas, models, methods, and innovative thinking. In fact, any physicist, biologist, mathematician, or researcher in any number of fields developing or improving products and systems will find the answers and ideas they need. As with the first edition, the new edition not only stands as a record of accomplishment in control engineering but provides researchers with the means to make further advances.