Control Strategies for Multi-Evaporator Vapor Compression Cycles

Next-generation military aircraft must be able to handle highly transient thermal loads that exceed the ability of current aircraft thermal subsystems. Vapor compression cycle systems are a particular refrigeration technology that is an attractive solution for dealing with this challenge, due primarily to their high efficiency. However, there are several barriers to realizing the benefits of vapor cycles systems for controlling thermal loads in military aircraft. This thesis focuses on addressing the challenge of controlling vapor cycles in the presence of highly transient evaporator heat loads. Specifically, a linear quadratic regulator (LQR) is designed for a simple vapor cycle system, and closed-loop performance is compared with a set of proportional-integral (PI) controllers. Simulation results show significant advantages of using the LQR method, and the same approach is repeated for a larger dual-evaporator vapor cycle system. The LQR method retains some of its benefits, but several issues associated with relying on a single linear model for the full nonlinear system are identified, and recommendations for future work are made at the end

Evaporator Disturbance Rejection in Vapor Compression Cycles with a Linear Quadratic Regulator

Excerpt from Introduction: All aircraft have some form of thermal management system to handle the waste heat that is inevitably generated in the various mechanical and electrical machines throughout the system. Left alone, the buildup of this heat would eventually degrade performance, overheat components, and cause system failure. Next-generation military aircraft are anticipated to require more power than ever before, and this necessarily drives a requirement for better thermal management systems. To meet this challenge, the Air Force Research Laboratory (AFRL) is working in collaboration with other research institutions to study new thermal management technologies

Control of Vapor Compression Cycles under Transient Thermal Loads

Excerpt: This paper designs a linear quadratic regulator for a simple VCS architecture, and compares performance with a traditional PI controller. Our results show the performance improvements associated with LQG control in a simulated disturbance rejection case study

Societal transformation in response to global environmental change: a review of emerging concepts

The study of societal transformation in response to environmental change has become established, yet little consensus exists regarding the conceptual basis of transformation. This paper aims to provide structure to the dialog on transformation, and to reflect on the challenges of social research in this area. Concepts of transformation are identified through a literature review, and examined using four analytical criteria. It is found that the term ‘transformation’ is frequently used merely as a metaphor. When transformation is not used as a metaphor, eight concepts are most frequently employed. They differ with respect to (i) system conceptualization, (ii) notions of social consciousness (deliberate/emergent), and (iii) outcome (prescriptive/descriptive). Problem-based research tends to adopt concepts of deliberate transformation with prescriptive outcome, while concepts of emergent transformation with no prescriptive outcome tend to inform descriptive-analytical research. Dialog around the complementarities of different concepts and their empirical testing are priorities for future research