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Ejector as a work recovery device offers potential for developing energy efficient heating and cooling systems based on vapor compression technology. For applications like automobile air conditioning, the operating conditions vary significantly which can lead to considerable performance degradation when the system is operated in off-design conditions. Therefore, system designing warrants development of accurate ejector performance models for a wide range of operating conditions. In this paper, a novel methodology for ejector performance maps is proposed using ejector efficiency as performance parameter and volumetric entrainment ratio as characterization parameter. The proposed performance map is developed after conducting experiments to find appropriate performance representation where ejector driven flow can be characterized using ejector motive flow. The developed performance map can predict ejector pressure lift within an accuracy of 20% using an iterative solver.

In the air conditioning system, flow-induced noise is very disturbing, including the noise generated in the expansion device and the heat exchangers. In the past few decades, most researches related to flow-induced noise focused on the relationship between the flow regimes near the expansion device and the amplitude of flow-induced noise when the measurements are not synched. In this paper, an experimental approach is used to explore the simultaneous relationships between flow-induced noise characteristics and flow regimes at the inlet of TXV of evaporators used in automobiles. A pumped R134a loop with microphones and transparent visualization sections is used to simulate the vapor compression system. Also, the paper evaluates the severity of flow-induced noise from not only the amplitude of noise but also the frequency of noise with a parameter called psychoacoustic annoyance (PA).

In this paper, a MATLAB-Simulink based general co-simulation approach is presented which supports multi-resolution simulation of distributed models in an integrated architecture. This approach was applied to simulating aircraft thermal performance in our Vehicle Systems Model Integration (VSMI) framework. A representative advanced aircraft thermal management system consisting of an engine, engine fuel thermal management system, aircraft fuel thermal management system and a power and thermal management system was used to evaluate the advantages and tradeoffs in using a co-simulation approach to system integration modeling. For a system constituting of multiple interacting sub-systems, an integrated model architecture can rapidly, and cost effectively address technology insertions and system evaluations. Utilizing standalone sub-system models with table-based boundary conditions often fails to effectively capture dynamic subsystem interactions that occurs in an integrated system.

Advancement in modern aircraft with the development of more dynamic and efficient technologies has led to these technologies increasingly operated near or at their operation limits. More comprehensive analysis methods based on high-fidelity models co-simulated in an integrated environment are needed to support the full utilization of these advanced technologies. Furthermore, the additional information provided by these new analyses needs to be correlated with updates to traditional metrics and specifications. One such case is the thermal limit requirement that sets the upper bound on a thermal system temperature. Traditionally, this bound is defined based on steady-state conditions. However, advanced thermal management systems experience dynamic events where the temperature is not static and may violate steady-state requirements for brief periods of time.

Design of modern aircraft relies heavily on modeling and simulation for reducing cost and improving performance. However, the complexity of aircraft architectures requires accurate modeling of dynamic components across many subsystems. Integrated power and thermal modeling necessitates dynamic simulations of liquid, air, and two-phase fluids within vapor cycle system components, air cycle machine and propulsion components, hydraulic components, and more while heat generation of many on-board electrical components must also be precisely calculated as well. Integration of these highly complex subsystems may result in simulations which are too computationally expensive for quickly modeling extensive variations of aircraft architecture, or will require simulations with reduced accuracy in order to provide computationally inexpensive models.

As the cost and complexity of modern aircraft systems increases, emphasis has been placed on model-based design as a means for reducing development cost and optimizing performance. To facilitate this, an appropriate modeling environment is required that allows developers to rapidly explore a wider design space than can cost effectively be considered through hardware construction and testing. This wide design space can then yield solutions that are far more energy efficient than previous generation designs. In addition, non-intuitive cross-coupled subsystem behavior can also be explored to ensure integrated system stability prior to hardware fabrication and testing. In recent years, optimization of control strategies between coupled subsystems has necessitated the understanding of the integrated system dynamics.

Future aircraft systems are projected to have order of magnitude greater power and thermal demands, along with tighter constraints on the performance of the power and thermal management subsystems. This trend has led to the need for a fully integrated design process where power and thermal systems, and their interactions, are considered simultaneously. To support this new design paradigm, a general framework for codifying and checking specifications and requirements is presented. This framework is domain independent and can be used to translate requirement language into a structured definition that can be quickly queried and applied to simulation and measurement data. It is constructed by generalizing a previously developed power quality analysis framework. The application of this framework is demonstrated through the translation of thermal specifications for airborne electrical equipment, into the SPecification And Requirement Evaluation (SPARE) Tool.

Model based design is a standard practice within the aerospace industry. However, the accuracies of these models are only as good as the parameters used to define them and as a result a great deal of effort is spent on model tuning and parameter identification. This process can be very challenging and with the growing complexity and size of these models, manual tuning is often ineffective. Many methods for automated parameter tuning exist. However, for aircraft systems this often leads to large parameter search problems since frequency based identification and direct gradient search schemes are generally not suitable. Furthermore, the cost of experimentation often limits one to sparse data sets which adds an additional layer of difficulty. As a result, these search problems can be highly sensitive to the definition of the model fitness function, the choice of algorithm, and the criteria for convergence.

This paper presents a simulation model for a reversible air conditioning and heat pump system for electric vehicles. The system contains a variable speed compressor, three microchannel heat exchangers, an accumulator, and two electronic expansion valves. Heat exchangers are solved by discretizing into cells. Compressor and accumulator models are developed by fitting data with physical insights. Expansion valves are modeled by isenthalpic processes. System performance is calculated by connecting all parts in the same way as the physical system and solved iteratively. The model is reasonably validated against experimental data from a separate experimental study. Future improvement is needed to take into account maldistribution in outdoor heat exchanger working as an evaporator in HP mode. Charge retention in components also requires further study.

Increasing energy costs justify research on how to improve utilization of low-grade energy that is abundantly available as waste heat from many thermodynamic processes such as internal combustion engine cycles. One option is to directly generate cooling through absorption/adsorption or vapor jet ejector cycles. As in the case of power generation cycles, cooling cycle efficiencies would increase if the heat input were available at higher temperature. This paper assesses the feasibility of a novel idea that uses a vortex tube to increase the available temperature levels of low-grade heat sources. The desired temperature increase is achieved by sending a stream of vapor that was heated by the waste heat source through a vortex tube, which further elevates the temperature used in a heat driven ejector cooling cycle.

This paper presents the experimentally obtained performance characteristics of an air conditioning-heat pump system that uses heat exchangers from a commercially available Nissan Leaf EV. It was found that refrigerant charge needed for cooling operation was larger than that for heating function with the test setup. The effects of: a). indoor air flow rate, b). outdoor air flow rate, and c). compressor speed on heating capacity and energy efficiency were explored and presented. Appropriate opening size of expansion valve that controlled subcooling for better energy efficiency was discussed and results were presented. Expansion valve opening size also strongly affected charge migration. Warm-up tests at different ambient conditions showed the necessity of a secondary heater to be reserved for very low ambient temperature.

This paper presents the experimental analysis of separation in vertical headers based on flow visualization. Two-phase separation phenomena inside the header is observed and quantified. Driving forces are analyzed to study the mechanisms for two-phase flow motion and flow regimes. Main tube of the header is made of clear PVC for visualization study. R-134a is used as the fluid of interest and the mass flux from the inlet pass is 55 kg/m2s - 195 kg/m2s. Potential ways to improve two-phase separation are discussed. A model is built to show how separation brings potential benefits to MAC heat exchangers by arranging the flow path.

An IPTMS hardware facility has been established in the laboratories of the Aerospace Systems Directorate of the Air Force Research Laboratory (AFRL) at Wright-Paterson Air Force Base (WPAFB). This hardware capability was established to analyze the transient behavior of a high power Electrical Power System (EPS) coupled virtually to a Thermal Management System (TMS) under fast dynamic loading conditions. The system incorporates the use of dynamic electrical load, engine emulation, energy storage, and emulated thermal loads operated to investigate dynamics under step load conditions. Hardware architecture and control options for the IPTMS are discussed. This paper summarizes the IPTMS laboratory demonstration system, its capabilities, and preliminary test results.

Much attention has been given in recent years to the use of two-phase ejectors and particularly to the performance of the standard ejector cycle with a liquid-vapor separator. However, this cycle may not be the best choice for automotive applications due to the large size required by an efficient separator as well as the cycle's performance at conditions of lower ejector potential. A limited amount of recent research has focused on alternate two-phase ejector cycles that may be better suited for automotive applications. One of these cycles, using the ejector to allow for evaporation at two different temperatures and eliminating the need for a separator, will be the subject of investigation in this paper. Previous investigations of this cycle have been mainly theoretical or experimental; this paper aims to provide a numerical analysis of the effect of evaporator design on the performance of the ejector cycles.

Numerous previous studies have highlighted the potential efficiency improvements which can be provided to aircraft thermal management systems by the incorporation of vapor cycle systems (VCS), either in place of, or in conjunction with, standard air cycle systems, for providing the needed thermal management for aircraft equipment and crews. This paper summarizes the results of a cycle-based VCS control architecture as tested using the Vapor Cycle System Research Facility (VCSRF) in the Aerospace Systems Directorate of the Air Force Research Laboratory at Wright-Patterson Air Force Base. VCSRF is a flexible, dynamic, multi-evaporator VCS which incorporates electronic expansion valves and a variable speed compressor allowing the flexibility to test both components and control schemes. The goal of this facility is to reduce the risk of incorporating VCS into the thermal management systems (TMS) of future advanced aircraft.

As the cost and complexity of modern aircraft systems advance, emphasis has been placed on model-based design as a means for cost effective subsystem optimization. The success of the model-based design process is contingent on accurate prediction of the system response prior to hardware fabrication, but the level of fidelity necessary to achieve this objective is often called into question. Identifying the key benefits and limitations of model fidelity along with the key parameters that drive model accuracy will help improve the model-based design process enabling low cost, optimized solutions for current and future programs. In this effort, the accuracy and capability of a vapor cycle system (VCS) model were considered from a model fidelity and parameter accuracy standpoint. A range of model fidelity was evaluated in terms of accuracy, capability, simulation speed, and development time.

The paper presents a semi-empirical model to predict refrigerant and lubricant inventory in both evaporator and condenser of an automotive air conditioning (MAC) system. In the model, heat exchanger is discretized into small volumes. Temperature, pressure and mass inventory are calculated by applying heat transfer, pressure drop and void fraction correlations to these volumes respectively. Refrigerant and lubricant are treated as a zeotropic mixture with a temperature glide. As refrigerant evaporates or condenses, thermophysical properties are evaluated accordingly with the change of lubricant concentration. Experimental data is used to validate the model. As a result, refrigerant and lubricant mass is predicted within 20% in the evaporator. However, in the condenser, lubricant mass was consistently under-predicted while refrigerant mass was predicted within 15% error. Moreover, the lubricant under-prediction becomes more significant at higher Oil Circulation Ratio (OCR).

Lubricant in compressor usually flows out with refrigerant. Thus, it is evitable for lubricant to be present in the heat exchanger, which significantly affects the heat exchanger performance. This paper is to investigate the effects of PAG oil on R134a distribution in the microchannel heat exchanger (MCHX) with vertical headers and to provide a tool to model R134a (with oil) distribution and its effects on MCHX capacity. The flow configuration in MCHX under the heat pump mode of the reversible system is mimicked in the experimental facility: refrigerant-oil mixture is fed into the test header from the bottom pass and exits through the top pass. It is found that a small amount of oil (OCR=0.5%) worsen the distribution. But further increasing OCR to 2.5% and 4.7%, the distribution becomes better.

A hot and cold water mixing process with a steam condenser and a chilled water heat exchanger is set up for an engine EGR fouling test. The test rig has water recycled in the loop of a pump, heat exchangers, a three-way mixing valve, and a test EGR unit. The target unit temperature is controlled by a heating, cooling and mixing process with individual valves regulating the flow-rate of saturated steam, chilled water and mixing ratio. The challenges in control design are the dead-time, interaction, nonlinearity and multivariable characteristics of heat exchangers, plus the flow recycle in the system. A systems method is applied to extract a simple linear model for control design. The method avoids the nonlinearity and interaction among different temperatures at inlet, outlet and flow-rate. The test data proves the effectiveness of systems analysis and modeling methodology. As a result, the first-order linear model facilitates the controller design.

Vapor compression systems (VCS) offer significant benefits as the backbone for next generation aircraft thermal management systems (TMS). For a comparable lift, VCS offer higher system efficiencies, improved load temperature control, and lower transport losses than conventional air cycle systems. However, broad proliferation of VCS for many aircraft applications has been limited primarily due to maintenance and reliability concerns. In an attempt to address these and other VCS system control issues, the Air Force Research Laboratory has established a Vapor Cycle System Research Facility (VCSRF) to explore the practical application of dynamic VCS control methods for next-generation, military aircraft TMS. The total refrigerant mass contained within the closed refrigeration system (refrigerant charge) is a critical parameter to VCS operational readiness. Too much or too little refrigerant can be detrimental to system performance.