4 research outputs found
Assessing the Impact of Using Very Low GWP Alternatives to R-404A
Global pressures on hydrofluorocarbon (HFC) refrigerants have reached new levels. With ongoing country ratifications of the Kigali Amendment to the Montreal Protocol and refrigerant shortages across Europe driven by the F-Gas regulations, equipment manufacturers are working hard to implement lower global warming potential (GWP) solutions. R-404A is one of the higher GWP refrigerants (GWP100 Year = 3,922, per AR4) used widely in commercial refrigeration. Several very low GWP (LGWP) candidates have emerged as potential replacements. For many hermetic and split system applications, hydrofluoroolefin-based (HFO) blends represent lower flammability alternatives to hydrocarbon (HC) refrigerants, that also allow for significantly larger charge sizes. Two mildly flammable, very LGWP blends, XL40 (R-454A) and XL20 (R-454C) were tested and compared to the R-404A baseline performance of a commercially available, double-door, upright reach-in freezer via soft-optimization testing. Refrigerant compatibility with lubricants and other system materials was also examined. Miscibility, water solubility, and dielectric properties were also characterized
The Consequences of Long Term Unemployment: Evidence from Matched Employer-Employee Data
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Advanced robot locomotion.
This report contains the results of a research effort on advanced robot locomotion. The majority of this work focuses on walking robots. Walking robot applications include delivery of special payloads to unique locations that require human locomotion to exo-skeleton human assistance applications. A walking robot could step over obstacles and move through narrow openings that a wheeled or tracked vehicle could not overcome. It could pick up and manipulate objects in ways that a standard robot gripper could not. Most importantly, a walking robot would be able to rapidly perform these tasks through an intuitive user interface that mimics natural human motion. The largest obstacle arises in emulating stability and balance control naturally present in humans but needed for bipedal locomotion in a robot. A tracked robot is bulky and limited, but a wide wheel base assures passive stability. Human bipedal motion is so common that it is taken for granted, but bipedal motion requires active balance and stability control for which the analysis is non-trivial. This report contains an extensive literature study on the state-of-the-art of legged robotics, and it additionally provides the analysis, simulation, and hardware verification of two variants of a proto-type leg design