1,726,800 research outputs found
Accelerating growth of HFC-227ea (1,1,1,2,3,3,3-heptafluoropropane) in the atmosphere
No full textWe report the first measurements of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), a substitute for ozone depleting compounds, in air samples originating from remote regions of the atmosphere and present evidence for its accelerating growth. Observed mixing ratios ranged from below 0.01 ppt in deep firn air to 0.59 ppt in the current northern mid-latitudinal upper troposphere. Firn air samples collected in Greenland were used to reconstruct a history of atmospheric abundance. Year-on-year increases were deduced, with acceleration in the growth rate from 0.029 ppt per year in 2000 to 0.056 ppt per year in 2007. Upper tropospheric air samples provide evidence for a continuing growth until late 2009. Furthermore we calculated a stratospheric lifetime of 370 years from measurements of air samples collected on board high altitude aircraft and balloons. Emission estimates were determined from the reconstructed atmospheric trend and suggest that current "bottom-up" estimates of global emissions for 2005 are too high by a factor of three
A Reduced GWP Replacement for HFC-134a in Centrifugal Chillers: XP10 Measured Performance and Projected Climate Impact
No full textThe performance of XP10, a new refrigerant with a reduced GWP, in a centrifugal chiller designed for HFC-134a with a cooling capacity of 1969.44 kW (560 tons) was measured under full and part load conditions and compared to performance with HFC-134a. Measured chiller energy efficiencies with XP10 were comparable to those with HFC- 134a. They resulted in 0.6% higher energy consumption for XP10 when integrated over a representative profile of partial loads as described by AHRI Standard 550/590. Based on the measured chiller performance, XP10 could be considered a near drop-in replacement for HFC-134a in centrifugal chillers. It could replace HFC-134a in existing chillers or enable optimized new chiller designs without extensive equipment and no flammability code modifications. The Total Equivalent Warming Impact (TEWI) of a chiller with XP10 was estimated under representative scenarios and compared to TEWI with HFC-134a. Use of XP10 could significantly reduce chiller global warming impact relative to HFC-134a, when chiller refrigerant losses are unavoidably high or when electricity is generated with low GHG emissions. XP10 has the potential to be a more environmentally sustainable future option for medium pressure centrifugal chillers
Experimental Investigation on Evaporation Heat Transfer and Pressure Drop Characteristics of HFC-161 in a Horizontal Smooth Tube
No full textThe evaporation heat transfer and pressure drop characteristics of HFC-161 in a horizontal smooth tube with an inside diameter of 9 mm was experimentally investigated. The local heat transfer coefficient and total pressure drop were measured at the heat flux ranging from 15 – 25 kW/m2, the mass flux ranging from 100 – 200 kg/(m2·s), and the evaporation temperature of 5, 10 ℃. The experimental results showed that the evaporation heat transfer coefficient increased with the vapor quality except in the high vapor quality region, increased with the mass flux and the heat flux, and decreased with the saturation temperature across the experimental conditions. By comparison, the measured heat transfer coefficient of HFC-161 is higher than that of R22. In addition, the measured total pressure drop of two-phase HFC-161 in the test tube increased strongly with the mass flux within the experimental range. The presented results are helpful in designing more compact and effective heat transfer exchangers for the air-conditioning systems using HFC-161
Model outputs, related figures and input data for inversions of HFC-125, HFC-134a and SF6 emissions over Europe
No full textModel outputs, related figures and input data for inversions of HFC-125, HFC-134a and SF6 emissions over Europ
Measurements of PVTx Properties of HFC-32/HFC-125 and HFC-32/HFC-125 HFC-134a
No full textapplication/pdfThe PVTx properties for the binary mixtures of HFC-32/HFC-125 and HFC-32/ HFC-125 /HFC-134a were measured with the use of a constant volume apparatus in the range of temperatures from 320 K to 450 K and pressures up to 16 MPa along the several isochores of 165-443kg/m3. The experimental PVTx property data were compared with the equation of state correlated
by Piao et al. The data in the critical region agree with Piao's equation of state within the deviation of 150 kPa in pressure. The uncertatntles of these expenmental data were estimated to be within ±4 mK in temperature, ±1.7 kPa in pressure, ±0.23% in density and ±0.33mol% in composition. The purities of the sample used were 99.99% for HFC-32, 99.7% for HFC-125, and 99.9% for HFC-134a.departmental bulletin pape
Polymer precursor-derived HfC-SiC ultrahigh-temperature ceramic nanocomposites
No full textDue to poor mechanical properties and antioxidation properties, etc of single phase ultrahigh-temperature ceramics (UHTCs), the second phase such as SiC was usually introduced for improving those properties. Herein, a novel stratagem for synthesis of binary HfC-SiC ceramics has been presented. A Hf-O-Hf polymer as a HfO2 precursor has been synthesized for preparing soluble HfC-SiC precursors with high solid content and low viscosity solutions without additional organic solvents. The structure of PHO was characterized by FTIR and H-1-NMR, the crystalline behavior and morphologies of polymer-derived ceramics were identified by XRD, SEM-EDS, and TEM. It was shown that PHO firstly transformed into HfO2, and then reacted with in situ carbon derived from DVB and PCS thus producing cubic HfC through carbothermal reduction. In addition, the obtained HfC-SiC nanopowders exhibited spherical morphology with a diameter less than 100 nm, while the Hf, Si, and C are homogeneously distributed
Time series of hydrofluorocarbon HFC-134a concentration at Jungfraujoch in 2011
No full textTime series of hydrofluorocarbon HFC-134a concentration at Jungfraujoch in 201
Baseline and monitoring methodologies for HFC mitigation action
No full textMRV standardisation and streamlining as well as accounting of HFC mitigation – including energy efficiency improvement – under the Kigali Amendment and Paris Agreement.
There is a wide range of cooling sector-related baseline and monitoring metholodogies in the context of different crediting mechanisms (e.g. the Clean Development Mechanism (CDM) or the Joint Crediting Mechanism). These address both improving energy efficiency of cooling equipment as well as reduction of HFC emissions, but not all specific activity types that are principally available. The methodologies either apply a projected BAU approach or a default baseline scenario. None of the methodologies would meet the Art. 6 criteria for additionality determination and baseline setting and could be directly applied to an Art. 6 activity. Therefore, the development of an Art. 6 activity in the cooling sector requires a thorough upgrade of the existing methodologies
Time series of hydrofluorocarbon HFC-125 concentration at MteCimone in 2011
No full textTime series of hydrofluorocarbon HFC-125 concentration at MteCimone in 201
Time series of hydrofluorocarbon HFC-134a concentration at MteCimone in 2011
No full textTime series of hydrofluorocarbon HFC-134a concentration at MteCimone in 201
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