Experimental investigation on the influencing factors of a transcritical CO2 heat pump

The concept of “the optimal heat rejection pressure” has attracted wide attention in refrigeration community. Unlike the conventional refrigerants, the heat rejection pressure and temperature of the gas-cooler in the transcritical CO2 cycle are usually decoupled in the transcritical cycle. Besides, there exists an optimal heat rejection pressure under which the maximum cycle efficiency can be achieved. Therefore, the interaction effect between heat rejection pressure and system performance has been studied by many researchers. The heat rejection pressure of the gas-cooler has great impact on the COP of the transcritical CO2 system, but the investigation on the influence factors of the heat rejection pressure is quite rare in open literature. In this paper, the effects of the water inlet temperatures and the water flow rates on the heat rejection pressure of a water-to-water transcritical CO2 refrigeration heat pump with single-stage expansion system have been investigated. Furthermore, the operation parameters and the performance of the system are also evaluated

Design and Setup of the Micro-Turboexpander Transcritical CO2 System

As the potential Eco-friendly refrigerant, CO2 regains more and more attentions. It has various advantages over conventional refrigerants, such as non-flammability, non-toxicity, high volumetric refrigerant capacity and excellent heat transfer properties. Because the heat rejection temperature in a transcritical CO2 heat pump or a transcritical CO2 refrigeration system is higher than the critical temperature of CO2, the transcritical vapor compression cycle becomes the best choice for transcritical CO2 systems. However, the relative low COP caused by the throttle valve limited the further development. The replacement of a throttle valve with a turboexpander, an ejector or a vortex tube is leading to the way for improving the COP of a transcritical CO2 system. With the advantages of high efficiency, high compactness, high reliability and long-life time, turboexpanders have been widely used in gas lique faction devices (below 120K) and most of the reverse Brayton refrigeration systems. It is also one of the most ideal expansion devices for transcritical CO2 systems. However, its applications are limited by the difficulties of high pressure and super high rotating speed operation. With the development of manufacturing technology and gas bearing technology, it becomes possible to use turboexpanders in transcriticalCO2 systems. In this paper, two turboexpanders with 10 mm radial reaction turbine wheel and 9 mm rotor diameter were designed for the 15 kW transcritical CO2 refrigeration system, and the rotating speed is about 200 krpm.The proposed turboexpanders outlet states are CO2 two-phase flow and subcooled CO2 liquid flow, respectively. This study will lay a foundation for the application of turboexpanders in transcritical CO2 systems

spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models

The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site complete graph extended with on-site repulsion is obtained from the underlying spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic ground state is realized for 1 and N+1 electrons only. We identify the large density of states to be responsible for the suppression of the ferromagnetic state and argue that a similar situation is encountered in the Kagome, pyrochlore, and other lattices with flat bands in their one-particle density of states.Comment: 7 pages, 1 figur

Investigation of bonded hydrogen defects in nanocrystalline diamond films grown with nitrogen/methane/hydrogen plasma at high power conditions

In this work, we investigate the influence of some growth parameters such as high microwave power ranging from 3.0 to 4.0 kW and N2 additive on the incorporation of bonded hydrogen defects in nanocrystalline diamond (NCD) films grown through a small amount of pure N2 addition into conventional 4% CH4/H2 plasma using a 5 kW microwave plasma CVD system. Incorporation form and content of hydrogen point defects in the NCD films produced with pure N2 addition was analyzed by employing Fourier-transform infrared (FTIR) spectroscopy for the first time. A large amount of hydrogen related defects was detected in all the produced NCD films with N2 additive ranging from 29 to 87 µm thick with grain size from 47 nm to 31 nm. Furthermore, a specific new H related sharp absorption peak appears in all the NCD films grown with pure N2/CH4/H2 plasma at high powers and becomes stronger at powers higher than 3.0 kW and is even stronger than the 2920 cm−1 peak, which is commonly found in CVD diamond films. Based on these experimental findings, the role of high power and pure nitrogen addition on the growth of NCD films including hydrogen defect formation is analyzed and discussed

B→DsπB \to D_s \pi and the tree amplitude in B→π+π−B \to \pi^+ \pi^-

The recently-observed decay $B^0 \to D_s^+ \pi^-$ is expected to proceed mainly by means of a tree amplitude in the factorization limit: $B^0 \to \pi^- {(W^+)}^*$, ${(W^+)}^* \to D_s^+$. Under this assumption, we predict the corresponding contribution of the tree amplitude to $B^0 \to \pi^+ \pi^-$. We indicate the needed improvements in data that will allow a useful estimate of this amplitude with errors comparable to those accompanying other methods. Since the factorization hypothesis for this process goes beyond that proved in most approaches, we also discuss independent tests of this hypothesis.Comment: 7 pages, LaTeX, 1 figure, to be submitted to Phys. Rev. D (Brief Reports

Fast determination of thiacloprid by photoinduced chemiluminescence

This paper was published in Applied Spectroscopy and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/as/abstract.cfm?URI=as-68-6-642. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.A new and sensitive application of the chemiluminescence detection has been developed for the determination of the pesticide thiacloprid in water. It was based on the on-line photoreaction of thiacloprid in basic medium, with quinine acting as sensitizer of the chemiluminescent response; Cerium (IV) in sulfuric acid medium was used as oxidant. A high automation and reproducibility was provided by a flow injection analysis (FIA) manifold. The validation of the method was performed in terms of selectivity, linearity, LOD, precision and accuracy. Liquid chromatography with UV detection was used as reference for mineral, tap, ground and spring water samples. The proposed method is fast (throughput of 130 h-1), sensitive (LOD of 0.8 ng mL-1 without preconcentration steps and 0.08 ng mL-1 with solid phase extraction (SPE)), low-cost and possible to couple with separative methods for the simultaneous determination of other pesticides. The enhanced chemiluminescence intensity was linear with thiacloprid concentration over the (2-80) and (80-800) ng mL-1 ranges. A possible reaction mechanism is also discussed.The authors thank the Ministerio de Educacion y Ciencia of Spain and the Fondo Europeo de Desarrollo Regional for financial support, Project CTM2006-11991.Catalá Icardo, M.; López Paz, JL.; Pérez Plancha, LM. (2014). Fast determination of thiacloprid by photoinduced chemiluminescence. Applied Spectroscopy. 68(6):642-648. https://doi.org/10.1366/13-07330S642648686Tomizawa, M., & Casida, J. E. (2005). 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Lepton Polarization and Forward-Backward Asymmetries in b -> s tau+ tau-

We study the spin polarizations of both tau leptons in the decay b -> s tau+ tau-. In addition to the polarization asymmetries involving a single tau, we construct asymmetries for the case where both polarizations are simultaneously measured. We also study forward-backward asymmetries with polarized tau's. We find that a large number of asymmetries are predicted to be large, >~ 10%. This permits the measurement of all Wilson coefficients and the b-quark mass, thus allowing the standard model (SM) to be exhaustively tested. Furthermore, there are many unique signals for the presence of new physics. For example, asymmetries involving triple-product correlations are predicted to be tiny within the SM, O(10^{-2}). Their observation would be a clear signal of new physics.Comment: 21 pages, LaTeX, 4 figures (included). Paper somewhat reorganized, references greatly expanded, conclusions unchange