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• Transcritical CO 2 heat pump for residential heating combined with mechanical subcooling is proposed. • Maximum COP is obtained at the optimum discharge pressure and subcooling degree. • Seasonal performance factor (SPF) is the highest when STD-FCU is utilized as heating terminal. • Exergy efficiency can be apparently improved for severe cold region by using FCR or N-FCU. • Purchased equipment cost and electricity cost of CO 2 HP DMS system are both reduced. A transcritical CO 2 heat pump (HP) system for residential space heating integrated with direct dedicated mechanical subcooling (DMS) is proposed, and mathematical models are developed to study the annual energetic and economic performances considering the influence of frosting. The operation characteristics by adopting different heating terminals used in five typical cities are also assessed. The results show a maximum coefficient of performance (COP) is achieved at the optimum discharge pressure and subcooling degree. The COP is promoted by 24.4% and the discharge pressure is decreased by 2.093 MPa at the ambient temperature of −10 °C and water supply/return temperature of 45/40 °C. The seasonal performance factor (SPF) is enhanced more noticeably for severe cold region. For the case of Harbin using floor-coil radiator (FCR) or normal fan-coil unit (N-FCU) as heating terminal, SPF is improved by 32.0%. The highest SPF is achieved when small temperature difference fan-coil unit (STD-FCU) is employed. The exergy efficiency can also be apparently improved, especially for the cities located in severe cold region and using FCR or N-FCU as heating terminal due to the reduction in throttling loss of CO 2 system. The purchased equipment cost and electricity cost of the CO 2 HP with DMS are both lower than those of traditional CO 2 heat pump system. The CO 2 HP DMS system using STD-FCU as heating terminal shows superior economical efficiency to traditional system, with levelized annual total cost reduced by 7.51–15.27%. [ABSTRACT FROM AUTHOR]

• An improved method is proposed to compute the heat transfer coefficient on 3D airfoil. • The model of airfoil ice shape and crack growth was established by the self-developed C-DEICE program. • The 2D and 3D simulation calculation of crack propagation and the ice shape are achieved. • The fluid–solid coupling method is reliable for determining the initial crack location. For aircraft ice accumulation, this paper analyzed airfoil icing with OpenFOAM software, including the ice shape analysis, ice crack propagation analysis and ice stress intensity analysis. The direction of water overflow is divided along the chordwise and spanwise of the airfoil. And the heat and mass transfer process of icing is investigated by modifying the classical Messinger icing thermodynamic model. Based on the traditional calculation method of 2D surface heat transfer coefficient, an improved 3D airfoil surface heat transfer coefficient calculation method is proposed. And ice accretion is along the direction normal to the surface. The model of airfoil ice shape and crack growth was established by the self-developed C-DEICE program. The flow field of the 2D and 3D ice shape obtained by reverse modeling were calculated by the C-DEICE program. The crack propagation and ice shedding shape were simulated in 2D and 3D. Icing completely changes the pressure distribution on the airfoil surface, and the aerodynamic performance is decreased by 91.6%. The displacement of ice body above the crack increases significantly with the crack propagation, and the displacement increases with the distance from the crack tip, which is consistent with the 2D crack propagation simulation results. Furthermore, the self-developed C-DEICE program can better capture the trend of ice shape and the range of ice covering on the airfoil surface. It is found that the fluid–solid coupling method is reliable for determining the initial crack location. Meanwhile, it also lays a theoretical foundation for the follow-up study of ice shedding trajectory. [ABSTRACT FROM AUTHOR]

• Experimental study on the impact freezing characteristics of droplets on different cold surfaces (hydrophilic/superhydrophobic surface). • The effects of droplet impact velocity and surface temperature on water droplet morphology evolution, water droplet spreading factor, water droplet height factor and freezing time are analyzed. • In this paper, the lowest surface temperature can reach −25 °C, which further expands the experimental data of water droplet impacting cold surface. • The results of this paper can provide effective anti-icing methods for practical application. The freezing of supercooled water droplets (SCWD) on the aircraft surface is the cause of aircraft icing, which seriously affects the safe flight of the aircraft. In order to explore safe, efficient and energy-saving anti-icing method, this paper conducts experimental study on the impact freezing characteristics (heat and mass transfer) of water droplets on cold surfaces with different materials (hydrophilic/superhydrophobic surface). The effects of water droplet impact velocity and different surface temperature on water droplet morphology evolution, water droplet spreading factor (WDSF), water droplet height factor (WDHF) and freezing time are analyzed. It can be found that the freezing characteristics of water droplets impacting different materials are different. When water droplets impact the hydrophilic surface at the same temperature, the MSF of water droplets increases significantly with the increase of We number, and the oscillation time of water droplets decreases, and the amplitude decreases gradually. And the surface temperature is less than -10 °C, the water droplet spreading time is less than 10 ms. Then, when the superhydrophobic surface temperature is 10 and 20 °C, the water droplets bounce many times; the surface temperature is 0 and -5 °C, the water droplets bounce only once and then adhere to the surface for continuous oscillation and the surface temperature is less than -10 °C, water droplets cannot effectively bounce off the surface. Meanwhile, singular jet phenomena are observed in the experiment. Additionally, with the decrease of surface temperature, the freezing rate of water droplet decreases. Compared with the hydrophilic surface, the decrease of water droplet freezing rate is more pronounced with the decrease of superhydrophobic surface temperature. Finally, the superhydrophobic surface temperature is low (such as T s = -20 or -25 °C), its hydrophobic ability decreases. [ABSTRACT FROM AUTHOR]

Abstract: The surface damage experiments of gallium arsenide (GaAs) single crystal irradiated by 1.06 and 0.53μm nanosecond irradiations are carried out with fundamental and frequency-doubled Nd:YAG laser, respectively. The surface damage thresholds for both wavelengths are experimentally determined and the damaged morphologies and elementary component are analyzed with electron probe microanalyzer (EPM). It is found that the components of Ga and As almost keep constant in our experiments when the irradiated fluence is just around the surface damage threshold and no oxygen is found at all. The theoretical calculations on temperature rise for both wavelengths are carried out using the purely thermal model. It is shown that for irradiation with photon energy above the corresponding band gap the theoretical calculation is in good agreement with the experimental results; however, for that with photon energy just below the band gap, the experimental results cannot be effectively explained by the purely thermal heating mechanism. Combining with the experiment of multi-shot damage from references we finally conclude that the damage by laser irradiation with photon energy below the band gap should be explained by the micro-defect accumulation and consequently enhanced absorption heating mechanism. [ABSTRACT FROM AUTHOR]

The Kigali Amendment to the Montreal Protocol encourages replacing hydrofluorocarbons or HFCs with natural refrigerants such as carbon dioxide. Since current CO 2 transcritical systems have lower efficiency as compared to HFC systems, this study is proposed to carry out theoretical and experimental investigations of CO 2 pool boiling heat transfer performance for efficiency improvements. The theoretical and experimental investigations are carried out for a smooth and three mechanically enhanced tubes under heat flux values ranging from 10 to 50 kW m−2 and evaporating pressures ranging from 2 to 4 MPa. The special structures of enhanced tube surface are favorable for the formation and maintenance of vaporization cores and for expelling the gas bubbles in the evaporation tubes. Results from the experimental investigations suggest that the heat transfer coefficient can be improved by a factor of 1.50–1.70, 1.58–1.82, and 1.94–2.23 respectively when using the three mechanically enhanced as compared to using the smooth tube. Such improvements in heat transfer coefficient can translate to an energy efficiency improvement of approximately 15.2%, 18.6% and 24.8% respectively. Based on the experimental data, a robust and simplified model for computing heat transfer coefficient is further proposed as a correlation of evaporating pressure and heat flux. The maximum deviation of the calculated and tested heat transfer coefficient is within ±8.73% for smooth tube and within ±15% for mechanically enhanced tubes. Findings from this study can provide a fundamental basis for improving the heat transfer performance of CO 2 systems from the perspective of engineering design. [ABSTRACT FROM AUTHOR]

• CO 2 heat pump with vapor injection and dedicated mechanical subcooling (VIDMS) is proposed. • Life cycle energy consumption, pollutant emissions, and economic evaluation model is developed. • COP and primary energy consumption of VIDMS is superior to the other transcritical CO 2 systems. • LCCP of VIDMS is the lowest, and gaseous and particulate matter emissions are reduced. • Life cycle cost (LCC) by using VIDMS is much lower than the other transcritical CO 2 systems. Heat pump is an efficient method to substitute traditional boilers for cleaner space heating. A new configuration of CO 2 heat pump system integrated with vapor injection and dedicated mechanical subcooling (VIDMS) is proposed, and compared with five configurations of CO 2 heat pump system and three traditional heating methods. The life cycle model of energy consumption, pollutant emissions, and economic performance is developed. Assessment is conducted by taking seven typical cities located in different climate regions of China as scenarios. Coefficient of performance (COP) of VIDMS system is superior to other transcritical CO 2 systems, and the COP is enhanced more notably in the case of severe cold or cold regions. The COP reaches up to 2.13 at the low ambient temperature of −20 °C, 36.51% higher than the baseline (BASE) CO 2 system. The primary energy consumption (PEC) of the other five CO 2 systems and coal-fired boiler (CFB) can decrease by 4.15–18.26% and 19.27%, respectively, when VIDMS is adopted. Moreover, the PEC reduction is more prominent when used in severe cold region. Life cycle climate performance (LCCP) decreases significantly by employing VIDMS compared with other transcritical CO 2 systems and traditional heating methods. CO 2 emissions can be reduced by 13.81–23.20% and 16.56–34.31% in contrast to BASE and CFB, respectively. Furthermore, the gaseous (NO x and SO 2) and particulate matter (PM 2.5 and PM 10) emissions also decrease. Life cycle cost (LCC) by using VIDMS is much lower than the other transcritical CO 2 systems. The payback period is reduced from 5.58 to 3.55 years if the price of electricity and CO 2 compressor are both reduced by 20%. The new proposed VIDMS is a more promising CO 2 heat pump solution to replace traditional heating methods. [ABSTRACT FROM AUTHOR]

A new sampled fiber grating scheme is investigated for WDM signal queuing in time domain. The queuing is aimed at achieving very short constant time intervals down to picoseconds (ps) for many wavelength channels by a single fiber device. Theory and modeling predict that a consistence of linear spectral profiles exists between reflectivity or transmission spectrum and time delay spectrum. A sampled fiber grating based on Gaussian beam writing is proposed to offer a large number of wavelength channels and time delays within an approximate linear profile. Results for simulating a Gaussian sampled fiber grating show that the time delay minima of 8 channels within a section of the spectral profile have an average time delay step of 2.83 ps and standard deviation of 7.4% from linearity. Fiber gratings were successfully written by Gaussian laser beam in fabrication. A Gaussian sampled fiber grating was measured for time delay spectrum of 4 wavelength channels. An average time delay step of 9.67 ps is obtained. Some issues and related analysis and discussion are given. Our preliminary experiment suggests that the sampled fiber grating scheme can achieve ps-time steps for WDM signal queuing such as high-resolution time delay lines. [ABSTRACT FROM AUTHOR]

• In this paper, based on our research experience in this field and a survey of the development of crystalline Raman yellow lasers over the past two decades, the implementation methods, experimental results, and research progress of crystalline Raman yellow lasers in different fields and different types are briefly analyzed through typical work cases reported to date. It is a report on a comprehensive review of the field of crystalline Raman yellow lasers. Yellow light sources, emitting between 570 nm and 600 nm, are interesting for their potential in several application fields and are irreplaceable to a certain extent in certain characteristic domains. Therefore, it has been a research hotspot in the field of laser technology. A crystalline Raman yellow laser is an important approach to achieving yellow light sources. This paper focuses on an important branch of all-solid-state yellow laser, i.e. crystalline Raman yellow laser, and discusses its research progress in the past twenty years by summarizing a few classic works. The paper clarifies the implementation schemes of crystalline Raman yellow lasers for different application requirements, providing a reference for future research in this field. [ABSTRACT FROM AUTHOR]

Abstract: The optical activity and acoustic properties of La3Ga5SiO14 (LGS) were studied. The optical transmission between parallel polarisers was measured at various wavelengths. Specific rotations were obtained by TU1901 UV–vis spectrophotometer. The experiments indicated that specific rotations of La3Ga5SiO14 were smaller than that of α-SiO2. From Christoffel equation the slowness curves on (100), (010) and (001) planes were plotted and acoustic velocities were calculated, showing that the acoustic velocities of LGS crystal were generally smaller than that of α-SiO2. Therefore, LGS was a good acousto-optic material. [Copyright &y& Elsevier]

• Flow boiling of large temperature glide zeotropic mixture CO 2 /R152a is tested. • Flow pattern, heat transfer and pressure drop characteristics are conducted. • Mass transfer resistance and deterioration effect of sensible heat are discussed. • A model used for large temperature glide mixture is proposed with deviation of 16.9 %. • The heat transfer correlation is validated with existing zeotropic mixture data. The flow boiling characteristics of CO 2 /R152a zeotropic mixtures with three mass fractions (22.1/77.9, 47.4/52.6 and 65.3/34.7 wt.%) and the pure components in a 2 mm horizontal tube are experimentally studied. The flow boiling characteristics are tested in the range of temperature glide of 30.9∼38.3 °C, mass flux of 200∼400 kg/m2s, heat flux of 12∼36 kW/m2, and saturation temperature of 5∼15 °C. Flow patterns are observed and the flow pattern map is also described, and the heat transfer and pressure drop characteristics of working fluid are also conducted. Furthermore, a new correlation to predict the heat transfer coefficient of large temperature glide working fluid is proposed. The results show 7 types of flow patterns are recorded, showing the flowing characteristic between the conventional and microscale channel. The heat transfer coefficient of CO 2 /R152a increases slowly with vapor quality, and decrease rapidly when vapor quality reaches to the initial dryout vapor quality, which is lower than that of pure CO 2. The mass transfer resistance and sensible heat resistance shows a severe deterioration effect on the flow boiling heat transfer due to the high temperature glide as the sensible heat accounts for 13.12∼15.44 % for the mixture CO 2 /R152a. The frictional pressure drop gradient of CO 2 /R152a increases with mass flux, and decreases with the increase of saturation temperature and mass fraction of CO 2. Considering the mass transfer resistance and effects of non-negligible sensible heat contribution, a new heat transfer correlation is proposed, with the mean absolute deviation of 16.9 %, which shows an acceptable prediction accuracy compared with the reported data in the literatures. [ABSTRACT FROM AUTHOR]

• Water film flowing on horizontal metal surface with high-speed air shear driven. • The wavy characteristics of water film were experimentally investigated. • The wind speed is at 15.59 ∼ 52.20 m/s and the water volume flow rate is at 100 ∼ 900 ml/min. • By using the BBLIF technique, the reconstruction diagrams of flow regimes were achieved. • The influence of surface tension, shear force and inertia term on the structure of the gas-liquid interface 18 was discussed. Driven by low-temperature and high-speed airflow, the water droplets impinging the surface of the aircraft will gather into water film, affecting the aerodynamic characteristics and endangering flight safety. In this paper, a high-speed video system with the brightness-based laser-induced fluorescence (BBLIF) technique was used to analyze the transient water film thickness and wavy characteristics on a horizontal metal plate. A series of experiments were performed over a wide range of wind speeds (15.59 m/s ∼ 52.20 m/s) and water volume flow rates (100 ml/min ∼ 900 ml/min). According to the interfacial phenomena observed in the experiment, the water film flow is classified into five regimes: two-dimension-wave, ripple-wave, dual-wave, roll-wave, and entrainment. The water film characteristics such as mean film thickness, film roughness, wave frequency, and rolling wave intermittency are studied under the influences of air velocity and water flow rate. The results show that the complex fluctuation characteristics of water film are the result of the joint action of surface tension, interfacial shear force and inertia term of water film, and are closely related to the water film flow regime. The findings could contribute to a better understanding of the shear-driven water film wavy characteristics and the optimization of the anti-icing or de-icing system. [ABSTRACT FROM AUTHOR]

[Display omitted] • For the first time, we report a new strategy of colloid carbonization to synthesize highly active and stable Ru catalyst for NH 3 synthesis. • The developed Ru2.1-CC exhibits a NH 3 synthesis rate 9.4-fold that of Ru2.2-IM synthesized by impregnation method. • Ru2.1-CC catalyst displays high stability without aggregation of Ru nanoparticles after 100 h stability test. • The formation of ample B5 active sites and Ru-C interaction via colloid carbonization account for high reactivity and stability. Ruthenium-based catalysts are widely used in ammonia (NH 3) synthesis because of a high affinity for N 2 activation, while confronting the challenge of facile deactivation due to sintering. Herein, for the first time, we develop a highly active and sintering-resistant Ru2.1-CC catalyst via colloid carbonization (CC) for NH 3 synthesis. It exhibits a superior NH 3 synthesis rate around 9.4-fold that of Ru catalyst synthesized by impregnation method, displaying extremely high stability without aggregation of Ru nanoparticle after 100 h stability test. Our studies show that Ru2.1-CC possesses the average Ru particle size of 2.1 nm with narrow size distribution and thus exposes more active sites for N 2 activation. Moreover, the formation of Ru-C interaction via colloid carbonization over Ru2.1-CC can stabilize Ru particle size to realize high stability, meanwhile reduce work function and upshift the d-band center of Ru metal to accelerate its electron transfer for N 2 activation and NH 3 synthesis. This study provides a new strategy for simple synthesis of noble metal-based catalysts that are highly active and stable for NH 3 synthesis. [ABSTRACT FROM AUTHOR]

• The dual-crystal hybrid gain laser can operate efficiently across a broad pulse repetition frequencies range. • Quasi-linear polarized light was achieved without the aid of additional polarized optical components. We propose and experimentally demonstrate a high-efficient and high-polarization-ratio acousto-optic (AO) Q-switched dual-crystal hybrid gain laser. Combing the advantages of Nd:YAG and Nd:YVO 4 crystals, it exhibits excellent power performance across a broad pulse repetition frequencies (PRFs) range while maintaining satisfactory polarization characteristics without the aid of additional polarized optical components. Under 42.00-W incident pump power, the maximum average output power rises from 12.10 W to 19.64 W as the PRFs variates from 10 kHz to 200 kHz. The corresponding optical-to-optical efficiency increases from 28.81% to 46.76%. The pulse durations at maximum average output powers are 28.2 ns, 17.2 ns and 24.2 ns, respectively, when the laser operates at the PRFs of 10 kHz, 110 kHz and 200 kHz. The laser polarization ratios at maximum average output power are accordingly ∼7.6, ∼10, and ∼11. [ABSTRACT FROM AUTHOR]

Abstract: Pulverized coal is important for gasification to convert carbonaceous fuel to gaseous products with a usable heating value; it is cohesive with a poor flowability, typical of Group C powders. The fluidization behaviors of pulverized coal in a fluidization column and in a Perspex hopper were investigated. The pulverized coal was extremely hard to be fluidized and its experimental incipient fluidizing velocity was much larger than expected. The discharge of pulverized coal from a carbon steel hopper under several aeration rates was studied. Four flow regions were developed, and the major phenomena that occurred during the discharge were analyzed. The mechanism of aerated discharge was probably the integration of various effects, all of which were confirmed by the experimental data. [Copyright &y& Elsevier]

Crystals of Sr3NbGa3Si2O14 (SNGS) with ordered langasite structure were grown using the Czochralski (CZ) method along the Cartesian Y-axis [12.0]. The as-grown crystals exhibit high optical quality and structure perfection. Giant optical rotation was observed by polarized microscope. Optical transmission was measured at various wavelengths between crossed polariser. Optical activities were obtained by TU1900 spectrophotometer and found SNGS crystals showed unusually large values of ρ. [Copyright &y& Elsevier]

Abstract: The interference patterns of polarized light are measured by polarizing microscopy. The specific rotation ρ of Ca3TaGa3Si2O14 (CTGS) piezoelectric single crystal is determined from 200 to 850nm by measuring the optical transmission between parallel polarizers in <001> direction. It is shown that Ca3TaGa3Si2O14 has quite large a value of ρ which is a little smaller than that of Ca3NbGa3Si2O14 (CNGS). [Copyright &y& Elsevier]

The use of carbon dioxide (CO 2) as refrigerant is driven by the need to phase down the traditional synthetic refrigerant so as to mitigate the warming climate. In this study, the thermal performance of a two-stage compression transcritical CO 2 refrigeration system with R290 mechanical subcooling unit is conducted. The goal is to obtain the maximum coefficient of performance (COP) of five different mechanical subcooling systems under the optimal subcooling temperature and compressor discharge pressure. The two-throttling and two-stage compression high-pressure mechanical subcooling system is found to have a higher COP. When the evaporation temperature is −30 °C, the COP of the two-throttling and two-stage compression high-pressure mechanical subcooling system is improved by 76.74%. The COP of the two-throttling and two-stage compression high-pressure mechanical subcooling system is 1.52 at an ambient temperature of 40 °C, which is 21.87% higher than that of the two-throttling and two-stage compression low-pressure mechanical subcooling system. The power consumption ratio of one-throttling and two-stage compression low-pressure mechanical subcooling system is significantly higher than that of other systems. From a comprehensive analysis of the proposed four systems, the two-throttling and two-stage compression high-pressure mechanical subcooling system has the best performance over all other systems. • Two-stage compression transcritical CO 2 refrigeration systems with R290 mechanical subcooling are analyzed. • Two-throttling, two-stage high-pressure mechanical subcooling is most advantageous. • Two-stage compression transcritical CO 2 cycle with R290 mechanical subcooling unit is suitable for warm and hot regions. [ABSTRACT FROM AUTHOR]