A novel profile with high efficiency for hydrogen-circulating Roots pumps used in FCVs

Low flow rate is one of the primary disadvantages of Roots pumps when they are applied in hydrogen fuel cell vehicles. A novel profile for Roots pumps was developed in this paper to increase the working volume and reduce the internal leakage. The available range of the design parameters of the Roots pump with the new profile was determined analytically, and an improvement in the working volume was validated. The flow dynamics inside the traditional and new pumps were investigated by experiments and numerical simulations. The analytical results indicated that the maximum area utilization of the new profile was approximately 10.4% higher than that of the traditional profile at the same lobe number. The numerical results demonstrated the superiority of the proposed profile in high flow rate and sealing. The tip concentric arcs of the new profile reduced the internal leakage via the radial gap. The characteristic of multipoint meshing within a certain range of rotational angles reduced the interlobe leakage.     

Experimental study on combustion stability and performance of hydrogen-enriched compressed natural gas of a free-piston linear generator

Free Piston linear Generator (FPLG) engine fueled by compressed natural gas (CNG) has recently gained increased research attention. However, due to the low-velocity burning and poor lean limit of CNG fuel, the FPLG engine combustion stability, performance, and efficiency are still low. Hydrogen has a greater burning velocity with wider flame limits that could extend the lean burn limits and combustion characteristics of CNG. This paper compares pure CNG and 10% hydrogen-enriched CNG at various ignition speeds (0.6 ms, 0.8 m/s, and 1 m/s), injection positions (0 mm, 5 mm, 10 mm and 15 mm), and lambda ratios (0.9, 1.4 and 1.7) on the combustion characteristics, performance, and conversion efficiency are duly discussed. The findings show that the FPLG combustion stability limits increase with the hydrogen addition into the CNG. The CNG in-cylinder pressure increases significantly when the injection position is advanced, whereas the hydrogen addition reduces the influence of the injection position. The heat release rate increases by 15.62% and 23.72% with hydrogen addition, corresponding to the advanced and retarded injection positions. Consequently, the hydrogen addition increases the power RMS to 209.21 W and 232.64 W with an increment of 3.46% and 3.13%, respectively. Conclusively, the hydrogen addition into the CNG evidently shortens the combustion duration while improving the heat release rate, combustion stability, power RMS, Cycle-to-Cycle variation, and conversion efficiency.     

液体饮料PET无菌灌装工艺与装备研发进展

文章对目前液体饮料PET无菌灌装工艺与装备进行了归纳与总结，并对其研发趋势进行了展望，以期为液体饮料生产中PET无菌灌装技术的应用及优化提供相关依据。     

Comparison of thermophilic and hyperthermophilic dark fermentation with subsequent mesophilic methanogenesis in expanded granular sludge bed reactors

Herein, dark fermentation (DF, V = 5.5 L) and subsequent mesophilic methanogenesis (V = 43.5 L) are run as expanded granular sludge bed reactors (EGSB) at thermophilic (υDF = 60 °C) and hyperthermophilic (υDF = 80 °C) temperatures. A synthetic glucose wastewater is run with a 22.5 g/L chemical oxygen demand (COD) and 48–9 h hydraulic retention times (HRTs), giving organic loading rates (OLRs) of 11–60 g COD/L/d for DF. The maximum hydrogen production rate (HPR) is HPR = 3.0 m³/m³/d for HRT = 9 h with a 50 L/kg COD hydrogen yield (HY) and 40 vol% H₂. Methane production rate (MPR) reaches MPR = 2.6 m³/m³/d with 70 vol% CH₄ at HRT = 2.8 d. The highest H₂ yields are HY = 180 L/kg COD with 53 vol% H₂ (thermophilic, HRT = 48 h). Hyperthermophilic temperatures led to lower HPRs (0.7 m³/m³/d) and MPRs (1.6 m³/m³/d). 53% of Thermoanaerobacterium thermosaccharolyticum as an H₂ producer are found. Discoloration of granular sludge from black to white and granule stability was observed in DF.     

Slow strain rate technique for studying hydrogen induced cracking in 34CrMo4 high strength steel

Alloy hardened steels offer excellent combination of mechanical properties, hardenability and corrosion resistance. 34CrMo4 is a medium carbon, low alloy steel widely used due to a good combination of high-strength, toughness and wear resistance. However, this steel experiences hydrogen embrittlement (HE), a complex phenomenon depending on the composition and microstructure. This work estimates de loss of the mechanical properties caused by hydrogen in electrochemically H-charged specimens in absence of mechanical stress but also, at low strain rate and constant load. H-charging for 2 and 6 h induce YS losses of about 40% and 71% and UTS losses of 39% and 59%, respectively. The synergistic effect of the stress and the H-charging process leads to a higher loss, 91%, and a faster brittle fracture even though hydrogen content is similar to those firstly H-charged and then tested in air.     

The effects of warmth and CO2 concentration,with and without bioeffluents,on the emission of CO2 by occupants and physiological responses

The emission rate of carbon dioxide (CO₂) depends on many factors but mainly on the activity level (metabolic rate) of occupants. In this study, we examined two other factors that may influence the CO₂ emission rate, namely the background CO₂ concentration and the indoor temperature. Six male volunteers sat one by one in a 1.7 m³ chamber for 2.5 h and performed light office-type work under five different conditions with two temperature levels (23 vs. 28°C) and three background concentrations of CO₂ (800 vs. 1400 vs. 3000 ppm). Background CO₂ levels were increased either by dosing CO₂ from a cylinder or by reducing the outdoor air supply rate. Physiological responses to warmth, added CO₂, and bioeffluents were monitored. The rate of CO₂ emission was estimated using a mass-balance equation. The results indicate a higher CO₂ emission rate at the higher temperature, at which the subjects were warm, and a lower emission rate in all conditions in which the background CO₂ concentration increased. Physiological measurements partially explained the present results but more measurements are needed.     

CO_2 conversion by thermal plasma with carbon as reducing agent: high CO yield and energy efficiency

A key problem in CO_2 conversion by thermal plasma is suppressing the inverse reactions,CO?+?O?→?CO_2 and CO?+?0.5O_2?→?CO_2, to simultaneously obtain high CO yield and energy efficiency. This can be done by quickly quenching the decomposed gas or rapidly taking away free oxygen from decomposed gas. In this paper, experiments of CO_2 conversion by thermal plasma with carbon as a reducing agent are presented. Carbon quickly devoured free oxygen in thermal plasma decomposed gas, and not only is the inverse reaction completely suppressed, but the discharge energy to form oxygen atoms, oxygen molecular, and thermal energy is also reused.A CO_2 conversion rate of 67%–94% and the corresponding electric energy efficiency of about 70% are achieved, both are much higher than that seen so far by other plasma implementations.     

Study of spatial and temporal evolution of Ar and F atoms in SF6/Ar microsecond pulsed discharge by optical emission spectroscopy

The study of sulfur hexafluoride (SF₆) discharge is vital for its application in gas-insulated equipment. Direct current partial discharge (PD) may cause SF₆ decomposition, and the decomposed products of SF₆, such as F atoms, play a dominant role in the breakdown of insulation systems. In this study, the PD caused by metal protrusion defects is simulated by a needle-plate electrode using pulsed high voltage in SF₆/Ar mixtures. The spatial and temporal characteristics of SF6/Ar plasma are analyzed by measuring the emission spectra of F and Ar atoms, which are important for understanding the characteristics of PD. The spatial resolved results show that both F and Ar atom spectral intensities increase first from the plate anode to the needle and then decrease under the conditions of a background pressure of 400 Pa, peak voltage of −1000 V, frequency of 2 kHz, pulse width of 60 μs, and electrode gap of 5–9 mm. However, the distribution characteristics of F and Ar are significantly different. The temporal distribution results show that the spectral intensity of Ar decreases first and then increases slowly, while the spectral intensity of F increases slowly for the duration of the pulsed discharge at the electrode gap of 5 mm and the pulse width of 40–80 μs.