Modeling of Hydrogen Blending on the Leakage and Diffusion of Urban Buried Hydrogen-Enriched Natural Gas Pipeline

With the introduction of various carbon reduction policies around the world,hydrogen energy,as a kind of clean energy with zero carbon emission,has attracted much attention.The safe and economical transportation of hydrogen is of great significance to the development of hydrogen energy industries.Utilizing natural gas pipelines to transport hydrogen is considered to be an efficient and economical way.However,hydrogen has a higher risk of leakage due to its strong diffusion capacity and lower explosive limit than conventional natural gas.Therefore,it is of great significance to study the leakage and diffusion law of hydrogen-enriched natural gas(HENG)pipelines for the safe transportation of hydrogen energy.In this study,the leakage and diffusion characteristics of urban buried HENG pipelines are investigated numerically,and the dangerous degree of leakage is analyzed based on the time and area when the gas concentration reaches the lower explosive limit.The influences of hydrogen blending ratio(HBR),operating pressure,leakage hole size and direction,as well as soil type on the leakage and diffusion law of HENG are analyzed.Results show that the hydrogen mixing is not the key factor in increasing the degree of risk after gas leakage for urban buried HENG pipelines.When the HBR is 5%,10%,15% and 20%,the corresponding first dangerous time is 1053,1041,1019 and 998 s,respectively.Thiswork is expected to provide a valuable reference for the safe operation and risk prevention of HENG pipelines in the future.

Domain structure and dielectric diffusion-relaxation characteristics of ternary Pb(In_(1/2)Nb_(1/2))O_(3)-Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)ceramics

Relaxor-based ternary Pb(In1/2Nb1/2)O_(3)-Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)(PIN-PMN-PT)single crystals and ceramics are promis­ing candidates for high-performance electromechanical conversion devices.It is known that the domain structure and dielectric diffusion-relaxation characteristics are crucial to the excellent performances of relaxor ferroelectrics.In this work,we prepared the PIN-PMN-PT ceramics with various PIN/PMN proportions and systematically investigated their domain structure and dielec­tric diffusion-relaxation properties.The effect of PIN/PMN proportion on the domain size and dielectric diffusion-relaxation characteristics was also studied.The investigations showed that PIN-PMN-PT ceramics presented multi-type domain patterns comprising irregular island domains and regular lamellar domains.Moreover,the dependent relations of PIN/PMN proportions on the dielectric diffusion and domain size indicated that the PIN composition has a stronger lattice distortion than PMN composi­tion;increasing the PIN proportion can enhance the dielectric diffusion and decrease the domain size.Our results could deepen the understanding of structure-property relationships of multicomponent relaxor ferroelectrics and guide the design and exploration of new high-performance ferroelectric materials.

Design of a wideband random phase gradient metasurface by using line-shaped element

Based on phase randomization theory, a method for manufacturing metasurface with diffuse scatter performance is proposed. By using the line-shaped elements with random rotate angles and random distributing positions, the metasurface can achieve good diffusion scatter performance with polarization independent characteristic. This paper studies the effects of the length of line-shaped elements on the metasurface response frequency and the radar cross section (RCS) reduction bandwidth. The simulated result shows that the wideband properties of metasurface benefit from two different length line-shaped elements. The proposed metasurface can reduce the RCS significantly for both normal and oblique incident waves. The line-shaped element is suitable for all sizes of detected objects and it can be directly sprayed on the detected object surface. To demonstrate the effectiveness of the proposed method, the metasurface prototype is fabricated and measured. Experimental results show that the fabricated metasur-face can effectively reduce RCS, and it has great application prospects in stealth technology. Keywords: Diffuse scatter characteristics;polarization independent;radar cross section reduction.