Dynamic and energy analysis of a liquid piston hydrogen compressor

Liquid piston compressor is the most promising compressor to be used for hydrogen-refueling stations. However, their energy transfer and the energy dissipation processes of are poorly studied and not well understood. In this paper, a new energy analysis method for an ionic-liquid type liquid piston compressor is proposed. In the compressor section, porous media is used to promote heat transfer from the hydraulic oil during the compression process. A mathematical model has been formulated considering the heat transfer and damping effects of the porous media on the compressor performance. Moreover, the compressibility of the hydraulic oil and its overflow loss on the compressor performance were also established. In the model, the seven stages of the entire working cycle of the compressor were look into in detail, alongside with its energy efficiency. The results show that the key parameters governing the energy efficiency of the compressor are the heat transfer efficiency of the compressor and the overflow losses of the hydraulic oil.     

Polymer electrolyte fuel cell stack thermal model to evaluate sub-freezing startup

For passenger fuel cell vehicles (FCVs), customers will expect to start the vehicle and drive almost immediately, implying a very short system warmup to full power. While hybridization strategies may fulfill this expectation, the extent of hybridization will be dictated by the time required for the fuel cell system to reach normal operating temperatures. Quick-starting fuel cell systems are impeded by two problems: (1) the freezing of residual water or water generated by starting the stack at below freezing temperatures and (2) temperature-dependent fuel cell performance, improving as the temperature reaches the normal range. Cold start models exist in the literature; however, there does not appear to be a model that fully captures the thermal characteristics of the stack during sub-freezing startup conditions. Existing models lack the following features: (1) modeling of stack internal heating methods (other than stack reactions) and their impact on the stack temperature distribution and (2) modeling of endplate thermal mass effect on end cells and its impact on the stack temperature distribution.The focus of this research is the development and use of a sub-freezing thermal model for a polymer electrolyte fuel cell stack. Specifically, the work has focused on the generation of a model in which the fuel cell is separated into layers to determine an accurate temperature distribution within the stack. Unlike a lumped model, which may use a single temperature as an indicator of the stack's thermal condition, a layered model can reveal the effect of the endplate thermal mass on the end cells, and accommodate the evaluation of internal heating methods that may mitigate this effect.     

Fabrication and mechanical properties of lightweight ZrO2 ceramic corrugated core sandwich panels

ZrO₂ ceramic corrugated core sandwich panels were fabricated using gelcasting technique and pressureless sintering. The nominal density of the as-prepared ZrO₂ ceramic corrugated panel was only 2.4 g/cm³ (42.9% of bulk ceramic). Lightweight was realized through this sandwich structured design. The three-point bending strength was measured to be 298.4 MPa. And the specific bending strength was as high as 124.3 (114% higher than bulk ceramic). The compressive strength was 20.2 MPa. High strength was also realized through this sandwich structured design. The stress distribution during three-point bending and compression testing was finally simulated using finite element analysis (FEA) method.     

Helios prototype flying program hits problems

The Helios prototype solar-electric flying wing has suffered problems during a check-out flight at the US Navy’s Pacific Missile Range Facility (PMRF). Aloft for about 15 h at altitudes up to 52 000 feet (16 km), engineers checked out modifications and upgrades made to the aircraft over the past two years.This is a short news story only. Visit www.re-focus.net for the latest renewable energy industry news     

Starck,Webasto develop automotive SOFC stacks

In Germany, H.C. Starck GmbH and Webasto Thermosysteme GmbH will jointly develop high-temperature SOFC stacks for automotive auxiliary power units. The partners also plan to establish a basis for later series production.     

Parametric studies of tube in tube heat exchanger coupled to a panel of collectors

This paper deals with the transient analysis of a one pass, tube in tube heat exchanger coupled to a panel of flat plate collectors under both cocurrent and counter-current modes of flow. Explicit expressions for the temperatures of the cold and hot fluid streams have been developed as a function of the time and space coordinates for both modes of flow. To make a quantitative assessment of the analytical results, numerical calculations have been carried out for a typical winter day, i.e., 13 February 1985 at Delhi. The effects of several parameters, viz. length of the heat exchanger, mass flow rate, radii of heat exchanger tube, etc., have been studied in detail.     

Sizing of a fuel cell electric vehicle: A pinch analysis-based approach

Polymer electrolyte fuel cells are considered as a promising alternative to mitigate the CO₂ emission in the transport sector. To achieve an efficient and cost-effective system, hybridisation of the energy storage system with a fuel cell is important. Efficient management of energy is the key in order to achieve an efficient and cost-effective configuration for fuel cell electric vehicle. Optimum sizing of the power source and energy storage system, which is capable of meeting the load requirement of the driving cycle is the key challenge for achieving efficient and cost-effective system. In this work, an alternative methodology based on the principles of pinch analysis is proposed, for sizing the energy storage system and the fuel cell for fuel cell-based electric vehicle, and validated for the Worldwide Harmonized Light Vehicle Test Cycle (WLTC) class-3 driving cycle.     

Novel closed anode pressure-swing system for proton exchange membrane fuel cells

To overcome the low system efficiency and fuel efficiency in conventional recirculation systems and purging systems, a new anode closed pressure-swing system for proton exchange membrane fuel cells (PEMFCs) is proposed in this paper. Only two pressure regulators set at different pressures and a buffer tank are applied to produce pressure-swing inside the anode through the process of hydrogen feed and reaction, thereby achieving the anode-dead-end (ADE) operation (no purging). This system was successfully tested on a 20-cell open-cathode stack. The results indicate that the performance of the stack with the developed system is stable and efficient over 13,000 s, while its performance in ADE mode without purging deteriorates rapidly because of active area reduction. It can be concluded that the pressure swing system provides the following advantages: close to 100% hydrogen utilization; improved stack performance of around 12.5% for the power compare to the ADE mode with intermittent purging at 12 V load; improved humidification of the anode and membrane; and ease of implementation as there are no extra pumps.     

WE43镁合金SLM成形数值模拟及试验验证

目的 研究WE43镁合金激光选区熔化(SLM)成形过程、成形后变形及应力分布的变化规律,得到SLM态WE43常温拉伸力学模型。方法 采用SLM方法制备了WE43镁合金悬臂梁及拉伸试样,通过对比悬臂梁局部切割翘曲试验结果与数值模拟结果,得到WE43镁合金固有应变模型,实现WE43镁合金SLM成形过程的模拟及变形预测;对SLM态WE43镁合金开展拉伸试验,使用金相显微镜及扫描电镜进行微观组织及断口形貌观察;采用Normalized Cockcroft & Latham模型对拉伸试验进行模拟,实现SLM态WE43常温拉伸过程分析。结论 常温SLM态WE43的抗拉强度为313 MPa,屈服强度为236 MPa,延伸率为7.6%,试样中存在不规则孔洞缺陷;在SLM成形过程中,WE43镁合金固有应变值exx、eyy、ezz分别为−0.002 5、−0.002 5、−0.011 5,悬臂梁最大翘曲高度为1.99 mm,模拟结果显示未切割悬臂梁最大等效应力为12.3 MPa;当NC& L断裂准则临界损伤值为0.1时,WE43常温拉伸过程模拟结果与试验结果最为接近,预测准确率为93%。