Membrane technology applied to the separation of gaseous mixtures competes with conventional unit operations (e. g., distillation, absorption, adsorption) on the basis of overall economics, safety, environmental and technical aspects. Since the first industrial installations for hydrogen separation in the early eighties, significant improvements in membrane quality have been achieved in air separation as well as in CO2 separation. However, beside the improvement in the materials as well as in membrane module design, an important point is represented by a correct engineering of these separation processes. The recovery of high value co-products from different industrial streams (e.g. organic vapours from off-gas streams, helium from natural gas) is an interesting application, which created a new market for gas separation membranes, coupling environmental and economic benefits. The opportunity to integrate membrane operations in ongoing production cycles for taking advantage from their peculiar characteristics has been proved as a viable approach. In this ambit, membrane systems in appropriate ranges of operating conditions meet the main requirements such as purity, productivity, energy demand of specific industrial processes. A critical discussion about the role of membrane material and engineering aspects is given. Finally, this work intends to give a brief overview of the development of the membrane technology for gas separation in the last 30 years, addressing open problems and strategies proposed in applications of industrial interest.

Fast depletion of fossil fuels is demanding an urgent need to carry out research work to find out the viable alternative fuels for meeting sustainable energy demand with minimum environmental impact. in the future, our energy systems will need to be renewable and sustainable, efficient and cost-effective, convenient and safe. The technology for producing hydrogen from a variety of resources, including renewable, is evolving and that will make hydrogen energy system as cost-effective. Hydrogen safety concerns are not the cause for fear but they simply are different than those we are accustomed to with gasoline, diesel and other fossil fuels. For the time being full substitution of diesel with hydrogen is not convenient but use of hydrogen in a diesel engine in dual fuel mode is possible. So Hydrogen has been proposed as the perfect fuel for this future energy system. The experiment is conducted using diesel-hydrogen blend. A timed manifold induction system which is electronically controlled has been developed to deliver hydrogen on to the intake manifold. The solenoid valve is activated by the new technique of taking signal from the rocker arm of the engine instead of cam actuation mechanism. In the present investigation hydrogen-enriched air has been used in a diesel engine with hydrogen flow rate at 0.15 kg/h. As diesel is substituted and hydrogen is inducted, the NOx emission is increased. In order to reduce NOx emission an EGR system has been developed. In the EGR system a lightweight EGR cooler has been used instead of bulky heat exchanger. In this experiment performance parameters such as brake thermal efficiency, volumetric efficiency, BSEC are determined and emissions such as oxides of nitrogen, carbon dioxide, carbon monoxide, hydrocarbon, smoke and exhaust gas temperature are measured. Dual fuel operation with hydrogen induction coupled with exhaust gas recirculation results in lowered emission level and improved performance level compared to the case of neat diesel operation. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

The major challenges facing fuel cells in light-duty vehicle applications relate to the high cost of the fuel cell stack components (membrane, electro-catalyst and bipolar plate) which dictate that new manufacturing processes and materials must be developed. initially, the best fuel for a mass market light-duty vehicle will probably not be the best fuel for the fuel cell (hydrogen); refueling infrastructure and energy density concerns may demand the use of an on-board fuel processor for petroleum-based fuels since this will increase customer acceptance. The use of fuel processors does, however, reduce the fuel cell system's efficiency. Moreover, if such fuels are used then the emissions benefit associated with fuel cells may come with a significant penalty in terms of added complexity, weight, size and cost. However, ultimately, fuel cells powered by hydrogen do promise to be the most efficient and cleanest of automotive powertrains.

Numerical models such as computational fluid dynamics (CFD) models are increasingly used in life safety studies and other types of analyses to calculate the effects of fire and explosions. The validity of these models is usually established by benchmark testing. This is done to quantitatively measure the agreement between the predictions provided by the model and the real world represented by observations in experiments. This approach assumes that all variables in the real world relevant for the specific study are adequately measured in the experiments and in the predictions made by the model. In this paper the various definitions of validation for CFD models used for hazard prediction are investigated to assess their implication for consequence analysis in a design phase. In other words, how is uncertainty in the prediction of future events reflected in the validation process? The sources of uncertainty are viewed from the perspective of the safety engineer. An example of the use of a CFD model is included to illustrate the assumptions the analyst must make and how these affect the prediction made by the model. The assessments presented in this paper are based on a review of standards and best practice guides for CFD modeling and the documentation from two existing CFD programs. Our main thrust has been to assess how validation work is performed and communicated in practice. We conclude that the concept of validation adopted for numerical models is adequate in terms of model performance. However, it does not address the main sources of uncertainty from the perspective of the safety engineer. Uncertainty in the input quantities describing future events, which are determined by the model user, outweighs the inaccuracies in the model as reported in validation studies. (C) 2013 Elsevier Ltd. All rights reserved.

Reliable hydrogen sensors are essential to detect accidental hydrogen releases when hydrogen will be used to fuel future vehicles. To assess the performance of hydrogen safety sensors under conditions typical of automotive applications a test protocol has been defined. It has been experimentally evaluated by performing tests on commercially available hydrogen sensors. Catalytic sensors measured hydrogen concentration accurately and sensor response was largely independent of ambient parameters. However they were significantly cross sensitive to carbon monoxide and the detection limit was high. metal-oxide semiconductive sensors had a low detection limit and showed a low cross sensitivity to carbon monoxide however almost all of these samples showed poor accuracy and a strong dependence on ambient parameters. Electrochemical sensors also had a low detection limit however ambient parameters, cross sensitivity and accuracy tests showed a high variation in results. Tests on a limited number of thermal conductivity sensors highlighted their high detection limit and strong dependence on temperature. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

A facility for testing the performance of hydrogen safety sensors under a wide range of ambient conditions is described. A specific test protocol was developed to test sensors under conditions which could reasonably be expected during the sensors' service life. The tests were based on those described in IEC 61779 and were adapted following consultation with car manufacturers and after careful consideration of the sensors expected service environmental conditions. The protocol was evaluated by using it to test a large number of commercially available sensors. Observations made and experience gained during the testing campaign allowed the test protocol to be fine-tuned bearing in mind the sensor performance and behaviour during tests. The result of this work is an experimentally evaluated methodology which may be used as a guideline for testing the suitability of hydrogen sensors for automotive applications. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

A market survey has been per-formed of commercially available hydrogen safety sensors, resulting in a total sample size of 53 sensors from 21 manufacturers. The technical specifications, as provided by the manufacturer, have been collated and are displayed herein as a function of sensor working principle. These specifications comprise measuring range, response and recovery times, ambient temperature, pressure and relative humidity, power consumption and lifetime. These are then compared against known performance targets for both automotive and stationary applications in order to establish in how far current technology satisfies current requirements of sensor end users. Gaps in the performance of hydrogen sensing technologies are thus identified and areas recommended for future research and development. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Response time is a critically important property of hydrogen safety sensors. Recovery times are less important from a safety perspective, but are often quoted as an indication of the speed of operation of a sensor. However, the measured values depend highly on the method used to evaluate them. The purpose of this work is to assess the suitability of different methods, both flow and diffusion-based, for the measurement of sensor response and recovery times. Four methods have been tested in terms of their repeatability and practicality of execution, as well as the accuracy of their results compared to the manufacturer's specifications. It was found that each method has its own advantages and limitations, which are discussed herein. For the measurement of response times, a diffusion-based method was found to give the shortest and most precise values and is therefore recommended. However, the flow-based method was found to be the most convenient experimentally and is the only method that is suitable for the measurement of recovery times over a wide concentration range. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

A current knowledge gap in hydrogen safety research concerns the influence of mixture non-uniformity on explosion processes. Spacial mixture composition gradients are likely to form in real-world accident scenarios. In this work, the influence of such gradients on flame acceleration is experimentally investigated in an entirely closed channel at laboratory scale. Experiments show that concentration gradients can lead to significantly stronger flame acceleration compared to homogeneous mixtures. Optical measurements reveal that flame shapes differ between homogeneous and inhomogeneous mixtures in the unobstructed channel configuration. An enlargement of flame surface area in inhomogeneous mixtures leads to a higher integral reaction rate, which in turn supports flame acceleration. In obstructed channel configurations, however, mixture properties dominate flame propagation. An analytical model based on the integral balancing of mixture properties is proposed and validated by means of experimental data.