A solution to renewable hydrogen economy for fuel cell buses – A case study for Zhangjiakou in North China

Fuel cell vehicles fueled with renewable hydrogen is recognized as a life-cycle carbon-free option for the transport sector, however, the profitability of the H₂ pathway becomes a key issue for the FCV commercialization. By analyzing the actual data from the Zhangjiakou fuel cell transit bus project, this research reveals it is economically feasible to commercialize FCV in areas with abundant renewable resources. Low electricity for water electrolysis, localization of H₂ supply, and curtailed end price of H₂ refueling effectively reduce the hydrogen production, delivery and refueling cost, and render a chance for the profitability of refueling stations. After the fulfillment of the intense deployment of both vehicles and hydrogen stations for the 2022 Winter Olympics, the H₂ pathway starts to make a profit thereafter. The practices in the Zhangjiakou FCB project offer a solution to the hydrogen economy, which helps to break the chicken-egg dilemma of vehicles and hydrogen infrastructure.     

A Modified Entropy Generation Number for Heat Exchangers

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A hydrogen standard for future energy accounting?

Present methods of energy accounting include both primary energy and final energy consumption. Both these methods have inconsistencies, although today their impact is minor. Some level of inconsistency and approximation in energy accounting is unavoidable when energy inputs come from such heterogeneous sources. We argue that in the decades to come, renewable energy will probably come to dominate the energy supply system, with most from intermittent energy sources, particularly wind and solar. In such an energy system, existing measures will become increasingly irrelevant for tracking energy use over time, for assessing a renewable energy source’s technical potential, and in determining future energy infrastructure needs. Further, conversion of most primary electricity to a storable energy form will be needed, with some then perhaps converted back to electricity as needed. We propose that in this case energy production and demand, and technical potential for renewable energy sources, will be more accurately measured by use of a new energy accounting framework, based on the energy content of hydrogen.     

A Model for Flooding Prediction in Circular Tubes

Flooding phenomenon limits the stability and the flow of a liquid film falling along the walls of a channel in which a gas is flowing upwards.As known, the entrainment effect can completely prevent the liquid to fall from its natural flow. The present work proposes a new mechanistic model for the prediction of the onset of flooding in vertical and inclined pipes in the presence of obstructions, as well as taking into account the viscosity effect. The good performance of the model in the different geometrical conditions and for variable viscosities of the liquid component assesses the validity of the hypothesis that the instability of a wavelike disturbance limits the countercurrent flow in a channel.     

A Model for Predicting Laminar Gas Flow Through Micropassages

INTRODUCTIONModerntechnologieshavedevelopedrapidlyinfab-ricatingmicroelectronics,miniaturizedmanufacturingandbiomedicalengineeringetc.Thefiuidflowandheattransferinmicropassageshasbecomeoneofthemostimportantresearchfieldsofheatandmasstrans-fer.Thepioneerexperimentsearliestinvestigationsonthefluidflowandheattransferinmicromachinedstructurewithplate-finandpin-finheatsinkwerereportedbyTuckermanandPeasein1984l1].WuandLittle(1984)[2'3]measuredthefrictionfactorforgasflowandheattransferinthemicr…     

A Boosted P′ Method for Fully Parabolized Flows

A novel iterative method for solving the incompressible, fully parabolized Navier-Stokes equations is described. It is a modification of the classical so-called P′ method. The central modification is to boost the computed pressure changes during the iterations. The method is shown to produce robust convergence for the considered application in a simple way.     

A Versatile Numerical Tool for Simulating Combustion Features at Small-Scales

A versatile numerical tool based on the open-source framework Open FOAM has been developed in this paper for modeling time-accurate,low-Mach number reacting flows,with a particular interest in small-scale flames.This tool consists of a gas-phase Navier-Stokes solver and a solid-wall heat conduction solver which can be implemented alone,or used together in a coupled means to reveal the small-scale combustion’s characteristics of significantly enhanced flame-wall thermal coupling.Validation works has proved that the tool is capable of reproducing experimental flames at various scales(from conventional to small scales),including well-recognized micro-flame features in literature such as three modes of premixed flame dynamics(weak flames,flames with repetitive extinction and ignition,and stable flames).Then,an experimentally-already-found but rarely-simulated unique phenomenon of diffusion flame street is successfully reproduced with well-captured flame structures.Moreover,the conjugate heat transfer model with the specific formulation of solid-wall heat conduction enables an attempt to simulate a novel,thermally-orthotropic combustor with its axial thermal conductivities superior to the transverse ones.Finally,computational performance of the developed Open FOAM solver is compared to that of the previously-used compressible flow solver Eilmer.The Open FOAM solver is found to show better wave-damping abilities for overcoming acoustic wave effects at the initial stage of simulations,and is much more efficient in terms of the computational cost.     

A New Algorithm of Auto—Modelling for Fluid Network

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A feasibility study on solar-wall systems for domestic heating – An affordable solution for fuel poverty

A Solar Wall Heating (SWH) system was developed to provide low cost space heating in traditional solid stone-walled tenement buildings in Scotland. The SWH system uses the internal solid walls to store the solar heat collected during the day and heat the bedrooms during the night.A physical laboratory model with attached solar hot water system and a computational model of it were developed to investigate the dynamic performance of the system in use and test the cost benefits of iterations of its modes of use. The temperatures throughout the wall structure were measured under the variant solar input of a 24-h cycle. An unsteady state CFD model was developed and validated using the measured data and setup to test a number of key variables of the solar wall heating system in use. These included optimisation control strategies and maximisation strategies for the collection and storage of solar heat under various conditions. This paper presents the modelled results of the solar thermal storage and optimisation system and strategies for internal solid stone walls in a typical Scottish tenement flat in the Scottish climate.In addition the study analysed the solar availability, heating demand and domestic water supply of two typical dwellings based on two reliable methods: (a) a purpose built dynamic thermal model and (b) data collected in previous studies.The study demonstrated that the solar collection of current solar hot water systems can be improved upon so that, even in Scotland, more solar power can be harvested to contribute not only to domestic hot water, but also domestic space heating, particularly in buildings occupied over 24 h with heavy thermal mass. The cost analysis of the system in use suggested a 16 year payback period for such a system for a tenement flat.     

A Mathematical Model for the Heat Radiation Characteristics of Materials

Based on the model of harmonic oscillators, a mathematical model for the heat radiation characteristics of materials such as semiconductors, metals, plasmas and ionic crystals is established in this paper. The main factors affecting the heat radiation characteristics of materials are also analyzed at length. The emissivity is calculated for revealing the mechanism of emitting, absorbing, transmitting and reflecting the heat radiation wave.     

Anthracite pretreatment for high-performance direct carbon solid oxide fuel cell — A green pathway for power generation

Coal-fueled direct carbon solid oxide fuel cell (DC-SOFC) is a very attractive electrochemical conversion device. However, coal contains a certain amount of ash, such as Al, Si, S, etc., which are toxicants for SOFC components. To solve the above problem, anthracite is pyrolyzed at 600 °C to obtain semi-coking coal results in better cell performance. The results show that the higher carbon gasification oxidation activity of semi-coking coal is due to the higher amount of fixed carbon and catalyst. Therefore, more fuel gas (CO) is available in the anode chamber for the Boudouard reaction. Also, the electrochemical performance of both coals as DC-SOFC fuel was compared using La_0·4Sr_0·6Co_0·2Fe_0·7Nb_0·1O_3-δ (LSCFN) as anode. The maximum power density (MPD) of the DC-SOFC with semi-coking coal is 596 mW cm⁻² at 850 °C, much higher than that of the SOFC using anthracite (396 mW cm⁻²) as the fuel. Furthermore, at the same fuel content, the cell fueled with semi-coking coal has a longer discharge time (30 h), which shows a better stability.     

A Prediction Model for Condensation on Single Horizontal Rectangular Fin Tube

INTRODUCTI0NItiswellknownthatusingintegralfinnedtubet0replacesm0othtubemayenhancecondensati0nheattransfer.Predictingcondensationheattransfercoeffi-cientofthefinnedtubeisnecessaryforapplicationandf0ranalyzingtheeffectsofworkingcondition,work-ingfluidpropertiesandfingeometry.Therefore,re-searchersalwayspayattentiontoit.Thefirstm0delwasbuiltbyBeattyandKatz[11.Itisagravity-drivingm0delthatneglectstheinfluence0fsurfacetensi0n.Althoughitmaywellpredictc0ndensationoflowsur-facetensionfluidsonlow…     

A Force-Based Grid Manipulator for ALE Calculations in a Lobe Pump

In this paper, a time-dependant calculation of flow in a lobe pump is presented. Calculations are performed using the arbitrary Lagrangean Eulerean (ALE) method. A grid manipulator is needed to move the nodes between time steps. The used grid manipulator is based on the pseudo-force idea. This means that each node is fictitiously connected with its 8 neighbours via fictitious springs. The equilibrium of the resulting pseudo spring forces defines the altered position of the nodes. The grid manipulator was coupled with a commercial flow solver and the whole was tested on the flow through a three-lobe lobe pump. Results were obtained for a rotational speed of 460 rpm and incompressible silicon oil as fluid.     

LCA of renewable energy for electricity generation systems—A review

Sustainable development requires methods and tools to measure and compare the environmental impacts of human activities for various products (goods and services). Providing society with goods and services contributes to a wide range of environmental impacts. Environmental impacts include emissions into the environment and the consumption of resources as well as other interventions such as land use, etc. Life cycle assessment (LCA) is a technique for assessing environmental loads of a product or a system. The aim of this paper is to review existing energy and CO₂ life cycle analyses of renewable sources based electricity generation systems.The paper points out that carbon emission from renewable energy (RE) systems are not nil, as is generally assumed while evaluating carbon credits. Further the range of carbon emissions from RE systems have been found out from existing literature and compared with those from fossil fuel based systems, so as to assist in a rational choice of energy supply systems.     

A New Method for Analyzing Heat Exchangers- Matching of Temperature Field

In heat exchangers, the magnitude of Nu of each duct is influenced by the temperature field, since the ratio of heat capacity rate will influence the matching status of the temperature field between contacting ducts, the total heat transfer coefficient is related with the ratio of heat capacity rate. Considering this relationship, a new method for analyzing heat exchanger is proposed - matching of temperature field. First, for a single duct with the temperature field varying exponentially along the flow direction, its Nu is calculated. Then under the hypothesis that the thermal resistance of the wall is negligible, the matching condition was set like this: both the temperature and heat flux are equal for the hot and cold fluids at the wall, so the matching relationship of parameter that describes the temperature field of the hot and cold fluids, was obtained. Finally the relationship between the total Nu and the ratio of heat capacity rate along with the ratio of inherent thermal resistance is obtained. Compared with traditional analyzing methods, the temperature matching method can be used to get the total heat transfer coefficient directly, and also be used for optimization of heat exchanger design. For a parallel flow, the optimal ratio of heat capacity rate is reciprocal to the ratio of inherent thermal resistance, and for a counter flow, the optimal ratio of heat capacity rate is zero or infinity.     

Biomass today: A new beginning for an old resource?

Biomass, the oldest ‘new and renewable’ source of energy currently provides about 12% of the world's total energy supply. This is predominantly in the form of combustion for use in domestic cooking or heating. There are strong economic, environmental and social drivers to move away from traditional biomass combustion to advanced thermochemical biomass conversion technologies. Peter Fardy, First Renewables UK Ltd provides an overview of the latest developments in this emerging area.     

A Mathematical Model for Differential—Velocity Circulating Fluidized Bed Boiler

INTRODUCTIONIt'ssoconspicuousofthedevelopmentofthecirculatingfluidizedbed(CFBC)recentlywhichistakenasamosteffectiveandcleancoalcombustiontechnology.ThermalEngineeringDepartmentofTsinghuaUniversityhasbeenlongengagedintheresearchofCFBCbothindesignandmo...     

Bond Resistance and Design Temperatures for High-Finned Tubes—A Reappraisal

The subject of bond resistances and maximum acceptable operating temperatures for various types of high-finned tubes is updated from the status of the last pertinent publications in the 1960s. The formation mechanism of the bond resistance under high and low temperatures is analyzed. Presently accepted industrial practices are critically evaluated. The lack of progress in the standardization of test procedures is noted with regret.     

Bio-diesel as an alternative fuel for diesel engines—A review

The present review aims to study the prospects and opportunities of introducing vegetable oils and their derivatives as fuel in diesel engines. In our country the ratio of diesel to gasoline fuel is 7:1, depicting a highly skewed situation. Thus, it is necessary to replace fossil diesel fuel by alternative fuels. Vegetable oils present a very promising scenario of functioning as alternative fuels to fossil diesel fuel. The properties of these oils can be compared favorably with the characteristics required for internal combustion engine fuels. Fuel-related properties are reviewed and compared with those of conventional diesel fuel. Peak pressure development, heat release rate analysis, and vibration analysis of the engine are discussed in relation with the use of bio-diesel and conventional diesel fuel. Optimization of alkali-catalyzed transesterification of Pungamia pinnata oil for the production of bio-diesel is discussed. Use of bio-diesel in a conventional diesel engine results in substantial reduction in unburned hydrocarbon (UBHC), carbon monoxide (CO), particulate matters (PM) emission and oxide of nitrogen. The suitability of injection timing for diesel engine operation with vegetable oils and its blends, environmental considerations are discussed. Teardown analysis of bio-diesel B20-operated vehicle are also discussed.