Cost analysis of commerical solar absorption coolers using a detailed simulation procedure

Commerical solar absorption systems are now available for residential space cooling purposes. We have undertaken a cost analysis, based on a detailed simulation procedure, of a two-ton system to cool a proposed residence in Kufra, Libya. The meteorological data used for this study are measured daily insolation, ambient temperature and humidity records for an entire cooling season. The performance curves of the absorption chiller, cooling tower and collector, reported by the manufacturer have been modelled. These are used for the determination of hourly generator and storage temperatures. Finally, various energy transfers and seasonal solar fractions are obtained.Analysis is made by comparing the actual costs of a solar absorption cooler with those of a conventional vapour-compression machine. The results showed that the solar system is still more expensive than the conventional system. However, the potential of the absorption system to offset twice the cooling load of its rated capacity, which is manifest in dry, arid conditions, makes it economically competitive in addition to conserving 50 per cent of fossil fuels.     

Numerical analysis of refrigerant flow along non-adiabatic capillary tubes using a two-fluid model

This work presents a numerical model to simulate steady state refrigerant flow along capillary tube-suction line heat exchangers, commonly used in small refrigeration systems. The flow along the straight and horizontal capillary tube is divided into two regions: a single-phase and a two-phase flow region. The flow is taken as one-dimensional and the metastable flow phenomenon is neglected. The two-fluid model is employed for the two-phase flow region, considering the hydrodynamic and the thermodynamic non-equilibrium between the liquid and vapor phases. Comparisons are made with experimental measurements of the mass flow rate and temperature distribution along capillary tube-suction line heat exchangers working with refrigerant R134a in different operating conditions. The results indicate that the present model provides a good estimation of the refrigerant mass flow rate. Moreover, comparisons with a homogeneous model are also made. Some computational results referring to the quality, void fraction and velocities of each phase are also presented and discussed.     

Predicting the syngas hydrogen composition by using a dual stage equilibrium model

This paper presents an analysis of hydrogen syngas composition obtained by biomass gasification when simulated by a dual stage equilibrium model. The numerical model takes advantage of the carbon boundary point (CBP) concept to study the hydrogen production at maximum energetic and exergetic efficiencies. The numerical simulation was carried out using three large biomass residues available in Portugal: coffee husks, pine residues and vine pruning wastes. It was concluded that the three biomass substrates showed similar trends at different operating conditions and the vine pruning wastes showed the best hydrogen outputs. The computed results were also compared with pilot scale experimental data obtained for coffee husk residues. The numerical results differ from experimental data, but in both cases the hydrogen composition has similar changes taking into consideration the effect of different operating conditions. It was concluded that the hydrogen molar composition increases steeply with a steam to biomass ratio (SBR) below the CBP and with a slow rate above the CBP, up to an asymptotic value. Similar behavior was found considering the temperature effect on hydrogen production. It was also found that energy efficiency first increases with the SBR up to a maximum value and then decreases.     

General equilibrium, electricity generation technologies and the cost of carbon abatement: A structural sensitivity analysis

Electricity generation is a major contributor to carbon dioxide emissions, and abatement in this sector is a key determinant of economy-wide regulation costs. The complexity of an integrated representation of economic and electricity systems makes simplifying assumptions appealing, but there is no evidence in the literature on how important the pitfalls may be. The aim of this paper is to provide such evidence, drawing on numerical simulations from a suite of partial and general equilibrium models that share common technological features and are calibrated to the same benchmark data. We report two basic findings. First, general equilibrium inter-sectoral effects of an economy-wide carbon policy are large. It follows that assessing abatement potentials and price changes in the electricity sector with a partial equilibrium Marshallian demand can only provide a crude approximation of the complex demand-side interactions. Second, we provide evidence that widely used top-down representations of electricity technologies produce fuel substitution patterns that are inconsistent with bottom-up cost data. This supports the view that the parametrization of substitution possibilities with highly aggregated production functions is difficult to validate empirically. The overall picture that emerges is one of large quantitative and even qualitative differences, highlighting the role of key structural assumptions in the interpretation of climate policy projections.     

Validation of the high-temperature structural integrity procedure R5 by component testing

Large-scale component tests enable: (i) direct substantiation of continued plant operation; (ii) validation of life monitoring procedures based on accumulated strain or damage; and (iii) validation of analysis-based structural integrity assessment procedures. This paper concentrates on their use in support of the high-temperature assessment procedure R5. The most common locations of cracking or damage in plant are at welds and the paper concentrates on tests on welded components. Tests on both defect-free and defective components are described. The data required from the tests, their use within R5 validation, and their limitations are discussed.     

Performance optimization of solar-powered heat engine using a multiobjective accelerated algorithm

In this study, a multiobjective optimization approach was used to conduct a thermodynamic investigation of a solar Brayton and endoreversible heat engine. The thermo-economic performance capabilities of such machines with hybrid input power, solar-fuel, are examined numerically. Throughout this study, three performance indicators of the cycle, including the power output, the thermo-economic performance function, and the thermal efficiency are optimized concurrently employing a multiobjective steepest descent method, named the Accelerated Diagonal Steepest Descent algorithm. Furthermore, to properly analyze the error, three strategies are employed in the decision-making step to identify the optimal compromise solution, and the deviation indices under these strategies are analyzed. The numerical experiments reveal that the present algorithm outperforms the two popular multiobjective algorithms: the multiobjective particle swarm optimization method and the elitist nondominated sorting genetic algorithm. The relevance of the presented algorithm with respect to the previous ones is examined by means of a deviation index. Finally, these experiments show the optimal design parameters which lead to the best performance of the heat engine.     

Efficient hydrogen production using a multi-layered photobioreactor and a photosynthetic bacterium mutant with reduced pigment

A multi-layered photobioreactor (MLPR), where the light paths were formed by the localization of bacterial cells, was constructed for efficient hydrogen production. The performance was investigated under several conditions in order to clarify the effect of this reactor on hydrogen production. An analysis of the hydrogen production profile showed that the MPLR utilizes both the light that directly illuminates its surface and the light induced and diffused from its light paths for hydrogen production. It was also found that the hydrogen productivity in the MLPR was more than twice that in a plate-type reactor. When a photosynthetic bacterium mutant with reduced pigment, MTP4, was used, the maximum hydrogen production rate reached 2.0 l/m² h, which was 38% higher than that of a conventional plate-type reactor. The synergistic effect of the improvement in the reactor and the modification of the bacteria was brought about by the combination of the MLPR and MTP4, and resulted in an improvement in the hydrogen production.     

Water－Aromatic Liquid－Liquid－Vapour Equilibrium Calculation Using a Cubic Equation of State

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斜坡太阳能热气流发电的可行性分析

本文论述了一种利用阳面坡地建造斜坡太阳能热气流发电系统的可行性，指出太阳辐射是一种资源，气温日较差是一种资源，坡地地形也是一种资源，斜坡太阳能热气流发电是将三者资源合理利用的一种极具竞争力的低成本的发电方式。     

Theoretical analysis of thermal radiative equilibrium via a radiosity method

We propose a theoretical consideration of thermal radiative equilibrium via a radiosity method. According to G. Kirchhoff's research on cavity radiation, the condition of radiative equilibrium arises in a cavity in which the internal wall temperature is uniform. Furthermore, by considering the balance of energy on the wall surfaces in the cavity, the relationship, emittance ? = absorptance α, is obtained. Adversely, in the present study, we developed a method to prove the conclusion of the uniformity and uniqueness of radiative equilibrium in the cavity (independent of the emittance of the interior wall surfaces) by considering the relationship ? = α on the wall surfaces to be a supposition. Using the concept of radiosity, we proved that the radiosities on the internal wall surfaces can be kept uniform in the enclosed system of thermal radiative equilibrium. This knowledge is advantageous for inspecting the benchmarks of various programs for radiative analysis. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20372     

Thermodynamic equilibrium model and second law analysis of a downdraft waste gasifier

The management of municipal solid waste (MSW) and the current status of world energy resources crisis are important problems. Gasification is a kind of waste-to- energy conversion scheme that offers the most attractive solution to both waste disposal and energy problems. In this study, the thermodynamic equilibrium model based on equilibrium constant for predicting the composition of producer gas in a downdraft waste gasifier was developed. To enhance the performance of the model, further modification was made by multiplying the equilibrium constants with coefficients. The modified model was validated with the data reported by different researchers. MSW in Thailand was then used to simulate and to study the effects of moisture content (MC) of the waste on the gasifier's performance. The results showed that the mole fraction of H₂ gradually increases; CO decreases; CH₄, which has a very low percentage in the producer gas increases; N₂ slightly decreases; and CO₂ increases with increasing MC. The reaction temperature, the calorific value, and the second law efficiency, decrease when MC increases.     

求根公式与牛顿迭代模型解决牵引计算出坡速度试凑

为了解决牵引计算中列车出坡速度试凑问题，引入线性查值法计算非特征点下列车的单位合力，在列车运动方程的基础上结合剩余坡段长度建立关于出坡速度的一元二次方程，通过求根公式一次性计算出列车的出坡速度。采用直线模拟列车单位合力曲线，通过积分解算出一种与《列车牵引计算规程》不同的列车运动方程的一般形式，而后引入牛顿迭代法，求解列车的出坡速度。     

Hydrogen production and storage analysis of a system by using TRNSYS

In this study, hydrogen production and storage were investigated. The Transient System Simulation Program (TRNSYS) and Generic Optimization Program (GenOpt) packages were combined for the design and optimization of a system that produces hydrogen from water and stores the hydrogen it produced in the compressed gas tank. The system design is based on the electricity grid. Electrical energy produced in photovoltaic (PV) panels was used to electrolyze water. The systems for Izmir, Istanbul and Ankara provinces which are in different climate zones of Turkey were optimized and the annual system performances based on the optimum angles were analyzed. For the mentioned provinces, the PV tilt angles which minimize electricity drawn from the grid at the electrolyzer are also investigated. The electrical energy produced in the photovoltaic panels, the hydrogen and oxygen amounts produced, the efficiency of the electrolyzer, the gas and pressure levels in the hydrogen tank were compared. According to the results of the analysis, the annual total power produced in photovoltaic panels is 42803.66 kW in İzmir, 42573.74 kW in Istanbul and 44613.95 kW in Ankara. Hydrogen levels produced in the system are calculated as 10488.39 m³ year⁻¹ in Izmir, 9824.70 m³ year⁻¹ in Istanbul, and 10368.65 m³ year⁻¹ in Ankara.     

Fracture analysis of laser beam welded superalloys Inconel 718 and 625 using the FITNET procedure

This paper presents results of the analysis for residual strength prediction of two laser beam welded superalloys (Inconel 625 and 718) using the fitness-for-service (FFS) procedure FITNET. The analysis is based on Option 3 of the Fracture Module of the procedure arising from the European Community funded project FITNET (www.eurofitnet.org). Analysis option 3 requires full stress–strain curves of the materials as input data. Since the strength mismatch ratio (M) between the weld and the base metals for both alloys was less than 10%, a homogeneous solution route has been used for welded tension loaded specimens containing through thickness central cracks. The FITNET predictions of the attained maximum load levels of the specimens were verified with the generated experimental results. The analysis methodology, as well as comparison between predictions and experimental results are provided. Accurate yet conservative estimation of the maximum load carrying capacities have been achieved depending on the input data; as the input data becomes more detailed, the degree of conservatism decreases.     

Large-eddy simulation of a bluff-body-stabilized non-premixed flame using a recursive filter-refinement procedure

A large-eddy simulation (LES) of a bluff-body-stabilized flame has been carried out using a new strategy for LES grid generation. The recursive filter-refinement procedure (RFRP) has been used to generate optimized clustering for variable density combustion simulations. A methane-hydrogen fuel-based bluff-body-stabilized experimental configuration has been simulated using state-of-the-art LES algorithms and subfilter models. The combustion chemistry is described using a precomputed, laminar flamelet model-based look-up table. The GRI-2.11 mechanism is used to build the look-up table parameterized by mixture fraction and scalar dissipation rate. A beta function is used for the subfilter mixture fraction filtered density function (FDF). The simulations show good agreement with experimental data for the velocity field. Time-averaged profiles of major species and temperature are very well reproduced by the simulation. The mixture fraction profiles show excellent agreement at all locations, which helps in understanding the validity of flamelet assumption for this flame. The results indicate that LES computations are able to quantitatively predict the flame structure quite accurately using the laminar flamelet model. Simulations tend to corroborate experimental evidence that local extinction is not significant for this flame.     

辐射对流条件下肋片散热的数值计算和结构优化

本文利用matlab对一种矩形肋片进行了散热数值计算 ,以金属热强度为结构优化的目标函数 ,通过对计算结果的分析得出了此种肋片的最佳肋高尺寸 ,同时 ,认为利用matlab来解决这类肋片优化问题是非常方便的。     

Cross-plane thermal conductivity of superlattices with rough interfaces using equilibrium and non-equilibrium molecular dynamics

This paper describes a heat transfer study of binary Lennard Jones superlattices, focusing on the influence of interface topology on cross-plane thermal conductivity, by using both non-equilibrium and equilibrium molecular dynamics methods. Both methods reveal the same trends of thermal conductivity. In particular, interfacial roughness is shown to slightly increase cross-plane thermal conductivity in comparison to smooth interfaces. Our results highlight paths for optimizing superlattices for thermoelectric conversion applications and for thermal management solutions in micro- and nano-systems.     

Enhanced water removal in a fuel cell stack by droplet atomization using structural and acoustic excitation

This work examines new methods for enhancing product water removal in fuel cell stacks. Vibration and acoustic based methods are proposed to atomize condensed water droplets in the channels of a bipolar plate or on a membrane electrode assembly (MEA). The vibration levels required to atomize water droplets of different sizes are first examined using two different approaches: (1) exciting the droplet at the same energy level required to form that droplet; and (2) by using a method called ‘vibration induced droplet atomization’, or VIDA. It is shown analytically that a 2 mm radius droplet resting on a bipolar-like plate can be atomized by inducing acceleration levels as low as 250 g at a certain frequency. By modeling the direct structural excitation of a simplified bipolar plate using a realistic source, the response levels that can be achieved are then compared with those required levels. Furthermore, a two-cell fuel cell finite element model and a boundary element model of the MEA were developed to demonstrate that the acceleration levels required for droplet atomization may be achieved in both the bipolar plate as well as the MEA through proper choice of excitation frequency and source strength.     

Effect of equilibrium shift by using lithium silicate pellets in methane steam reforming

Equilibrium shifting is considered to be effective for promoting H₂ production by methane (CH₄) steam reforming. In this study, a packed bed reactor with a mixture of reforming catalyst and CO₂ absorbent was used. Pellets of lithium silicate (Li₄SiO₄), which Toshiba has developed, were applied as the absorbent. This is a report on the relationship between CO₂ absorption by Li₄SiO₄ pellets and the equilibrium-shift effect for overall reactions. Experiments showed that there was a strong influence of temperature on the equilibrium-shift effect. The effect was obvious, which resulted in keeping not only the concentration of H₂ above 93 vol% but also that of CO below 0.2 vol% at 550 °C.     

A procedure for accelerated determination of main heat engineering parameters of flat-plate solar collectors for heating of a heat transfer fluid

A procedure for accelerated determination of main heat engineering parameters of flat-plate solar collectors (FSCs) for heating of a heat transfer fluid (HTF) according to the results of their short-term thermal testing in full-scale quasi-stationary conditions has been proposed and implemented.