Chimney effect in a “T” form cavity with heated isothermal blocks: The blocks height effect

In this paper, a numerical study of natural convection from a two dimensional “T” form cavity with rectangular heated blocks is conducted. The blocks are identical, and the domain presents a symmetry with respect to a vertical axis passing through the middle of the opening. The governing equations are solved using a control volume method, and the SIMPLER algorithm for the velocity–pressure coupling is employed. Special emphasis is given to detail the effect of Rayleigh number and block height on the heat transfer and the flow rate generated by the chimney effect. The results are given for the parameters of control as, 10⁴Ra3×10⁶, Pr=0.71, opening diameter (C=l^′/H^′=0.15), blocks gap (D=d^′/H^′=0.5) and blocks height (1/8B=h^′/H^′1/2). These results show that the heat transfer variation with Ra is in the same manner as those met in the case of the vertical smooth or ribbed channels.     

THE “EVAPORATIVE CAPACITY” AS A PERFORMANCE INDEX FOR A SOLAR-DRIER AIR-HEATER

This paper presents a new index, called the “evaporative capacity”, for rating the performance of the solar air heater in a solar drier consisting of solar air heater and a drying chamber in series. The proposed index complements the widely-used “collector efficiency” as a performance indicator of the solar collector, by taking into account the specific use that is to be made with the heated air. Presented is a detailed method for calculating the evaporative capacity, and a comparison of this new index with the thermal efficiency index, demonstrating its superiority. General charts for a rapid determination of the evaporative capacity are presented, and some possible applications of these charts are described.     

“Key” sectors in final energy consumption: an input–output application to the Spanish case

In this paper we analyze the determination of “key” sectors in the final energy consumption. We approach this issue from an input–output perspective and we design a methodology based on the elasticities of the demands of final energy consumption. As an exercise, we apply the proposed methodology to the Spanish economy. The analysis allows us to indicate the greater or lesser relevance of the different sectors in the consumption of final energy, pointing out which sectors deserve greater attention in the Spanish case and showing the implications for energy policy.     

Thermal modeling of integrated roof air heater for passive solar space heating of a non-air-conditioned building

This communication presents the periodic heat transfer analysis for solar space heating of an unconditioned building with an integrated roof air heater. The system consists of an air duct within the roof such that the air is continuously or intermittently forced to circulate the cooler room air through the inlet of the air duct. Time dependence of the air flow is represented by a step function of time for daily operation and, hence, has been expressed as a Fourier series in time. The analysis takes into account air ventilation, ground heat conduction and furnishings. The effects of depth of the air duct from the outer surface of the roof and the magnitude and duration of air flow rate on indoor air temperature have been studied for a typical cold winter day in Delhi. It is seen that a time dependent air flow through the duct is desirable from the point of view of increasing the indoor air temperature in the case of a bare roof. However, in the case of a blackened and glazed roof, continuous air flow is needed for increasing the room air temperature. The results are desirable from the point of view of efficient space heating of solar passive buildings.     

Thermal performance of “still on roof” system

This paper presents an analysis of periodic heat flux through a roof, on which a solar still has been placed. It is seen that on a typical hot day in Delhi, for high reflectivity of the bottom of the basin (on account of deposits or otherwise) the daily heat flux in the room gets reduced by 40% and the production of distilled water is 0.6 kg/m² day; the produced swings in the heat flux also get reduced in magnitude. For a typical cold day in Delhi, if a black dye is mixed with basin water the daily heat flux in the room increases by a factor of two and the yield of the distillate becomes 5.0 kg/m² day.     

Thermal performance of the “Rohini”—An improved wood cookstove

A detailed thermal analysis of the “Rohini”, a new damperless, three-pot, L-shaped improved cooking stove, developed by the authors, is reported. The stove was designed for an optimum power output at a wood-burning rate of 1.0 kg/h, which is the average rating of the stove used in rural areas. The performance of this stove has been evaluated at different power outputs. The study shows that the thermal efficiency of the stove is not unduly affected by operation at burning rates lower than the design value but shows a fall at the higher burning rate of 1.5 kg/h. The rate of heat gained by the individual pots and the various heat losses, such as convection, radiation and flue gas losses, at different burning rates, are also discussed. This study shows that widespread use of this stove in India could save nearly 150 MT wood/yr.     

Assessment of an “Energy Tower” potential in Australia using a mathematical model and GIS

“Energy Tower” is a technology for producing renewable and clean electricity by means of cooling hot and dry air, which is continuously supplied to arid lands. We assess the potential of an Energy Tower by incorporating topographic and meteorological parameters into a computational model, providing evaluations for the net power production and the electricity production cost. We formulate a highly simplified model for the Energy Tower’s flow, setup and process a spatial dataset of topographic and Meteorological upper air parameters. The model was applied to the Australian continent. A model simulation of one annual cycle enabled the ranking and selection of promising sites. The highest potential for energy towers is in the Port Hedland region, where favorable meteorological and topographic conditions would result in high average net power (≈370 ± 160 MW), potentially providing the electricity needs of 0.5 million people, for an economically competitive costs (3.5 ¢kWh).     

Optimization of heat pipe with axial “Ω”-shaped micro grooves based on a niched Pareto genetic algorithm (NPGA)

A niched Pareto genetic algorithm based approach is utilized to optimize a heat pipe with axial “Ω”-shaped micro grooves. The effects of the structural parameters are evaluated and optimized with respect to the heat transfer performance in order to model the heat transfer capability and total thermal resistance of this novel heat pipe. Using the heat transfer capability and total thermal resistance as the objective function and the structure parameters as the decision variable, the optimization design for the heat pipe is performed using the niche genetic algorithm. The results indicate that the heat transfer capability and the total heat resistance are inversely coupled and as a result, the optimization must be constructed on the application objective. Using the niched Pareto genetic algorithm and the pre-specified application constraints, a Pareto-optimal solution set can be determined and the optimal design for a given application is selected.     

Erratum to “Steady-state analysis of PV supplied separately excited DC motor fed from IDB converter” [Sol. Energy Mater. Sol. Cells 71 (4) (2002) 493–510]

Interleaved dual boost converter is capable of extracting more amount of power from the photovoltaic source than the conventional boost converter. Power extraction capabilities of the conventional boost and interleaved dual boost converters from the photovoltaic array are verified through experimental studies. As an application the effectiveness of this interleaved dual boost converter for PV supplied separately excited DC motor is studied through simulation. Extensive studies are made by formulating the mathematical models for photovoltaic source, interleaved dual boost converter, DC motor and load. Steady-state performance of the motor coupled to centrifugal pump load is analyzed for maximum power, gross mechanical energy operations. From the simulation studies, it is found that the motor performance is improved with gross mechanical energy output operation as compared to maximum power operation of solar cell array. Furthermore, the use of interleaved dual boost converter reduces the ripple content both in the source and load waveforms, thus resulting in reduced filtering requirements and improved photovoltaic array performance.     

Evaluation of the biomass “date stones” as a fuel in furnaces: A comparison with coal combustion

The present investigation gives insight into the potential of the biomass fuel “date stones” as an energy source for furnaces. This is accomplished by comparing combustion and heat transfer characteristics obtained in a furnace fueled with both fuels: date stones and a type of coal.The analysis of the two fuels investigated and the combustion experiments conducted reveal that date stones contain much volatile material that is released during the pyrolysis process, and ultimately burned under diffusion or partially premixed flame conditions. Heterogeneous reactions are found to be of lower importance in this case; contrasting the case of coal combustion. The results obtained highlight superiority of the date stones.     

Erratum to “Assessing the suitability of Input-Output analysis for enhancing our understanding of potential effects of Peak-Oil” [Energy (2008) 34: 284–290]

Given recent developments on energy markets and skyrocketing oil prices, we argue for an urgent need to study the potential effects of world oil production reaching a maximum (Peak Oil) in order to facilitate the development of adaptation policies. We consider input–output (IO) modelling as a powerful tool for this purpose. However, the standard Leontief type model implicitly assumes that all necessary inputs to satisfy a given demand can and will be supplied. This is problematic if the availability of certain key inputs becomes restricted and it is therefore only of limited usefulness for the study of the phenomenon of Peak Oil. Hence this paper firstly reviews two alternative modelling tools within the IO framework: supply-driven and mixed models. The former has been severely criticised for its problematic assumption of perfect factor substitution and perfect elasticity of demand as revealed by Oosterhaven [Oosterhaven J. On the plausibility of the supply-driven IO model. J Reg Sci 1988; 28:203–17. [1]]. The supply-constrained model on the other hand proved well suited to analyse the quantity dimension of Peak Oil and is therefore applied empirically in the second part of the paper, using data for the UK, Japanese and Chilean economy. Results show how differences in net-oil exporting and net-oil importing countries are clearly visible in terms of final demand. Industries, most affected in all countries, include transportation, electricity production and financial and trade services.     

Environmental assessment and extended exergy analysis of a “zero CO2 emission”, high-efficiency steam power plant

Aim of this paper is to analyze the performance of an innovative high-efficiency steam power plant by means of two “life cycle approach” methodologies, the life cycle assessment (LCA) and the “extended exergy analysis” (EEA).

The plant object of the analysis is a hydrogen-fed steam power plant in which the H₂ is produced by a “zero CO₂ emission” coal gasification process (the ZECOTECH^© cycle). The CO₂ capture system is a standard humid-CaO absorbing process and produces CaCO₃ as a by-product, which is then regenerated to CaO releasing the CO₂ for a downstream mineral sequestration process.

The steam power plant is based on an innovative combined-cycle process: the hydrogen is used as a fuel to produce high-temperature, medium-pressure steam that powers the steam turbine in the topping section, whose exhaust is used in a heat recovery boiler to feed a traditional steam power plant.

The environmental performance of the ZECOTECH^© cycle is assessed by comparison with four different processes: power plant fed by H₂ from natural gas steam reforming, two conventional coal- and natural gas power plants and a wind power plant.     

Comparative studies of “all sol–gel” electrochromic devices with optically passive counter-electrode films, ormolyte Li ion-conductor and WO3 or Nb2O5 electrochromic films

Laminated electrochromic (EC) devices are becoming increasingly important for making “smart” windows and switchable displays. Mostly, polymeric Li⁺ ionic conductors in combination with vacuum deposited active electrochromic and counter-electrode films are used. In this paper we report on the development of all sol–gel EC devices, that is, those where all three internal layers are prepared via the sol–gel route, including the ionically conductive inorganic–organic hybrid (ormolyte). The electrochemical and optical properties of EC devices are presented and the cycling stability and reversibility of their optical modulation assessed. The results show that WO₃/ormolyte/SnO₂ : Mo, WO₃/ormolyte/SnO₂ : Sb, WO₃/ormolyte/SnO₂ : Sb : Mo, Nb₂O₅/ormolyte/SnO₂ : Sb : Mo and WO₃/ormolyte/LiCo-oxide exhibit a transmission modulation dependent on the thickness of the active electrochromic and counter-electrode films and the thickness of the ormolyte layer. Electrochemical and optical properties of individual films are described and correlated with the stability of the all sol–gel EC devices.     

Preparation and properties of LiCoyMnxNi1−x−yO2 as a cathode for lithium ion batteries

The preparation of LiCo_yMn_xNi_1−x−yO₂ from LiOH·H₂O, Ni(OH)₂ and γ-MnOOH in air was studied in detail. Single-phase LiCo_yMn_xNi_1−x−yO₂ (0y0.3 and x=0.2) is obtained by heating at 830–900°C. The optimum heating temperatures are 850°C for y=0–0.1 and 900°C for y=0.2–0.3. Excess lithium (1z1.11 for y=0.2) and the Co doping level (0.05y0.2) do not significantly affect the discharge capacity of Li_zCo_yMn_0.2Ni_0.8−yO₂. The doping of Co into LiMn_0.2Ni_0.8O₂ accelerates the oxidation of the transition metal ion, and suppresses partial cation mixing. Since the valence of the manganese ion in LiMn_0.2Ni_0.8O₂ is determined to be 4, the formation of a solid solution between LiCo_yNi_1−yO₂ and Li₂MnO₃ is confirmed.