International Journal of Energy Research

Published by Wiley
Online ISSN: 1099-114X
Publications
Article
A reliable process for compressing hydrogen and for removing all contaminants is that of the metal hydride thermal compression. The use of metal hydride technology in hydrogen compression applications though, requires thorough structural characterization of the alloys and investigation of their sorption properties. The samples have been synthesized by induction - levitation melting and characterized by Rietveld analysis of the X-Ray diffraction (XRD) patterns. Volumetric PCI (Pressure-Composition Isotherm) measurements have been conducted at 20, 60 and 90 oC, in order to investigate the maximum pressure that can be reached from the selected alloys using water of 90oC. Experimental evidence shows that the maximum hydrogen uptake is low since all the alloys are consisted of Laves phases, but it is of minor importance if they have fast kinetics, given a constant volumetric hydrogen flow. Hysteresis is almost absent while all the alloys release nearly all the absorbed hydrogen during desorption. Due to hardware restrictions, the maximum hydrogen pressure for the measurements was limited at 100 bars. Practically, the maximum pressure that can be reached from the last alloy is more than 150 bars.
 
Article
Flow characteristics of an adiabatic capillary tube in a transcritical CO2 heat pump system have been investigated employing the homogeneous model. The model is based on fundamental equations of mass, energy and momentum which are solved simultaneously. Two friction factor empirical correlations (Churchill, Lin et al., Int. J. Multiphase Flow 1991; 17(1):95–102) and four viscosity models (Mcadams, Cicchitti, Dukler and Lin) are comparatively used to investigate the flow characteristics. Choked condition at the outlet is also investigated for maximum mass flow rate. Subcritical and supercritical thermodynamic and transport properties of CO2 are calculated employing a precision property code. Choice of viscosity model causes minor variation in results unlike in chlorofluorocarbons (CFCs) refrigerants. Relationships between cooling capacity with capillary tube diameter, length and maximum mass flow rate are presented. A lower evaporating temperature yields a larger cooling capacity due to the unique thermodynamic properties of CO2. It is also observed that an optimum cooling capacity exists for a specified capillary tube. Copyright
 
Article
This paper presents the description and operation of a solar-powered modified two-bed adsorption air-conditioning system with activated carbon and methanol as the working pair. A simple lumped parameter model is established to investigate the performance of this continuous adsorption cycle consisting of a twin adsorber immersed in water tanks, which is measured in terms of the temperature histories, gross solar coefficient of performance and specific cooling power. In addition, the influence of some important design and operational parameters on the performance of the system has been studied. Compared with the conventional system, it is found that the modified system can operate more cycles and at a higher efficiency. The parametric study also shows that the adsorbent mass and the solar collector area have significant effect on the system performance as well as on the system size. Finally, when the system uses gas heater as an auxiliary heat source, it is found that the system can provide a stable cooling effect for a longer period of operation. Copyright © 2008 John Wiley & Sons, Ltd.
 
Article
This study sets out to determine whether agricultural consumers of natural gas are responsive to changes in the relative prices of different types of energy. A demand model is specified and estimated. The conclusions strongly suggest that not only is the price of natural gas a factor impacting the quantity of natural gas demanded by agriculture, but that other types of energy are substitutes for natural gas and that income and weather (measured by heating degree days) likewise affect natural gas demand.
 
Article
There has been considerable interest in producing fuels from biomass and wastes since the oil crises of the last two decades which has been reinforced by subsequent environmental concerns and recent political events in the Middle East. This project was undertaken to provide a consistent and thorough review of the full range of processes for producing liquid fuels from biomass to compare both alternative technologies and processes within those technologies in order to identify the most promising opportunities that deserve closer attention.
 
Article
Hydrogen is the most promising alternative fuel for spark-ignited engines. This paper experimentally investigated the performance of a pure hydrogen-fueled SI engine at idle and lean conditions. The experiment was carried out on a four-cylinder gasoline-fueled SI engine equipped with an electronically controlled hydrogen port-injection system and a hybrid electronic control unit which was used to govern the hydrogen injection duration. The engine original electronic control unit was used to adjust the opening of idle bypass valve and spark timing to enable the engine to be run around its target idle speed. The test results showed that the fuel energy flow rate was reduced with the increase of excess air ratio for the pure hydrogen-fueled engine at idle and lean conditions. When excess air ratio increased from 2.08 to 3.2, the hydrogen energy flow rate was decreased from 11.79 to 9.97MJ/h. Both the flame development and propagation periods were increased with the increase of excess air ratio. Because of the increased opening of idle bypass valve and dropped cylinder temperature, both pumping and cooling losses were reduced when the engine was leaned out. NOx and CO emissions were negligible, but HC and CO2 were still existed for the pure hydrogen-fueled SI engine due to the possible burning of the blow-by lubricant oil gas. Copyright (c) 2013 John Wiley & Sons, Ltd.
 
Article
Process conditions for the direct solar decomposition of sulfur trioxide have been investigated and optimized by using a receiver–reactor in a solar furnace. This decomposition reaction is a key step to couple concentrated solar radiation or solar high-temperature heat into promising sulfur-based thermochemical cycles for solar production of hydrogen from water. After proof-of-principle a modified design of the reactor was applied. A separated chamber for the evaporation of the sulfuric acid, which is the precursor of sulfur trioxide in the mentioned thermochemical cycles, a higher mass flow of reactants, an independent control and optimization of the decomposition reactor were possible. Higher mass flows of the reactants improve the reactor efficiency because energy losses are almost independent of the mass flow due to the predominant contribution of re-radiation losses. The influence of absorber temperature, mass flow, reactant initial concentration, acid concentration, and residence time on sulfur trioxide conversion and reactor efficiency has been investigated systematically. The experimental investigation was accompanied by energy balancing of the reactor for typical operational points. The absorber temperature turned out to be the most important parameter with respect to both conversion and efficiency. When the reactor was applied for solar sulfur trioxide decomposition only, reactor efficiencies of up to 40% were achieved at average absorber temperature well below 1000°C. High conversions almost up to the maximum achievable conversion determined by thermodynamic equilibrium were achieved. As the reradiation of the absorber is the main contribution to energy losses of the reactor, a cavity design is predicted to be the preferable way to further raise the efficiency.
 
Article
The significance of the thermal stratification for the energy efficiency of small solar thermal hot water heat stores is pointed out. Exemplary the thermal stratification build-up with devices already marketed as well as with devices still in development has been investigated experimentally and theoretically, taking into account different realistic operation conditions. The methods (selective temperature measurement, non-invasive field measuring methods PIV and LIF, computational fluid dynamics (CFD)) suitable for the experimental and theoretical analysis of thermal stratification devices are introduced. Copyright © 2007 John Wiley & Sons, Ltd.
 
Article
Hot water seasonal heat stores (HWSHS) carry the solar thermal energy from energy-rich seasons of the year over to energy-poor seasons so as to ensure the availability of solar energy throughout the year. Momentum diffusers and flow guides are designed to charge and discharge the harvested solar thermal energy within HWSHS in a stratified manner to enhance the efficiency of the solar systems. To evaluate the efficiency of an HWSHS, a characterization scheme developed for general stratified thermal energy stores (TES) (Sol Energy 2007; 81:1043–1054) is used. It addresses the First Law and Second Law concerns over a TES simultaneously. This study is confined to systems that use the same nozzles at fixed positions in both charging and discharging cycles. Different parameters related to axial, conical and radial diffusers as well as a variety of flow-guide designs are studied. The results suggest that a nozzle that brings about better diffuser action by minimizing entropy generation may not necessarily improve the energy response and guarantee better overall efficiency of the HWSHS. Of all, the different nozzle designs experimented with the conical diffusers with smaller angles of diffusion produced the best overall efficiency. Copyright © 2008 John Wiley & Sons, Ltd.
 
Article
Energy lost due to fouling of heat exchangers accounts for at least 2% of the total world energy production per year. The overwhelming proportion of these losses is compensated by additional consumption of fossil energy carriers. Not surprisingly, this comes with an enormous energy price-tag as well as considerable green-house gas emissions, acidification of water resources and release of chemical fouling inhibitors. Any solution towards the mitigation of fouling will, therefore, provide significant economic and environmental benefits. In the present paper, the performance of innovative nano-modified surfaces is described when subjected to calcium sulphate scale deposition during convective heat transfer. Two types of non-structured and structured nano-modified surfaces are examined. The experimental results demonstrate that such coatings will significantly increase the induction time before fouling starts and also reduce the subsequent fouling rate, in comparison with untreated stainless steel surfaces. Considering these promising results and the potential application of nanotechnology to combat fouling, the paper continues by discussing the demands on thermal and mechanical stabilities that such coatings will have to satisfy. Copyright © 2009 John Wiley & Sons, Ltd.
 
Article
The properties of the components of a membrane electrode assembly in a polymer electrolyte fuel cell (PEFC) determine its efficiency and performance. This paper aims at demonstrating the importance of nanoscale properties of PEFC membranes and electrodes and discussing the information obtained by various experimental techniques. The nanostructure and conductivity of freshly prepared as well as artificially degraded Nafion membranes and Pt/C electrodes are investigated by contact atomic force microscopy (AFM), conductive AFM, pulsed force mode (PFM)-AFM, in situ scanning tunnelling microscopy (STM), and scanning electron microscopy. The different techniques can provide complementary information on structure and conductivity. With in situ STM on Pt catalyst covered graphite, a layer of very small Pt particles between the catalyst particles is imaged, which is probably not visible with TEM and can explain a systematic discrepancy between TEM and XRD in particle size distribution. Conductive AFM is used to investigate the conductivity of Nafion. The images show a quite inhomogeneous distribution of current at the surface. The percentage of conductive surface increases with humidity, but regions without any current still present up to 80% of relative humidity (RH). Comparison with PFM-AFM images, where differences in adhesion forces are measured, indicates that hydrophobic regions are present at the surface with comparable dimensions, which are attributed to non-conductive PTFE-like polymer backbone. The changes in hydrophilic and hydrophobic parts after artificial degradation by plasma etching in air plasma can be imaged by PFM. High-resolution current images of the membrane were used to directly compare the measured nanostructure of the single conductive channels with model predictions from the literature. Recent models in the literature propose the formation of water-filled inverted micelles, with a mean diameter of 2.4 nm, and their agglomeration into clusters agrees well with the current images
 
Article
A two-step thermochemical cycle for solar production of hydrogen from water has been developed and investigated. It is based on metal oxide redox pair systems, which can split water molecules by abstracting oxygen atoms and reversibly incorporating them into their lattice. After successful experimental demonstration of several cycles of alternating hydrogen and oxygen production, the present work describes a thermodynamic study aiming at the improvement of process conditions and at the evaluation of the theoretical potential of the process.
 
Article
A typical 1000 MW pressurized water reactor nuclear power plant is considered for optimization. The thermodynamic modeling is performed based on the energy and exergy analysis, while an economic model is developed according to the total revenue requirement method. The objective function based on the exergoeconomic analysis is obtained. The exergoeconomic optimization process with 10 decision variables is performed using a hybrid stochastic/deterministic search algorithm namely as genetic algorithm. The results that are obtained using optimization process are compared with the base case system and the discussion is presented. Copyright © 2009 John Wiley & Sons, Ltd.
 
Article
Ejector refrigeration systems can use low grade thermal energy, at temperatures as low as 60°C, to provide space cooling. Since this waste energy is widely available and the cost of its supply is negligible in many cases, cooling costs can be lower than conventional systems, which makes the method very attractive. The present study describes a computer simulation model for ejector refrigeration systems that was developed using an existing ejector theory. This model allows for internal irreversibilities within the ejector to be included and caters for the addition of a regenerator and a precooler for improving the system coefficient of performance. The study shows that HCFC-123 is a suitable replacement for CFC-11 in this application. Results also indicate that the use of a variable geometry ejector can maintain the optimum performance of refrigeration systems when operating conditions change.
 
Article
The performance of a vapour-compression system was examined with both R12/mineral oil and R134a/mineral oil charges. The mineral oil was then removed from the system using a multiple flushing method and the experiments repeated using a charge of R134a and an ester-based lubricant to establish the effect of the oil on the performance of the system. Results were compared with theoretical data for R134a and R12 refrigerants.
 
Article
A 1700 m2 solar pond was constructed in the desert of Kuwait where severe weather conditions prevail in all seasons. The paper describes in detail a diffuser design for the gradient establishment, gradient stability, and thermal performance of the pond. The main problem encountered in operating the pond was mixing between the upper zone and the gradient zone, even when the wind speed was as low as 5 m/s. No mixing between the gradient and the lower connective zone was observed. The wind effect was severe in causing mixing even when the upper convective zone increased to 0.90 m.
 
Article
This paper discusses the design and construction philosophy of the Kuwait solar-pond/multistage-flash system. The present work came about to study the performance of a solar pond as a main source for energy collection and storage and to use the collected heat in producing fresh water, which is difficult to obtain in remote areas. The pond is built with 1700 m2 of surface area and 45° sloping sides. Taking the natural surroundings and the nature of the climate into account, the pond is estimated to perform at 18% efficiency. The collected energy, which is estimated at 1800 kWh/day, will be used to produce 25 m3 of fresh water daily.
 
Article
A heat pump can be used to recover, upgrade and recycle heat from the condenser of the distillation column to its reboiler. In recent years there has been a growing interest in the various methods of using heat pumps to recycle energy in distillation columns. More than one hundred and fifty references for heat pump assisted distillation systems have been listed and classified under the following categories: heat pump assisted distillation (1) with an external working fluid, (2) using one of the distillation components as the working fluid, (3) overall assessments and (4) experimental data. The classification of more than one hundred and fifty references reported in this paper was made in order to help people to make better use of existing data and to encourage further research in heat pump assisted distillation systems.
 
Article
The generation, consumption and pricing of electricity in the member states of the European Community is modelled over the period from 1953–1986. Theoretical demand functions are developed and optimality conditions for equilibrium are established.
 
Article
The paper reports the results of a simple cointegration analysis applied to bivariate causality models and quarterly data on crude oil consumption, GDP and inflation in Thailand to investigate the long-term relationships in the sense of Granger between oil and these two major macroeconomic aggregates. For the period from January 1966 to January 1991, the empirical evidence indicates that oil consumption, output growth and inflation rate, as formulated in our models, are not random walks. In addition, oil consumption is significantly cointegrated with economic growth and, unfortunately, inflation rate.
 
Article
The decade of the 1980s was marked by very large changes in all factors controlling oil demand, supply and price. On the demand side, in the OECD nations, the early 1980s saw an apparent break or discontinuity in long-established relations between economic growth and energy demand. On the supply side, the apparent "disaggregation' of OPEC in its cartel aspects, massive debt problems for most non-OECD oil exporters, changes in OECD oil demand, and the explosive growth of market and trading as the major price fixer, all contributed to downward price trends. These reached their peak in the price collapse of 1986. This is taking place in a vigorous upward cyclic economic context, where economic recovery and growth in the OECD is being led by industry and manufacturing. Overall, the implications are that oil price growth will not fall to the rate of general inflation before 1991. -from Author
 
Article
This study analyses sectoral energy and exergy utilization in Turkey between 1999 and 2000. Total energy and exergy utilization efficiencies are calculated to be 43.24 and 24.04% in 1999, and 44.91 and 24.78% in 2000, respectively. In order to calculate these efficiency values, Turkey is subgrouped into four main sectors, namely utility, industrial, transportation and commercial-residential. The energy efficiency values are found to be 23.88, 30.10, 68.97 and 57.76% in 1999, and 23.71, 30.11, 68.81 and 57.05% in 2000 for transportation, utility, industrial and commercial-residential sectors, respectively. Besides this, the exergy efficiency values are obtained to be 23.80, 30.28, 35.97 and 8.12% in 1999, and 23.65, 30.47, 35.51 and 8.02% in 2000 for the same order of sectors. The present study has clearly shown the necessity of the planned studies towards increasing exergy efficiencies in the sectors studied. Copyright © 2004 John Wiley & Sons, Ltd.
 
Article
This paper reports the results of energy analysis of two 210 MW coal-fired thermal power stations located a good distance apart. A new and simple method for evaluation of thermal efficiency has been presented. Measures for improvement in plant performance in the coal, air, water and steam circuits as well as auxiliary power and secondary oil have been depicted, based on the analysis and existing field conditions.
 
Article
In the present work, exergy analysis of a coal-based thermal power plant is done using the design data from a 210 MW thermal power plant under operation in India. The entire plant cycle is split up into three zones for the analysis: (1) only the turbo-generator with its inlets and outlets, (2) turbo-generator, condenser, feed pumps and the regenerative heaters, (3) the entire cycle with boiler, turbo-generator, condenser, feed pumps, regenerative heaters and the plant auxiliaries. It helps to find out the contributions of different parts of the plant towards exergy destruction. The exergy efficiency is calculated using the operating data from the plant at different conditions, viz. at different loads, different condenser pressures, with and without regenerative heaters and with different settings of the turbine governing. The load variation is studied with the data at 100, 75, 60 and 40% of full load. Effects of two different condenser pressures, i.e. 76 and 89 mmHg (abs.), are studied. Effect of regeneration on exergy efficiency is studied by successively removing the high pressure regenerative heaters out of operation. The turbine governing system has been kept at constant pressure and sliding pressure modes to study their effects.
 
Article
In this paper, an experimental study on the heat transfer characteristics of two-phase flow boiling of some alternative refrigerants to HCFC-22, on air/refrigerant horizontal enhanced surface tubing, is presented. Correlations have been proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of alternatives to R-22; such as R-507, R-404A, R-407C, R-410A and R-408A in two-phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition. It was found that the correlations were applicable to the entire heat and mass flux, investigated in the present study, for the proposed blends under question. The deviation between the experimental and predicted values for the heat transfer coefficient and pressure drop were less than ±20, and ±35 per cent, respectively, for the majority of data. Copyright © 2000 John Wiley & Sons, Ltd.
 
Article
In this paper, a performance evaluation of a newly developed blend of HFCs and HCFCs, as a substitute for CFC-12, CFC-502, and HCFC-22, is presented. The blend's performance has been evaluated using water/air, air/air and water/water heat pumps, as well as a domestic refrigerator. The test results showed that the blend is not only environmentally sound, but it also enhances the performance by 7% to 30%, depending upon the application.
 
Article
In this paper, a numerical model is presented for predicting capillary tube performance using new alternative refrigerants to HCFC-22. The model has been established after the fluid flow conservation equations written for a homogeneous refrigerant fluid flow under saturated, sub-cooled and two-phase conditions.Numerical results showed that the proposed model in question fairly simulated our experimental data and fairly predicted the capillary tube behaviour under different conditions. The results also indicated that a system using R-407C would experience smaller pressure drop compared to R-410A and R-410B. Copyright © 2000 John Wiley & Sons, Ltd.
 
Article
In this paper, an experimental study is presented to enhance our understanding of the capillary tube behaviour using some new alternative refrigerants to HCFC-22. An experimental setup fully instrumented was used to gather the behaviour of three different capillary tube geometries with R-410B, R-407C, and R-410A under various conditions; saturated, sub-cooled and two-phase. Experimental data showed that R-410B has the highest pressure drop along the capillary tubes compared to the alternatives under question and also has the highest temperature drop along the capillary tube. The data also showed that R-407C has similar capillary behaviour to that of R-22. The results clearly demonstrated that the pressure drop is significantly influenced by the diameter of the capillary tube, the type of refrigerant and inlet conditions to the capillary tube. The data also showed that the capillary pressure drop decreases with the increase of the capillary diameter. There is clear evidence that the component concentration of the refrigerant mixture significantly affects the capillary tube behaviour and particularly the pressure drop along the capillary tube length. Copyright © 2001 John Wiley & Sons, Ltd.
 
Cross-sectional view of the fuel channel (dimension in cm): (1) original CANDU square lattice cell and (2) Equivalent diameter, used in calculations.
Setting of 37-fuel rods in the fuel bundle (dimension in cm).
The lattice criticality k∞ and the fuel burn-up grade as a function of plant operation period by full power.
Density variations of the main fissionable Uranium isotopes in the fuel bundle for the 98% ThC2+2% 233UC2 mixed fuel composition (solid lines, central fuel row; broken lines, peripheral fuel row).
Temporal variation of the accumulated densities of fissile isotopes (233U+235U+239Pu+241Pu) in the fuel bundle for the 98% ThC2+2% 233UC2 mixed fuel composition (solid lines, central fuel row; broken lines, peripheral fuel row).
Article
233U isotope is used as a booster fissile fuel material in the form of mixed ThC2/233UC2 fuel in a Canada Deuterium Uranium (CANDU) fuel bundle in order to assure the initial criticality at startup. Three different fuel compositions have been used: (1) 97% ThC2+3% 233UC2, (2) 98% ThC2+2% 233UC2 and (3) 99% ThC2+1% 233UC2. The temporal variation of the criticality k∞ and the burn-up values of the reactor have been calculated by full-power operation for a period of 20 years. The criticality starts by k∞=1.541, 1.355 and 0.995 for modes of (1), (2) and (3) fuel compositions, respectively. A sharp decrease in the criticality has been observed in the first 2 years as a consequence of rapid 233U burnout fuelling with (1) and (2) modes. The criticality becomes quasi-constant after the second year and remains above k∞∼1.06 for 20 years. After the second year, the CANDU reactor begins to operate practically as a thorium burner. Very high burnup could be achieved with the same fuel materials (up to 500 000 MWday t−1), provided that the fuel rod claddings would be replaced periodically (after every 500 00 or 100 000 MWday t−1). The reactor criticality will be sufficient for fuelling with (1) and (2) modes until a great fraction of the thorium fuel is burnt up. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically. Copyright © 2010 John Wiley & Sons, Ltd.
 
Article
Low temperature plasma nitriding is developed to meet the requirements for corrosion resistance and interfacial contact resistance (ICR) of stainless steel 304L as the bipolar plate for PEMFC. A dense and supersaturated-nitrogen nitrided layer has formed on the surface of the stainless steel 304L. Electrochemical behavior for the untreated and plasma-nitrided 304L was measured in H2SO4 (pH=1–5)+2 ppm F− simulating PEMFC environment, and the ICR was evaluated before and after corrosion tests. The experimental results have shown that the ICR for the plasma nitrided 304L is lower than the requirement of U.S. DOE (<10 mΩ cm2 to 2010). Corrosion resistance and the ICR at the compaction force of 150–200 N cm−2 increase with increasing pH value for the untreated and plasma-nitrided 304L. The passive current densities for the untreated and plasma-nitrided 304L are all lower than 16 µA cm−2. The ICR between passive film and carbon paper are increased markedly because of passive film formed on the surface of both studied 304L. However, the passive current density and the ICR are lower for the plasma nitrided 304L than those for the untreated one at the given pH value, which results from the different composition of the stable passive film formed on the surface. The low temperature plasma nitriding provides a promising method for 304L using as bipolar plate for PEMFC. Further research is needed to evaluate the long-term stability of passive film and the performance of single fuel cell. Copyright © 2010 John Wiley & Sons, Ltd.
 
Article
This paper presents a periodic analysis of a three zone solar pond as a solar energy collector and long term storage system. We explicitly take into account the convective heat and mass flux through the pond surface and evaluate the temperature and heat fluxes at various levels in the pond during its year round operation by solving the time dependent Fourier heat conduction equation with internal heat generation resulting from the absorption of solar radiation in the pond water. Eventually, an expression, for the transient rate at which heat can be retrieved from the solar pond to keep the temperature of the zone of heat extraction as constant, is derived. Heat retrieval efficiencies of 40.0 per cent, 32.1 per cent, 28.3 per cent and 25.5 per cent are predicted at collection temperatures of 40, 60, 80 and 100°C, respectively. the retrieved heat flux exhibits a phase difference of about 30 to 45 days with the incident solar flux; the load levelling in the retrieved heat flux improves as the thickness of the non-convective zone increases. the efficiency of the solar pond system for conversion of solar energy into mechanical work is also studied. This efficiency is found to increase with collection temperature and it tends to level around 5 per cent at collection temperatures about 90°C.
 
Article
A 3D Lagrangian particle model has been presented for the atmospheric dispersion of the toxic pollutants released from industrial stacks. As the mean wind speed and direction is changed with height in a real atmosphere, the height of the exhaust stack may have a strong impact on the pollutant dispersion and ground concentrations.An elevated continuous release of non-buoyant gas in a neutrally stratified atmosphere has been simulated, for various stack heights. The turbulent atmospheric parameters like vertical profiles of fluctuat ing wind velocity components and eddy lifetime were calculated using a semi-empirical mathematical model.The numerically calculated horizontal and vertical dispersion coefficients (σy and σz) are compared with the Pasquill's empirical σ's. The ground concentration as a function of downwind distance has been compared with the Green glow data. The ground concentrations for various release heights were compared with the Gaussian plume model. The comparison indicated a need for using either a modified Gaussian model or a 3D numerical mathematical model for pollutant dispersion and ground concentration calculations. Copyright © 2002 John Wiley & Sons, Ltd.
 
Article
Gas turbine (GT) output power is affected by temperature, gas turbine inlet air‐cooling systems are used to solve this. In the present work, the effect of using absorption chiller in GT power plants for two regions in Iran, namely Tabas with hot–dry and Bushehr with hot–humid climate conditions is conducted. Therefore, output power, first and second law efficiencies, environmental and electrical costs for GT power plant with inlet air cooler are calculated for two mentioned regions, respectively. Results show that using this system in hot months of a year is economical. In addition, using absorption chiller leads to increasing the output power 11.5 and 10.3%, for Tabas and Bushehr cities, respectively. Moreover, by using this method the second law efficiency is increased to 22.9 and 29.4% for Tabas and Bushehr cities, respectively. In addition, the cost of electricity production for Tabas and Bushehr cities decreases to about 5.04 and 2.97%, respectively. Copyright © 2011 John Wiley & Sons, Ltd.
 
Article
This article presents a steady-state model of a vapour compression refrigerating machine using a ternary refrigerant mixture R-407C. When using a zeotropic mixture in a refrigerant cycle, the circulating composition does not agree with the composition of the original charged mixture. It is mainly due to the temperature glide and the vapour–liquid slip ratio. As a result of the composition shift and its magnitude, the system performance changes depending on the system design, especially the presence of liquid receiving vessels. In this paper, a method that predicts the circulating composition has been associated to a refrigerating machine model. The results obtained with this model show an enrichment in the most volatile components of about 1% for the circulating composition, which is sufficient to decrease the system performance by about 3%. Factors affecting the overall performance have been investigated. The results show a very strong performance dependence on the refrigerant charge. The COP can decrease by 25% when the refrigerant charge is insufficient. An initial charged composition variation of 2% involves variations of the cooling capacity of about 5%. Furthermore, our model was employed to compare the performance for both R-22 and R-407C. The cooling capacity for R-22 is slightly greater in comparison to R-407C and the COP is almost constant. Copyright © 2002 John Wiley & Sons, Ltd.
 
Article
Combined cycle power plants (CCPPs) have an important role in power generation. The objective of this paper is to evaluate irreversibility of each part of Neka CCPP using the exergy analysis. The results show that the combustion chamber, gas turbine, duct burner and heat recovery steam generator (HRSG) are the main sources of irreversibility representing more than 83% of the overall exergy losses. The results show that the greatest exergy loss in the gas turbine occurs in the combustion chamber due to its high irreversibility. As the second major exergy loss is in HRSG, the optimization of HRSG has an important role in reducing the exergy loss of total combined cycle. In this case, LP-SH has the worst heat transfer process. The first law efficiency and the exergy efficiency of CCPP are calculated. Thermal and exergy efficiencies of Neka CCPP are 47 and 45.5% without duct burner, respectively. The results show that if the duct burner is added to HRSG, these efficiencies are reduced to 46 and 44%. Nevertheless, the results show that the CCPP output power increases by 7.38% when the duct burner is used. Copyright
 
Article
A numerical model is presented in this paper, for predicting capillary tube performance using new alternative refrigerants to CFC-502. The model has been established after the fluid flow conservation equations written for a homogeneous azeotropic refrigerant fluid flow under saturated, sub-cooled and two-phase conditions. The study was limited to the following azeotropic mixtures; R-507, R-404A, and quaternary mixture (R32/R125/R134a/R143a). Numerical results showed that the proposed model in question fairly simulated our experimental data and fairly predicted the capillary tube behaviour under different conditions. The results also indicated that a system using R-507 would experience smaller pressure drop across the capillary compared to the other alternatives under question. Copyright © 2001 John Wiley & Sons, Ltd.
 
Article
Numerical calculations have been carried out to explain the effect of self absorption on the nature of the emitted intensity of the Na-5890 Å line of the sodium doublet in water gas combustion plasma. The self absorption is purely an effect caused by the presence of cold wall boundary layers in an MHD duct. The effect of seed concentration, core temperature, wall temperature, boundary layer thickness and profile parameter on line shapes has been studied. It has been found that seed percentage is the major factor influencing the line shape parameters and core temperature is the major factor affecting the maximum radiated monochromatic line intensity.
 
Article
A nonlinear programming optimization problem is considered for the case in which the decision vector is the vector of zonal irradiation while the objective function is the equilibrium fuel feed rate with a CANDU-600 reactor subject to certain restrictions regarding the reactivity excess and the maximum powers per channel and bundle. The objective and restriction functions of the system are estimated within a time average approximation of a three-dimensional two-group diffusion type, with the control systems uniformly immersed within the reactor, and also considering the newest increments of the parasitic absorbents using FMDP program. The optimization problem is solved by means of the SUMT method, modified so as to become a technique of sequential solving for certain subproblems of linear optimization through the application of LPROG program. The results are presented as optimal vectors of zonal irradiation and as optimal values of fuel feed rate, with some two-zone cases, which establish the best zonal configuration. This configuration is then extended to a four-zone case which is analysed in a similar manner, evidencing a saving potential which gives the possibiliy of increasing the reactor performance.
 
Article
The exergy–enthalpy and temperature–exergy diagrams have been generated in the range 0.1–10 MPa and from the triple point to 500 K. These diagrams on the International Temperature Scale (ITS-90) have been generated using a calculation scheme proposed by Jacobsen et al. A computer program is developed for calculating the thermodynamic properties of nitrogen, including exergy as a property, from the triple point to 800 K at pressures up to 30 MPa. These exergy based thermodynamic property charts can be useful in the energy efficiency analyses of cryorefrigeration cycles involving nitrogen as a working medium. A sample analysis is included. © 1997 by John Wiley & Sons, Ltd.
 
Article
Hydrogen absorption behaviour of intermetallic absorbers strongly depends upon the contribution of the surface layers into the overall rate of the hydrogenation process. Activation process, which is normally required to initiate and facilitate the initial hydrogen uptake, may be waved by modifying the surface behaviour, thus offering obvious practical benefits. In the present work a surface nanoengineering approach was developed to enhance the hydrogenation ability of rare earth-containing AB5-type hydride-forming intermetallics. The modification involves three successive steps; (a) fluorination to form a surface-covering REF3 layer with a high specific surface area; (b) surface functionalization by γ-APTES; (c) deposition of Pd nanoparticles into the surface nanocavities of the fluoride. The surface functionalization step was applied to immobilize Pd nuclei inside the nanocavities of the REF3 layer. The deposited Pd nanoparticles exhibited a high degree of coalescence, and were further transformed into a continuous surface layer. Pd/fluoride modified materials exhibited exceptional Pd coating densities and imposed a large facilitation in the kinetics of hydrogenation compared with the conventional nonmodified intermetallics. The approach has a potential in the directed design of new classes of highly efficient and robust composite hydrogen sorption materials for hydrogen storage, separation and purification. Large improvements in the kinetics of hydrogenation of the Pd/fluoride modified intermetallics also manifested by extraordinary surface poisoning tolerance towards oxygen and water vapour, as compared with that of the nonmodified, or just fluorinated/Pd modified intermetallic alloys. The developed classes of highly efficient and robust composite hydrogen sorption materials have the potential for application as sorption media for the high efficiency hydrogen storage, separation and purification systems and may facilitate progress towards the implementation of the key elements of future hydrogen economy. Copyright © 2009 John Wiley & Sons, Ltd.
 
Article
Data collected from a single grow-out tank in an abalone farm in southern New Zealand has highlighted hygiene maintenance problems in the use of semi-closed water conditioning systems for the aquaculture of New Zealand black foot abalone Haliotis iris. The data shows that semi-closed systems can have high concentrations of un-ionized ammonia, which is harmful to the animals. In this paper an alternative open flow-through system is suggested where energy demand is limited by heat recovery at the grow-out tank outlet. Using temperature data collected over 1 year, and a previously obtained expression for standing losses, a simple energy model is presented for an open system with heat recovery. To compliment the energy model, a function has been established for abalone production with respect to the concentration of un-ionized ammonia and water temperature. The energy model and production function are combined to determine the impact of plant design and tank conditions on the economics of the operation for the southern New Zealand climate. It is demonstrated that temperature control is financially preferable to an open system with no temperature control, and estimates of optimum operating conditions are given. Copyright © 2004 John Wiley & Sons, Ltd.
 
Article
Twenty-six absorbent—refrigerant combinations, holding good promise as fluid systems, have been considered for single stage absorption air conditioning system. These fluids have been compared on the basis of solution characteristics, life expectancy characteristics and refrigeration cycle characteristics. The mass flow rates of rich and poor solutions per ton of refrigeration capacity and the coefficient of performance (CP) were compared for an evaporator temperature of 5°C, absorber and condenser temperatures of 35°C and a generator temperature of 120°C (low grade energy sources). More than half of the waste energy available in industry happens to be at a temperatures below 200°C. Other types of low grade thermal energy such as solar energy and geothermal energy can be used in operating vapour absorption refrigeration and air-conditioning systems.
 
Article
This paper presents an investigation on using an ammonia refrigerant with liquid/solid absorbents in an absorber heat recovery cycle where heat released during the absorption process is used to heat up the strong solution coming out of the absorber, thereby reducing the generator heat input and hence improving the coefficient of performance. A comparative thermodynamic study is made with NH3-H2O and NH3-LiNO3 pairs as working fluids for both conventional absorption and absorber heat recovery systems. It is found that an improvement of about 10 per cent in COP for the absorber heat recovery cycle is achieved over the conventional absorption cycle and the NH3-LiNO3 system yields a higher COP than for NH3-H2O over a wide range of generator temperatures and condenser/absorber temperatures. A detailed parametric study is also presented in this paper.
 
Article
The emission of toxic metals from the combustion of fossil fuels is an important global environmental issue. Solid absorbents can be used to control the emission of toxic trace elements from coal combustion. In this paper, limestone, CaSO4, bauxite, kaolinite and CaO are employed for this purpose and experiments are carried out in an electrically heated drop-tube furnace. The trace elements investigated are Pb, Cd, Cr and As. It is observed that the absorptive capacity is related to the qualities of the absorbents (type, amount and particle size) and the combustion temperature. The results also show that some absorbents can reduce SO2 emission simultaneously, but no influence on NOx emission. Copyright © 2001 John Wiley & Sons, Ltd.
 
Article
Spray-pyrolysed selective cobalt-oxide (CoOx) coatings were prepared on the surface of a bright nickel-plated copper tubular absorber (α = 0.89–0.91 and ϵ100°C = 0.18) for operation in conjunction with a prototype linear Fresnel reflector solar concentrator (LFRSC). Some preliminary tests were conducted to study the optical and thermal performance characteristics of the selective cobalt-oxide coated absorber in the concentrated solar flux. The tests conducted included determination of the overall heat loss coefficient UL of the absorber at temperatures from 50 to ∼ 120°C, and the optical efficiency ηo of the concentrator-absorber system, and measurement of the stagnation temperature of the absorber with the prototype solar concentrator. Based on the results of UL and ηo measurements, the thermal efficiency η of the concentrator-absorber system at a working temperature of 115°C has been determined for a typical beam radiation Ib of 600 W/m2. Further, comparison of the results of this study with those obtained using a dimensionally identical black-painted absorber indicates that the performance of the selective cobalt-oxide coated absorber is considerably superior to that of an ordinary black-painted absorber.
 
Article
Experiments have been carried out to determine the effect of absorber reflux on the performance of a water-lithium-bromide absorption cooler. The reflux ratio was varied for two mass flow rates of solution leaving the absorber and two absorber temperatures. It has shown that absorber reflux can be used to decrease both the temperature and the concentration in the generator. The coefficient of performance and heat loads tend to have optimum values at a particular reflux ratio.
 
Article
A simulation code was developed to predict the indirect solar dryer performance of the thin beds of discs of potato, subjected to time-varying air conditions. Two mathematical models are developed separately; the first allows the determination of the thermal performances of the solar collector with offset rectangular plate fin absorber-plate and the second, allows to determine the kinetics of drying for the data input of the air at the exit of the collector. The latter takes into account calorific losses through the walls of the dryer and shrinkage of discs. Experimental results of the solar dryer thermal performances, using sunlight in Valenciennes (in the North of France), will be compared with the results obtained by the theoretical model suggested. Copyright © 2005 John Wiley & Sons, Ltd.
 
Article
Two different approaches for designing a linear Fresnel reflector solar concentrator (LFRSC) with a flat horizontal absorber are described. The performance characteristics of both the designs are studied in detail. The distribution of local concentration ratio on the surface of the absorber, for each design, is investigated using the ray trace technique. Results of some typical numerical calculations are presented graphically and discussed.
 
Article
The aim of this study is to provide a remedy for the low thermophysical properties of air, which is used as a fluid of transfer in solar collectors. A fully developed flow needs to be created by the use of staggered fin rows soldered under the absorber plate. The fluid flow undergoes contractions followed by expansions, which creates a fully developed turbulent flow, and increases the thermal heat transfer between the absorber plate and the air. The fins increase the heat transfer surface, from which an appreciable improvement of the thermal heat performance of solar air heaters has been found in comparison to those of solar air heaters with a plane absorber. In this work we have tested the influence of the dimension of the fins and the influence of the space between consecutive fin rows mounted in staggered rows.
 
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