Showing papers in "International Journal of Energy Research in 2008"

Renewable hydrogen production

Abstract: The U.S. Department of Energy and the National Renewable Energy Laboratory are developing technologies to produce hydrogen from renewable, sustainable sources. A cost goal of $2.00–$3.00 kg−1 of hydrogen has been identified as the range at which delivered hydrogen becomes cost competitive with gasoline for passenger vehicles. Electrolysis of water is a standard commercial technology for producing hydrogen. Using wind and solar resources to produce the electricity for the process creates a renewable system. Biomass-to-hydrogen processes, including gasification, pyrolysis, and fermentation, are less well-developed technologies. These processes offer the possibility of producing hydrogen from energy crops and from biomass materials such as forest residue and municipal sewage. Solar energy can be used to produce hydrogen from water and biomass by several conversion pathways. Concentrated solar energy can generate high temperatures at which thermochemical reactions can be used to split water. Photoelectrochemical water splitting and photobiology are long-term options for producing hydrogen from water using solar energy. All these technologies are in the development stage. Copyright © 2007 John Wiley & Sons, Ltd.

Green electricity production with living plants and bacteria in a fuel cell

Abstract: SUMMARY The world needs sustainable, efficient, and renewable energy production. We present the plant microbial fuel cell (plantMFC), a concept that exploits a bioenergy source in situ. In the plant-MFC, plants and bacteria were present to convert solar energy into green electricity. The principal idea is that plants produce rhizodeposits, mostly in the form of carbohydrates, and the bacteria convert these rhizodeposits into electrical energy via the fuel cell. Here, we demonstrated the proof of principle using Reed mannagrass. We achieved a maximal electrical power production of 67 mW m � 2 anode surface. This system was characterized by: (1) nondestructive, in situ harvesting of bioenergy; (2) potential implementation in wetlands and poor soils without competition to food or conventional bioenergy production, which makes it an additional bioenergy supply; (3) an estimated potential electricity production of 21 GJ ha � 1 year � 1 ð5800 kWh ha � 1 year � 1 Þ in Europe; and (4) carbon neutral and combustion emission-free operation. Copyright # 2008 John Wiley & Sons, Ltd.

Microbial fuel cells based on carbon veil electrodes: Stack configuration and scalability

Abstract: SUMMARY The aim of this study was to compare the performance of three different sizes of microbial fuel cell (MFC) when operated under continuous flow conditions using acetate as the fuel substrate and show how small-scale multiple units may be best configured to optimize power output. Polarization curve experiments were carried out for individual MFCs of each size, and also for stacks of multiple small-scale MFCs, in series, parallel and series–parallel configurations. Of the three combinations, the series–parallel proved to be the more efficient one, stepping up both the voltage and current of the system, collectively. Optimum resistor loads determined for each MFC size during the polarization experiments were then used to determine the long-term mean power output. In terms of power density expressed as per unit of electrode surface area and as per unit of anode volume, the small-sized MFC was superior to both the medium- and large-scale MFCs by a factor of 1.5 and 3.5, respectively. Based on measured power output from 10 small units, a theoretical projection for 80 small units (giving the same equivalent anodic volume as one large 500 mL unit) gave a projected output of 10 W m � 3 , which is approximately 50 times higher than the recorded output produced by the large MFC. The results from this study suggest that MFC scale-up may be better achieved by connecting multiple small-sized units together rather than increasing the size of an individual unit. Copyright r 2008 John Wiley & Sons, Ltd.

Exergy analysis of a 420 MW combined cycle power plant

Abstract: 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 © 2007 John Wiley & Sons, Ltd.

Latent heat storage above 120°C for applications in the industrial process heat sector and solar power generation

Abstract: This paper is focussed on thermal storage technologies using phase change materials (PCMs) in the temperature range of 120-300 °C for solar thermal power generation and high temperature process heat. As state-of-the-art reference system a steam accumulator is described, which typically has a volume-specific thermal energy density of 20-30 kWh/m³. Regarding efficiency, a fundamental demand on thermal storage is the minimization of temperature differences between working fluid and storage medium. This requires isothermal storage systems for processes using water/steam. An obvious solution is, therefore, the application of PCMs. The selection of the PCMs depends strongly on the operation conditions of the respective application. At present, the main emphasis is directed to alkali metal nitrates and nitrites and their mixtures. For example, the eutectic mixture of the binary system KNO3-NaNO3 has been identified as an excellent system to be used for processes using saturated steam at around 25 bar. At around 5 bar the ternary system KNO3-NaNO2-NaNO3, commonly used as heat transfer fluid, can also be used as a PCM. To overcome the low thermal conductivity of the salt systems, approaches of increased surfaces area and increased thermal conductivity using expanded graphite (EG) have been investigated. Using EG/PCM-composites the effective thermal conductivity can be increased from below 0.5 W/(mK) to 3-20 W/(mK). Three design concepts have been developed. In the macro-encapsulated design, the PCM is enclosed in metal tubes, giving a short distance for heat transfer and increasing the heat transfer area. In the second design, the heat exchanger tubes are embedded in EG/PCM-composite storage material. The third design option uses graphite foils arranged perpendicularly onto the heat exchanger tubes and a suitable salt system filled in between. The upgrade of existing steam accumulators using these PCM concepts is also proposed.

Determination of the enthalpy of PCM as a function of temperature using a heat-flux DSC—A study of different measurement procedures and their accuracy

Abstract: Thermal energy storage by latent heat allows storing high amounts of energy working in narrow margins of temperature. The use of phase change material (PCM) for the latent heat storage has been studied in different applications and it has been commercialized in containers to transport blood, products sensible to temperature, to decrease their energy demand. The use of PCM in cooling and refrigeration has been attracting a lot of interest lately, but for all applications, the properties of these materials need to be known with sufficient accuracy. Regarding heat storage, it is necessary to know the enthalpy as a function of temperature. The most widely used calorimeter is the heatflux differential scanning calorimetry (hf-DSC). The objective of this study is to investigate different methods for hf- DSC analysis, namely the dynamic method and the step method, and to test their accuracy in the determination of enthalpy–temperature relationship of PCM. For the dynamic method, a strong influence of heating/cooling rate was observed. For the step method, the resulting enthalpy–temperature relationship is independent of heating/cooling rate. Commercial PCM RT27 was chosen as sample material to avoid subcooling and kinetic effects in the test measurements. The approach introduced in this study can be used to carry out similar investigations for other classes of PCM and/or other DSC instruments.

Effect of energy storage medium (black granite gravel) on the performance of a solar still

Abstract: In this study, a detailed experiment has been conducted on a single-basin solar still which is modified with energy storage medium of black granite gravel. An attempt has been made to utilize the maximum amount of solar energy and to reduce the heat loss from the sides and bottom of the still. The conventional still is modified with an energy storage medium of black granite gravel of 6 mm size which is provided in the basin for different (quantity) depths. The black granite gravel functions as energy storage medium and also as an insulation layer to reduce the bottom and side loss coefficients. The black gravel is used for absorbing the excess heat energy from solar radiation during the noon hours. Due to this, the heat accumulated in the space between the water and glass surface is reduced and hence the temperature difference between the water and glass surfaces increases. The depth (quantity) of the gravel layer in the basin will influence the performance of the still and some of the parameters like basin temperature, water temperature, glass temperature and still productivity. This study deals with the effect of aforesaid parameters on the performance of the still. An attempt has been made to optimize the still performance for the above-mentioned parameters. A mathematical model is developed to estimate the water, gravel, and inside glass temperatures theoretically and to estimate the hourly and daily yield. To show the effectiveness of the modification, its performance is compared with the conventional still under the same climatic condition. It is found that the still yield is increased by 17-20% with almost no cost for this modification as black granite gravel is very cheap. Error analysis was done by comparing the theoretical and experimental results to show the validity of the mathematical model. It is found that the maximum percentage of discrepancy for all the parameters is about ±18%. Theoretical value of yield per day has 8% discrepancy over experimental value.

Experimental investigations on single stage, two stage and three stage conventional savonius rotor

Abstract: The performance of single stage (rotor aspect ratio of 1.0), two stage Savonius rotor with rotor aspect ratios of 1.0 and 2.0 (stage aspect ratios of 0.50 and 1.0) and three stage Savonius rotor with rotor aspect ratios of 1.0 and 3.0 (stage aspect ratios of 0.33 and 1.0) are studied at different Reynolds numbers and compared at the same Reynolds number. The results show that the coefficient of power and the coefficient of torque increase with the increase in the Reynolds numbers for all the rotors tested. The coefficient of static torque is independent of the Reynolds number for all the rotors tested. The performance of two stage and three stage rotors remains the same even after increasing the stage aspect ratio and the rotor aspect ratio by a factor of two and three, respectively. For the same rotor aspect ratio of 1.0, by increasing the number of stages (stage aspect ratio decreases), the performance deteriorates in terms Cp and Ct. However, at the same stage aspect ratio of 1.0 and same Reynolds number, two and three stage rotors show the same performance in terms of coefficient of power and coefficient of torque. The variation in coefficient of static torque is lower for a three stage rotor when compared with the variation of coefficient of static torque for two stage or single stage rotor. Copyright © 2008 John Wiley & Sons, Ltd.

Status and development of PEM fuel cell technology

Abstract: Fuel cells are an emerging technology with applications in transportation, stationary and portable power generation, with outputs ranging from mW to MW. The most promising and most widely researched, developed and demonstrated type of fuel cells is proton exchange membrane (PEM) fuel cell. State of the art in PEM fuel cell technology and challenges in their development and widespread applications are discussed. Copyright © 2007 John Wiley & Sons, Ltd.

Optimal location of wood gasification plants for methanol production with heat recovery

Abstract: Second generation biofuels from wood gasification are thought to become competitive in the face of effective climate and energy security policies. Cost competitiveness crucially depends on the opti ...

A grey-box model of next-day building thermal load prediction for energy-efficient control

Abstract: Accurate building thermal load prediction is essential to many building energy control strategies. To get reliable prediction of the hourly building load of the next day, air temperature/relative humidity and solar radiation prediction modules are integrated with a grey-box model. The regressive solar radiation module predicts the solar radiation using the forecasted cloud amount, sky condition and extreme temperatures from on-line weather stations, while the forecasted sky condition is used to correct the cloud amount forecast. The temperature/relative humidity prediction module uses a dynamic grey model (GM), which is specialized in the grey system with incomplete information. Both weather prediction modules are integrated into a building thermal load model for the on-line prediction of the building thermal load in the next day. The validation of both weather prediction modules and the on-line building thermal load prediction model are presented. Copyright © 2008 John Wiley & Sons, Ltd.

Exergoeconomic analysis of a combined heat and power (CHP) system

Abstract: This study deals with exergoeconomic analysis of a combined heat and power (CHP) system along its main components installed in Eskisehir City of Turkey. Quantitative exergy cost balance for each component and the whole CHP system is considered, while exergy cost generation within the system is determined. The exergetic efficiency of the CHP system is obtained to be 38.33% with 51 475.90 kW electrical power and the maximum exergy consumption between the components of the CHP system is found to be 51 878.82 kW in the combustion chamber. On the other hand, the exergoeconomic analysis results indicate that the unit exergy cost of electrical power produced by the CHP system accounts for 18.51 US$ GW−1. This study demonstrates that exergoeconomic analysis can provide extra information than exergy analysis, and the results from exergoeconomic analysis provide cost-based information, suggesting potential locations for the CHP system improvement. Copyright © 2007 John Wiley & Sons, Ltd.

An examination of exergy destruction in organic Rankine cycles

Abstract: The exergy topological method is used to present a quantitative estimation of the exergy destroyed in an organic Rankine cycle (ORC) operating on R113. A detailed roadmap of exergy flow is presented using an exergy wheel, and this visual representation clearly depicts the exergy accounting associated with each thermodynamic process. The analysis indicates that the evaporator accounts for maximum exergy destroyed in the ORC and the process responsible for this is the heat transfer across a finite temperature difference. In addition, the results confirm the thermodynamic superiority of the regenerative ORC over the basic ORC since regenerative heating helps offset a significant amount of exergy destroyed in the evaporator, thereby resulting in a thermodynamically more efficient process. Parameters such as thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy-based design of devices. This paper also examines the impact of operating parameters such as evaporator pressure and inlet temperature of the hot gases entering the evaporator on ORC performance. It is shown that exergy destruction decreases with increasing evaporator pressure and decreasing turbine inlet temperatures. Finally, the analysis reveals the potential of the exergy topological methodology as a robust technique to identify the magnitude of irreversibilities associated with real thermodynamic processes in practical thermal systems. Copyright © 2008 John Wiley & Sons, Ltd.

Capric acid and stearic acid mixture impregnated with gypsum wallboard for low-temperature latent heat thermal energy storage

Abstract: A novel form-stable phase change wallboard (PCW) was prepared for low-temperature latent heat thermal energy storage by incorporating eutectic mixture of capric acid and stearic acid and gypsum wallboard. Thermal properties of form-stable PCW were measured by DSC analysis. The form-stable PCW has good thermal reliability with respect to the changes in its thermal properties after accelerated thermal cycling. Thermal performance test indicated that the use of such a type of PCW can decrease indoor air temperature fluctuation due to absorption of heat by the eutectic phase change material. Copyright © 2007 John Wiley & Sons, Ltd.

A review on macro-level modeling of planar solid oxide fuel cells

Abstract: In this review paper, a comprehensive literature survey on macro-level modeling of solid oxide fuel cells (SOFCs) is presented. First, the current status of the SOFC modeling is assessed. Second, modeling techniques are discussed in detail. These include the thermodynamics, electrochemistry and heat transfer aspects of the modeling. Thermodynamic relations for pure hydrogen as the fuel and then gas mixture as the fuel are given. Additionally, exergy destructed due to polarizations is shown. Then, modeling equations for ohmic, activation, and concentration polarizations are given. Handling the carbon deposition problem in the modeling is discussed. The inclusion of the convection and radiation heat transfer processes to the modeling is explained. Finally, the models in literature are compared in terms of the methodology used and suggestions for increasing the accuracy of the future models are given. Copyright © 2007 John Wiley & Sons, Ltd.

An experimental study of hybrid photovoltaic thermal (PV/T)‐active solar still

Abstract: SUMMARY In this paper a new self-sustainable hybrid photovoltaic thermal (PV/T)-integrated-active solar still has been designed and tested for composite climate at I.I.T. New Delhi (28832 0 N; 77812 0 E). The PV system is used to generate electricity to run the pump (60 W and 18 V) as well as thermal energy to heat the water in the collector. The proposed design of hybrid-active solar still can be used at any remote location because of its self-sustainability. The experiments were performed on the set-up for different water depths and for different running duration of the pump. It has been observed that the hybrid-active solar still gives a higher yield (more than 3.5 times) than the passive solar still. It has also been observed that the daily distillate yield and thermal efficiency of the hybrid-active solar still remain almost the same for all water depths in the basin by reducing the daily running period of the pump from 9 to 5 h. This running period of the pump reduced saves 43% of the power used to run the pump with 9 h running, without affecting the performance of the solar still. This work also deals with exergy analysis of the system. Copyright # 2008 John Wiley & Sons, Ltd.

High-temperature thermal stability of molten salt materials

Abstract: This paper focuses on thermal stability of molten salts consisting of potassium nitrate, sodium nitrite, sodium nitrate and one kind of additives such as A, B and C at a high temperature. The multi-component molten salts were prepared by mixing the pure salts, heating statically to the melting state and then cooling to room temperature to form the mixed molten salts. The stability experiments were carried out at 500 and 550°C, and the experiment found that the molten salt with 5% additive A performed better high-temperature thermal stability and its optimum operating temperature was increased to 550 from 500°C. XRD and DSC analyses indicated that the molten salt with 5% additive A had a lower freezing point and a higher phase change latent heat. Besides, the concentration of NO 2 anion in the molten salt was analyzed and the results showed that the main reaction for the molten salts in air was nitrite thermal oxidation at 500 and 550°C. In addition, the energy used for the oxidation of nitrite would be increased with an increase in additives and the prolonging of reaction time at the same time.

Spray properties of alternative fuels: A comparative analysis of biodiesel and diesel

Abstract: Physical properties of biodiesel play an important role in the injection, atomization and combustion performance. An experiment was carried out to investigate the spray properties of biodiesel. The experimental setup was based on an electronic unit-pump (EUP) bench, a constant volume chamber and a high-speed digital camera. The photographs of spray were dealt with by using an image processing procedure. Then the spray tip penetrations and cone angles were obtained and analyzed. The experimental results indicate that the spray tip penetrations and cone angles of biodiesel increase with increasing injection duration. In addition, with decreasing ambient pressure the spray tip penetrations increase while the cone angles decrease. Furthermore, ambient pressure has a stronger effect on the spray properties of biodiesel than injection pressure. On the macroscopically view, the shape of biodiesel spray is similar to that of diesel. The final tip penetrations and cone angles of biodiesel are greater than those of diesel due to its higher viscosity, density and bulk modulus. Copyright © 2008 John Wiley & Sons, Ltd.

Development of an optimization model for energy systems planning in the Region of Waterloo

Abstract: In this study, a large-scale dynamic optimization model (University of Regina Energy Model, UREM) has been developed for supporting long-term energy systems planning in the Region of Waterloo. The model can describe energy management systems as networks of a series of energy flows, transferring extracted/imported energy resources to end users through a variety of conversion and transmission technologies over a number of periods. It can successfully incorporate optimization models, scenario development and policy analysis within a general framework. Complexities in energy management systems can be systematically reflected; thus, the applicability of the modeling process can be highly enhanced. Four scenarios (including a reference case) are considered based on different energy management policies and sustainable development strategies for in-depth analysis of interactions existing among energy, socio-economy and environment in the Region. Useful solutions for the planning of energy management systems have been generated, reflecting trade-offs among energy-related, environmental and economic considerations. They are helpful for supporting (a) adjustment or justification of the existing allocation patterns of energy resources and services, (b) allocations of renewable energy resources, (c) formulation of local policies regarding energy consumption, economic development and energy structure, and (d) analysis of interactions among economic cost, system efficiency, emission mitigation and energy-supply security. Results also indicate that UREM can help tackle dynamic and interactive characteristics of the energy management system in the Region of Waterloo and can address issues concerning cost-effective allocation of energy resources and services. Thus, it can be used by decision makers as an effective technique in examining and visualizing impacts of energy and environmental policies, regional/community development strategies and emission reduction measures within an integrated and dynamic framework. Copyright © 2008 John Wiley & Sons, Ltd.

Efficient design of feedwater heaters network in steam power plants using pinch technology and exergy analysis

Abstract: A design method is presented based on pinch technology and exergy analysis to reduce heat transfer irreversibility of the feedwater heaters network in steam power plants. In order to show the effects of this method, an extensive study was performed on four steam power plants. The results show that applying this method can decrease the fuel consumption and the condenser load. It also increases the boiler, the feedwater heaters network, and the turbine exergetic efficiencies. On the whole, the results show that applying this method, with a target pinch temperature of 3°C, increases the cycle 2nd law efficiency 0.3–1.3% and the fossil fuel consumption decreases about 64 × 106kg annually for 8000 operating hours per year of the studied steam power plants. Copyright © 2007 John Wiley & Sons, Ltd.

A model on CO2 emission reduction in integrated steelmaking by optimization methods

Abstract: The iron and steel industry is a large energy user in the manufacturing sector. Carbon dioxide from the steel industry accounts for about 5-7% of the total anthropogenic CO2 emission. Concerns abou ...

Cycle improvements to ejector‐expansion transcritical CO2 two‐stage refrigeration cycle

Abstract: In this paper, a new configuration of ejector-expansion transcritical CO2 (TRCC) refrigeration cycle is presented, which uses an internal heat exchanger and intercooler to enhance the performance of the new cycle. The theoretical analysis on the performance characteristics was carried out for the new cycle based on the first and second laws of thermodynamics. It was found that, compared with the conventional transcritical CO2 cycle and ejector-expansion transcritical CO2 cycle, the simulation results show that the coefficient of performance and second law efficiency of the new cycle were increased by about 55.5 and 26%, respectively, under the operating conditions that evaporator temperature is 10°C, gas cooler outlet temperature is 40°C and gas cooler pressure is optimum pressure. It is also concluded that the entrainment ratio for the new ejector-expansion TRCC cycle is on average 35% higher than that of the conventional ejector-expansion TRCC cycle. The analysis results are of significance to provide theoretical basis for design optimization of the transcritical CO2 refrigeration cycle with an ejector-expansion device, internal heat exchanger and intercooler. Copyright © 2007 John Wiley & Sons, Ltd.

Thermoeconomic modeling of micro‐CHP (micro‐cooling, heating, and power) for small commercial applications

Abstract: The increasing demand for electrical power as well as energy for heating and cooling of residences and small commercial buildings is a growing worldwide concern. Micro-cooling, heating, and power (micro-CHP), typically designated as less than 30 kW electric, is decentralized electricity generation coupled with thermally activated components for residential and small commercial applications. The number of combinations of components and parameters in a micro-CHP system is too many to be designed through experimental work alone. Therefore, theoretical models for different micro-CHP components and complete micro-CHP systems are needed to facilitate the design of these systems and to study their performance. This paper presents a model for micro-CHP systems for residential and small commercial applications. Some of the results that can be obtained using the developed model include the cost per month of operation of using micro-CHP versus conventional technologies, the amount of fuel per month required to run micro-CHP systems, the overall efficiency of micro-CHP systems, etc. A case study is used to demonstrate differences in the system performances of micro-CHP systems driven by a natural gas internal combustion engine and a diesel engine. Some of the results show that both systems have similar performance and that system total efficiencies in cooler months of up to 80% could be obtained. Also, modeling results show that there is a limit in fuel price that economically prevents the use of CHP systems, which is $11 MBTU−1 for this specific case. Copyright © 2008 John Wiley & Sons, Ltd.

Thermodynamic analysis of steam reforming of ethanol for hydrogen generation

Abstract: Thermodynamic equilibrium of ethanol steam reforming has been studied by Gibbs free energy minimization method for hydrogen production in the ranges of water-to-ethanol ratio from 0 to 20, reaction temperature from 400 to 2000 K, pressure from 1 to 60 atm, argon-to-ethanol ratio from 0 to 100. The optimal conditions suitable for the use in molten carbonate fuel cell and solid oxide fuel cell were obtained as follows: 900–1200 K, water-to-ethanol ratio of 3:6, and 1 atm. Under the optimal conditions, complete conversion of ethanol, 60.52–83.58% yield of hydrogen and 32.82–79.60% yield of carbon monoxide could be obtained and no coke forms. Higher pressures have a negative effect, but inert gases have a positive effect, on the hydrogen yield. Coke tends to form at lower temperatures and lower water-to-ethanol ratios. Copyright © 2008 John Wiley & Sons, Ltd.

Optimal geometry and flow arrangement for minimizing the cost of shell‐and‐tube condensers

Abstract: This paper presents a model for estimating the total cost of shell-and-tube heat exchangers (HEs) with condensation in tubes or in the shell, as well as a designing strategy for minimizing this cost. The optimization process is based on a genetic algorithm. The global cost includes the energy cost (i.e. pumping power) and the initial purchase cost of the exchanger. The choice of the best exchanger is based on its annualized total cost. Eleven design variables are optimized. Ten are associated with the HE geometry: tube pitch, tube layout patterns, baffle spacing at the center, baffle spacing at the inlet and outlet, baffle cut, tube-to-baffle diametrical clearance, shell-to-baffle diametrical clearance, tube bundle outer diameter, shell diameter, and tube outer diameter. The last design variable indicates whether the condensing fluid should flow in the tubes or in the shell. Two case studies are presented and the results obtained show that the procedure can rapidly identify the best design for a given heat transfer process between two fluids, one of which is condensing. Copyright © 2008 John Wiley & Sons, Ltd.

Techno‐economic study on compact heat exchangers

Abstract: Compact heat exchangers (CHEs), including plate-fin, plate and spiral plate heat exchangers, are widely used in many thermal process systems. Under certain operating condition, the optimal heat exchanger with lowest cost and highest efficiency becomes the ultimate objective pursued by engineers and researchers. In addition, an economic evaluation can also possess a major impact on the selection of technical solution and project profitability. Therefore,it is important to use a proper techno-economic approach that may give enough references to choose an appropriate alternative. This paper gives an overview of the most common methods used in the techno-economic analysis of heat exchangers. Based on the optimum designs with the objective of minimum pressure drop, an optimal CHE is selected from the technical and economic standpoints. The material purchasing, equipment abrasion and power consumption have been considered comprehensively.

Performance and exergetic analysis of vapor compression refrigeration system with an internal heat exchanger using a hydrocarbon, isobutane (R600a)

Abstract: Hydrocarbons (HCs) are excellent refrigerants in many ways such as energy efficiency, critical point, solubility, transport and heat transfer properties, but they are also flammable, which causes the need for changes in standards, production and product. There are increasing number of scientists and engineers who believe that an alternative solution, which has been overlooked, may be provided by using HCs. The main objective of this study is to perform energy and exergy analyses for a vapor compression refrigeration system with an internal heat exchanger using a HC, isobutene (R600a). For a refrigeration capacity of 1 kW and cold chamber temperature of 0°C, energy and exergy balances are taken into account to determine the performance of the refrigeration system. Energy and exergy fluxes are determined, and irreversibility rates are calculated for every component of the system. It is seen that the compressor has the highest irreversibility rate, and the heat exchanger has the lowest. Also from the result of the analysis, it is found that condenser and evaporator temperatures have strong effects on energetic and exergetic performances of the system such as coefficient of performance (COP), efficiency ratio (τ), exergetic efficiency (ξ) and irreversibility rate. Copyright © 2008 John Wiley & Sons, Ltd.

A sustainable energy future: Construction of demand and renewable energy supply scenarios

Abstract: The creation of energy scenarios, usually describing future situations of interest, involves three steps: (1) Determining the activities in the target society that involves energy of one or another form. Examples of carrying out such an analysis are presented, with end-use demands distributed on energy forms (qualities) as the deliverable outcome. (2) Determining the available energy resources in the society in question. This is done for renewable energy resources and presented as potential energy supply, with a discussion of the aggressivity of exploiting such sources. Finally (3) Matching demand and supply under consideration of the energy forms needed, with the use of intermediate conversions, storage and transmission and signalling unused surpluses that may be exported from the society in consideration, or deficits that have to be imported. An example of such a matching is presented in an accompanying article. Copyright © 2007 John Wiley & Sons, Ltd.

Improving the efficiency of pyroelectric conversion

Abstract: Pyroelectric conversion utilizes low-grade waste heat as a heat source, and thus produces clean energy. Low-grade heat is abundant in the various industries and it is practically free. It can be converted to high-voltage electricity by pyroelectric conversion. Our pyroelectric converter uses copolymer of poly-vinylidene fluoride with trifluoroethylene [60/40% P(VDF-TrFE)]. Previously, we encountered a substantial power loss due to internal leakage at high temperature and voltage. In order to increase the power output, we examined the effect of polymer purification using solvent extraction. We compared the electrical properties of purified copolymer with those of 'as-received' copolymer. Although we removed only 0.4wt% of the copolymer by solvent extraction, the electrical resistivity of purified copolymer was 35% higher than that of the 'as-received' copolymer. We also observed that thin films produced using purified copolymer were able to withstand 50% higher electric field before they were ruined by the electrical short circuit. Subsequently, we conducted pyroelectric conversion using 25 μm thick 60-40% P(VF 2 -TrFE) copolymer films. Copolymer purification resulted in a three-fold increase in net power output. Net power output per unit volume of the 'as-received' copolymer was 95 J L -1 but it increased to 279 J L -1 for purified copolymer. © Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2007.

Potential applications using LNG cold energy in Sicily

Abstract: According to previsions, natural gas could be the main energy source worldwide, inducing relevant geopolitical changes. Most likely, such problems will be solved with the development of a gas transportation mode alternative to traditional pipelines: liquefied natural gas (LNG). The global LNG trade has increased rapidly during recent years. A significant amount of energy is consumed to produce low-temperature LNG, which has plenty of cryogenic exergy/energy. Therefore, the effective utilization of the cryogenic energy associated with LNG vaporization is very important. Sicily, with more than five million inhabitants, is the second biggest region of Italy and in this region will be realized two of the 11 gasification plants planned in Italy according to the regional energy master-plan. This paper shows some interesting applications for the cold produced in gasification plants, e.g. for seawater desalination and for fresh and frozen food production and conservation. These applications seem very interesting for Sicilian situation and also can contribute to energy saving and greenhouse gases reduction to match Kyoto Protocol targets. Copyright © 2008 John Wiley & Sons, Ltd.