Showing papers in "International Journal of Energy Research in 2003"
TL;DR: In this paper, the authors applied this property to the enhancement of boiling heat transfer and found that a surface coated with TiO2 exhibits an extremely high affinity for water when exposed to UV light and the contact angle decreases nearly to zero.
Abstract: Titanium Dioxide, TiO2, is a photocatalyst with a unique characteristic. A surface coated with TiO2 exhibits an extremely high affinity for water when exposed to UV light and the contact angle decreases nearly to zero. Inversely, the contact angle increases when the surface is shielded from UV. This superhydrophilic nature gives a self-cleaning effect to the coated surface and has already been applied to some construction materials, car coatings and so on. We applied this property to the enhancement of boiling heat transfer. An experiment involving the pool boiling of pure water has been performed to make clear the effect of high wettability on heat transfer characteristics. The heat transfer surface is a vertical copper cylinder of 17 mm in diameter and the measurement has been done at saturated temperature and in a steady state. Both TiO2-coated and non-coated surfaces were used for comparison. In the case of the TiO2-coated surface, it is exposed to UV light for a few hours before experiment and it is found that the maximum heat flux (CHF) is about two times larger than that of the uncoated surface. The temperature at minimum heat flux (MHF) for the superhydrophilic surface is higher by 100 K than that for the normal one. The superhydrophilic surface can be an ideal heat transfer surface. Copyright © 2002 John Wiley & Sons, Ltd.
200 citations
TL;DR: In this article, the usefulness of exergy analysis in providing insights into the behavior and performance of thermal energy storage (TES) systems, by providing an overview of many investigations by the authors on this topic.
Abstract: The usefulness is illustrated of exergy analysis in providing insights into the behaviour and performance of thermal energy storage (TES) systems, by providing an overview of many investigations by the authors on this topic. Several topics are covered. First, exergy analysis is described and thermodynamic considerations in TES evaluation are discussed. Then, the exergy analysis of a closed TES system is detailed, highlighting two critical factors: appropriate TES efficiency measures and the importance of temperature in TES evaluations. Next, applications of exergy to several TESs are discussed, including aquifer systems, stratified storages and cold TES. Finally, uses of exergy methods in optimization and design are illustrated by determining optimal discharge periods. Copyright © 2003 John Wiley & Sons, Ltd.
149 citations
TL;DR: In this paper, an analytical and experimental studies were performed on a directexpansion solar-assisted heat pump (DX-SAHP) water heating system, in which a 2 m2 bare flat collector acts as a source as well as an evaporator for the refrigerant.
Abstract: Analytical and experimental studies were performed on a direct-expansion solar-assisted heat pump (DX-SAHP) water heating system, in which a 2 m2 bare flat collector acts as a source as well as an evaporator for the refrigerant. A simulation model was developed to predict the long-term thermal performance of the system approximately. The monthly averaged COP was found to vary between 4 and 6, while the collector efficiency ranged from 40 to 60%. The simulated results were used to obtain an optimum design of the system and to determinate a proper strategy for system operating control. The effect of various parameters, including solar insolation, ambient temperature, collector area, storage volume and speed of compressor, had been investigated on the thermal performance of the DX-SAHP system, and the results had indicated that the system performance is governed strongly by the change of solar insolation, collector area and speed of compressor. The experimental results obtained under winter climate conditions were shown to agree reasonably with the computer simulation. Copyright © 2003 John Wiley & Sons, Ltd.
123 citations
TL;DR: In this article, a mathematical PEM fuel cell model is developed that simulates both CO poisoning and oxygen bleeding, and obtains excellent agreement with published, experimental data, indicating that CO adsorption and desorption follow a Temkin model.
Abstract: Fuel gas containing carbon monoxide severely degrades the performance of a polymer electrolyte membrane (PEM) fuel cell. However, CO poisoning can be mitigated by introducing oxygen into the fuel (oxygen bleeding). A mathematical PEM fuel cell model is developed that simulates both CO poisoning and oxygen bleeding, and obtains excellent agreement with published, experimental data. Modelling efforts indicate that CO adsorption and desorption follow a Temkin model. Increasing operating pressure or temperature mitigates CO poisoning, while use of reformate fuel increases the severity of the poisoning effect. Although oxygen bleeding mitigates CO poisoning, an unrecoverable performance loss exists at high current densities due to competition for reaction sites between hydrogen adsorption and the heterogeneous catalysis of CO. Copyright © 2003 John Wiley & Sons, Ltd.
110 citations
TL;DR: In this paper, the steady state natural convection in a square porous enclosure using a thermal non-equilibrium model for the heat transfer between the fluid and the solid phases is studied.
Abstract: The aim of the present paper is to study the steady state natural convection in a square porous enclosure using a thermal non-equilibrium model for the heat transfer between the fluid and the solid phases. The analysis assumes that the porous medium is homogeneous and isotropic. The present study also assumes the non-Darcy model of natural convection in porous media. It is assumed that the heat generation is only in solid phase. Two dimensional steady convection in a cavity bounded by isothermal walls at constant temperatures has been studied numerically by adopting a two-temperature model of microscopic heat transfer. Such a model. which allows the fluid and solid phases not to be in local thermal equilibrium, is found to modify the flow behaviour and heat transfer rates. Knowledge of this behaviour is very important for the design of the many engineering applications.
99 citations
TL;DR: In this paper, a two-zone model for the calculation of the closed cycle of a direct injection (DI) diesel engine is presented, where the cylinder contents are taken to comprise a non-burning zone of air and another homogeneous zone in which fuel is continuously supplied from the injector holes during injection and burned with entrained air from the air zone.
Abstract: A two-zone model for the calculation of the closed cycle of a direct injection (DI) diesel engine is presented. The cylinder contents are taken to comprise a non-burning zone of air and another homogeneous zone in which fuel is continuously supplied from the injector holes during injection and burned with entrained air from the air zone. The growth of the fuel spray zone, consisting of a number of fuel–air conical jets equal to the injector nozzle holes, is carefully modelled by incorporating jet mixing to determine the amount of oxygen available for combustion. Application of the mass, energy and state equations in each one of the two zones yields local temperatures and cylinder pressure histories. For calculating the concentration of constituents in the exhaust gases, a chemical equilibrium scheme is adopted for the C–H–O system of the 11 species considered, together with chemical rate equations for the calculation of nitric oxide (NO). A model for the evaluation of soot formation and oxidation rates is incorporated. A comparison is made between the theoretical results from the computer program implementing the analysis, with experimental results from a vast experimental investigation conducted on a fully automated test bed, direct injection, standard ‘Hydra’, diesel engine located at the authors' laboratory, with very good results, following a multi-parametric study of the constants incorporated in the various sub-models. Pressure indicator diagrams and plots of temperature, NO, soot density and of other interesting quantities are presented as a function of crank angle, for various loads and injection timings, elucidating the physical mechanisms governing combustion and pollutants formation. Copyright © 2003 John Wiley & Sons, Ltd.
96 citations
TL;DR: In this article, simple models have been presented to evaluate the performance of rotary desiccant wheels based on different kind of solid desiccants e.g. silica gel and LiCl.
Abstract: In the present communication, simple models have been presented to evaluate the performance of rotary desiccant wheels based on different kind of solid desiccants e.g. silica gel and LiCl. The first part of the paper presents ‘Model 54’ which is developed for silica gel desiccant rotor. The model has been derived from the interpolation of experimental data obtained from the industry and the correlations have been developed for predicting outlet temperature and absolute humidity. The ‘Model 54’ consists of 54 coefficients corresponding to each correlation for outlet absolute humidity and temperature and it is found that the model predicts very well the performance of silica gel desiccant rotor (Type-I). In the second part of the paper, a psychrometric model has been presented to obtain relatively simple correlations for outlet temperature and absolute humidity. The developed psychometric model is based on the correlations between the relative humidity and enthalpy of supply and regeneration air streams. The model is used to predict the performance of three type of desiccant rotors manufactured by using different kind of solid desiccants (Type I, II and III). The model is tested corresponding to a wide range of measurement data. The developed psychometric model is simple in nature and able to predict very well the performance of different kind of desiccant rotors. Copyright © 2002 John Wiley & Sons, Ltd.
78 citations
TL;DR: In this article, a comparative numerical study is employed to investigate the heat and mass transfer between air and falling film desiccant in parallel and counter flow configurations, where Nanoparticles suspensions are added to the falling-film desiccants to study heat transfer enhancements, and numerical results show that the parallel flow channel provides better dehumidification and cooling processes of the air than counter flow configuration for a wide range of pertinent parameters.
Abstract: A comparative numerical study is employed to investigate the heat and mass transfer between air and falling film desiccant in parallel and counter flow configurations. Nanoparticles suspensions are added to the falling film desiccant to study heat and mass transfer enhancements. The numerical results show that the parallel flow channel provides better dehumidification and cooling processes of the air than counter flow configuration for a wide range of pertinent parameters. Low air Reynolds number enhances the dehumidification and cooling rates of the air and high air Reynolds number improves the regeneration rate of the liquid desiccant. An increase in the channel height results in enhancing the dehumidification and cooling processes of air and regeneration rate of liquid desiccant. The dehumidification and cooling rates of air are improved with an increase in the volume fraction of nanoparticles and dispersion factor. Copyright © 2003 John Wiley & Sons, Ltd.
72 citations
TL;DR: In this article, the authors compared three methods: the engineering method (EM), the conditional demand analysis (CDA) method, and the neural network (NN) method for modeling residential energy consumption.
Abstract: Three methods are currently used to model residential energy consumption at the national level: the engineering method (EM), the conditional demand analysis (CDA) method, and the neural network (NN) method. While the use of the first two methods has been established over the past decade for residential energy modelling, the use of NN method is still in the development and verification phase.
The EM involves developing a housing database representative of the national housing stock and estimating the energy consumption of the dwellings in the database using a building energy simulation program. CDA is a regression-based method in which the regression attributes consumption to end-uses on the basis of the total household energy consumption. The NN method models the residential energy consumption as a neural network, which is an information-processing model inspired by the way the densely interconnected, parallel structure of the brain processes information.
In this paper, the three methods are briefly described and a comparative assessment of the three methods is presented. Copyright © 2003 John Wiley & Sons, Ltd.
66 citations
TL;DR: In this article, the authors deal with the onset of convection in a porous layer heated from below, by considering the case when the fluid and solid phases are not in local thermal equilibrium and when form-drag and boundary effects are included in the analysis.
Abstract: The paper deals with the onset of convection in a porous layer heated from below, by considering the case when the fluid and solid phases are not in local thermal equilibrium and when form-drag and boundary effects are included in the analysis. Analytical progress is facilitated by taking stress-free boundaries conditions. Asymptotic solutions for both small and large values of the scaled inter-phase heat transfer coeffcient, H, are presented and comparisons with the numerical solutions are performed. Excellent agreement is obtained between the asymptotic and the numerical results.
63 citations
TL;DR: In this article, thermal performance of randomly mixed PCM and laminated PCM-wallboard systems have been numerically evaluated and results compared and the laminated system displayed up to 50% increment in heat flux enhancement and about 18% increase in heat transfer rates.
Abstract: Heat transfer barriers and other practical difficulties do currently hamper the development and application of (phase change materials) PCM–wallboard systems. In this study thermal performance of randomly mixed PCM and laminated PCM–wallboard systems have been numerically evaluated and results compared. The laminated system displayed up to 50% increment in heat flux enhancement and about 18% increase in heat transfer rates. Consequently, the laminated PCM–wallboard system has greater potential for heating and cooling application in buildings than the randomly mixed system. Experimental validation and investigation into manufacturing techniques are however needed to establish the commercial viability. Copyright © 2002 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors presented the theoretical analysis of the use of single stage and double absorption heat transformers operating with the water-lithium bromide mixture coupled to a butane and pentane distillation column in a Mexican refinery.
Abstract: This paper presents the theoretical analysis of the use of single stage and double absorption heat transformers operating with the water–lithium bromide mixture coupled to a butane and pentane distillation column in a Mexican refinery. A mathematical model of the heat transformers was developed in FORTRAN and integrated as a user model to the Aspen Plus simulation code. Both components coupled to the column were modelled on steady-state conditions. The results show that it is theoretically possible to reduce the energy consumed in the reboiler between 26 and 43% by the use of single stage heat transformer at specific conditions, and between 28 and 33% with double absorption heat transformers for a wide range of operating conditions. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, a case study highlights the importance of taking into consideration diurnal variations of wind velocity for wind energy resources assessment, where the timing of the energy output is essential to meet electricity loads.
Abstract: This case study highlights the importance of taking into consideration diurnal variations of wind velocity for wind energy resources assessment. Previous studies of wind energy distribution that are based on the two-parameter Weibull density function have so far neglected to consider time of day fluctuations in wind speed, instead concentrating primarily on seasonal deviations. However, this has serious implications where such a wind energy model is the underpinning of calculations for the potential power production from a wind turbine and in particular where the timing of the energy output is essential to meet electricity loads. In the case of Grenada the energy output from a wind turbine during the day is approximately two times the output at night thereby fluctuating enormously around the seasonal mean distribution. When this is not taken into account the economic and technological viability of a wind turbine project may be overestimated or not even be identified. This work shows how a wind energy resources assessment based on the Weibull distribution model can be done and how the power output of a horizontal axis turbine is calculated. An analysis of the recorded wind data confirms the application of the Weibull density function as a suitable tool for modelling wind regimes. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, a two-dimensional mathematical model is used to investigate the parameter effects on the performance of Proton exchange membrane fuel cells with an inter-digitated flow field, and the theoretical results illustrate the importance of increasing the porosity of the gas diffusion layer to achieve a higher cell performance.
Abstract: A two-dimensional mathematical model is used to investigate the parameter effects on the performance of Proton exchange membrane fuel cells with an interdigitated flow field. In the interdigitated flow field mass transfer to the reaction sites is predominantly by force convection, thus much higher limiting current density and maximum power density can be achieved compared with conventional types of flow fields. The parameter effects on the fuel cell with interdigitated flow fields are performed under a different cathode porosity, inlet oxygen mole fraction, operating temperature and pressure to obtain the overall cell potential and power density. By setting appropriate boundary conditions, especially at the cathode gas diffusion layer inlet and at the reaction surface of the gas diffusion layer/catalyst layer interface, the performance of the fuel cell with interdigitated flow fields is studied in terms of the overall cell potential. The theoretical results illustrate the importance of increasing the porosity of the gas diffusion layer to achieve a higher cell performance. Similarly, an increase in the mole fraction, operating pressure or temperature of the oxygen entering the cathode gas diffusion layer leads to a greater overall cell performance.
TL;DR: In this article, the effect of anionic surfactant (sodium dodecyl sulphate (SDS) on natural gas storage in hydrates is more pronounced compared to a non-ionic surface agent (dodecyl polysaccharide glycoside (DPG)).
Abstract: Hydrate formation rate plays an important role in making hydrates for the storage and transport of natural gas. Micellar surfactant solutions were found to increase gas hydrate formation rate and storage capacity. With the presence of surfactant, hydrate could form quickly in a quiescent system and the energy costs of hydrate formation reduced. Surfactants (an anionic surfactant, a non-ionic surfactant and their mixtures) and liquid hydrocarbons (cyclopentane and methylcyclohexane) were used to improve hydrate formation. The experiments of hydrate formation were carried out in the pressure range 3.69–6.82 MPa and the temperature range 274.05–277.55 K. The experimental pressures were kept constant during hydrate formation in each experimental run. The effect of anionic surfactant (sodium dodecyl sulphate (SDS)) on natural gas storage in hydrates is more pronounced compared to a non-ionic surfactant (dodecyl polysaccharide glycoside (DPG)). The induction time of hydrate formation was reduced with the presence of cyclopentane (CP). Cyclopentane and methylcyclohexane (MCH) could increase hydrate formation rate, but reduced hydrate storage capacity The higher methylcyclohexane concentration, the lower the hydrate storage capacity. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this article, a high temperature curing Phenolic (phenol formaldehyde) resin and a two-component Bisphenol resin with amine-based slow curing agent were used to construct DPL reinforced composites.
Abstract: Several panels of date palm leave (DPL) reinforced composites were fabricated using either autoclaving technique with vacuum bagging or press moulds with controlled temperature. Several fibre orientation and dimensions were tested. Two types of resins were selected. The first was a high temperature curing Phenolic (phenol formaldehyde) resin. The second was a two-component Bisphenol resin with amine-based slow curing agent. The panels exhibited very low thermal conductivities ranging between 0.17 and 0.24 W m–1 K–1 for the Phenolic resin (depending on the curing pressure) and between 0.16 and 0.20 W m–1 K–1 for the bisphenol. The main factors affecting the thermal conductivity were the resin type, fibre to resin ratio and curing pressure. The fibre orientation and size had no measurable effect on the thermal conductivity. The produced laminates were very stable to handle all required machining processes as construction panels. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, a parametric analysis of psychrometric processes using the concept of exergy was carried out to determine the variation of second-law efficiency as a function of mass flow rate, relative humidity and temperature.
Abstract: The relation between work and changes in entropy generation arises from the simultaneous treatment of the first and second laws referred to as exergy (or available energy) analysis. In this paper, we discuss thermodynamic analysis of various psychrometric processes using the concept of exergy. A parametric study of each of the processes is carried out to determine the variation of second-law efficiency as a function of mass flow rate, relative humidity and temperature. Other trends such as variation of temperature with relative humidity are also shown where applicable. Irreversible losses are calculated by applying an exergy balance on each system. In this regard, an engineering equation solver (EES) programme is used, which is unique because it has built-in functions for most thermodynamic and transport properties; removing the need for approximate equations. The concept of total exergy as the sum of thermomechanical and chemical parts is employed in calculating the flow exergies for air and water vapor mixtures. It is shown for some processes investigated that an increase in the relative humidity of the incoming air stream increases second-law efficiency. We notice that a decrease in mass flow rate of fresh air (second incoming stream) in the case of adiabatic mixing decreases the second-law efficiency of the process. Also, it is shown that the mass flow rate (of both water and steam) has almost a linear relationship with relative humidity in the range investigated. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, the energy and exergy analyses of sugar production stages by using the operational data from Bor Sugar Plant, Turkey, were analyzed by employing the first and second law of thermodynamics.
Abstract: This paper presents the energy and exergy analyses of sugar production stages by using the operational data from Bor Sugar Plant, Turkey. For these purposes, all stages of sugar production, considered as a steady-state open thermodynamic system, were analysed by employing the first and second law of thermodynamics. In this regard, the first and second law efficiencies, the magnitude and place of exergy losses in these production stages were estimated and discussed in detail. It was concluded that the exergy loses took place mostly during the sherbet production process (ηI,sp=96.8% ηII,sp=49.3%) because of the irreversibility in the sub-operation stages, which are vapour production, circulation sherbet mixing and bagasse compression. Therefore, it is generally suggested that the irreversibility, mostly stem from the finite temperature differences at the production stages, should be reduced to conduct more productively the sugar production process. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this article, an artificial species, which displaces added CO2 in the fuel- and oxidizer-sides and has the same thermochemical, transport, and radiation properties to that of added CO 2, is introduced to extract pure chemical effects in flame structure.
Abstract: Numerical simulation of CO2 addition effects to fuel and oxidizer streams on flame structure has been conducted with detailed chemistry in H2–O2 diffusion flames of a counterflow configuration. An artificial species, which displaces added CO2 in the fuel- and oxidizer-sides and has the same thermochemical, transport, and radiation properties to that of added CO2, is introduced to extract pure chemical effects in flame structure. Chemical effects due to thermal dissociation of added CO2 causes the reduction flame temperature in addition to some thermal effects. The reason why flame temperature due to chemical effects is larger in cases of CO2 addition to oxidizer stream is well explained though a defined characteristic strain rate. The produced CO is responsible for the reaction, CO2+H=CO+OH and takes its origin from chemical effects due to thermal dissociation. It is also found that the behavior of produced CO mole fraction is closely related to added CO2 mole fraction, maximum H mole fraction and its position, and maximum flame temperature and its position. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: The kinetics of the thermal decomposition of thiophene diluted in argon have been studied behind reflected shock waves in a single pulse shock tube over the temperature range 1598-2022 K and pressures between 2.5 and 3.44 bar as discussed by the authors.
Abstract: The kinetics of the thermal decomposition of thiophene diluted in argon have been studied behind reflected shock waves in a single pulse shock tube over the temperature range 1598-2022 K and pressures between 2.5 and 3.44 bar. Product yields and composition were determined using capillary column gas chromatography with flame ionization detection and flame photometric sulphur selective detection. The principal hydrocarbon -product at all temperatures was ethyne. Ethanethiol was found to be the major sulphun product together with H 2 S formed in significant concentrations at lower temperatures. Carbon disulphide was also formed at higher temperatures. Additional reaction products were CH 4 , C 2 H 4 , C 3 H 4 , C 4 H 3 , C 4 H 6 , C 4 H 4 , C6H6 and C 4 H 2 with some traces were found of C 5 and C 6 H 5 species. It was concluded that pyrolysis of thiophene is initiated by C-S bond fission to form the C 4 H 4 S radical which reacts to give C 4 H 3 + SH together with the reaction giving C 3 H 4 + CS. The rate expression obtained for the pyrolysis reaction was k (C4H4S) =2.2 × 1011 exp (270 kJ mol -1 ) s -1 .
TL;DR: In this article, a model of a solar-operated liquid desiccant system (using calcium chloride) for air dehumidification is developed and integrated with a solar heat source for performance evaluation at a wide range of recorded ambient conditions for Beirut city.
Abstract: Humidity and indoor moist surrounding affect air cleanliness and protects harmful microorganisms when relative humidity is above 70%. In humid climates, the humidity issues are a major contributor to energy inefficiency in HVAC devices. The use of liquid desiccant dehumidification systems of supply air is a viable alternative to reduce the latent heat load on the HVAC system and improve efficiency. Thermal energy, at a temperature as low as 40–50°C, required for the operation of a liquid desiccant hybrid air conditioner can be efficiently obtained using a flat-plate solar collector.
In this work a model of a solar-operated liquid desiccant system (using calcium Chloride) for air dehumidification is developed. The system utilizes packed beds of counter flow between an air stream and a solution of liquid desiccant for air dehumidification and solution regeneration. The desiccant system model is integrated with a solar heat source for performance evaluation at a wide range of recorded ambient conditions for Beirut city. Standard mass and energy balances are performed on the various components of the system and a computer simulation program is developed for the integrated system analysis.
The desiccant system of the current study replaces a 3 TR (10.56 kW) vapour compression unit for a typical house as low latent load application, and is part of a hybrid desiccant–vapour compression system for a high latent load application, namely a small restaurant with an estimated cooling load of 11.39 TR (40 kW), including reheat. The relevant parameters of the desiccant system are optimized at peak load, and it is found out that there is an important energy saving if the ratio of the air flow rate in the regenerator to that in the dehumidifier is about 0.3 to 0.4. The COP of the desiccant unit is 0.41 for the house, and 0.45 for the restaurant. The size of the vapor compression unit of the restaurant is reduced to 8 TR when supplemented by a desiccant system.
The performance is studied of the desiccant system integrated with a solar collector system and an auxiliary natural gas heater to heat the regenerator. The transient simulation of the solar desiccant system is performed for the entire cooling season. The solar fraction for the house is equal to 0.25, 0.47, and 0.68 for a collector area of 28.72, 57.44, and 86.16 m2, respectively. The solar fraction for the restaurant is 0.19, 0.38, and 0.54, for the same collector areas. The life cycle savings for the house run solely on desiccant system were positive only if natural gas is available at a cheap price. For the restaurant, the economic benefit of the desiccant system is positive, because the need for reheat in the vapor compression system is eliminated. For a gas price of 0.5638 $/kg, the payback period for the restaurant turned out to be immediate if the energy is supplied solely by natural gas, and 11 years if an 86.16 m2 solar collector is implemented to reduce the fuel consumption. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, the overall effectiveness of a wet six-row wickless heat pipe-heat exchanger (HPHX) for tropical building HVAC systems was simulated using a computer simulation program.
Abstract: The overall effectiveness of a wet six-row wickless heat pipe-heat exchanger (HPHX) for tropical building HVAC systems was simulated using a computer simulation program. This computer program, utilizing Fortran source code, was developed based on the effectiveness-NTU method together with the ridge model for predicting the film condensation and uses the concept of iteration to predict the temperature distribution across the HPHX and its overall effectiveness. The effects of inclination angle and inlet evaporator relative humidity on heat transfer coefficient for the HPHX were determined using TRNSYS Type98 component. The wet HPHX effectiveness and relative humidity were also studied in this research experimentally. Copyright © 2002 John Wiley & Sons, Ltd.
TL;DR: In this paper, typical solar radiation data were obtained for Istanbul, Turkey both from measured data and synthetic generation, and the daily global solar radiation as typical data for Istanbul was presented throughout a year in a tabular form.
Abstract: Typical solar radiation data are very important as input in modelling, designing and performance evaluation of solar energy applications. In this study, typical solar radiation data were obtained for Istanbul, Turkey both from measured data and synthetic generation. Firstly, a test reference year for daily global solar radiation on a horizontal surface was generated using 19 years measured data. The daily global solar radiation as typical data for Istanbul was presented throughout a year in a tabular form. Secondly, the daily global solar radiation for Istanbul was expressed with a trigonometric equation using long-term measured data. It is expected that the typical data and the equation derived will be useful to the designers of solar energy systems as well as those who need to have fairly good estimates of daily global solar radiation for Istanbul. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, an exergetic analysis of a vapour compressor refrigeration plant when the refrigeration capacity is controlled by varying the compressor speed is presented, in order to determine the relative irreversibility of the plant components.
Abstract: The paper presents an exergetic analysis of a vapour compressor refrigeration plant when the refrigeration capacity is controlled by varying the compressor speed. The aim is performance evaluation of both the whole plant and its individual components. The analysis of the exergy flow destroyed in each device of the plant varying the compressor speed has been carried out in order to determine the relative irreversibility of the plant components. The vapour compression plant is subjected to a commercially available cold store. The compressor working with R22, R407C and R507 and designed for a revolution speed corresponding to 50 Hz supply current frequency, has been used varying the frequency in the range 30–50 Hz. In this range, the most suitable working fluids proposed as substitutes of R22, as R407C (R32/R125/R134a 23/25/52% in mass), R507 (R125/R143A 50/50% in mass) and R417A (R125/R134a/R600 46.6/50/3.4% in mass), have been tested. The variable-speed compressor is fitted with a pulse-width modulated source inverter (PWM) predominantly used in medium power applications due to its relatively low cost and high efficiency. The basic difference between variable speed refrigeration and conventional refrigeration systems is in the control of the system capacity at part-load conditions. The conventional refrigeration systems are characterized by compressor on/off cycles arising from by the thermostatic control. On the contrary when the inverter is used the capacity of the refrigeration system is matched to the load regulating the compressor motor speed. When the control of the compressor capacity is obtained by varying its speed there is an energy saving with respect to the thermostatic control. The best results of the exergetic analysis have been obtained using R22 followed by the non-azeotropic mixture designed as R407C that confirms, among the fluid candidates R22 substitution a better performance, shown also at the compressor nominal speed. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: A direct route to the construction of effective tree-shaped flow structures by optimization of the shape of each elemental area, such that the length of the flow path housed by the element is minimized.
Abstract: In this paper, we review the fundamental problem of how to design a flow path with minimum overall resistance between one point (O) and many points situated equidistantly on a circle centred at O This is a fundamental problem in energy engineering: the distribution of fluid, energy, electric power, etc, from points to surrounding areas This problem is also fundamental in heat transfer and electronics cooling: how to bathe and cool with a single stream of coolant a disc-shaped area or volume that generates heat at every point This paper outlines, first, a direct route to the construction of effective tree-shaped flow structures The starting point is the optimization of the shape of each elemental area, such that the length of the flow path housed by the element is minimized Proceeding towards larger and more complex structures—from elements to first constructs, second constructs, etc—the paper develops tree-shaped flow structures between one point and a straight line, as an elemental problem, and a circle and its centre We also consider the equivalent tree-shaped networks obtained by minimizing the pressure drop at every step of the construction, in accordance with geometric constraints The construction method is applied to a fluid flow configuration with laminar fully developed flow It is shown that there is little difference between the two methods The minimal-length structures perform very close to the fully optimized designs These results emphasize the robustness of optimized tree-shaped flows Copyright © 2003 John Wiley & Sons, Ltd
TL;DR: In this article, a study is carried out to describe irreversibilities in one stage refrigerating process for vapour compression cycle with refrigerant mixtures R-404A, R-410A,R-410B and R-507 as working fluids.
Abstract: A study is carried out to describe irreversibilities in one stage refrigerating process for vapour compression cycle with refrigerant mixtures R-404A, R-410A, R-410B and R-507 as working fluids. They are calculated as exergy losses by an algorithm developed on the basis of thermodynamics. The proposed relationships have been derived from exergy balances on the system components. Emphasis is placed on parameters influencing the losses and the related results are presented through Grassmann diagrams (diagrams of exergy fluxes). Furthermore, detailed information on the variation of cycle's exergy efficiency with evaporating and condensing temperatures is given. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, a two-dimensional mathematical model which considers complex heat and mass transfer and fluid flow during the hydriding process is accomplished in this study, where coupled differential equations are solved with numerical method based on integrations of governing equation over finite control volumes.
Abstract: This paper presents a numerical investigation of hydrogen storage in a metal hydrid bed. For this purpose, a two-dimensional mathematical model which considers complex heat and mass transfer and fluid flow during the hydriding process is accomplished in this study. The coupled differential equations are solved with numerical method based on integrations of governing equation over finite control volumes. The driving force for fluid flow is considered to be pressure difference due to the temperature distribution in the system. It is found that fluid flow enhances the local hydriding rate in the system by driving the hot fluid to the colder regions. The numerical results were found to agree satisfactorily with the experimental data available in the literature. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this article, the effects of energy projects on global carbon dioxide emissions were assessed using a pre-existing carbon dioxide trading system, which is an important feature of a future international CO2 trading system.
Abstract: Methodologies to assess the effects of energy projects on global carbon dioxide emissions will be an important feature of a future international carbon dioxide trading system. In this paper, we pre ...
TL;DR: In this article, the authors highlight the current enviromental issues and potential solutions to these issues, identify the main steps for implementing energy conservation programs, and provide assessments for energy conservation potentials for countries, as well as various practical and environmental aspects of energy conservation.
Abstract: Energy conservation is now playing a key role in industrial development and is vital for sustainable development. Therefore, it should be implemented by all possible means, despite of its own limitations. This study highlights the current enviromental issues and potential solutions to these issues, identifies the main steps for implementing energy conservation programs and the main barriers to such implementations, and provides assessments for energy conservation potentials for countries, as well as various practical and environmental aspects of energy conservation. It is believed that this paper will be beneficial to energy policy makers particularly for energy conservation programmes. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, a series of recent results based on the geometric minimization of the resistance to flow between one point (source, sink) and a volume or an area (an infinity of points) are discussed.
Abstract: This lecture reviews a series of recent results based on the geometric minimization of the resistance to flow between one point (source, sink) and a volume or an area (an infinity of points). Optimization is achieved by varying the geometric features of the flow path subject to volume constraints. The method is outlined by using the problem of steady volume-point conduction. Optimized first is the smallest elemental volume, which is characterized by volumetric heat generation in a low-conductivity medium, and one-dimensional conduction through a high-conductivity ‘channel’. Progressively larger volumes are covered by assemblies of previously optimized constructs. Tree-shaped flow structures spring out of this objective and constraints principle. Analogous problems of fluid flow, and combined heat and fluid flow (convection, trees of fins) are also discussed. The occurrence of similar tree structures in nature may be reasoned based on the same principle (constructal theory) (Bejan, 2000). Copyright © 2003 John Wiley & Sons, Ltd.