Showing papers in "Journal of The Energy Institute in 2010"

Unsteady numerical simulation of solar chimney power plant system with energy storage layer

Abstract: Numerical simulations were carried out to analyse the performance of the solar chimney power plant systems with energy storage layer in this paper. Mathematical models were developed to describe the flow and heat transfer mechanisms of the collector, chimney and the energy storage layer, and the responses of different energy storage materials to the solar radiation, and the effects of these materials on the power output with different solar radiations were analysed. Numerical simulation results show the following: first, soil and gravel both have suitable values of the property of thermal inertia, and they could be used as energy storage material for the solar chimney system; second, energy storage layer with comparatively higher heat capacity can store more energy on sunny days and can thus effectively decrease the variations of the chimney outlet parameters caused by the fluctuations in solar radiation related to the day-night cycle; third, the higher the temperature of the energy storag...

Simple analysis on thermal performance of solar chimney power generation systems

Abstract: A simple analysis is made on the air flow through a solar chimney power generation system and a thermodynamic cycle of the system including the environment is established. Later, mathematical models for the ideal and actual cycle efficiencies are also established. The research results show that the ideal cycle efficiency and actual efficiency of standard Brayton cycle corresponding to medium scale solar chimney power generation system are 1?33 and 0?3% respectively, while the same parameters for large scale solar chimney power generation systems are 3?33 and 0?9% respectively. The results can give a theoretical guidance to the commercial application of solar chimney power generation systems in China.

Effects of variable specific heat ratio of working fluid on performance of endoreversible Diesel cycle

Abstract: The performance of a Diesel cycle with heat transfer loss and variable specific heat ratio of working fluid is analysed. Using finite time thermodynamics, the characteristic curves of the work output v. compression ratio, the thermal efficiency v. compression ratio and the work output v. thermal efficiency are obtained. Moreover, the effects of variable specific heat ratio of working fluid on the cycle performance are significant. The results obtained in this work can help to understand how the cycle performance is influenced by the variation specific heat ratio, and they should be considered in practical cycle analysis.

Extreme working temperature differences for thermoelectric refrigerating and heat pumping devices driven by thermoelectric generator

Abstract: The extreme working temperature differences of combined thermoelectric devices, i.e. thermoelectric generator driven thermoelectric refrigerator or heat pump, are analysed using nonequilibrium thermodynamics. The extreme working temperature differences versus the ratio of numbers of thermoelectric elements, i.e. the ratio of the number of thermoelectric elements of the generator to the total number of thermoelectric elements of the combined devices, of the two models are obtained. The effects of the hot junction temperature of the generator on the extreme working temperature differences are analysed. The results show that, if a thermoelectric generator works under a condition of 150 K temperature difference, y60 K temperature difference for cooling or 200 K temperature difference for heating could be reached. The coefficient of performance can reach to 0?08–0?15 which is considerable for application in a wide scale for specific purposes. For a fixed ratio of numbers of thermoelectric elements, there is a fixed extreme working temperature difference, the larger working temperature difference, the smaller cooling (heating) load and coefficient of performance. The results obtained herein may provide guidelines for the design and application of practical combined thermoelectric devices.

Comparison of allocation approaches in soybean biodiesel life cycle assessment

Abstract: This work shows the influence of using different allocation approaches when modelling the inventory analysis in a soybean biodiesel life cycle assessment (LCA). Results obtained using mass, energy and economic based allocations are compared, focusing on the following aspects: normalised potential environmental impact (PEI) categories, total PEI and relative contributions to the total PEI from each life cycle stage and environmental impact category. Similar results are obtained either using economic and energy based allocations. However, different results are obtained when mass based allocation is used when compared with the other two. This study also illustrates that using different allocation approaches in biodiesel LCA may influence the final conclusions, especially in comparative assertions, emphasising the need to perform a sensitivity analysis in the LCA interpretation step.

Thermogravimetric analysis and pyrolysis kinetic study of Malaysian refuse derived fuels

Abstract: Refuse derived fuel (RDF), containing mainly paper and plastics, is a waste material that has potential to be used for energy or fuel production. This paper reports on a thermogravimetric study and kinetic analysis of the thermal decomposition of Malaysian RDF. It was found that Malaysian RDF contained 59·8 wt-% plastics, 28·6 wt-% cardboard, 5·1 wt-% newspapers and 6·5 wt-% other materials. The plastics consisted of 64·6% polyethylene, 17·5% polypropylene, 10·1% polystyrene and 7·8% other plastics (polyethylene terephthalate, formaldehyde based resin, polyamides, acrylonitrile butadiene styrene and polycarbonate). Results obtained from sample weight loss thermograms showed significant differences in their characteristic data (degradation temperature, rate of weight loss, etc.). The kinetic parameters have been derived from non-isothermal thermogravimetric data at a temperature range from room temperature up to 650°C using a constant heating rate of 20°C min−1. The thermal degradation of...

Development and analysis of industrial waste heat based trigeneration for combined production of power heat and cold

Abstract: In this study, a novel trigeneration system is proposed as an idea for future research based on the industrial waste heat recovery operated steam generator for process heat, and produces both power and refrigeration simultaneously with stack gases, using ammonia-water mixture as the working fluid. An extensive review of various energy and exergy based approach used in the analysis of different cogeneration and trigeneration cycles is reported. Energy and exergy efficiencies have been defined, and computational analysis is performed to investigate the effects of exhaust gas inlet temperature and gas composition on first law efficiency, electrical/thermal energy ratio and exergy efficiency of an industrial waste heat recovery based trigeneration system. The variation in specific heat with exhaust gas composition and temperature is accounted in the analysis for further discussion. The first law (energy) efficiency increases while electrical/thermal energy ratio and exergy efficiency decrease ...

Co-firing of refuse derived fuels with coals in cement kilns: combustion conditions for stable sintering

Abstract: Usage of refuse derived fuels (RDFs) in cement clinker processes has grown considerably in the last decade. It has been demonstrated that RDFs can partially substitute fossil fuels without ...

Performance of diesel engine using gas mixture with variable specific heats model

Abstract: A thermodynamic, one-zone, zero-dimensional computational model for a diesel engine is established in which a working fluid consisting of various gas mixtures has been implemented. The results were compared to those which use air as the working fluid with variable specific heats. Most of the parameters that are important for compression ignition engines, such as equivalence ratio, engine speed, maximum temperature, gas pressure, brake mean effective pressure and cycle thermal efficiency, have been studied. Furthermore, the effect of boost pressure was studied using both the gas mixture and dependent temperature air models. It was found that the temperature dependent air model overestimates the maximum temperature and cylinder pressure. For example, for the air model, the maximum temperature and cylinder pressure were about 1775 K and 93·5 bar respectively at 2500 rev min−1, and the fuel/air equivalence ratio Φ = 0·6. On the other hand, when the gas mixture model is used under the same con...

Prediction of NOx and unburned carbon in ash in highly staged pulverised coal furnace using overfire air

Abstract: NOx emissions from power plants burning pulverised coal are subject to increasingly stringent regulations, and this has a consequential effect on the amount of unburned carbon (UBC) produced. The prediction of both is important, and a number of modelling techniques are available, but there could be difficulties especially under highly staged combustion. This is because these regions have low oxygen concentrations where char gasification reactions might take place in addition to the normal combustion. The present paper discusses the role of these reactions mainly within a staged tangentially T fired furnace, which uses overfire air for NOx reduction, but it also considered a wall fired case. Predictions for UBC and NOx in these furnaces, which are represented by a series of slices, were made with and without the gasification equations and are compared with test data from furnaces. These results indicate that the char gasification reactions play only a small role even under highly staged c...

Biodiesel production from waste melon seeds and using it as alternative fuel in direct injection diesel engine

Abstract: Melon seeds containing ∼30% oil are wasted after the fruit is consumed. The chemical and physical properties of melon seed oil are very similar to vegetable oils used as biodiesel fuel. There are no studies regarding the use of melon seed oil or its esters as fuel in literature. In this study, oil was extracted from waste melon seeds and transformed to melon seed oil methyl ester (MSOME) by transesterification process. This fuel is used in a four stroke single cylinder direct injection diesel engine, and its effects on performance and emissions were investigated for various engine speeds at full load. In addition, diesel fuel no. 2 and soy bean oil methyl ester (SOME) is used as fuel under the same operating conditions for comparison purposes. According to the experiment results, specific fuel consumption is found to be more in both biodiesel fuels compared to diesel fuel, and the engine torque is 1-6% lower with MSOME and 3-5% with SOME compared to diesel fuel. Exhaust gas temperature is ...

Ecological performance optimisation for an open-cycle ICR gas turbine power plant Part 1 - thermodynamic modelling

Abstract: Considering the flow processes of the working fluid with the pressure drops, a thermodynamic model for open cycle intercooled and regenerated gas turbine power plant is established using finite time thermodynamics in Part 1 of this article. The flow processes of the working fluid with the pressure drops of the working fluid and the size constraints of the real power plant are modelled. There are 19 flow resistances encountered by the working fluid for the cycle model. Five of these, the frictions through the blades, vanes of the compressors and the turbines, are related to the isentropic efficiencies. Three of these, the frictions through the intercooler and the regenerator, are related to the effectiveness of the heat exchangers. The remaining flow resistances are always present because of the changes in the flow cross-section at the compressor inlets and outlets, the intercooler inlet and outlet, the regenerator inlet and outlet, the combustion chamber inlet and outlet, and the turbine i...

Effects of mass transfer laws on finite time exergy

Abstract: The problem of the maximal work that can be extracted from a system consisting of one infinite chemical potential reservoir and one subsystem is investigated in this paper. Finite time exergy is derived for the fixed duration of the process by applying optimal control theory. Effects of mass transfer laws on the finite time exergy and the corresponding optimal mass transfer processes are analysed. The optimal thermodynamic processes for the finite time exergy include two categories: one is that the chemical potential of the subsystem is a constant and the chemical potential difference between the reservoir and the subsystem is also a constant during the mass transfer process, and the other is that the chemical potential of the subsystem switches between two optimal values during the mass transfer process. Mass transfer laws have significant effects on the optimal thermodynamic process for the finite time exergy, and the necessary and sufficient condition to determine the optimal thermodyna...

Heat transfer enhancement by filling metal porous medium in central area of tubes

Abstract: Given that the fluid within the tubes of some industrial heat exchangers is under a state of fully developed laminar flow with a constant Nu number, increasing the surface area for heat transfer will significantly increase the flow resistance. In this paper, we filled metal porous medium with high thermal conductivity, high porosity and high filling radius in the central area of fully developed laminar flow within the tube, and established corresponding numerical models for fluid flow and heat transfer. Numerical simulation results indicate that after filling the tube with metal porous medium, the temperature profiles within the porous medium area are very uniform, and the temperature difference between the tube wall and the fluid decreases significantly which correspondingly results in a notable increase of Nu number; meanwhile, the characteristic of flow field redistribution occurs within the enhanced tube, but the total flow resistance composed of the Darcy resistance and inertial resis...

Ecological performance optimisation for an open-cycle ICR gas turbine power plant Part 2 - optimisation

Abstract: The ecological performance of an open-cycle intercooled and regenerated gas turbine power plant with pressure drop irreversibilities is optimised based on the model established using finite time thermodynamics in Part 1 of this article by adjusting the mass flowrate (or the distribution of pressure losses along the flow path) and the intercooling pressure ratio. It is shown that there are an optimal air mass flowrate (or the distribution of pressure losses along the flow path) and an intercooling pressure ratio which maximise the ecological performance, and the maximum ecological function has an additional maximum with respect to the compressor total pressure ratio. The effects of the effectiveness of the intercooler and the regenerator on the cycle ecological performance and its corresponding parameters are analysed. When the optimisation is performed with the constraints of the plant size, the ecological performance can be maximised again by properly allocating the fixed flow area betwee...

Equivalent turbocharger model of regulated two-stage turbocharging system

Abstract: A theoretical study on the regulated two-stage turbocharging (R2S) system is conducted based on the equivalent turbocharger concept. Expressions for the equivalent turbine flow area and the equivalent turbocharger efficiency of the R2S system were derived. The equivalent turbine flow area can be used in the analysis of the regulating capacity of the R2S system, according to which the combination of the high and low pressure stage turbochargers is determined. The equivalent turbocharger efficiency gives the criteria for matching the R2S system with diesel engine, which is optimising the exhaust energy distribution between the two-stage turbines to maintain high equivalent turbocharger efficiency. The paper closes with a computational analysis of the characteristic of the R2S system, and the application of the equivalent turbocharger model for matching and optimisation of the R2S system is studied.

Design methods for fluidised bed gasifiers: comparison of three approaches

Abstract: An effort is made here to develop a systematic design method for fluidised bed gasifiers. Three design approaches are considered: equilibrium approach, residence time approach and kinetic model approach. The equilibrium approach, which only predicts the gas composition, has two models: simple stoichiometric model and more comprehensive model. The latter gives better prediction of maximum achievable gas yield for a given set of feedstock and operating conditions. The residence time approach is primarily based on experimentally derived char gasification time and provides a good option for sizing of a gasifier, especially for carbonaceous fuels. The kinetic model, which is generally used for simulation of an existing gasifier, has been used here for the design considering the rate of reactions and effect of geometry and bed hydrodynamics on the gasifier performance. Because of its complexity, the kinetic model is most difficult to implement for initial design of a gasifier. More than three de...

Ecological optimisation of chemical engines with irreversible mass transfer and mass leakage

Abstract: Optimal ecological performance of chemical engine cycles with irreversible mass transfer and mass leakage, in which the mass transfer obeys both linear and diffusive mass transfer laws, is derived by taking an ecological optimisation criterion as the objective, which consists of maximising a function representing the best compromise between the power output and entropy production rate of the chemical engine. Numerical examples are provided to show the effects of mass reservoir chemical potential ratio, mass transfer coefficient ratio and mass leakage coefficient on the ecological function versus the efficiency characteristic of the cycles. The results can provide some theoretical guidelines for the design of practical chemical engines.

Investigation of combustion characteristics and emissions in SI engine fuelled with LHV gas

Abstract: In this study, an experimental research on the combustion and emission characteristics of a spark ignition engine fuelled with a blended gas was performed at different engine load operations. The blended gas, which was composed by the compressed natural gas and nitrogen, was lower heating value gas. In the experiments, the parameters of combustion characteristics were analysed under 0-35% nitrogen volume fraction in the blends. The results show that the maximum cylinder pressure, the maximum rate of pressure rise and the maximum rate of heat release decrease with increasing nitrogen fraction. The flame development duration and the main combustion duration increase with the higher level of the nitrogen fraction. Meanwhile, the HC, CO emission increase and the NOx decreases remarkably with the increase in the nitrogen volume fraction.

Analysis of exergy and energy of sugar production process in sugar plant

Abstract: In this paper, the energy and exergy analysis results of sugar production processes were presented by using operational system data from the Kayseri sugar plant, Turkey. All sugar production processes were thought as a steady state open thermodynamics system and employed the energy and exergy analyses, based on the first and second laws of thermodynamics. The best values of the energy and exergy efficiencies were obtained as 95·1% for the juice production process and 74·3% for the juice concentration process respectively. Moreover, the location of the energy degradation and the irreversibility were determined during the whole sugar production processes. Consequently, it has been pointed out that the energy and exergy efficiencies can be improved if the rates of the energy degradation and irreversibility in the sugar production processes are reduced.

Empirical formula for temperature integral in non-isothermal kinetics for exponential heating

Abstract: Exponential temperature change in non-isothermal kinetics has been discussed. A new empirical formula for the temperature integral has been presented, which has the form . A comparison of the proposed approximation has been made with the approximation proposed by Gorbachev (V. M. Gorbachev: J. Therm. Anal., 1977, 11, 125-128). The results have shown that the new approximation is more accurate than the Gorbachev approximation and deviates by <0·0035% for x(E/RT) as low as five. An analysis of the relative error involved in the activation energy obtained from the integral methods has been performed, and the validity of the integral method has been examined with some theoretical data.

Characterisation of heat transfer and flame length in a semi-scale industrial furnace equipped with HiTAC burner

Abstract: This paper investigates the effects of multiple burner nozzles on the combustion characteristics, such as flame volume, heat transfer and NOx emission in a high temperature air combustion (HiTAC) industrial furnace. Experiments were carried out in one semi-industrial furnace located in Kungliga Tekniska Hogskolan (Stockholm, Sweden). Three different types of burners were tested, including both regenerative and recuperative types. Variable flame temperature and oxygen concentration were applied in experiments. Heat transfer characteristics of HiTAC are studied in this paper, and the influences of a variety of inertial fuel/air jets are investigated for both flame length and NOx emission. One improved correlation between chemical flame length and flame Froude number is established for HiTAC with manifold nozzles. NOx emission is also correlated to the flame Froude number. The HiTAC recirculation system effects on flame shape, NOx emission and heat transfer were also examined.

Development of pattern recognition based ANN for energy auditing and inefficiency diagnostics of influential design elements utilising electrical energy data

Abstract: The objective of this study is to develop a pattern recognition based artificial neural network (ANN) for energy auditing and inefficiency diagnostics of the most influential design elements in buildings. The influential design elements examined include: envelope insulation, glazing insulation, glazing size, infiltration, economiser, building direction and orientation, and daylighting control. For generating the data bank needed for training the ANN, several buildings with different floor areas and known inefficiencies are simulated and their energy performance patterns, in terms of monthly energy demand and consumption, are determined. Monthly energy performance data including energy demand and consumption information for one year as well as building floor area are input. The developed ANN is validated and it is found that the expert auditing tool developed is effective for diagnosing the inefficient design elements. The application of the developed algorithm for real buildings and actual data is recommended for future work.

Substitute procedure for engine deposition test to investigate diesel and biodiesel fuel deposits

Abstract: The aim of this study was to investigate fuel deposit development and its influences using simplified methods, which are referred to as the hot surface deposition test (HSDT) instead of using the engine deposition test. Both the HSDT and the engine deposition test have similar tendencies in terms of deposit development and soot fraction in deposits. The fuels tested are diesel fuel (DF), palm oil based methyl ester biodiesel fuel (B100) and bioblended DFs (B50, B20 and B5). Deposit development in the HSDT depended on the droplet impingement intervals, hot surface temperatures, fuels, deposit properties, initial stage of deposition and competition phenomena during the deposit formation. These factors determined the existence of the wet surface condition and the amounts of deposits accumulated. The initial wet surface condition was not the main reason for the rapid development of deposits. Biodiesel fuel and bioblended DF showed rapid development tendencies. Fewer amounts of deposits from ...

Statistical process control for coal fired power plant system

Abstract: In this study, the coal feeding process from Garp Lignite Enterprise (GLE) in Kutahya, Turkey to the nearby Tuncbilek Power Plant (TPP) was evaluated from statistical process control point ...

Study on combustion stability of DI-HCCI engine fuelled with dimethyl ether

Abstract: Characteristics of direct injection (DI) combustion, direct injection-homogeneous charge compression ignition (DI-HCCI) combustion and HCCI combustion in an engine fuelled with dimethyl ether are investigated. The combustion stabilities of three combustion modes are compared, and the effects of premixed ratio, speed and load on them are given. The analysis shows that the maximum values of pressure, heat release rate, pressure rise rate and acceleration of DI combustion are lower than those of HCCI combustion and their phases are retarded. The combustion duration of DI combustion is shorter than that of HCCI combustion. In DI-HCCI combustion, with increasing premixed ratio, the maximum values of pressure, pressure rise rate and acceleration increase, and their phases advance respectively, and the combustion duration shortens evidently. The coefficient of variation (COV) of maximum pressure of DI combustion is much larger than that of HCCI combustion at 1100 and 1500 rev min−1. In DI-HCCI co...

Optimal performance of irreversible absorption refrigerator with four heat sources

Abstract: A model for an irreversible four-heat-source absorption refrigerator with continuous flow, which considers the irreversibilities resulting from thermal resistance and internal dissipations of the working fluid, is established. In this model, an absorption refrigerator is treated as a combined cycle system of an irreversible Carnot heat engine driving an irreversible Carnot refrigerator. Two parameters I he and I r are introduced to characterise the internal irreversibilities of the heat engine and refrigerator in the equivalent cycle system respectively. Under a given total heat conductance of the heat exchangers, the optimal relation between the cooling rate and coefficient of performance is derived, and the conditions for the optimal design of the system are determined. Then, this relation is used to deduce some new performance bounds. Moreover, the effects of the internal irreversibility parameters I he and I r on the optimal performance of the system are also investigated. The results...

Research on fault detection and identification of gas turbines sensors based on wavelet entropy

Abstract: Thermal parameters are usually used in computation and assessment of performance in gas turbine power plants. It is very important to obtain accurate and real values of thermal parameters. ...

Impact of climate change on cooling energy consumption

Abstract: Studies conducted in the recent past revealed that the changes in climate may probably lead to an increment in the mean outdoor temperature, inducing an increment in the cooling energy consumption in indoor environments. The present study estimated the present and the forecasted values of set point temperature and cooling energy consumption for the summer season in the humid region of northwestern Spain. The results of these evaluations revealed a clear increment in the value of outdoor temperature during all the seasons, particularly during spring. Furthermore, the increment in daily cooling energy consumption was ∼3·2 kWh. This value could be reduced to 60% by employing adaptive models to define the indoor air set point of building air conditioning systems in this region, with solutions based on passive methods.

Laser-induced fluorescence measurements in venturi cascaded propane gas jet flames

Abstract: A propane jet diffusion flame at a burner exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The venturi cascading technique resulted in a decrease of 33% in NO emission index along with a 24% decrease in soot emission from the flame, compared to the baseline condition (same flame without venturis). The temperature measurements showed that, in the near-burner region, the venturi cascaded flame has an average temperature lower by 5% than the baseline flame. However, in the mid-flame and far-burner regions, it has a temperature 13 and 12% higher, respectively. The NO composition measurements revealed that in the near-burner, mid-flame and far-burner regions, the venturi cascaded flame has lower NO concentrations by 16, 5 and 3%, in average values respectively, compared to the baseline case. In order to understand the above results and observations, Laser induced fluorescence (LIF) spectroscopy was employed to detect the minor species (...