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[en] Highlights: • We study the effect of phase change materials integration on the thermal performances of an ICSSWH. • Two kinds and tree radiuses of the PCM layer are studied and the most appropriate design is presented. • The use of phase change materials in ICSSWH is determined to reduce the night thermal losses. • Myristic acid is the most appropriate PCM for this application regarding the daily and night operation. - Abstract: In this paper, we propose a numerical study of an integrated collector storage solar water heater (ICSSWH). Two numerical models in three-dimensional modeling are developed. The first one which describes a sensible heat storage unit (SHSU), allowing validating the numerical model. Based on the good agreement between numerical results and experimental data from literature, and as this type of solar water heater presents the disadvantage of its high night losses, we propose to integrate a phase change material (PCM) directly in the collector and to study its effect on the ICSSWH thermal performance. Indeed, a second 3D CFD model is developed and series of numerical simulations are conducted for two kind (myristic acid and RT42-graphite) and three radiuses (R = 0.2 m, R = 0.25 m and R = 0.3 m) of this PCM layer. Numerical results show that during the day-time, the latent heat storage unit (LHSU) performs better than the sensible one when myristic acid is used as PCM. Regarding the night operating of this solar system, it is found that the LHSU is more effective for both PCMs as it allows lower thermal losses and better heat preservation
[en] Highlights: • Diesel engine exhaust contains 40% energy which can be used to produce extra power. • Extra 11% power gained with optimized heat exchangers using water as working fluid. • As a result brake specific fuel consumption improved by 12%. • Parallel arrangement of heat exchangers showed better performance than series. • Optimum working fluid pressure varies with the engine power. - Abstract: Exhaust heat from diesel engines can be an important heat source to provide additional power using a separate Rankine Cycle (RC). In this research, experiments were conducted to measure the available exhaust heat from a 40 kW diesel generator using two ‘off-the-shelf’ heat exchangers. The effectiveness of the heat exchangers using water as the working fluid was found to be 0.44 which seems to be lower than a standard one. This lower performance of the existing heat exchangers indicates the necessity of optimization of the design of the heat exchangers for this particular application. With the available experimental data, computer simulations were carried out to optimize the design of the heat exchangers. Two heat exchangers were used to generate super-heated steam to expand in the turbine using two orientations: series and parallel. The optimized heat exchangers were then used to estimate additional power considering actual turbine isentropic efficiency. The proposed heat exchanger was able to produce 11% additional power using water as the working fluid at a pressure of 15 bar at rated engine load. This additional power resulted into 12% improvement in brake-specific fuel consumption (bsfc). The effects of the working fluid pressure were also investigated to maximize the additional power production. The pressure was limited to 15 bar which was constrained by the exhaust gas temperature. However, higher pressure is possible for higher exhaust gas temperatures from higher capacity engines. This would yield more additional power with further improvements in bsfc. At 40% part load, the additional power developed was 3.4% which resulted in 3.3% reduction in bsfc
[en] Graphical abstract: The Figure shows the variations of volume fractions, granular temperatures, solid temperatures and carbon molar fractions of coal and biomass particles with time at x/R = 1/2 and z = 0.2 m. From the figure, an inverse relationship is shown between molar concentration of carbon and solid temperature. This is because the high temperature has a positive effect on carbon oxidation. For biomass particles, the granular temperature and the solid temperature increase with the volume fraction decreased in section a. In the sections b and c, the granular temperature has a similar trend with the volume fraction of particles. The granular temperature reflects the fluctuating intensity of particles, which indicates that the change of solid volume fraction can cause the granular temperature an increase and correspondingly influences the reaction process. For coal particles, the temperature of coal tends to be steady and the carbon produced by coal is fully consumed. - Highlights: • The KTGM model is developed for multi-component particle phases to simulate the coal/biomass co-gasification in ICFB. • A typical core-annulus flow structure in an inner combustor and the bubble motion in an outer gasifier are captured. • The change of solid volume fraction results in an increase of the granular temperature. • The high reaction temperature promotes the fluctuating velocity of fuel particles. • The granular temperature of biomass particles is higher than that of coal particles in the whole computational domain. - Abstract: A multi-fluid Eulerian model with the kinetic theory of granular mixture (KTGM) is employed for multi-component particles to simulate the coal/biomass co-gasification process in the internal circulating fluidized bed (ICFB). The hydrodynamic characteristic and chemical reaction kinetics are analyzed. The simulations with the KTGM model are in good agreement with experimental data. The instantaneous variables of volume fraction of particles, molar fraction of gas, molar concentration of carbon and temperature are described for the coal/biomass co-gasification process. The time-averaged distributions of volume fraction and velocity for both coal and biomass particles are given. The profiles of granular temperature with solid volume fraction and temperature are also discussed. The results reveal that the granular temperatures of both biomass and coal particles are obvious at a high temperature and a low solid volume fraction. Biomass particles have a higher granular temperature compared to coal particles.
[en] Highlights: • We model an experimental design of thermal electrical generator. • Electrical parameters were collected under the solar radiation. • All the calculated values were obtained from collected data. • Generated power and electrical efficiency were changed by thermal gradient. - Abstract: In this paper we present an experimental design of new solar based thermoelectric generator with wind chimney. Presented generator mainly consists of four parts: a heat pipe with solar collector tube for solar heating, a wind chimney for cooling, a thermoelectric (TE) module for electricity generation and measurement devices-sensors. Presented generator based on experimental design. Aim of this experimental design is to show an alternative way for cheap and efficiently renewable energy producing. The most important features of presented generator are uncomplicated structure, efficiently and cheapness. This experimental design can be improved and used for domestic and commercial application. For this reason, main parts of system can be enhanced and system can be improved. To evaluate of presented generator we collected some experimental data on designed system. Then maximum output power, electrical efficiency and Seebeck coefficient are calculated from obtained data. Results of the measurement are displayed in the form of graphs and tables. Our experiment was carried out on 16th and 21th August, in Samsun, on the north coast of Turkey with the exact location 41°14′N 36°26′E with sea level. Collection of the data was performed from 8:30 a.m. to 4 p.m
[en] Highlights: • New homogeneous generation period (HGP) concept is proposed. • Method for ex-post quantification of wind generation variation is developed. • Homogeneity is introduced as a measure of variation (uniformity). • Method yields HGP distributions by class, length and ramp. • Method is validated against numerical set-up of Lithuanian wind power cluster. - Abstract: The paper presents a novel method for statistical quantification of wind power variation based on a new concept of homogeneous generation periods (HGPs). It starts with the state-of-the-art review of approaches addressing the quantification of wind power variation. The suggested method is based on identification of (a) wind generation gradients (positive, negative, insignificant and ineligible) for the time steps and (b) HGPs (increasing, decreasing, constant and null-generation). In result, the method provides a statistical evaluation on variation of wind generation process in observation period in terms of statistical characteristics of HGPs. The validation of method is performed on a numerical set-up representing Lithuanian wind power cluster in a windy 13-day period. The validation results point to the effectiveness of the suggested method for the ex-post quantification of wind generation variation in a short-term time span
[en] Highlights: • Methodology for dynamic indicator model construction and forecasting of indicators. • Application of dynamic indicator model for energy system development scenarios. • Expert judgement involvement using Bayesian method. - Abstract: The methodology for the dynamic indicator model construction and forecasting of indicators for the assessment of energy security level is presented in this article. An indicator is a special index, which provides numerical values to important factors for the investigated area. In real life, models of different processes take into account various factors that are time-dependent and dependent on each other. Thus, it is advisable to construct a dynamic model in order to describe these dependences. The energy security indicators are used as factors in the dynamic model. Usually, the values of indicators are obtained from statistical data. The developed dynamic model enables to forecast indicators’ variation taking into account changes in system configuration. The energy system development is usually based on a new object construction. Since the parameters of changes of the new system are not exactly known, information about their influences on indicators could not be involved in the model by deterministic methods. Thus, dynamic indicators’ model based on historical data is adjusted by probabilistic model with the influence of new factors on indicators using the Bayesian method
[en] Highlights: • The combustion of pyrolysis oil and ethanol in a gas turbine was modeled using CFD. • The multicomponent nature of pyrolysis oil was approximated using a discrete fuel model. • Comparative simulations were performed to evaluate different model settings. • Validation was performed with available outlet CO_2 and temperature experimental data. - Abstract: The growing demand for the use of biofuels for decentralized power generation initiates new research in gas turbine technology. However, development of new combustors for low calorific fuels is costly in terms of time and money. To give momentum to biofuels application for power generation robust numerical models for multicomponent biofuels must be developed. This paper discusses the use of CFD techniques for modeling the combustion of pyrolysis oil in a new burner geometry from OPRA Turbines. Pyrolysis oil contains many different compounds, which are represented by a discrete fuel model consisting of seven components. The components and their initial fractions approximate the volatility, water content, elemental composition and heating value of a typical fast pyrolysis oil. Simulations have been carried out for both the multicomponent pyrolysis oil and, as a reference, ethanol, a single-component biofuel with a higher volatility. Comparative simulations have been performed to examine the influence of the initial droplet size and to evaluate different combustion models. The results were compared to available experimental data for pyrolysis oil and ethanol combustion. A qualitatively good agreement was achieved.
[en] Highlights: • A novel dynamic borehole heat exchanger model is presented. • Theoretical approach for model parameters calculation is described. • The short-term model is validated against experimental data of a real GSHP. • Strong dynamic conditions due to the ON–OFF regulation are investigated. - Abstract: Models of ground source heat pump (GSHP) systems are used as an aid for the correct design and optimization of the system. For this purpose, it is necessary to develop models which correctly reproduce the dynamic thermal behavior of each component in a short-term basis. Since the borehole heat exchanger (BHE) is one of the main components, special attention should be paid to ensuring a good accuracy on the prediction of the short-term response of the boreholes. The BHE models found in literature which are suitable for short-term simulations usually present high computational costs. In this work, a novel TRNSYS type implementing a borehole-to-ground (B2G) model, developed for modeling the short-term dynamic performance of a BHE with low computational cost, is presented. The model has been validated against experimental data from a GSHP system located at Universitat Politècnica de València, Spain. Validation results show the ability of the model to reproduce the short-term behavior of the borehole, both for a step-test and under normal operating conditions
[en] Waste disposal represents an important problem in developed countries. Many different techniques are available to reduce the amount of waste production and its environmental impact. In most cases, sanitary landfills have been and continue to be one of the most common ways to dispose of urban and industrial wastes. It is well known how landfilling produces an important environmental drawback due to gaseous, liquid and solid emissions that are dangerous for the environment. Landfill biogas emissions contain mainly carbon dioxide and methane. In particular, the methane concentration can be higher than 50% by volume. This means that the calorific value of sanitary landfill biogas can be higher than 18,000 kJ/N m3. The utilization of such gas as fuel for electrical and thermal energy production can be an important way to reduce the landfill impact on the environment and represent an easy way to use a renewable energy source. In the following, the amount and composition of the biogas produced in a sanitary landfill situated in central Italy have been analysed. Experimental results have been discussed, and an energetic potential evaluation has been performed
[en] R22, the HCFC most widely used in refrigeration and air-conditioning systems in the last years, is phasing-out. R422D, a zero ozone-depleting mixture of R125, R134a and R600a (65.1%/31.5%/3.4% by weight, respectively), has been recently proposed as a drop-in substitute. For energy consumption calculations and temperature control, it is of primary importance to estimate operating conditions after substitution. To determine pressure drop in the evaporator and piping line to the compressor, in this paper the experimental adiabatic pressure gradients during flow boiling of R422D are reported for a circular smooth horizontal tube (3.00 mm inner radius) in a range of operating conditions of interest for dry-expansion evaporators. The data are used to establish the best predictive method for calculations and its accuracy: the Moreno-Quiben and Thome method provided the best predictions for the whole database and also for the segregated data in the annular flow regime. Finally, the experimental data have been compared with the adiabatic pressure gradients of both R22 and its much used alternative R407C available in the literature.