基于液态金属朗肯循环的空间双模式核热推进系统性能分析

随着深空探测技术的进步,空间核动力越来越成为载人航天任务的理想选择,将双模式空间核动力推进系统应用于航天推进系统已成为一种新的趋势。基于空间核能液态金属朗肯循环,提出一种新型的双模式核热推进系统,并对该推进系统发电模式下的液态金属朗肯循环进行了性能分析。利用能量分析和?分析的方法对双模式核热推进系统下的朗肯循环进行热力计算,得出各部件的能量损失和?损,找出损失最大的部件并分析原因,取不同的空间环境温度研究其对?损和?效率的影响,为系统的进一步优化提供理论依据。     

Exergy analysis and experimental study of heat pump systems

Exergy analysis of heat pump—air conditioner systems has been carried out. The irreversibilities due to heat transfer and friction have been considered. The coefficient of performance based on the first law of thermodynamics as a function of various parameters, their optimum values, and the efficiency and coefficient of performance based on exergy analysis have been derived. Based on the exergy analysis, a simulation program has been developed to simulate and evaluate experimental systems. The simulation of a domestic heat pump—air conditioner of 959 W nominal power (Matsushita room air conditioner model CS-XG28M) is then carried out using experimental data. It is found that COP based on the first law varies from 7.40 to 3.85 and the exergy efficiency from 0.37 to 0.25 both a decreasing function of heating or cooling load. The exergy destructions in various components are determined for further study and improvement of its performance.     

Thermodynamic analysis of a hybrid geothermal heat pump system

A thermodynamic analysis of a hybrid geothermal heat pump system is carried out. Mass, energy, and exergy balances are applied to the system, which has a cooling tower as a heat rejection unit, and system performance is evaluated in terms of coefficient of performance and exergy efficiency. The heating coefficient of performance for the overall system is found to be 5.34, while the corresponding exergy efficiency is 63.4%. The effect of ambient temperature on the exergy destruction and exergy efficiency is investigated for the system components. The results indicate that the performance of hybrid geothermal heat pump systems is superior to air-source heat pumps.     

Exergy analysis and investigation for various feed water heaters of direct steam generation solar–thermal power plant

The energy and exergy analysis has been carried out for the different components of a proposed conceptual direct steam generation (DSG) solar–thermal power plant (STPP). It has been found that the maximum energy loss is in the condenser followed by solar collector field. The maximum exergy loss is in the solar collector field while in other plant components it is small. The possibilities to further improve the plant efficiency are identified and exploited. For minimum exergy loss in receiver the inlet temperature of water to the receiver, which is governed by the number of feed water heaters (FWHs), bleed pressure and mass fraction of bleed steam, must be optimum. The only one FWH has been proposed in conceptual DSG STPP. In order to evaluate the optimum bleed pressure and mass fraction of bleed steam to maximize the STPP efficiency, the investigations are carried out for various bleed pressure and mass fractions of bleed steam of proposed conceptual DSG STPP having one FWH. The investigations for bleed pressure and mass fraction of bleed steam are also carried out by incorporating two and three FWHs. It has been found that there will be significant improvement in efficiency by using three FWHs and further gain in efficiency is possible by making provision for more FWHs.     

A review of thermodynamics and heat transfer in solar refrigeration system

Solar energy is one of the most efficient, clean and affordable energy alternatives available today. With the current concerns about global warming and ever increasing energy rates, countries are seriously looking for domestic and industrial usage of solar energy. In the present study, a detail review of the application of solar energy for refrigeration systems has been carried out. The utilization of solar energy for refrigeration systems would help in improvement of energy economics, energy consumption and energy efficiency. The review focuses especially on solar panel, desiccant fluid for icemaker and its components. The study also includes thermodynamic equation and material for making component of refrigeration to improve the coefficient of performance. Study around the economic evaluation and solar performance coefficient in the type of refrigerator, modeling and simulation, mathematical equation of heat transfer and type of absorption used are other topics that could be considered.     

Analytic method for thermal performance and optimization of an absorber plate fin having variable thermal conductivity and overall loss coefficient

The absorber of a collector receives solar energy which is delivered to the transport medium to be carried away as useful energy. During this process, temperature of the absorber plate increases and therefore, thermophysical parameters engaged to determine the thermal performance of an absorber plate varies with temperature of the plate. The present study demonstrates analytically to determine the performance of an absorber plate fin with temperature dependent both thermal conductivity and overall heat loss coefficient. The decomposition method is proposed for the solution methodology. An optimum design analysis has also been carried out. A comparative study has been executed among the present results and that of existed in the published work, and a notable difference in results has been found. Finally, unlike published work, dependency parameters on the performances and optimum design have been highlighted.     

Optimization of cycloidal water turbine and the performance improvement by individual blade control

This paper investigates an advanced vertical axis turbine to enhance power generation from water energy. The turbine, known as a cycloidal water turbine, is a straight-bladed type adopting a cycloidal blade system that actively controls the rotor blades for improved turbine efficiency, according to the operating conditions. These characteristics enable the turbine to self-start and produce high electric power at a low flow speed, or under complex flow conditions. A parametric study has been carried out by CFD analysis, with various characteristics including different number of blades, chord length variations, variety of tip speed ratios, various hydrofoil shapes, and changing pitch and phase angles. Optimal parameters have been determined, and the performance of the turbine has achieved approximately 70% better performance than that of a fixed pitch turbine. An experimental study has also been carried out which shows that the results correlate quite well with the theoretical predictions although the power output was reduced due to the drag forces of the mechanical devices. Another numerical optimization was carried out to improve the rotor performance by adopting an individual blade control method. Controllable pitch angles were employed to maximize the rotor performance at various operating conditions. The optimized result obtained using genetic algorithm and parallel computing, shows an improvement in performance of around 25% compared with the cycloidal motion.     

Evaluation of materials and components degradation of a PEM electrolyzer for marine applications

An investigation of components degradation in a polymer electrolyte membrane (PEM) electrolyzer technology for naval application is carried out. In naval applications, an electrolyzer has to work using treated seawater obtained on board. Electrolyzer performance is evaluated in terms of hydrogen production per unit of electrical energy input starting from a seawater desalination plant simulating the conditions on board of the ship. A desalinator plant, tailored for the specific application, is designed to produce water having a low ionic conductivity (<5 μS) compatible with the PEM stack electrolyzer requirements. Electrochemical characterizations are carried out on an in-house developed 9-cells PEM electrolyzer by using treated water. Several aspects related with the degradation of materials and components electrolyzer are investigated under oxidizing atmosphere. Specific tests are carried out in a corrosive ambient that simulates the sea environment in terms of humidity, salinity, corrosive conditions etc… In order to simulate highly oxidizing atmosphere, a Dry Corrosion Test Cabinet (DCTC^®) is used to test MEAs and electrolyzer components on the basis of specific international norms (ASTM standard). Both materials and components are characterized by electrochemical and physico-chemical analysis before and after the DCTC^® treatment.     

空气源热泵热水器季节性能实验及优化运行研究

提出并构建了一种测试空气源热泵热水器不同季节运行性能的实验装置。并在装备上进行了实验，实验结果表明，环境温度和水箱设定温度是影响空气源热泵热水器运行性能的重要参数。还提出了一套适用于空气源热泵热水器的控制方案，并通过经济性分析论证了控制方案的优越性。     

Exergetic optimization of a solar photovoltaic thermal (PV/T) air collector

In this paper, an exergetic optimization has been developed to determine the optimal performance and design parameters of a solar photovoltaic thermal (PV/T) air collector. A detailed energy and exergy analysis has been carried out to calculate the thermal and electrical parameters, exergy components, and exergy efficiency of a typical PV/T air collector. The thermal and electrical parameters of a PV/T air collector include solar cell temperature, back surface temperature, outlet air temperature, open‐circuit voltage, short‐circuit current, maximum power point voltage, maximum power point current, etc. An improved electrical model has been used to estimate the electrical parameters of a PV/T air collector. Furthermore, a new equation for the exergy efficiency of a PV/T air collector has been derived in terms of design and climatic parameters. A computer simulation program has been also developed to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Moreover, the simulation results obtained in this paper are more precise than the one given by the previous literature, and the new exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature. Finally, exergetic optimization has been carried out under given climatic, operating, and design parameters. The optimized values of inlet air velocity, duct length, and the maximum exergy efficiency have been found. Parametric studies have been also carried out. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal performance estimation for ventilated PV facades

This paper explores different approaches to thermal performance estimation for ventilated photovoltaic (PV) facades. In particular, an extension of the familiar heat loss and radiation gain factors (U and g values respectively) has been employed to take account of the energy transfer to the facade ventilation air. In total, four terms describing ventilation gains and transmission losses in terms of irradiance and temperature components are defined which characterise the performance of the facade in total. Steady state analysis has been applied in order to express these four parameters in terms of the detailed heat transfer process within the facade. This approach has been applied to the ventilated PV facade of the public library at Mataró, Spain. Monthly U and g values have been derived and the associated thermal energy gains calculated for various climates. An alternative, simpler approach views the ventilated façade as a single solar air collector. The applicability of the standard expression for solar collector efficiency has been investigated through examination of the Mataró data. Summer and winter energy yield calculations carried out on this basis have been compared to the four parameter approach.     

Multi absorber stand alone liquid desiccant air-conditioning systems for higher performance

Achieving comfortable environment with the use of renewable energy or waste heat without creating the hazardous effects over the earth atmosphere are major challenges in the field of air-conditioning. Liquid desiccant technology is a promising option. For the past few decades research is going on worldwide to commercialize such systems. Hybrid liquid desiccant systems (combination of vapor compression (V-C) and liquid desiccant system) have got more attention probably due to higher COPs and lower regeneration temperature for such systems.In the present communication the steady-state performance of stand alone liquid desiccant systems has been simulated and analyzed. Falling film designs of absorber and regenerator have been selected for the study due to their lower pressure drops. The simulation of these components has been carried out by solving the basic mass and energy balance equations. These are nonlinear coupled first order differential equations, which have been solved by using fourth order finite difference Runge-Kutta method. The overall system has been simulated using Warner’s technique. Two new stand alone liquid desiccant cycles utilizing the potential of desiccant fully through multiple absorbers have been proposed. The proposed new cycles improve the COP of stand alone systems significantly. A parametric study has also been carried out on these liquid desiccant cycles to identify the key design parameters affecting the performance of the system.     

Numerical and experimental studies on unitized regenerative proton exchange membrane fuel cell

Increasing energy need and running out of fossil-based fuels direct us to renewable energy resources. Although hydrogen is not an energy source by itself, it is an energy carrier with a high specific heat capacity. As it is used as fuel in unitized regenerative PEM fuel cells, water is separated in electrolyzer mode and stored by producing hydrogen when there is no need for energy. In this study, performance tests on the unitized regenerative PEM electrolyzer/fuel cell were carried out and numerical modelling has been performed. The validity of the developed model was confirmed by the results of the experimental study. Before starting the performance tests, the cell's leakproofness tests were carried out, and the appropriate torque force was optimized, reducing the contact resistance that causes performance loss. The material selection of the cell components and corrosion-resistant materials that can operate in both electrolyzer and fuel cell modes were preferred.In this study, 0.019 slpm of hydrogen and 0.0095 slpm of oxygen gas is produced in the electrolyzer mode, while a power density of 0.353 W/cm² is obtained in the fuel cell mode at 80 °C, from a unitized regenerative PEM fuel cell with a 5 cm² active area, whose cell elements are combined with a 3 Nm clamping torque by using 12 bolts.     

Optimal sizing of renewable hybrids energy systems: A review of methodologies

Taking into account oil depletion, increasing population, and increasing energy demand, electrical power generation has entered into a new phase of evolution, which can be characterized mainly by increasing concerns about climate change, by a transition from a hydrocarbon-based economy, and by an efficient utilization of energy. In this sense, it seems that alternative energies have gathered considerable momentum since 1970s oil crisis. Moreover, Earth seems to have enough power to cover World’s electrical power demand but not by a single source; for this reason, recent researches have been carried out in order to design in an optimal way system’s configuration. Nevertheless, because of the randomized nature of alternative energy sources, electrical load profile, as well as the non-linear response of system components, to mention a few, is not an easy to assess the hybrid energy system performance; therefore, hybrid energy system designing has been a complex task. For this reason, the aim of this paper is to present a brief review about the sizing methodologies developed in the recent years.     

In situ check of collector array performance

Within the scope of the EU-ALTENER project “Guaranteed Yield of Solar Water Heaters”, a procedure has been proposed for in situ check of collector array performance. The goal of the procedure is prediction of collector array long-term performance, yearly energy yield in particular. The prediction is carried out using the array parameters identified by short-term monitoring of array performance under non-stationary measurement conditions i.e. transient weather and the system operating conditions. The variability of the influencing variables determines accuracy of the identified parameters for the particular array. The necessary variability may be determined by the detailed performance simulation of a particular array, using the components design parameters of the solar system and the long-term, site-related weather data. The procedure is checked out on a solar water heater with 60 m² collector array. Satisfactory accuracy and repeatability of the significant identified array parameters are achieved. The prediction of the array yearly energy yield is accurate within ±5%.     

Transient characteristic of reciprocating compressors in household refrigerators

Reduction in energy consumption associated with household appliances is a challenging subject. One of the appliances with great contribution in energy consumption is the household refrigerators [1], [2]. Among the different components of a refrigerator, the compressor has the most effect on system energy consumption. A knowledge of the transient performance of compressors is vital for reduction of energy consumption and improving the overall performance of a refrigerator. In this paper the M7 model of 1/5 hp Nicchi compressor belonging to 12 ft³ refrigerators with refrigerant R12 is selected as a sample and different tests are carried out to determine its transient behavior. Based on the analysis of experimental results, the governing equations and the simulation program of transient behavior have been developed. Good agreement between theoretical and experimental results means that the simulation model could be an appropriate tool to study the transient behavior of reciprocating compressors in different conditions. Analysis of predicted and experimental results shows that refrigerators consume more power in the transient mode as compared to the steady mode, therefore shortening the transient period can lower the energy consumption of the system. Also an isentropic assumption for the hermetic compressor is not a correct assumption, especially for the transient mode. With appropriate design of compressor inlet which locates it near to the suction valve, the energy efficiency will be improved.     

A review of the performance of double pass solar air heater

Improvement of the thermal performance of a solar air heater can be obtained by enhancing the rate of heat transfer. The thermal efficiency of double pass solar air heater is higher in comparison to single pass with the concept involved of doubling the heat transfer area without increase in the system cost. Numbers of studies have been carried out on the performance analysis of double pass solar air heater provided with heat transfer augmentation techniques viz. using extended surfaces, packed bed, corrugated absorber were reported in the literature and found more increase in the thermal efficiency in comparison to conventional double duct solar air heater. These studies includes the design of double pass solar air heater, heat transfer enhancement, flow phenomenon and pressure drop in duct. This paper presents an extensive study of the research carried out on double pass solar air heater. Based on the literature review, it is concluded that most of the studies carried out on double pass solar air heater integrated with porous media and extended surfaces. Few studies were carried out with corrugated absorber. Further no study has been reported so far on double pass solar air heater with absorber plate artificially roughened from both the sides. Mathematical models based on energy analysis of some configurations of solar air heater have been discussed.     

Thermodynamic analysis of an integrated power generation system driven by solid oxide fuel cell

A new integrated power generation system driven by the solid oxide fuel cell (SOFC) is proposed to improve the conversion efficiency of conventional energy by using a Kalina cycle to recover the waste heat of exhaust from the SOFC-GT. The system using methane as main fuel consists an internal reforming SOFC, an after-burner, a gas turbine, preheaters, compressors and a Kalina cycle. The proposed system is simulated based on the developed mathematical models, and the overall system performance has been evaluated by the first and second law of thermodynamics. Exergy analysis is conducted to indicate the thermodynamic losses in each components. A parametric analysis is also carried out to examine the effects of some key thermodynamic parameters on the system performance. Results indicate that as compressor pressure ratio increases, SOFC electrical efficiency increases and there is an optimal compressor pressure ratio to reach the maximum overall electrical efficiency and exergy efficiency. It is also found that SOFC electrical efficiency, overall electrical efficiency and exergy efficiency can be improved by increasing air flow rate. Also, the largest exergy destruction occurs in the SOFC followed by the after-burner, the waste heat boiler, the gas turbine. The compressor pressure ratio and air flow rate have significant effects on the exergy destruction in some main components of system.     

Sizing of integrated renewable energy system based on load profiles and reliability index for the state of Uttarakhand in India

In recent years the decentralized rural electrification is becoming cost effective and convenient for areas where grid extension is very difficult. The present paper deals with the electrification of dense forest areas of Uttarakhand state in India by Integrated Renewable Energy Optimization Model (IREOM). The IREOM consists of locally available renewable energy resources such as Micro-Hydropower (MHP), biomass, biogas, wind and solar photovoltaic (SPV) systems have been used to meet electrical energy and cooking energy needs of a cluster of villages. The paper includes the selection of different system components, sizing and development of a general model to find out optimal combination of energy subsystems for the selected study area in order to minimize the cost of energy (COE) generation for a required reliability values. The sizing of different renewable energy system components has been carried out so that they are suitable for four different seasonal load profiles. The two reliability values are considered for the selection of optimum solution of year round application. The model developed for this purpose, has been found to be quite useful in optimizing the renewable energy system sizes that are available in market. The proposed model totally depends on the renewable energy systems and eliminates the use of conventional energy systems.     

Energy and environmental performance of a heat pump in different power grid scenarios

Electric-driven heat pumps are one of the most encouraging systems that could support the raising of renewables contribution in civil sector energy consumption, especially with reference to the Countries with a high contribution of renewable energy sources in electricity generation mix. However, the evaluation of the effective energy and environmental performance of an electric heat pump meeting the space heating and cooling requests of a building has to consider several factors that affect the results. Among them great attention should be given to the variability of weather conditions in which the system operates, the changeability of the efficiency and environmental indicators of power grid. The analysis becomes more complex if the variation of these parameters is considered in terms of time and geographic location but it leads to the actual evaluation of the energy conversion system performance that is neglected by European Regulations. This paper presents an energy and environmental analysis of an electric-driven air-source heat pump providing the space heating and cooling needs of the same building located in two different geographical locations by means of a dynamic simulation performed in TRNSYS 17. The analysis is carried out considering the average and time-dependent values of the carbon dioxide emission factors for electricity and the power grid efficiency indicators evaluated by means of the real electricity generation data. In addition, the paper proposes the evaluation of the average and hourly energy and environmental parameters referred only to the electricity market zones in which the buildings are located. These indices are considered in the analysis too. The results have highlighted that the assessment based on average and high-resolution parameters, as well the evaluation based on indicators referred to electricity market zones only, could return very different outcomes leading to a significant overestimation or underestimation of the energy and environmental performance of the system based on the electric-driven heat pump. Finally, a further analysis has been carried out to determine how the results can vary considering the average value of the electric efficiency indicator suggested by Italian Regulations and that of other European Countries.