Study of the Thermal Technical Characteristics of a Combined Solar Desalination and Drying Plant

The paper presents the results of calculated research on determining the thermal technical indicators of a combined solar desalinization and drying plant. The structure of the plant is developed and proposed. A mathematical model is developed that describes the thermal processes occurring in the plant based on heat-balance equations solved using the Laplace method.     

Hydrogen production costs of a polymer electrolyte membrane electrolysis powered by a renewable hybrid system

In this work, a novel approach related to the production of hydrogen using a polymer electrolyte membrane electrolysis powered by a renewable hybrid system is proposed. The investigation is carried out by establishing energy balances in the different components constituting the combined renewable system. A mathematical model to predict the production of electricity and hydrogen is proposed. The discrepancies between the numerical results and those from the literature review do not exceed 7%. The results show that the overall efficiency and the capacity factor of the combined renewable system without thermal storage are 20 and 34%, respectively. The levelized cost of hydrogen also is 6.86 US$/kg. The effect of certain physical parameters such as optical efficiency, water electrolysis temperature, unit electrolysis capital cost and solar multiple on the performance of the combined system is investigated. The results show that the performance of hydrogen production is optimal when the solar installation is three times oversized. The results also show that the levelized cost of hydrogen for the optimal sized is 4.07 US$/kg. Finally, the proposed combined system can produce low cost hydrogen and compete with hybrid sulfur thermochemical cycles, conventional photovoltaic installations, concentrated photovoltaic thermal systems and wind farms developed in all regions of the world.     

Analytical Model of a Combined Adsorption Cooling and Mechanical Vapor Compression Refrigeration System

ABSTRACT

A combined adsorption and mechanical vapor compression system is a reasonable option to reduce the consumption of fossil fuels for air conditioning by utilizing waste heat. Performance predictions of combined adsorption and mechanical vapor compression systems require detailed dynamic modeling because the transitional characteristics explain the nature of the adsorption system. It is, however, desirable to simplify the model for practical use at engineering stages. Since the mechanical vapor compression system is based on the steady-state thermodynamic cycle, a semi-steady-state modeling of adsorption cycles would be functional for analysis of combined systems. In our study, the analytical solution of transient simulation for adsorption cycles was combined with a steady-state mathematical model of the mechanical vapor compression system. The performance of the combined system was analyzed based on the model developed, taking into account the cycle time of the adsorption cycle. The results show the performance characteristics as well as the energy-saving potential of the combined system.     

Thermal analysis of a wet-disk clutch subjected to a constant energy engagement

A combined theoretical and experimental thermal analysis is conducted on the plates within a wet clutch for one engagement. An analytical model using the separation of variables technique is developed to simulate the temperature rise due to the non-conservative friction and relative motion between the steel plates and friction plates of the clutch. A complimentary numerical model is also developed to compute the temperature distribution in the steel plate. The experiment performed included a wet clutch instrumented with thermocouples and installed in a power-shift transmission where the temperature rise during one clutch engagement was measured. The total energy is then estimated by accounting for system inertia, torque and rotating speeds. Finally, the temperature rises predicted by the analytical and numerical models are validated with the experimental data.     

Ecological efficiency and thermoeconomic analysis of a cogeneration system at a hospital

This work aims with an approach for cogeneration plants evaluation based on thermoeconomic functional diagram analysis. The second law of thermodynamics is used to develop a methodology to analyse cogeneration systems, based on exergoeconomics evaluation. The thermoeconomic optimisation method developed is applied to allow a better configuration of the cogeneration plant associated to a university hospital. Also ecological efficiency is evaluated. The method was efficient and contributes for thermoeconomics modelling and analysis and can be applied to any sort of thermal system, especially those with combined heat and power in thermal parity.     

Eddy current and impedance evaluation using a two-dimensionalfinite element method

A finite element method is developed to evaluate cylindrical electromagnetic fields due to eddy currents inside linear conducting media. Boundary conditions are imposed in an integral form combined with Neumann conditions. The method is applied to a periodic system of slot embedded conductors in the rotor of an induction machine and is verified by comparison with an analytical method     

Experimental investigation of coupled conduction and laminar convection in a circular tube

Wall heat conduction effects on laminar flow heat transfer are experimentally investigated. The steady flow of water through a uniformly heated copper pipe is considered in the experiment, which covers a range of Reynolds numbers from 500 to 1900. The thermal behaviour of the test section is simulated numerically and the influence of conduction along the pipe wall is therefore accounted for in the reduction of the data. Fully developed flow results satisfactorily compare with predictions by a theoretical method previously developed by the authors [Heat Technol. 2,72 (1984)]. Results are also reported for the case where the velocity profile is partially developed at the inlet of the heat transfer section. The combined effects on heat transfer of flow development and of wall axial heat conduction are discussed.     

Simulation of a combined wind and solar power plant

The combined generation of electricity by wind and solar energy is a very attractive solution for isolated regions with high levels of yearly wind energy and insolation. A computer model is developed for the simulation of the electricity system of a Mediterranean island, including a wind power plant, a photovoltaic power plant and a storage system. In order to obtain an overall view of the system performance and economic aspects, the model also incorporates a number of diesel generators. Daily simulations for the Greek island Kythnos show that such a combined system of moderate size can provide a large fraction of the electrical energy requirements. Various parameters calculated in the simulation can be used to improve the configuration of the system and to estimate the cost of the electrical energy unit.     

Modeling and control of a SOFC-GT-based autonomous power system

In this article, a dynamic, lumped model of a solid oxide fuel cell (SOFC) is described, as a step towards developing control relevant models for a SOFC combined with a gas turbine (GT) in an autonomous power system. The model is evaluated against a distributed dynamic tubular SOFC model. The simulation results confirm that the simple model is able to capture the important dynamics of the SOFC and hence it is concluded that the simple model can be used for control and operability studies of the hybrid system. Several such lumped models can be aggregated to approximate the distributed nature of important variables of the SOFC. Further, models of all other components of a SOFC-GT-based autonomous power system are developed and a control structure for the total system is developed. The controller provides satisfactory performance for load changes at the cost of efficiency.     

Thermodynamic analysis of a photovoltaic thermal system coupled with an organic Rankine cycle and a proton exchange membrane electrolysis cell

In this study, the performance of a Photovoltaic Thermal-Organic Rankine Cycle (PVT-ORC) system combined with a Proton Exchange Membrane Electrolysis Cell (PEMEC) is investigated. A combined numerical/theoretical model of the system is developed and used to evaluate the effect of various system design parameters. In addition, the effects of using water, ethylene glycol, and a mixture of water and ethylene glycol (50/50) as the working fluid of the PVT system and R134a, R410a, and R407c as the working fluid of the ORC cycle on the performance of the PVT-ORC-PEMEC system are studied. Based on the results, R134a and water demonstrated the best performance as the working fluid of the ORC and PVT systems. Moreover, the electrical efficiency of the combined PVT-ORC system is 15.65% higher than the electrical efficiency of the conventional PVT system. Also, the maximum hydrogen production rate of the proposed PVT-ORC-PEMEC system is calculated to be 1.70 mol/h.     

CFD simulation of a floating offshore wind turbine system using a variable-speed generator-torque controller

Prediction and control of rotor rotational velocity is critical for accurate aerodynamic loading and generator power predictions. A variable-speed generator-torque controller is combined with the two-phase CFD solver CFDShip-Iowa V4.5. The developed code is utilized in simulations of the 5 MW floating offshore wind turbine (FOWT) conceptualized by the National Renewable Energy Laboratory (NREL) for the Offshore Code Comparison Collaboration (OC3). Fixed platform simulations are first performed to determine baseline rotor velocity and developed torque. A prescribed platform motion simulation is completed to identify effects of platform motion on rotor torque. The OC3’s load case 5.1, with regular wave and steady wind excitation, is performed and results are compared to NREL’s OC3 results. The developed code is shown to functionally control generator speed and torque but requires controller calibration for maximum power extraction. Generator speed variance is observed to be a function of unsteady stream-wise platform motions. The increased mooring forces of the present model are shown to keep the turbine in a more favorable variable-speed control region. Lower overall platform velocity magnitudes and less rotor torque are predicted corresponding to lower rotor rotational velocities and a reduction in generated power. Potential improvements and modifications to the present method are considered.     

Temperature distribution in a solar irradiated liquid film flowing over a solid wall

A mathematical model is developed to predict the thermal behavior of a thin liquid film flowing along an inclined surface and exposed to an intense solar radiation flux. The pertinent equations are solved assuming a uniform velocity across the film. Radiation losses are combined with convection through a heat transfer coefficient at the free surface of the film. Numerical data indicate that temperature differences on the order of 100°C can exist across the fluid layer although its thickness may not exceed 0.5 mm. An important conclusion of this study is that a moderately blackened heat transfer medium is sufficient to accomplish the required task in an optical cavity.     

焦载热部分气化燃煤联合循环系统性能分析

文中提出的一种新型燃煤联合循环发电技术,载热部分气化联合循环技术,经近几年的研究及运行实验,得到不断完善。最近,作为这种系统的改进型式－－焦载热部分气化联合循环已被提出,其焦载热炉及气化炉部分已在清华电厂投建,并进行冷态调试。本文在载热循环基础上,通过改变煤成分等参数对焦载热系统进行分析,得出结论认为煤气质量及流率的影响对整个整合循环系统极为关键。     

Implementation of a fast fluid dynamics model in OpenFOAM for simulating indoor airflow

ABSTRACT

This study implemented fast fluid dynamics (FFD) in Open Field Operation and Manipulation and used a local searching method that made the FFD solver applicable to unstructured meshes. Because the split scheme used in FFD is not conservative, this investigation developed a combined scheme that used a split scheme for the continuity and momentum equations and an iterative scheme for scalar equations. The combined scheme ensures conservation of the scalars. This investigation used two two-dimensional cases and one three-dimensional case, with the experimental data, to test the FFD solver. The predicted results were similar with different types of mesh and numerical scheme and agreed in general with the experimental data.     

Intelligent power management in a vehicular system with multiple power sources

This paper presents an optimal online power management strategy applied to a vehicular power system that contains multiple power sources and deals with largely fluctuated load requests. The optimal online power management strategy is developed using machine learning and fuzzy logic. A machine learning algorithm has been developed to learn the knowledge about minimizing power loss in a Multiple Power Sources and Loads (M_PS&LD) system. The algorithm exploits the fact that different power sources used to deliver a load request have different power losses under different vehicle states. The machine learning algorithm is developed to train an intelligent power controller, an online fuzzy power controller, FPC_MPS, that has the capability of finding combinations of power sources that minimize power losses while satisfying a given set of system and component constraints during a drive cycle. The FPC_MPS was implemented in two simulated systems, a power system of four power sources, and a vehicle system of three power sources. Experimental results show that the proposed machine learning approach combined with fuzzy control is a promising technology for intelligent vehicle power management in a M_PS&LD power system.     

Combustion modes periodical transition in a hydrogen-fueled scramjet combustor with rear-wall-expansion cavity flameholder

Cavity-stabilized combustion modes periodical transition in a laboratory hydrogen-fueled scramjet combustor were captured by high speed imaging. Experiments were performed with an isolator entrance Mach number of 2.92, and a sonic transverse fuel jet upstream of the cavity was employed. The reproducibility of the results had been tested in several repeated experiments. It is observed that, under a fixed combustor entry flow parameters and fuel equivalence ratio, after the flame has been fully developed, the flame structure may periodically transform between two different combustion modes. Specifically, under a moderate equivalence ratio, the flame structure switches between the cavity shear-layer stabilized mode and the combined shear-layer/recirculation stabilized mode, which shows an apparent periodicity with a period of about 7.5 ms. The formation mechanism for this novel phenomena is analyzed and some suppositions are given. When increasing the equivalence ratio to a high level, the flame structure shows a quasi-periodic low-frequency oscillation and the combustion mode changes between the combined shear-layer/recirculation stabilized mode and the cavity-assisted jet wake stabilized mode. At last, the formation mechanism and characteristics of the combined shear-layer/recirculation stabilized mode are detailed analyzed.     

Total-productivity analysis of a Nigerian petroleum-product marketing company

Productivity in Nigeria is decreasing: this has adversely affected the average standard-of-living of the population and led to economic hardship. HIV/AIDS, hunger, disease and wars have lowered African productivity and the effectivenesses of public utilities have declined, while unemployment and crime are on the increase. A computer program, which considers the combined concept of partial productivity, total productivity measurement and reliability in order to analyse the effectiveness of a firm, society or nation has been developed. Its predictions have been tested with data from a Nigerian petroleum-product marketing company, namely Rock Oil and Gas Ltd., Aba, Abia State: the management of this business is representative of those of many Nigerian firms. The developed software (see Appendix) can help in identifying the causes of productivity problems, which can so adversely affect the performance of any organisation.     

Gas turbine turbocharged by a steam turbine: a gas turbine solution increasing combined power plant efficiency and power

A new design of a combined-cycle gas turbine power plant CCGT with sequential combustion that increases efficiency and power output in relation to conventional CCGT plants is studied. The innovative proposal consists fundamentally in using all the power of the steam turbine to turbocharge the gas turbine. A computer program has been developed to carry out calculations and to evaluate performance over a wide range of operating conditions. The obtained results are compared with those of combined cycles where the gas turbines are not turbocharged and the gas and the steam turbines have independent power exits; the advantages of the new design are stated.     

一种高抗扭矩组合式凸轮轴的研制

采用内高压胀接成形的方法研制了某型发动机组合式凸轮轴。静态抗扭矩测试和动态耐久性疲劳测试结果表明:所研制的凸轮轴具有高抗扭矩、高耐磨性;与此同时，所开发的整套制造工艺及相关的专用制造设备也得到了有效论证。     

Thermal performance of a naturally ventilated cavity wall

Cavity walls are often proposed in the building envelope design as a solution for improving the thermal comfort of the occupants and reducing the adverse condensation effects on the building fabric. Although the behaviour of a non‐ventilated cavity wall is well‐known, more studies are required when cavity ventilation is allowed. In order to consistently predict the thermal behaviour of a naturally ventilated cavity wall, a convective model based on the integral equations of motion and enthalpy was developed and applied in the present study. The model is presented as a combination of two limiting cases of a steady laminar flow into the channel gap: fully developed flow and boundary layer flow. Conduction effects across the system are also included through a proper limiting case and then combined with the convective model. In addition a numerical CFD model was developed that provides solution for free convective flow configurations between two parallel conducting vertical walls. For comparison purposes, some test cases were simulated with the two models and a general good agreement was found between results. Finally, the integral model was applied to assess the thermal performance of a ventilated cavity wall for winter and summer conditions. Copyright © 2009 John Wiley & Sons, Ltd.