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The water medium hydraulic retarder is the latest type of auxiliary braking device and has the characteristics of high power density, large braking torque, and compact structure. During traveling, this device can convert the kinetic energy of a vehicle to the heat energy of the cooling liquid and replace the service brake under non-emergency braking conditions. With regard to the constant-speed function of the water medium hydraulic retarder, this study designs a controller based on the neural network proportional–integral–derivative (PID) algorithm to achieve the steady traveling of the vehicle at constant velocity during a downhill course by controlling the filling ratio of the water medium hydraulic retarder. To validate the algorithm’s effectiveness, the dynamic model of the heavy-duty vehicle in the downhill process and the physical model of the water medium hydraulic retarder are developed. Three operating conditions, including a fixed slope, step-changing slope, and continuous changing slope, are set, and a simulation test is carried out in the MATLAB/Simulink environment. The neural network PID algorithm has better adaptability in controlling than the traditional PID algorithm. Thus, it controls the water medium hydraulic retarder such that the braking requirements of heavy-duty vehicles under a changing slope working condition are satisfied, and it performs constant-speed control when the vehicle travels downhill. Therefore, the proposed control method can significantly improve the safety of road traffic.

Vaporisation (evaporation and boiling) through direct absorption solar collectors (DASCs) has recently drawn significant attention. Many studies suggested that plasmonic nanoparticles, such as gold nanoparticles, can significantly enhance the photo-thermal conversion efficiency of DASCs. However, there is still a lack of comparative studies of the feasibility of using gold nanoparticles for solar applications. This study performed well-controlled experiments for two different categorised particles, i.e., gold and carbon black suspended in water, and assessed their performance in terms of evaporation rate, materials cost and energy consumption. The results show that gold nanofluids are not feasible for solar evaporation applications, where the cost of producing 1 g/s vapour is ∼300 folds higher than that produced by carbon black nanofluids. This infeasibility is mainly due to the high cost and the low absorbance of gold comparing to carbon black nanoparticles. Moreover, this work reveals that with the increase of nanoparticle concentration or incident solar radiation, more energy is trapped in a small volume of the nanofluid near the interface, resulting in a local higher temperature and a higher evaporation rate. For efficient steam production, future optimisation of the system should consider concentrating more solar energy at the interface to maximize the energy consumed for evaporation.

The water medium (WM) retarder is an auxiliary braking device that could convert the kinetic energy of the vehicle to the thermal energy of the coolant, and it is used instead of the service brake under non-emergency braking conditions. This paper analyzes the flow distribution based on a mathematical model and analyzes the key factors that could affect the filling ratio and the braking torque of the WM retarder. Computational fluid dynamics (CFD) simulations are conducted to compute the braking torque, and theresults are verified by experiments. It is shown that the filling ratio and the braking torque can be expressed by the mathematical model proposed in this paper. Compared with the Reynolds averaged Navier-Stokes (RANS) turbulent model, the shear stress transport (SST) turbulent model can more accurately simulate the braking torque. Finally, the flow distribution and the flow character in the WM retarders are analyzed.

With the development of the road industry, heavy-duty vehicles now require additional braking power to fulfill their braking requirements. Auxiliary braking systems, which include a hydraulic retarder and an engine brake, can provide additional braking force in nonemergency braking conditions. A water medium retarder is a new type of hydraulic retarder that can convert the kinetic energy of a vehicle into the thermal energy of coolant. This study introduces a novel auxiliary braking system involving a water medium retarder and an engine brake for heavy-duty vehicles. The specific forces of heavy-duty vehicles and the auxiliary braking system are established. The control logic of the novel auxiliary braking system is assigned, and a main controller is designed to dynamically manage the entire braking process. The main controller includes controllers A and B, which handles the engine brake and water medium retarder, respectively. The heavy-duty vehicles dynamic system model is created using MATLAB/Simulink. Upon performance testing, simulation results show that the designed main controller can effectively and rapidly manage the auxiliary braking system, thus satisfying the braking requirements in any nonemergency braking condition. Even when the slope of a road changes, the main controller can extract dynamical forces as well as acceleration parameters and fulfill the braking requirements of vehicles.

Hydraulic retarders are auxiliary braking devices that reduce the velocity of a vehicle, particularly when a vehicle is driven downhill. Such velocity reduction could reduce the potential risk caused by brake failure caused by the service brake working for a long time and the temperature of the brake shoe becomes extremely high. This paper introduces the construction of the hydraulic retarder and proposes two mathematical models for the hydraulic retarder. The first mathematical model is deduced by using fluid mechanics, which is used to analyze the mechanism of how braking torque is produced and the key factors that can influence the value of the braking torque. The second mathematical model is deduced by using thermodynamics, which is used to quantify the heat produced by the hydraulic retarder. This research emphasizes that the flow rate and the average velocity of the working fluid in the working chamber mainly determine the braking torque of the hydraulic retarder. The flow rate into and out of the working chamber determines the temperature rise of the working fluid. Computational fluid dynamics (CFD) simulations are conducted with the Reynolds-averaged Navier-Stokes (RANS) and Shear Stress Transport (SST) turbulent models. Experiments are carried out to justify the two mathematical models and the CFD simulations. The results show that the mathematical models are capable of describing the force analysis and energy conversion of the hydraulic retarder and SST is more accurate for CFD simulation and the error is within 6 %.

Water medium retarders are auxiliary braking devices which can reduce the vehicle speed by converting the mechanical energy of a driving vehicle to the total energy of the working fluid. These retarders can replace service brakes in non-emergency braking conditions. This study analysed the dynamic and thermodynamic characteristics of water medium retarders. An observer was designed to identify the optimal braking power of the water medium retarder under different braking conditions. The braking process involving the retarder can be divided into three stages. The controller was designed separately at each stage to control the braking torque of the water medium retarder according to braking requirements. A combined dynamic and thermodynamic vehicle model was also constructed with MATLAB/Simulink. The effects of the controller on the vehicle feedback control system were analysed. The results show that the controller equipped with the observer can effectively control the water medium retarder to satisfy the braking requirements of vehicles on the assumption that the coolant circulation is sufficiently radiated. Finally, an experiment was conducted to determine the performance of the controller and to validate the simulation results.

A novel thermal energy storage system that can store large amounts of wind power by high temperature phase change materials (PCMs) has been developed. Wind power is growing rapidly due to the global environmental concern regarding green and clean energy. However, the extent of concerns become greater of wind curtailed loss due to insufficient transmission capacity, which contributes to serious wind power curtailment and reduction in economic benefits of wind farms. Large-scale thermal energy storage provides a solution to enhance wind power utilization. On the basis of high thermal capacity PCMs and cogeneration technologies, the uncertain wind power is converted into thermal energy, which can be stored in thermal energy storage. An optimized storage system and heat/electric cogeneration system is designed for wind power system. The stored thermal energy can be used for residents, such as hot water, heating, etc. In particular, it can satisfy heating demands such as household heating in the north of china. This system could be used instead of conventional heating boilers and reduce fossil fuel consumption.

BACKGROUND: Chemical looping combustion (CLC) is a promising environmentally friendly technology in which the greenhouse gas CO2 can be readily separated at high-purity, therefore providing an effective method of carbon capture. Its performance, however, is limited by the kinetics of oxidation of the oxygen carrier, whose size is typically in the range of micrometers to millimetres. This paper reports a new idea using metallic nanoparticles as potential oxygen carriers to improve the performance of chemical looping combustion. RESULTS: A detailed experimental study of the heating and oxidation of iron nanoparticles in a simultaneous TGA/DSC system was conducted. Kinetic analysis revealed improved reactivity of iron nanoparticles, as shown by a reduction in the activation energy, which is highly dependent upon the conversion ratio. The implication and potential application of nanoscale metallic nanoparticles as oxygen carriers in CLC are discussed. CONCLUSION: Compared with conventional sized iron particles, the reduction of particle size to nanoscale can offer a number of advantages, such as increased reactivity, reduced mass resistance and enhanced heat transfer, however, a number of practical factors associated with increased specific surface area need to be assessed carefully. Copyright © 2010 Society of Chemical Industry

This study investigates the heating and cooling of a shell−core structured Ni−Al functional particle through a molecular dynamics simulation. The functional nanoparitcle is constructed from their perfect crystal measuring 5.6 nm in diameter with a shell thickness of 0.5 nm. The simulation is carried out within a Nose−Hoover thermostat scheme of the NVT canonical ensemble and performed by an Embedded-Atom-Method (EAM) force field. The thermodynamic properties and structure evolution during continuous heating and cooling processes are investigated through the characterization of the gyration radius, radial distribution function (RDF), atom number distribution, mean-square-distance (MSD), and layered potential energy distribution. Some unique behaviors related to nanometer scale functional particles are identified that include two-way diffusion of aluminum and nickel atoms, enhanced melting of the aluminum core through the shell structure, glass phase formation for the fast cooling rate, and the Ll2 Ni3Al ph...

The sintering of two different-sized nickel nanoparticles is simulated by a molecular dynamics method in this work. The particles are partitioned into different regimes where tracing atoms are arranged to investigate the sintering kinetics. The detailed sintering process of two nanoparticles, 3.52 and 1.76 nm in diameter, respectively, is subsequently examined by the shrinkage ratio, gyration radius, mean square displacement, sintering diffusivity, and activation energy. A three-stage sintering scenario is established, and the layered structure shows a regime dependent behavior of diffusivity during the sintering process. Besides the surface diffusion, sintering of different-sized nanoparticles is found to be affected by a few other mechanisms.

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or "nanofluids," was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (�10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise. � 2009 American Institute of Physics.

Reactive metallic particles involve many complicated physical and chemical processes. Using molecular dynamics (MD) simulation as an example, this chapter explores the fundamental heating and reaction at the individual nanoparticle level. A brief overview of MD simulation is first introduced, and then the chapter focuses on the simulation of individual nanoparticle behavior related to ignition and combustion of energetic particles, which includes (i) size-dependent properties of individual nanoparticles, (ii) sintering and agglomeration of metallic nanoparticles, (iii) oxidation of nanoparticle in the presence of oxygen, and (iv) heating and cooling of core–shell-structured nanoparticles. This chapter provides some fundamental understanding the mechanism of reactive particles at the nanoscale, being complementary to bulk scale experiments and simulation.

Hydraulic retarders are auxiliary braking devices that reduce vehicle speed by converting its kinetic energy into thermal energy of a working fluid. This study analyzes the torque-output characteristics of a new type of hydraulic retarder and optimizes its control strategy under different braking conditions. The design of an observer is based on an analysis of the vehicle dynamic system to ensure that it sets the control target of the dynamic filling ratio for hydraulic control system. With the assistance of the observer, the hydraulic retarder can produce the required braking torque as quickly and as accurately as possible. This study simulates a feedback control system of the vehicle dynamic model with the observer. The results prove that even if the vehicle is driven under complex conditions wherein the slope of the road is changed, the observer effectively sets a control target of the filling ratio for the hydraulic control system. This mechanism strengthens the adaptability and accuracy of the hydraulic retarder control strategy.

This study presents an atomic level of molecular dynamic simulation of oxidation of silicon nanoparticle in use of a reactive force field (ReaxFF). The oxidation dynamics is revealed through the energy release, bond evolution and oxygen exchange processes. The oxidation is found to proceed in the manner of evolution of silicon-oxygen bond configuration, accompanied by the oxygen exchange process. The heat of reaction and the activation energy of the bond transformation process are also estimated, which indicates the capability of ReaxFF in the simulation of energetic materials.

The melting and sintering of two different-sized metallic nanoparticles are simulated by a molecular dynamics method in this work. The particles are partitioned into different regimes where tracing atoms are arranged to investigate the melting and sintering kinetics. The melting of individual particles is firstly investigated and compared with established studies, where the size-dependent melting depression and surface melting phenomenon are revealed. The detailed sintering process of two nickel nanoparticles, 3.52 and 1.76 nanometers in diameter respectively, is subsequently examined by the gyration radius, mean square displacement (MSD), root mean square displacement (RMSD), sintering diffusivity and activation energy. A three-stage sintering scenario is illustrated, and the layered structure shows the regime dependent behavior of diffusivity during the sintering process. Beside the surface diffusion, sintering of different-sized nanoparticles is found to be affected by a few other mechanisms.

This work reported an experimental investigation of complete oxidation of nickel nanoparticles using simultaneous thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Nickel nanoparticles and their elemental compositions were characterized by Brunauer-Emmett-Teller (BET) analysis, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The oxidation experiments were performed under isoconversion conditions for seven heating rates, varying from 2 to 20 K min(-1), with temperatures up to 1000 degrees C. The experiments revealed unique oxidation behaviour of nickel at the nanometre scale, such as early oxidation and melting phenomena, variable activation energies and different oxidation kinetics between low and high conversion ratios. Unlike its bulk counterpart where the activation energy is a constant, the activation energy of nickel nanoparticles depended on the conversion ratio, ranging between 1.4 and 1.8 eV. The oxidation kinetics of nickel nanoparticles changed from the classical diffusion controlled mechanism to a pseudo-homogeneous reaction as conversion ratios were over 50%. The oxidation mechanisms of nickel nanoparticles were further discussed and future studies to enhance understanding were identified.