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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.

This study presents a numerical analysis of the melting process of phase change materials (PCMs) within a latent heat thermal energy storage (LHTES) system employing zigzag plate. The numerical model used NaCl-MgCl2 mixture as PCMs and hot air as heat transfer fluid (HTF). An experimental system was built to validate the model, and the experimental data agrees reasonably well with the simulation results. The simulation results revealed the effects of the Reynolds and Stefan numbers and the surface topography of the zigzag plate on the charging process. Besides, the effect of the relationship between Reynolds and Stefan numbers on the charging process under a new boundary condition employing a fixed input power was studied. It is found that by modifying the shape of the zigzag plate surface it is feasible to enhance the heat transfer of the LHTES unit remarkably. The melting rate of PCMs increases with the value of Ste or Re numbers with only one of them changing; however, the melting rate of PCMs decreases with the increasing Ste (or decreasing Re) in a fixed input power condition.

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.