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Hydrogen refueling stations (HRSs) are among the most important infrastructures for fuel cell vehicles. However, the safety issue of HRSs has become a key constraint to the wide application and development of hydrogen energy. This article presents a quantitative risk assessment of the first liquid HRS (LHRS) in China and conducts a comprehensive assessment in terms of both individual (IR) and societal risks (SRs). The results showed that both the IRs and SRs related to the LHRS exceeded the risk acceptance criteria. The rupture of the flexible hose of the dispenser and the leak from the compressor are the main contributors to these risks. On the other hand, implementing appropriate mitigation measures on the level of the LHRS dispenser and compressor, including the addition of breakaway couplings in the flexible hose of the dispenser, the installation of hydrogen detection sensors, the arrangement of automatic and manual emergency shutdown buttons, and the elevation of the compressor, is capable of reducing the risk of the LHRS to be within the risk acceptance criteria. [ABSTRACT FROM AUTHOR]

[Objectives] This paper aims to analyze the dynamic cooling loads of ship on fixed routes and conclude with their changing laws.[Methods] To this end,the ship cabin is modelled to compare the dynamic cooling load changes in 6 different regions of the route(i.e. Hong Kong,Shantou,Fuzhou, Wenzhou,Shanghai,Dalian). Besides,the relation between the course angle and the sun azimuth angle is established to analyze the variation of dynamic cooling loads due to change of these angles.[Results] It is shown that the maximum total cooling load in Wenzhou area can reach 9.63 kW,while that in Shantou area only accounts for 53% of Wenzhou area,i.e. 5.11 kW. Course angle has great influence on the dynamic cooling load. At the course angle of 40° east by north,the total dynamic cooling load,the cooling load resulted from the heat penetration on wall surfaces(including windows)and the cooling load resulted from absorption of solar radiation increase by up to 21%,43% and 62% respectively. The greater the deviation from the normal north direction is,the greater the increase of the total dynamic cooling load will be. The increase of cooling load is related to the concentration time and the course angle.[Conclusions] The load variation caused by course angle during navigation should be considered, to accuately calculate the maximum load of air conditioning, and to select proper equipment model or optimal controlling strategy. Moreover,the air conditioning load calculation of each voyage should take into account the environmental conditions of covered areas.

Application of high-precision non-intrusive flow field measurement techniques in transonic cryogenic wind tunnels (CWT) is confined to the lack of suitable tracer particles. The present study explored the feasibility of utilizing non-equilibrium condensing nitrogen droplets as tracer particles. A numerical model of the nitrogen non-equilibrium condensation was established. Accordingly, the non-equilibrium condensation process of nitrogen droplets and feasibility analysis of tracing were investigated. The results reveal that the occurrence of nitrogen droplets as well as the droplet concentration and mean radius can be regulated in the nucleation zone and droplet growth zone by varying gas temperature or pressure. Furthermore, the feasibility of employing nitrogen droplets as tracer particles in the working conditions of CWT is confirmed through the analysis of tracking capability, response time, concentration, and duration of droplet traceability. Formulas correlating used to calculate duration of droplet traceability have been proposed. This study proved the potential application of condensing nitrogen droplets as tracer particles in CWT. [ABSTRACT FROM AUTHOR]

In the area of the heating industry, a heat pump is an efficient alternative technology to achieve energy saving and carbon emission reduction. The conventional heat pump has gradually been applied to replace the traditional direct electrical heating method while the required temperature is below 100 °C. A heat pump with temperatures between 100–140 °C is in the stage of rapid development. However, a heat pump with temperatures above 150 °C has received relatively little attention. In this paper, two systems combining a heat pump and water vapor compression (CHPVC and HPTVC) have been studied for waste heat recovery from 45 °C to a water vapor supply with a temperature above 150 °C. A thermodynamic model has been proposed to analyze the performance of the two systems, and a twin-screw compressor model has been developed to calculate the isentropic efficiency of the compressor applied in the heat pump. Four different parameters have been used to analyze the energy efficiency. The simulation results show that while the inlet water temperature is 45 °C and the required vapor temperature is 150 °C, the optimal COPs of CHPVC and HPTVC are 2.432 and 2.436, respectively. Moreover, CHPVC is more suitable for the large saturation temperature lift, and HPTVC is more suitable for a relatively small temperature difference between the inlet water and the required vapor. Compared with the direct electrical heating method or the conventional two-stage heat pump, these two systems are remarkably efficient and show good energy-saving potential. [ABSTRACT FROM AUTHOR]

Micro-structured surfaces can affect heat transfer mechanisms because of enlarged specific surface areas. However, employing the Leidenfrost effect during liquid nitrogen (LN2) droplet cooling of a heated micro-structured surface possessing a fin with a spacing much smaller than the diameter of the droplet has not yet been explored. In the present work, a direct numerical simulation (DNS) is carried out to investigate heat transfer mechanisms of the LN2 droplet, whose diameter is sufficiently larger than the structured spacing of fin, impinging on a micro-structured surface with variable velocities. For a comparative study, a smooth surface is also employed in numerical simulations. The spreading mechanisms and vaporization behavior of the droplet along with liquid film morphology at various conditions are investigated. Results show that a smaller fin size inhibits LN2 in entering into the grooves between the fins and left the surface untouched by the droplet completely, and eventually, a thinner liquid film is spread out in contrast to the smooth surface. Notably, at a low Weber number, the droplet can be shrunk or even rebounded away from the wall after impinging on the wall. The fastest vaporization behavior for both surfaces, namely smooth and micro-structured, is obtained at a Weber number of 180. Additionally, an effective heat transfer upon the micro-structured surface is observed at a low impinging velocity of the droplet. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration is acknowledged as a potential substitute for the conventional vapor-compression refrigeration technology, owing to its high efficiency and environmental friendliness. Existing magnetic refrigeration systems are mostly based on permanent magnets, owing to the characteristics of lower magnetic field intensity, non-uniform magnetic field distribution, and lower operating frequency due to the moving parts, which results in a low cooling capacity and small temperature difference. Thus, this study proposes the application of a pulsed magnetic field, with a high intensity and frequency, to a magnetic refrigeration system to achieve a high performance. A verified numerical model is established to investigate the thermodynamic cycle and cooling performance of an active magnetic regenerator (AMR). The transient and steady-state performances of AMR under pulsed and permanent magnetic fields are compared. The results suggest that an AMR can establish a stable temperature difference under a pulsed magnetic field that is 40 times faster than that under a permanent magnetic field. The maximum steady-state cooling capacity under a pulsed magnetic field is 2.5 times that under a permanent magnetic field when the temperature difference is 20 K. Additionally, the effects of pulsed magnetic field waveforms, frequency, and intensity on the performance of AMR are investigated under various utilization factors. These results can guide the improvement of room-temperature magnetic refrigerators. [ABSTRACT FROM AUTHOR]

In marine storage and transportation, the sloshing of liquid oxygen disturbs the thermodynamic equilibrium and induces stress on tank walls. Numerous problems are associated with the sloshing mechanism and demand a detailed investigation. In this study, a numerical model is developed by coupling the Eulerian framework and the algebraic interface area density (AIAD) method while considering the interphase drag force to investigate the thermal behavior of sloshing liquid oxygen. The effect of the sloshing frequency on the evaporation performance of liquid oxygen is studied. Moreover, anti-sloshing is conducted by employing a T-shaped baffle. The results show that the sloshing induced a vapor explosion phenomenon due to the invalidation of the surface impedance and thermal destratification to enhance free convection, resulting in rapid depressurization and increased evaporation loss. In addition, maximum evaporation loss occurred under the vapor–liquid coupling excitation condition. The T-shaped baffle has an excellent anti-sloshing effect because of the generating tip vortices and the enhanced shearing effect of the walls, which are regarded as motion damping factors. [ABSTRACT FROM AUTHOR]

Outer edge bending is already used on the axial fan blades of air conditioners, reducing the leakage flow loss at the blade tip and suppressing the tip vortex development, thereby improving fan aerodynamic and acoustic performance. However, there are few studies on the multi-parameter design and optimization of this complicated structure, and most studies only focus on the overall sound pressure level rather than the sound quality when evaluating the fan noise. This study investigated the effects of outer edge bending structure on the aerodynamic performance and sound quality of air conditioners' axial fans by experiments and numerical methods. Based on the orthogonal design method, the effects of three bending parameters, the circumferential starting angle, radial relative position, and the bending degree effects on the performance of the axial flow fan blade were analyzed, and the best efficiency scheme was selected. A comparative analysis of the preferred and the original bending schemes shows that the bending towards the blade suction surface successfully inhibits the development of tip leakage vortex at the blade tip, thereby achieving efficiency enhancement and noise reduction. The experimental results show that the preferred bending scheme with a 10° circumferential starting angle, 90% radial relative position, and 8% bending degree can effectively reduce the fan's broadband noise within 200~1000 Hz by 0.54~2.68 dB (A) at different operating conditions. Additionally, the preferred bending blade with reasonably designed bending effectively reduced the loudness and roughness of the fan noise in the rated conditions, and the sound quality of the studied fan was correspondingly improved. [ABSTRACT FROM AUTHOR]

The hydrogen Knudsen compressor has great potential to transport hydrogen and provide the required pressure in MEMS and microfluidic systems. The microchannel composed of cold and hot serrated surfaces is beneficial to the temperature control of the multistage Knudsen compressor. In the present study, a serrated hydrogen Knudsen compressor model is established initially, and the non-equilibrium evolution is numerically studied by using the method of N–S equations with the slip boundary. The key factors affecting the non-equilibrium evolution are comprehensively analyzed. The flow behaviors and performance of the serrated hydrogen Knudsen compressor in different times are studied. It is found that the main factors affecting the non-equilibrium evolution are the thermal expansion flow, thermal transpiration flow, and Poiseuille flow. Meanwhile, the serrated structure affects the local flow in the serrated microchannel at different times. Under the interaction of the thermal transpiration flow and the Poiseuille flow, the pressure difference between the two containers first increases rapidly and then decreases slowly, and finally approaches 1886 Pa. The research reveals the flow mechanisms of the hydrogen Knudsen compressor in the non-equilibrium evolution, which provides theoretical support for the safety and reliability of the hydrogen Knudsen compressor. • The flow evolution in the serrated hydrogen Knudsen compressor can be divided into four stages. • The main factors affecting the non-equilibrium evolution are analyzed. • The serrated structure has a great influence on the local flow in the serrated microchannel. • The pressure difference between the two containers increases first and then decreases. [ABSTRACT FROM AUTHOR]

Atomization with cryogenic fluids is complicated due to the combined effects of both the mechanical breakup and thermodynamic flashing. However, the weight of the two effects on the atomization has not been determined yet. This paper proposes a hybrid mathematical model to evaluate the weight of the thermodynamic effect and aerodynamic effect. The entire process of jet spray breakup, including the primary breakup and secondary atomization, is described in the model. A linear stability analysis is carried out using the dispersion equations for the primary breakup. In the secondary atomization, the Taylor analogy breakup and bubble micro-explosion models are employed to study aerodynamic and thermodynamic effects on the atomization, respectively. The homogeneous nucleation is implemented in the bubble micro-explosion models. A criterion is obtained which can be evaluated to predict the dominant effect. Accordingly, the influence of factors such as ambient pressure and other physical parameters on the atomization process is analyzed. The results reveal that, under low ambient pressure, thermodynamic flashing is stronger. Besides, the mechanical action is restrained when the surface tension is increased. [ABSTRACT FROM AUTHOR]

Chilldown process is usually the initial operation for storing and transporting cryogenic fluids. During this process, film boiling is of great importance in terms of the large time span. In this research, a numerical model was built to study the flow regime and heat transfer characteristics of the film boiling with cryogenic fluids. An algebraic interface area density framework was coupled in the model to calculate the drag force at the liquid-gas interface. Accordingly, the effects of wall superheat and mass flow rate on heat flux and film thickness were investigated. Furthermore, the variance analysis method was employed to evaluate the weight of the effects of superheat and inlet mass flow and their coupling effect on the heat transfer coefficient. The results reveal that the wall superheat effect prevails over the mass flux effect on the heat transfer coefficient. Moreover, the two factors have a relatively weak coupling impact on the heat transfer coefficient. Finally, the features of pressure drop in the tube were further analyzed. [ABSTRACT FROM AUTHOR]

In this study, a collaborative simulation method is proposed to predict dynamic variations of the thermal environment in an air-conditioned room. The room thermal environment was predicted and analyzed by varying the structural and control parameters of the air conditioner considering the dynamic coupling effect. Connections and regularities were established between the applicable parameters and evaluation indices of the thermal environment. The simulation results demonstrated the interactions among the system structural parameters, control parameters, and the thermal environment. Within a certain parameter range, the evaporator structure exhibited a significant effect on temperature uniformity and vertical air temperature difference, followed by predicted mean vote (PMV) and draught rate (DR). The associated evaluation indices were sensitive to fin spacing, tube spacing, and tube outer diameter, in the same order, which were structural parameters of the evaporator. The effect of the air supply angle on the vertical air temperature difference was evident; however, its influence on the PMV, DR, and temperature uniformity did not indicate consistent variations. [ABSTRACT FROM AUTHOR]

Multistage hydrogen Knudsen compressor based on the thermal transpiration effect has very exciting prospect for the hydrogen transmission in the micro devices. Understanding of the hydrogen flow characteristic is the key issue for the designs and applications of the hydrogen energy systems. Firstly, the numerical models of the multistage hydrogen Knudsen compressor are established. The distributions of the rarefaction, velocity and temperature at different stages of the hydrogen flow are calculated and presented. Moreover, the dimensional pressure increases of the hydrogen gas flow are analyzed, and the flow behaviors in the microchannel and the connection channel are discussed. Secondly, the numerical simulation at different connection channel height is implemented, and the hydrogen gas flow characteristics in the connection are analyzed. Especially, the performances of the pressure drop in the connection channel under different channel heights are studied, and the hydrogen gas compression characteristics of different cases are compared and discussed. Also, the effect of the connection channel height on the hydrogen gas pressure increase in the microchannel is investigated. The studies presented in this paper could be greatly beneficial for the hydrogen detection and transmission. • The hydrogen flow behaviors is investigated in the multistage hydrogen Knudsen compressor. • The multistage hydrogen Knudsen compressor has a single-stage replication characteristic. • The pressure drop phenomenon of the hydrogen flow in the connection channel is presented in this paper. • The increase of the connection channel height is beneficial to promote the pressure increase of the hydrogen flow. [ABSTRACT FROM AUTHOR]

The needle valve is a critical control unit for high-pressure hydrogen systems such as hydrogen refueling stations, which is the infrastructure of hydrogen energy. As an important part of the needle valve, the valve spool affects the flow characteristics of hydrogen in the valve and then affects the working performance and safety of the high-pressure hydrogen valve. In this paper, based on the real hydrogen gas model and the finite volume method, a CFD model of the high-pressure hydrogen needle valve is constructed to find out the influence of the valve spool shape on the performance and flow characteristics of the high-pressure hydrogen needle valve. The results show that high-pressure hydrogen will produce a sudden change in pressure around the valve spool and there will be a local high-speed area, and the turbulent intensity will also increase. The arc cone spool can increase the flow by 2%–8% at different openings of the valve, and reduce the maximum speed at the spool by 15% at small openings. In addition, the sudden change of pressure and the eddy current have also been improved. Flat-bottomed cone spool reduces turbulence intensity and energy consumption. Therefore, it can be concluded that changing the shape of the valve spool to have a larger flow area at a small opening can make the high-pressure hydrogen valve have a better flow field distribution. Flattening the cone angle of the spool can improve the turbulent flow in the valve. The research in this paper can provide research accumulation and theoretical support for the optimization design of the needle valve of the high-pressure hydrogen system. • A large pressure gradient of hydrogen flow will be generated at the valve spool. • The valve with arc cone spool has a larger flow rate and a smaller pressure drop. • The arc cone spool can reduce the high-speed zone and the eddy current in the valve. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a self adaptive chiller sensor fault detection strategy based on Principal Component Analysis (PCA) method, namely a self-Adaptive Principal Component Analysis (APCA) method. The original data set used to train the PCA model usually contains some error samples, whose useless residual subspace information make the threshold of Q-statistic higher than the expected threshold. This leads to a low sensitivity and low fault detection efficiency at low sensor fault levels. APCA is developed to automatically remove error samples in the original data set in order to improve fault detection efficiency especially for temperature sensor faults with absolute magnitude less than 1°C. The self adaptive process of APCA has been presented and been compared with the Normal Principal Component Analysis (NPCA) method. The APCA strategy is validated by the operational data of a screw chiller system in a real electric factory. The results show that the APCA method can significantly enhance the fault detection efficiency, and the symmetry for positive and negative fault levels with same absolute magnitude becomes better than NPCA method. [Copyright &y& Elsevier]