Abstract

With the advantages of simple structure, easy maintenance and low cost, the ejector is an ideal cycling device for proton exchange membrane fuel cells, but it is difficult to have a good performance at low power. Aiming at the problem that it is difficult to adapt the ejector to the circulation demand under full working conditions, this paper summarizes the general design flow of the fixed structure ejector by comparing the three design methods of one-dimensional computation, CFD simulation and algorithmic optimization, and describes the advantages and disadvantages of the various schemes by comparing the single ejector, a new structure of the ejector, a two-stage ejector in parallel, and a combination of the ejector and the hydrogen circulating pump for the hydrogen circulation. The advantages and disadvantages of each scheme are described, with a view to contributing to the research on the design of ejectors and hydrogen circulation schemes.

Abstract

Energy management in deep space exploration poses significant challenges for the stable and safe operation of thermal management systems. The critical heat flux (CHF) in flow boiling, as a key safety threshold for two-phase heat transfer systems, must be thoroughly investigated. The current work introduces a data-driven dimensional analysis method that can automatically discover characteristic dimensionless numbers from physical data. This approach addresses the issues of non-uniqueness and the inability to measure the importance of results inherent in the classic Buckingham Pi theorem. By collecting CHF datasets of different fluid media under both Earth’s gravity and space microgravity conditions in vertical tubes, the algorithm identified the most influential dimensionless number affecting the boiling number Bochf during boiling crises and determined the corresponding exponential scaling relationship. This led to the development of a new CHF predictive correlation applicable across different fluids and conditions. Comparison results with several other models indicate that the proposed correlation offers higher accuracy and can potentially be used in the design and optimization of high-power thermal management systems for space, lunar, and Martian environments.

Abstract

The vibration phenomenon widely existing in engineering is often ignored when considering the effect of the aspect ratio of the container on the melting of phase change material (PCM). In this paper, a melting model of PCM in a two-dimensional rectangular container with constant temperature boundary and variable length is constructed, and the influence of rectangular aspect ratio (AR) on the melting process of PCM under vibration is studied by numerical calculation. Our findings reveal that at a static state, larger aspect ratios enhance natural convection within the vessel, thereby modestly accelerating PCM melting. Paradoxically, this also leads to increased paraffin content, prolonging the melting of the contracting solid phase. However, when subjected to vibrations, every aspect ratio experiences an accelerated melting process, with the enhancement more pronounced at higher vibration frequencies. For example, when frequency is 5Hz, melting time in vessel (AR=0.4) is 2.4% shorter than static, while (AR=2) vessel’s time is 7% shorter. Notably, the larger aspect ratio vessels exhibit a more significant acceleration with frequency increase. Furthermore, the average Nusselt number during melting oscillates periodically with vibration, consistently exceeding its static-state counterpart.

Abstract

Due to an incomplete understanding of the superior thermal control performance of anisotropic composite phase change materials (CPCMs) compared to isotropic CPCMs with equivalent thermal conductivity additives, this study delves into the thermal regulation capabilities of anisotropic CPCMs through experimental and numerical analyses. Through the compression method, CPCMs with varying anisotropy were synthesized for thermal control experiments. Under identical energy storage conditions, it was observed that the decrease in axial thermal conductivity has a greater inhibitory effect on the heat transfer rate than the promotion effect of radial thermal conductivity on it. The simulation analyzed anisotropic CPCM’s thermal control on single and distributed heat sources in a constant space. It found that for single heat sources, there’s a critical φcv factor. Above φcv, anisotropic CPCM outperforms isotropic. As thermal diffusion directions increase, CPCM thickness decreases, reducing φcv, while EG content minimally impacts φcv. For distributed heat sources, anisotropic CPCM offers superior temperature control by effectively mitigating temperature gradients between sources.

Abstract

This paper seeks to identify the uncertainty factors in the hydrogen supply chain that affect supply chain costs through a systematic review of the existing literature from 2019 to 2023. 45 uncertainty factors are identified, which can be divided into two categories based on their impact scope. The factors in the first group impact the whole hydrogen supply chain, while the parameters in the second group affect one or several specific sectors in the supply chain. Hydrogen demands, electricity prices, and the capital expenditure of the electrolyzer are the most considered uncertainty factors in the existing literature. Additionally, it turns out that the current research on hydrogen supply chain uncertainty mainly focuses on the factors that affect the whole supply chain and the sector production, while the sectors of storage and transportation have received less attention in the current research.

Abstract

The demand for air conditioned cars has been increasing at a rapid rate due to increasing standard of living and adverse climatic conditions. The heating, ventilation and air conditioning system can reduce the fuel economy of a mid-size conventional vehicle by as much as 20%. Depending on the capacity of the air conditioning system and drive cycle, the range of Electric Vehicle (EV) and fuel economy of Hybrid Electric Vehicle (HEV) can reduce by approximately 40% under normal air conditioning loads. Thus, it is a challenge to maintain thermal comfort of the passengers and driver with minimum energy consumption. Hence proper indoor environment management of the passenger vehicle is of high priority. Thus, proper design, selection and operation of the car air conditioning system play an important role. The first step in this direction is proper estimation of cooling load on the car under various operating and environmental conditions. The aim of the present study is to develop a simple cooling load calculation model suitable for stationary and running conditions of a passenger car and study the effect of parking and operating conditions on the cooling load. The variation of cooling load of the running car is analysed by varying car speed, time of the day etc. Similarly, for the parked car the parametric analysis is done with respect to orientation of the car, exterior colour of car, ground reflectivity of parking zone base materials etc. Results show that there is 10% reduction in sensible cooling load as the car speed varies from 20 to 75 kilometers per hour. Choice of insulation material of car can affect the cooling load by about 3 %. The external colour and parking place ground reflectance can affect the heat transferred by about 14%. The heat transfer rate on the car reduced by 22.5 % when a white car with tinted glass at side windows and rear windshield, is parked on grass base, compared to a black car with normal glass parked on concrete base. It is expected that this study is useful in design of the energy efficient cars through suitable design and operating interventions.

Abstract

The staged adsorption/desorption employing adsorbent-adsorbate pairs with “S” shaped isotherms is a promising new concept for achieving efficient and effective mass transfer. This study carried out a thermodynamic analysis, demonstrating the superior regeneration efficiency of the ideal staged wheels compared to the traditional single-stage. Further, three engineering guidelines for the layout design of staged adsorbents along the channel were proposed. Under six classic conditions, the corresponding desiccant wheels with optimized stage configuration exhibited 10∼20℃ lower necessary regeneration temperature (Treg) than single-stage wheels.

Abstract

The introduction and expansion of locally produced and consumed energy systems by local governments and other entities are garnering considerable attention. This study evaluated a local energy supply project in Shinchi, Fukushima Prefecture, Japan. We specifically focused on a cogeneration-based local energy supply system and conducted a simulation to assess the CO2 reduction impact of expanding the supply area, increasing renewable energy integration, and implementing energy management technologies such as electric vehicle (EV) utilization, storage battery control, and demand response.

Abstract

This study presents a technological advancement in electric vehicle (EV) heat pump systems by integrating a phase change thermal storage unit (PCTSU). This integration optimizes waste heat supply under real-world conditions, enabling efficient system operation in low-temperature environments and reducing the risk of frost formation on the external heat exchanger. Analysis based on a 1D system simulation model shows that even at an ambient temperature of -10 °C, the system with PCTSU achieves a coefficient of performance (COP) exceeding 1.8, indicating an approximately 22% improvement in energy efficiency compared to the original system. Additionally, the PCTSU reduces the thermal load on the external evaporator, contributing to maintaining normal system operation in cold climates. Under various driving conditions, the PCTSU-enhanced system demonstrates higher COP and more stable thermal load distribution. PCTSU shows potential in enhancing the thermal performance and efficiency of EV heat pump systems.

Abstract

The temporal mismatch between renewable energy generation and energy consumption in residential buildings is highly dependent on user behavior, which is crucial for future home energy management and demand-side response solutions aimed at increasing renewable energy consumption. This study leveraged a custom-developed personal energy tracking app to conduct both a questionnaire survey on social attributes and a self-monitoring tracking survey of residents in Guangdong, China. 373 data on their 24-hour energy usage behaviors were collected and utilized clustering algorithms to extract typical usage times and patterns for various appliances. Additionally, the study examined the significance and importance of social characteristics affecting residents’ usage behaviors. The findings provide valuable insights for further investigation into residents’ willingness to participate in flexible energy regulation, the formulation of incentive policies, and the design of home energy management strategies.