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The time-dependent energy demand of energy islands may frequently change the operating condition of diesel generator (DG), leading to diesel engine operating under off-design conditions with low ef...

Previous studies on phase change material (PCM) selection for latent thermal energy storage (LTES) mainly focused on steady heat source conditions without considering the effects of thermal fluctuation of real heat sources, and how fluctuating heat sources will affect the charging performance of LTES and material selection is still unclear. This study aims to compare the difference in material selection for a shell-and-tube LTES under steady and fluctuating heat sources, which comprehensively considers the effects of PCM thermophysical properties including the melting temperature, density, specific heat capacity, thermal conductivity and latent heat, as well as their interaction effects. By taking heat storage capacity and charging rate as objectives, orthogonal experiment design and stepwise regression analysis have been conducted to specify the significant factors among these parameters under steady and fluctuating heat source conditions. To further investigate the difference in the ranking of candidate PCMs under two conditions, fourteen pre-screened PCMs are ranked under steady and fluctuating heat sources. The results show that the order of prominent factors for heat storage capacity is ρ · C p , followed by ρ · L under both conditions. However, when considering the charging rate, temperature fluctuation will weaken the effect of melting temperature, and strengthen the effect of specific heat capacity and latent heat. The order of prominent factors for charging rate is λ · C p and C p · L under fluctuating heat source. According to the ranking results, LiNO3-NaNO2 within the melting temperature of 100–200 °C has an excellent comprehensive charging performance under both conditions.

This study proposes a novel combined cooling, dehumidification and power system based on internal combustion engine (ICE) for high temperature and humidity regions. In the proposed system, the electricity demand is mainly provided by ICE while the cooling and dehumidification demands are totally satisfied by absorption chiller (AC) and liquid desiccant dehumidification (LDD) units driven by waste heat of engine exhaust and jacket water. In addition, the electricity demand can be supplemented by battery and Organic Rankine Cycle (ORC) units driven by abundant waste heat of ICE. The aim of this system is designed to succeed the highly efficient utilization of ICE waste heat among AC, LDD and ORC units, and satisfy the multi-energy demands of users by optimizing the operation strategy. Firstly, a case study based on the actual power, cooling and dehumidification demands of a hotel building in Singapore is conducted to assess the performance of the proposed system. The parametric study of prominent design parameters in this system is investigated first to explore their effects on the system performance. Next, considering annual total cost and CO2 emissions as evaluation objectives, augmented e-constraint method combined with improved Mutation particle swarm optimization (M-PSO) algorithm is used to conduct the multi-objective optimization of equipment capacity and operation. Finally, a sensitivity analysis of significant uncertainty factors is researched. The optimal results show that, compared to the traditional energy supply system, the annual carbon dioxide emission reduction ratio and total cost saving ratio can reach 35.91% and 25.46%, respectively.

The previous studies focus on the heat storage process of shell-and-tube latent thermal energy storage (LTES) under steady heat sources, without considering the fluctuating and intermittent characteristics of the most available heat sources in real applications. The effect of different fin sizes and locations on the charging performance of shell-and-tube LTES still keeps unclear under fluctuating heat source, and it is critical to improve the heat storage rate and density due to the low thermal conductivity of phase change materials (PCM). Consequently, this study aims to investigate the charging performance of a shell-and-tube LTES considering different fin layouts. Firstly, the effects of different fin number and configurations on heat storage process are performed under fluctuating heat sources. The case with comprehensive performance of high melting rate and large heat storage capacity is obtained. Then the effects of critical parameters on the charging process, including the fin angle, fin thickness, fin height and deviation distance of tube under fluctuating heat sources are further analyzed based on this case, and the results are compared with that of steady heat source. Results indicate that the fin height is the dominant factor influencing the heat storage rate and density under both steady and fluctuating heat source conditions, while the total melting time is shorter and the heat storage capacity is smaller, and the heat storage capacity is less obvious with the variation of fin parameters under the fluctuating heat source. In addition, the effect of downward deviation distance of tube on heat storage capacity is much obvious under fluctuating heat source than that of steady heat source.

The fluctuating and intermittent nature of industrial heat sources is a crucial technical barrier limiting the implementation of heat recovery energy systems. Latent Thermal Energy Storage (LTES) has the potential to overcome these issues by maintaining a Waste Heat Recovery (WHR) system within designed operation conditions to achieve effective and efficient operation. However, the dynamic heat transfer characteristics of LTES under fluctuating heat sources need to be studied further to better understand the effects of thermal fluctuation. In this work, the charging performance of a shell-and-tube LTES under fluctuating and steady heat source has been investigated and analysed. The effects of period and amplitude for the fluctuating heat source, as well as the Stefan number, are investigated in detail. Results indicate that large-period fluctuating heat sources can considerably reduce the total melting time but also reduce the energy storage capacity, whilst small-period fluctuating heat sources have almost no effect on the melting process of LTES. For the effects of fluctuating amplitude, both the total melting time and energy storage capacity decline at a decreasing rate with an increase of fluctuating amplitude. These results can bridge the knowledge gap needed for future designs of shell-and-tube LTES for fluctuating heat sources used with heat recovery applications.

Organic Rankine Cycle (ORC) is widely investigated for low-grade waste heat recovery, but its performance deteriorates under heat source with thermal power fluctuations. As the effects of fluctuating heat source on ORC system performance is less investigated, the operating rules of ORC systems under fluctuating heat source are not clear. In this study, the effects of fluctuating amplitude and period for fluctuating heat sources on the performance of a basic ORC system are studied in detail, considering the proposed indicators including safety and efficiency. Afterwards, the allowable fluctuation ranges of heat source are obtained based on requirements of safety and efficiency. Finally, the impact of the average temperature of fluctuating heat sources on the allowable fluctuation range is systematically investigated. The results indicate that the safety limitations and efficiency of the basic ORC system are generally negatively related to fluctuating amplitude and period, and the allowable fluctuation range is generally positively related to average temperature of heat source. To ensure the efficient operation of basic ORC, the allowable relative amplitude is 25–40 K under large fluctuating period while it is higher than 35 K with the fluctuating period smaller than 200 s. This study contributes to provide valuable reference for evaluating the performance of an existing ORC system under different fluctuating heat source conditions.

Thermal energy storage (TES) technology is considered to have the greatest potential to balance the demand and supply overcoming the intermittency and fluctuation nature of real-world heat sources, making a more flexible, highly efficient and reliable thermal energy system. This article provides a comprehensive state-of-the-art review of latent thermal energy storage (LTES) technology with a particular focus on medium-high temperature phase change materials for heat recovery, storage and utilisation. This review aims to identify potential methods to design and optimise LTES heat exchangers for heat recovery and storage, bridging the knowledge gap between the present studies and future technological developments. The key focuses of current work can be described as follows: (1) Insight into moderate-high temperature phase change materials and thermal conductivity enhancement methods. (2) Various configurations of latent thermal energy storage heat exchangers and relevant heat transfer enhancement techniques (3) Applications of latent thermal energy storage heat exchangers with different thermal sources, including solar energy, industrial waste heat and engine waste heat, are discussed in detail.