Shuli Liu

Review on Heat Transfer Mechanisms and Characteristics in Encapsulated PCMs

Latent heat storage (LHS) is a particularly promising technique compared with the conventional sensible heat storage (SHS) as it provides a high-energy storage density with a small volume. However, there are difficulties in practical engineering applications of LHS due to the heat releasing/absorbing, which involves phase transition and moving boundary problems and the unacceptable low thermal conductivity of the phase-change material (PCM). Furthermore, the encapsulation would affect the heat transfer characteristics of PCM significantly, depending on the parameters of various encapsulations and boundary conditions. Hence, this review analyzes heat transfer mechanisms during the phase-change process and numerical analysis for heat transfer in macroencapsulated PCMs according to the shape of containment. The effective heat capacity method and the enthalpy method, two of the most widely used numerical approaches for phase-change problems, are presented in detail. Besides numerical models for different PCM containment such as spherical, rectangular, and cylindrical containment models, PCM-based heat-sink models are reviewed, including several heat transfer enchantment technologies: finned structure and porous matrix. Finally, the challenges in numerical modeling and designing an LHS unit are also summarized in this article.

Serious games for energy social science research

This paper proposes a set of criteria for evaluation of serious games (SGs) which are intended as effective methods of engaging energy users and lowering consumption. We discuss opportunities for using SGs in energy research which go beyond existing feedback mechanisms, including use of immersive virtual worlds for learning and testing behaviours, and sparking conversations within households. From a review of existing SG evaluation criteria, we define a tailored set of criteria for energy SG development and evaluation. The criteria emphasise the need for the game to increase energy literacy through applicability to real-life energy use/management; clear, actionable goals and feedback; ways of comparing usage socially and personal relevance. Three existing energy games are evaluated according to this framework. The paper concludes by outlining directions for future development of SGs as an effective tool in social science research, including games which inspire reflection on trade-offs and usage at different scales.

Heating storage performance of a water tank–combined phase change material:An experimental case study

Water tank is a commonly used unit which has been frequently applied for thermal energy storage units. In order to enhance the thermal performance of the water tank, the phase change material is utilized by embedding paraffin into water tank. But the key question is whether a competitive charging could be achieved. Therefore, an experimental system has been constructed. In this article, two key indices, the energy storage capacity and the energy storage intensity, are investigated. The performances of the phase change material–thermal energy storage tank during the heat charging processes are investigated experimentally, and a series of experiments are carried out under different heat transfer fluid flow rates and distance between phase change material plates. The temperature evolutions of the phase change material plates and heat transfer fluid are obtained during the experiments. The thermal performance of the phase change material–thermal energy storage tank was observed to be more effective than the conventional sensible thermal energy storage tank. It is found that water flow rate of 1.3 m3/h is taken as the optimal working condition, and the 3-cm plate distance is considered as the optimal design.

Numerical study of the influences of geometry orientation on phase change material's melting process

The acceleration of the melting process of phase change materials caused by buoyancy-driven natural convection has been widely acknowledged, especially for rectangular geometries. This acceleration phenomenon exists in the cases where phase change materials are heated at the bottom boundary or at both upper and bottom boundaries. This article reveals how the melting rate could be affected by changing the orientation of a rectangular phase change material container with a constant temperature boundary. The transient melting processes of lauric acid in a two-dimensional rectangular container with five orientations (θ = 0°, 22.5°, 45°, 67.5°, and 90°) were simulated using the computational fluid dynamics software. The computational fluid dynamics model was validated against available experimental data obtained from published literature. Results show that when the rectangular geometry is rotated from vertical direction (θ = 0°) to horizontal direction (θ = 90°), the total melting time is increased by about five times. For all investigated orientations, the heat transfer rate at the heated boundary is found to first increase at the initial stage (within about 100 min) and then decrease during the following melting process. Moreover, the total amount of thermal storage for the horizontally placed case is slightly lower than the other cases.

Pulse width modulation (PWM) method for power components estimation in power meters

The scope of this paper is to present the Pulse Width Modulation (PWM) based method for Active Power (AP) and Reactive Power (RP) measurements as can be applied in Power Meters. Necessarily, the main aim of the material presented is a twofold, first to present a realization methodology of the proposed algorithm, and second to verify the algorithm’s robustness and validity. The method takes advantage of the fact that frequencies present in a power line are of a specific fundamental frequency range (a range centred on the 50 Hz or 60 Hz) and that in case of the presence of harmonics the frequencies of those dominating in the power line spectrum can be specified on the basis of the fundamental. In contrast to a number of existing methods a time delay or shifting of the input signal is not required by the method presented and the time delay by n/2 of the Current signal with respect to the Voltage signal required by many of the existing measurement techniques, does not apply in the case of the PWM method as well.

Smart metering and systems for low-energy households: challenges, issues and benefits

ABSTRACT As a critical step in the transition to a low-carbon economy, smart meters are being rolled out in large numbers throughout the world. To date, however, no systematic review of the development and implementation of smart meters have been published, so for maximizing the benefit of the benefit of smart meter, this study has been carried out to identify the main concepts and issues of promoting smart metering and related service system. Including key physical components and communication networks of smart meters compared to conventional meters, various policies to support smart meter roll-out and potential benefits to the participators. Challenges and issues involved in the deployment of smart meter infrastructure, such as technical, commercial and ethical debates, are also outlined. Results suggest that existing studies predominately focus on energy efficiency and demand management, while end-user engagement with smart metering systems, especially consumers’ social, economic and behavioural aspects, are rarely considered. Areas of future research should include consideration of privacy and security concerns of end-users, and the necessary learning/educating processes and behavioural change of end-users to maximize the benefit of smart metering systems.

Feasibility study on merging biogas into the natural gas pipe-network in China

Biogas is one of the options to improve the current serious energy and environment situation in China. However, biogas application is limited in China due to instabilities in quantity and quality of biomass. These instabilities are largely influenced by the local environment and climate. Merging non-upgraded biogas into the natural gas (NG) distributing system can (i) increase utilisation, (ii) reduce carbon intensity of gas pipe network and (iii) promote renewable energy usages. However, merging biogas into the gas pipe network comes with lots of challenges. This paper investigates the approaches of merging biogas into the NG distributing system. The interchangeabilities between the mixed bionatural gas and the Chinas 12T standard gas are evaluated based on several indices. This study results indicate that the maximal mixing volume ratio of non-upgraded biogas to the typical piped natural gas is 14.7% when the Wobbe number and combustion potential are used as determining indices.

Experimental Study of the Heat Transfer Performance of PCMs Within Metal Finned Containers

Latent heat thermal energy storages (LHTES) are particularly attractive methods owing to these factors: meet the time shift between energy supply and demand; provide a high energy storage capacity; store and release heat at a relatively constant temperature; provide constant comfort thermal environment without temperature swings when it is applied for space heating or cooling. Nevertheless, the efficiency of using the LHTES techniques is heavily affected by the low thermal conductivities of phase change materials (PCMs). This characteristic of PCMs prolongs the charging and discharging cycle and barriers the widely practical application of LHTES. Hence, researchers generated a lot of related technologies, such as metal fines, carbon fibres, metal honeycomb structure, etc, to overcome this issue and aimed to achieve reasonable thermal conductivities.