Dear Colleagues,

Renewable energy has seen growing development in recent years with the aim of peak carbon dioxide emissions and carbon neutrality. Thermal energy storage (TES) technology is considered to have the greatest potential to balance 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. TES is a crucial and widely recognized technology designed to capture renewables and recover industrial waste heat, helping to balance energy demand and supply on a daily, weekly, or even seasonal basis in thermal energy systems.

Adopting TES technology not only can store excess heat, alleviating or even eliminating thermal power fluctuations, but also mitigate mismatching in time and location between energy supply and the corresponding demand from consumers; therefore, thermally based energy storage technologies are attracting increasing attention from a diverse range of academic, industrial, government, and policy stakeholders, in particular for low-cost and large-scale applications. Generally, thermally based energy storage technologies can be categorized into thermal energy storage (e.g., sensible heat storage, latent heat storage and thermochemical heat storage), thermomechanical energy storage (e.g., compressed air energy storage, liquid air energy storage, pumped thermal energy storage), and so on.

This Special Issue focuses on recent research advances, case studies, and practices to promote thermally based energy storage technologies and aims to provide a stage for researchers to communicate up-to-date progress. Research related to thermally based energy storage technologies from the level of basic principles, materials, components, and systems is welcomed.

Dr. Zilong Wang
Dr. Guanhua Zhang
Dr. Yingying Yang
Guest Editors

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• heat and mass transfer
• novel composite materials
• numerical simulation
• phase change (solid-liquid, solid-solid, gas-liquid, and solid-gas)
• thermodynamic optimization

Title: Numerical investigation on heat transfer characteristics of microencapsulated PCM slurry in a circular tube based on DPM model
Authors: Guanhua Zhang; Bin Zhang
Affiliation: School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Abstract: Microencapsulated phase change material slurry (MPCS) has a large apparent specific heat. When MPCS flows in the pipeline, the micro convection effect between microencapsulated phase change material (MPCM) particles and fluid can enhance the heat transfer between fluids, thereby MPCS is often used as heat storage fluid and heat exchange medium. The DPM model in ANSYS Fluent is used to simulate the convective heat transfer characteristics of MPCS under turbulence flow. The phase change latent heat of MPCM is equivalent to the specific heat capacity. The heat transfer performance of MPCS in the pipe was investigated under different flow rates, particle mass fractions and heating conditions. The results show that for MPCS with flow rates of 1.0 m/s, 1.22 m/s and 1.4 m/s, local heat transfer coefficient increased with the increase of fluid flow. MPCS with mass fraction of 2 %, 5 % and 8 % can be completely melted, the local heat transfer coefficient of MPCS increased with the increase of concentration. The increase of heat flux can accelerate the melting process of MPCM and make the local heat transfer coefficient reach the maximum value faster.

Title: Convective heat transfer characteristics of two-degree-of-freedom vortex-induced vibration of tandem double cylinders at low Reynolds number
Authors: Zhiyun Wang; Gang Wang; Yongwei Wang
Affiliation: School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Abstract: The vorticity induced vibration of rigid tandem twin cylinders with fluid flow at low Reynolds number is studied numerically. The Reynolds number is 150 and the spacing ratio of the two cylinders is 8. The finite volume method is used to solve Navier-Stokes equations to obtain the flow field, and the fourth order Runge-Kutta algorithm is used to solve the cylinder motion. The influence of the vortex-induced vibration and heat transfer on the downstream 2DOF cylinder is studied under different reduced velocities Ur, when the upstream cylinder is fixed (Model A) and has 2DOF motion (Model B) respectively. Finally, the effects of different spacing ratios on heat transfer of downstream cylinder under vortex-induced vibration are studied. The numerical results show：In the range of the reduced velocity considered in this paper, the motion of the downstream cylinder is affected by the vortex generated by the upstream cylinder on its action mode and its own wake vortex shedding, which leads to different heat transfer results. Compared with models A and B, when Ur = 4 and Ur = 5, the vibration of the downstream cylinder is the most intense, and the heat transfer is also the strongest. Comparison of spacing ratio L / D = 4 and L / D = 8. In Model A, in the range of the reduced velocity studied in this paper, increasing the spacing ratio is conducive to the heat transfer of the downstream cylinder. For model B, increasing the spacing ratio is beneficial to the heat transfer of downstream cylinder only in the range of larger reduced velocity 5 < Ur ≤ 9.

Title: Effects of electrohydrodynamics on hot air drying characteristics and energy consumption of fruits and vegetables
Authors: Zhaofeng Meng; Xiangna Cui; Fengxian Wang
Affiliation: (School of Energy&Environment, Zhongyuan University of Technoiogy, Zhengzhou China
Abstract: The single-factor experimental method was used to study the hot air-drying characteristics of carrots and bananas under electrohydrodynamics (EHD) conditions of 5 mm, 55 °C. The experiment analyzed the changes of dry basis moisture content and wet basis moisture content, drying rate and dehydration rate of the sample. The results showed that adding EHD into hot air drying can improved the early drying rate and dehydration rate of fruits and vegetables. It could shorten the drying time by 16.67%, reduce the energy consumption by 17%, and increase the rehydration rate by 14%. The higher the initial moisture content of materials was, the more obvious the effect of EHD could been shown. Data fitting was performed, and the coefficient of determination and the root mean square error range were 0.9908-0.9983 and 0.01128-0.02282, respectively. It is confirmed that the Weibull distribution function model is suitable for EHD combined with hot air drying. The EHD has an effect of suppressing the growth of microorganisms and improving the quality of drying. The EHD has low energy consumption, obvious auxiliary drying effect, and has broad application prospects for food drying.

Title: Experimental study on condensation heat transfer performance of R410A outside the horizontal double-side enhanced tube
Authors: Lihao Huang *,; Zhenbin Yang
Affiliation: School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Abstract: Research on the surface structure of the enhanced tube can effectively enhance the condensation heat transfer performance outside the horizontal tube, and it is very important to reduce the tube consumption of the condenser. The condensation heat transfer characteristics of R410A refrigerant outside a smooth tube and three horizontal double enhanced tubes were studied. The experimental data were processed by using Gnielinski formula and heat- resistance-separating method, and the heat transfer coefficient in tube side, total heat transfer coefficient and heat transfer coefficient outside the tube were obtained. Some results were obtained: first, the enhanced condensation heat transfer performances were affected by the inlet water temperature, water flow rate and saturated temperature; second, the heat transfer coefficient outside the tube of type II was 1.1 times of that of type I, and the logical finned spacing design was beneficial to condensate drainage and increase the refrigerant heat transfer performance ; the third, the enhancement effect of different finned types on the heat transfer performance outside tube side was different, and the heat transfer coefficient outside the tube of type II is 1.34 times of that of type III. The liquid film thickness was the main factor of the thermal resistance outside the tube. The logical design of the finned shape and finned spacing for the enhanced tube played an important role in the condensation heat transfer performance, which provided the optimization direction for the development of the enhanced tubes.

Title: Thermodynamic analysis of an innovative cold energy storage system for multi-stage refrigeration temperature applications
Authors: Zhenzhen Liu; Hua Zhang; Jie Huang
Affiliation: School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Abstract: The cold energy required by ultra-low temperature (UTL) applications cannot be reached economically with single vapor compression refrigeration due to the pressure lift ratio of the compressor constraint. Cascade or multistage compression refrigeration could be executed to attain the desired working conditions accompanied by not only small cooling capacity and inefficiency but also complex and expensive, which affects our country to realize the target of "carbon neutral" and "carbon peak". A late-model concept of applying the principle of auto-cascade refrigeration (ACR) to store up cold energy has been conducted in response to the above-mentioned application problems. In this study, combinations of (R600a/R290/R170, R600a/R1270/R1150) three component zeotropic mixtures of five different refrigerants are used as environment-friendly refrigerants. The main aim of this work is to present the theoretical performance of ACR as an alternative for cold energy storage with optimal hydrocarbon mixtures from -100 ℃ to -50 ℃. The results show that constant temperature refrigeration and cooling capacity both can be provided above -80℃ with these mixtures. Cold energy storage with UTL is receiving a great deal of attention where researchers and companies are making effort to provide reliable and efficient means which be useful for the current and future industry practices.

Title: An investigation of assessment method on energy storage system for electric vehicles and experimental validation
Authors: Kang Li; Hua Zhang; Ni Liu; Lin Su
Affiliation: School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Abstract: Rapidly increasing market share of electric vehicles and driving range anxiety have put forward higher requirement of the energy storage systems. Efficient energy storage system needs to be integrated with vehicle, providing enough energy to ensure passenger comfort and maintaining adequate components operating range, especially for the power battery, motor and controller. Functions of the energy storage should meet the electric vehicles and its components demand accurately. In this paper, an assessment method was proposed to measure the applicability of the energy storage system in the electric vehicles. The energy storage function demand of target electric vehicle was determined firstly according to the vehicle driving conditions and components energy storage requirements. An assessment method was then discussed and applied for the target energy storage system, and shows a considerable advantage over two other benchmarks energy storage system which has been applied in mass-produced electric vehicles. Experimental validation was conducted at last and its cooling, heating and defrosting performance were measured. Target energy storage system could meet the function and teat demand. Meanwhile, the waste heat utilization heat pump system can effectively improve the mileage of electric vehicles. It shows potential for mass-production in electric vehicles.

Title: Thermal Management and Energy Consumption in Air、Liquid、Free Cooling System for Data Centers：A Review
Authors: Si Jun Xu; Hua Zhang; Zi Long Wang
Affiliation: Institute of Refrigeration and cryogenic Engineering, School of Energy and Power Engineering, University of Shanghai for Science and Technology
Abstract: The thermal management and reduction of energy consumption in cooling systems have become major trends with the continued growth of high heat dissipation data centers and the challenging energy situation. However, both studies have been limited to study the influence of individual factors which have not been systematically summarized. This paper reviews the key factors for achieving thermal management and reducing energy consumption in each cooling system, the corresponding research and optimization methods. For air cooling data centers, thermal management is mainly related to the uniform distribution of hot and cold air. Adjusting the porosity of perforated tiles can reduce energy consumption. For liquid cooling and free cooing systems, climate conditions, cooling system structural design, coolant type and flow rate are key factors in achieving thermal management and reducing energy consumption. This paper provides PUE of cooling system in some cases. A summary of the key factors can provide direction for research of thermal management and energy reduction, and a summary of previous research can provide a basis for future optimization.

Title: Influence of Copper Foam on the Thermal Characteristics of Phase Change Materials
Authors: Xiaokuan You; Jie Huang; Zi Long Wang; Hua Zhang
Affiliation: Institute of Refrigeration and cryogenic Engineering, School of Energy and Power Engineering, University of Shanghai for Science and Technology
Abstract: The phase change material is the hot pot of research in solar thermal storage systems. However, the thermal conductivity of pure phase change materials is usually low, which hinders its application in facilities. In this study, the copper foam is used to increase the thermal characteristics of the paraffin. Simulations are conducted to compare the melting characteristics of the pure paraffin and the paraffin/copper-foam composite phase change material. A visualized experimental set-up is established and the composite phase change material with 15 % copper foam is produced and tested. The simulation results agree well with the experimental results. The root mean square errors of the temperature for the pure paraffin and the composite phase change material are 0.0223 and 0.0179, respectively. The experimental results show that the copper foam can enhance the thermal conductivity and decrease the melting time. It takes 870 s for the composite phase change material to melt, which is 3.44 % less than that of the pure paraffin. This study deepens the understanding of the composite phase change material and it provides a reference for the design of thermal energy storage devices.