CONTENTS-Volume 29, Issue 2, March-April 2020
Springer Link: https://link.springer.com/journal/volumesAndIssues/11630
1. Editorial：Special Issue on Energy Storage
DING Yulong, CHEN Haisheng, LING Haoshu
Journal of Thermal Science, 2020, 29(2): 279.
https://doi.org/10.1007/s11630-020-1284-4
2. Photo-Isomerization Energy Storage Using Azobenzene and Nanoscale Templates: A Topical Review
LI Shuwei, WANG Hongqiang, FANG Juan, LIU Qibin, WANG Jiangjiang, GUO Shaopeng
Corresponding author: LIU Qibin, GUO Shaopeng
E-mail: qibinliu@iet.cn, guoshaopeng@163.com
Journal of Thermal Science, 2020, 29(2): 280-297.
https://doi.org/10.1007/s11630-020-1245-y
Keywords: azobenzene, graphene, hybrid material, solar energy, photo-isomerization energy storage
Abstract: Azobenzene (AZO) has attached tremendous attention in the field of photo-isomerization energy storage due to its advantages of absorbing light in ultraviolet-visible range and reversible isomerization. However, the issues of low energy density and short half-lifetime restrict the further development of AZO. Therefore, a method, by preparing hybrid photo-isomerization energy storage materials using nanoscale templates, was proposed to handle the above two issues. In this paper, a summary of hybrid photo-isomerization energy storage materials with AZO and nanoscale templates is conducted from the aspects of templates, preparation methods, derivatives and applications. The performances of template candidates, i.e. carbon nanotubes (CNTs) and graphene (GO) are reviewed and compared based on the analysis of grafting density, energy density, and half-lifetime of hybrid materials. Then, two major preparation methods of AZO hybrid materials including non-covalent and covalent functionalizations are discussed. Furthermore, the studies on AZO derivatives functionalized on nanoscale templates are summarized to further point to the direction of derivatization towards high performance AZO-functionalized materials. Finally, due to the superiority of AZO hybrid solid-state films in large-scale utilization, their current applications are reviewed to find out some promising applications.
3. Recent Developments in Integrated Solar Combined Cycle Power Plants
KHANDELWAL Neelam1, SHARMA Meeta1, SINGH Onkar, SHUKLA Anoop Kumar
Corresponding author:
KHANDELWAL Neelam, neelam.nk80@yahoo.com;
SHARMA Meeta, contactmeeta@yahoo.com
Journal of Thermal Science, 2020, 29(2): 298-322.
Keywords: CSP (Concentrated Solar Power), HTF (Heat Transfer Fluid), ISCC (Integrated Solar Combined Cycle), TES (Thermal Energy Storage), PCM (Phase Change Material)
Abstract: Global concern for depleting fossil fuel reserves have been compelling for evolving power generation options using renewable energy sources. The solar energy happens to be a potential source for running the power plants among renewable energy sources. Integrated Solar Combined Cycle (ISCC) power plants have gained popularity among the thermal power plants. Traditional ISCC power plants use Direct Steam Generation (DSG) approach. However, with the DSG method, the ISCC plant’s overall thermal efficiency does not increase significantly due to variations in the availability of solar energy. Thermal Energy Storage (TES) systems when integrated into the solar cycle can address such issues related to energy efficiency, process flexibility, reducing intermittency during non-solar hours. This review work focuses and discusses the developments in various components of the ISCC system including its major cycles and related parameters. The main focus is on CSP technologies, Heat Transfer Fluid (HTF), and Phase Change Material (PCM) used for thermal energy storage. Further, study includes heat enhancement methods with HTF and latent heat storage system. This study will be beneficial to the power plant professionals intending to modify the solar-based Combined Cycle Power Plant (CCPP) and to retrofit the existing Natural Gas Combined Cycle (NGCC) plant with the advanced solar cycle.
4. A Review of Rotating Stall in Vaneless Diffuser of Centrifugal Compressor
ZHANG Lei, HE Ruiyang, WANG Songling, ZHANG Qian
Corresponding author: ZHANG Qian
E-mail: zhangqian@ncepu.edu.cn
Journal of Thermal Science, 2020, 29(2): 323-342.
https://doi.org/10.1007/s11630-020-1261-y
Keywords: centrifugal compressor, vaneless diffuser, rotating stall, reverse flow, pressure fluctuation
Abstract: At present, off-design centrifugal compressor suffers from great instabilities, such as rotating stall and surge, which lead to work failure, strong pressure fluctuations, and violent vibrations of the entire system. One cause of these instabilities is the rotating stall occurring in vaneless diffuser. In this review, recent researches on rotating stall of vaneless diffuser in centrifugal compressor are reviewed, and its inductive mechanism and characteristic description are emphatically introduced. In vaneless diffuser, the rotating stall starts up and fully develops under non-design conditions with the characteristic of increasing pressure fluctuation amplitude. The negative effects of rotating stall include reverse flow and vortex, both of which have significant effects on the instability of centrifugal compressors. Some improvement methods of rotating stall are also introduced, and a lot of examples are given. Finally, some suggestions and discussions are put forward for the future work.
5. Heating Characteristics and Economic Analysis of a Controllable On-Demand Heating System Based on Off-Peak Electricity Energy Storage
YIN Shaowu, SHI Yongle1, TONG Lige, LIU Chuanping, WANG Li, DING Yulong
Corresponding author: YIN Shaowu
E-mail: yinsw@ustb.edu.cn
Journal of Thermal Science, 2020, 29(2): 343-351.
https://doi.org/10.1007/s11630-019-1258-6
Keywords: energy storage, on-demand heating, off-peak electricity, heating characteristics, heat storage characteristics
Abstract: The working principle of a controllable on-demand heating system based on off-peak electricity energy storage (COHSBOEES) is as follows: the cheap off-peak electricity energy is converted into heat energy for storage in the evening, and the heat energy can be extracted on demand for heating during daytime peak or flat electricity periods. This technology can promote the smooth operation of the power grid, solve the problem of peak regulation for the electrical network, and promote renewable energy consumption. Based on the controllable on-demand heating strategy, a COHSBOEES for a heating area of 1000 m2 was designed and built. Variations in the energy consumption and operating cost of the COHSBOEES in different heating situations were analyzed. The results showed that, off-peak electricity energy storage for heating was energy saving in comparison with central heating when the heating intensity of the COHSBOEES was 70 W/m2 and the on-demand heating rate was less than 73.0%, and the off-peak electricity energy storage for heating was energy saving at any on-demand heating rate when the COHSBOEES had a heating intensity of 50 W/m2. After the COHSBOEES has been running for three complete heating seasons, when the off-peak electricity price was 0.25 yuan/kW?h, the energy consumption cost of the COHSBOEES can be saved by 77.6% in comparison with central heating.
6. Estimating the Economics of Electrical Energy Storage Based on Different Policies in China
DING Jie, XU Yujie, WANG Ziyi, HU Shan, CHEN Haisheng
Corresponding author: CHEN Haisheng
E-mail: chen_hs@mail.etp.ac.cn
Journal of Thermal Science, 2020, 29(2): 352-364.
https://doi.org/10.1007/s11630-020-1274-6
Keywords: energy storage, Chinese power market, economic assessment, benefit estimation, policy comparison
Abstract: This paper assesses the value of bulk grid-scale energy storage (GES) technologies in six electric power districts of China. The economic feasibility of GES under three different types of compensation mechanisms was analyzed. Based on a careful investigation of China’s existing power system, a unit commitment model that comprehensively reflects the production costs (including reduction of fuel consumption, grid loss, ancillary services and so on) of the entire power grid has been proposed. The benefits of GES can be obtained by comparing the production costs of two different scenarios: with and without GES. Results show that under the current scheduling methods and compensation mechanisms, in most provinces in China, the energy storage’s revenue is lower than the value that it brings.
7. Simulation Study on Hydrogen-Heating-Power Poly-Generation System based on Solar Driven Supercritical Water Biomass Gasification with Compressed Gas Products as an Energy Storage System
JIN Hui, WANG Cui, FAN Chao
Corresponding author: JIN Hui
E-mail: jinhui@mail.xjtu.edu.cn
Journal of Thermal Science, 2020, 29(2): 365-377.
https://doi.org/10.1007/s11630-020-1222-5
Keywords: biomass, supercritical water gasification, poly-generation system, thermodynamics analysis, energy storage, life cycle assessment
Abstract: Supercritical water gasification driven by solar energy is a promising way for clean utilization of biomass with high moisture content, but direct discharge of liquid residual causes energy waste and decreases energy efficiency. To reduce energy waste, a poly-generation system for hydrogen-rich gas production coupling heat supply and power generation based on supercritical water gasification of biomass driven by concentrated solar energy was established in this paper, which also provided a novel energy storage method to overcome the shortcomings of solar discontinuity. Thermodynamic model of the system was proposed and life cycle assessment (LCA) of the system was conducted. Influence of different parameters (temperature of 600°C to 800°C, outlet temperature of heat exchanger of 42°C to 56°C, biomass slurry concentration of 5% to 6.5%) on the gasification performance, energy and exergy efficiency, energy distribution and global warming potential (GWP) was discussed. The results indicated that hydrogen yield increased as gasification temperature increased since free radical reaction was enhanced which gas production reaction was classified into. Molar fraction of hydrogen increased as gasification temperature increased and reached 65.6% at 750°C. Energy and exergy efficiency of the system reached 74.84% and 34.87% at 700°C and 600°C respectively and that of gas production was 18.15% at 650°C, which was the highest. Increasing reaction temperature and decreasing biomass slurry concentration were effective ways to decrease GWP. Optimal operating parameter was reaction temperature of 650°C, outlet temperature of heat exchanger of 50°C and biomass concentration of 5%.
8. Dynamic Simulation of a Novel Solar Polygeneration System for Heat, Power and Fresh Water Production based on Solar Thermal Power Tower Plant
LI Xing, WANG Zhifeng, YANG Ming, YUAN Guofeng
Corresponding author: WANG Zhifeng
E-mail: zhifeng@vip.sina.com
Journal of Thermal Science, 2020, 29(2): 378-392.
https://doi.org/10.1007/s11630-020-1163-z
Keywords: polygeneration, solar thermal power, dynamic simulation, absorption heat pump, humidification-dehumidification
Abstract: A novel solar polygeneration system for heat, power and fresh water production with absorption heat pump (AHP) and humidification-dehumidification (HDH) desalination system was proposed for high-efficiency utilization of solar energy. A case study of the proposed system was investigated based on 1 MW solar thermal power (STP) tower plant located in Beijing. Depending on mathematical modeling of the proposed system, corresponding modules were developed in TRNSYS. Meanwhile, control and operation strategies were fully studied with principal of solar energy cascade utilization. The thermodynamic performance of the proposed system was dynamically simulated at one minute intervals in a typical day. It was found that solar energy utilization level was improved with the help of solar thermal storage system and continuous heating in different operation modes met well with flexible heating loads from 93.76 kW to 169.49 kW. During AHP operation period, its Coefficient of Performance (COP) varied from 1.39 to 1.73 due to recoverable condensate heat restricted by heating demand. Meanwhile, fresh water production of HDH increased from 352.05 kg/h to 416.62 kg/h with Gained Output Ratio (GOR) increase from 2.48 to 2.67. Compared with original STP tower plant, maximum power generation efficiency was increased from 18.66% to 19.22% with power from 1169.69 kW to 1204.44 kW.
9. An Efficient Summer Operation Scheme for a Thermal Power Plant Air Cooling System based on Electric Peak Shaving
HU Hemin, LIANG Shiqiang, JIANG Yuyan, GUO Yongxian
Corresponding author:
HU Hemin, huhemin@iet.cn;
JIANG Yuyan, yyjiang@iet.cn
Journal of Thermal Science, 2020, 29(2): 393-407.
https://doi.org/10.1007/s11630-020-1227-0
Keywords: thermal power reconstruction, air cooled condenser (ACC), indirect air cooling system, peak-shaving, absorption-generation equipment
Abstract: We proposed a novel efficient operation scheme for a thermal power plant’s air-cooling system based on peak shaving, in order to cope with high ambient temperature in summer. We introduced an absorption - generation equipment with water/lithium working pairs into the air cooled condenser (ACC) to reconstruct the traditional thermal power plant, and established a dynamic thermodynamic model adopting Ebsilon code. We studied the thermodynamic performance variation of the reconstructed thermal power plant throughout a 24-hour cycle and found that the fluctuation ratio of the turbine back pressure decreased to 6% from 78%, which is beneficial for the stable and safe operation of the electric power system. The thermal performance improvement benefited from the exploitation of the heat transfer potential of ACC, which realized via cold duty schedule throughout the day, under different ambient temperature conditions. In this system, the generated power was higher at relatively high ambient temperature than that at relatively low ambient temperature, which solved the electricity demand-supply imbalance problem under high ambient temperature. Finally, the same optimization effects for power thermal plants with an indirect air-cooling system were obtained using the same operation scheme.
10. Exergy Analysis of Electric Vehicle Heat Pump Air Conditioning System with Battery Thermal Management System
Zhang Kexin, Li Ming, Yang Changhai, Shao Zhiyuan, Wang Lihong
Corresponding author: YANG Changhai
E-mail: kether163@163.com
Journal of Thermal Science, 2020, 29(2): 408-422.
https://doi.org/10.1007/s11630-019-1128-2
Keywords: electric vehicle, heat pump, exergy, efficiency, battery thermal management
Abstract: The exergy analysis of an electric vehicle heat pump air conditioning system (HPACS) with battery thermal management system was carried out by studying the exergy loss of each component. The results indicate that the compressor is the main source of system exergy loss in all operation conditions. The exergy loss distribution of HPACS is almost the same when the battery thermal management system integrated into the HPACS in cabin and battery mixed cooling mode and the system exergy loss was linearly related to the compressor speed in cooling modes. The performance of the HPACS is better than that of the positive temperature coefficient (PTC) heater in cabin heating mode. The degree of exergy efficiency improvement of the alternative mode was discussed at all operation conditions in cabin heating mode. The results indicate that the optimization effect using the electric vehicle HPACS to replace the PTC heater is obvious at lower compressor speed, surrounding temperature and internal condenser air flow rate.
11. Design of a Centrifugal Compressor with Low Solidity Vaned Diffuser (LSVD) for Large-Scale Compressed Air Energy Storage (CAES)
LIANG Qi, ZUO Zhitao, ZHOU Xin, TANG Hongtao, CHEN Haisheng
Corresponding author: ZUO Zhitao
E-mail: zuozhitao@iet.cn
Journal of Thermal Science, 2020, 29(2): 423-434.
https://doi.org/10.1007/s11630-019-1204-7
Keywords: compressed air energy storage (CAES), centrifugal compressor, aerodynamic design, low solidity vaned diffuser (LSVD), Two-Zone model, blade design
Abstract: Compressed Air Energy Storage (CAES) has tremendous promotional value in the intermittent renewable energy supply systems. CAES has special requirements for compressor (e.g. heavy load, high pressure ratio, wide range). With advantages of higher efficiency and wider operation range, IGC (Integrally Geared Compressors) is selected to fulfill the special requirements of the large-scale CAES. To get a better aerodynamic performance, in this paper, based on the analysis of internal flow of centrifugal compressor, a multi-objective one-dimensional optimization design program was put forward combined with modified Two-Zone model and a low solidity vaned diffuser (LSVD) design method. Then, a centrifugal compressor aerodynamic component optimization design system was established with the three-dimensional blade optimization design method based on neural network and genetic optimization algorithm. Then a validation was done by redesigning the Krain-Impeller to get better performance. Finally, the aerodynamic design of the first stage of IGC was completed. The CFD calculation results indicated that the total-to-total pressure ratio of the first stage was 2.51 and the polytropic efficiency was 91.0% at the design point. What’s more, an operation margin and surge margin of the compressor was about 26.5% and 16.4% respectively.
12. Experimental Study on Inducement and Development of Flow Instabilities in a Centrifugal Compressor with Different Diffuser Types
XUE Xiang, WANG Tong
Corresponding author: WANG Tong
E-mail: twang@sjtu.edu.cn
Journal of Thermal Science, 2020, 29(2): 435-444.
https://doi.org/10.1007/s11630-020-1223-4
Keywords: compressed air energy storage, centrifugal compressor, flow instability, stall
Abstract: A centrifugal compressor is a typical compressed air energy storage device. In order to ensure the safety of the compressed energy storage process in the compressor, the internal unsteady flow phenomena need to be closely monitored, especially some serious ones like stall and surge. It is necessary to explore the mechanism of flow instabilities under different conditions. A centrifugal air compressor was tested with a vaneless diffuser and a variable vaned diffuser with five different vane setting angles, respectively. Various diffuser types resulted in various modes of flow instabilities prior to surge. The vaneless region between the impeller and the diffuser was focused on. Multiple high-speed sensors were arranged along the circumferential direction. The pressure signals at all these positions were being measured and collected in real time as the compressor was slowly throttled into surge. This paper emphasizes on the influence of matching between the impeller and the diffuser on the flow instability. The experimental results showed that the diffuser vane setting angle affected the stall characteristics. Due to the asymmetry of the volute, the circumferential pressure distribution was always severely distorted prior to surge. A high-pressure region appeared near the volute tongue, and a low-pressure region was formed away from the volute tongue. In the case of the vaned diffuser with non-design installation angle and the vaneless diffuser, the rotating stall signal was originated in the low-pressure region and propagated circumferentially. However, in the case of the vaned diffuser with the design installation angle, the circumferential high-pressure region became the most sensitive region for the generation of stall, and another form of instability occurred there. Both the inducement and development of these flow instabilities have been studied. The dynamic experimental research on the compressor matching different types of diffusers could be a good case supplement.
13. Thermodynamic Analysis of Packed Bed Thermal Energy Storage System
GUO Huan, XU Yujie, GUO Cong, CHEN Haisheng, WANG Yifei, YANG Zheng, HUANG Ye, DOU Binlin
Corresponding author: XU Yujie
E-mail: xuyujie@iet.cn
Journal of Thermal Science, 2020, 29(2): 445-456.
https://doi.org/10.1007/s11630-019-1115-7
Keywords: packed bed thermal energy storage, thermocline, steady, thermodynamic analysis, stable operation
Abstract: A packed-bed thermal energy storage (PBTES) device, which is simultaneously restricted by thermal storage capacity and outlet temperatures of both cold and hot heat transfer fluids, is characterized by an unstable operation condition, and its calculation is complicated. To solve this problem, a steady thermodynamics model of PBTES with fixed temperatures on both ends was built. By using this model, the exergy destruction, thermocline thickness, thermal storage capacity, thermal storage time, and other key parameters can be calculated in a simple way. In addition, the model explained the internal reason for the change of thermocline thickness during thermal storage and release processes. Furthermore, the stable operation of the PBTES device was analyzed, and it was found that higher inlet temperature of hot air, and lower temperature difference between cold and hot air can produce less exergy destruction and achieve a larger cycle number of stable operation. The work can be employed as the basis of the design and engineering application of PBTES.
14. Experimental Study on Melting Process in an Industrial Level Molten Salt Tank
LI Zhi, ZHANG Qiangqiang, WANG Zhifeng, LI Jun
Corresponding author: WANG Zhifeng
E-mail: zhifeng@vip.sina.com
Journal of Thermal Science, 2020, 29(2): 457-463.
https://doi.org/10.1007/s11630-019-1125-5
Keywords: molten salt, melting, concentrating solar power, thermal energy storage
Abstract: Thermal energy storage (TES) is an important part of concentrating solar power (CSP) plants. The primary advantage of TES in CSP plants is the ability to dispatch electrical output to match peak demand periods and reduce the levelized cost of electricity. The major challenge of the molten salt is its high freezing point, leading to additional complicating freeze protection. This paper presents the experimental results of melting process of a mixed nitrate salt with a melting temperature of 115°C in a 20 m3 industrial level tank. Twenty electrical heaters inside the tank are used to heat the salt with a total maximum input power of 240 kW. In order to ensure a safe and fast melting process, the whole process adopted an operating strategy of combining automatic control with manual control. The whole melting process lasted for 314 hours. The salt temperature showed the greatest increase in the first 38 hours. Finally, an economic operation mode of molten salt heat storage tank was obtained.
15. Influence of NO2— on the Microscopic Structure and Physical Properties of the Binary Nitrate Salts: a Molecular Dynamics Simulation Study
NI Haiou, WU Jie, SUN Ze, LU Guimin, YU Jianguo
Corresponding author:
SUN Ze, E-mail: zsun@ecust.edu.cn;
LU Guiming, gmlu@ecust.edu.cn
Journal of Thermal Science, 2020, 29(2): 464?476.
https://doi.org/10.1007/s11630-020-1226-1
Keywords: molten salt, molecular dynamics simulation, nitrate, nitrite
Abstract: Molecular dynamics simulation method was used to study the influence of on both the structure and properties of the binary nitrate salts (60 wt.% NaNO3 + 40 wt.% KNO3). The density and viscosity of the mixtures were experimentally measured and the simulation results met well with the experimental ones. The simulation results showed that, with the addition of , the ionic clusters tended to loose and the mobilities of all the ions tended to increase. The density, viscosity, and heat capacity decreased while the thermal conductivity increased with the increase of concentration. The correlation between the microscopic structure and physical properties of the mixtures were discussed and revealed.
16. Synthesis and Characterization of Disodium Hydrogen Phosphate Dodecahydrate-Lauric-Palmitic Acid Used for Indoor Energy Storage Floor Units
XU Qian, AKKURT Nevzat, ZOU Zhenwei, LIU Yang, FENG Junxiao, YU Chuqiao, DING Chong, XIONG Yaxuan, ZHOU Jingzhi, ZANG Yong, DING Yulong
Corresponding author: FENG Junxiao, fengjx_ustb@126.com
YU Chuqiao, yuchuqiao@bit.edu.ru
Journal of Thermal Science, 2020, 29(2): 477-485.
https://doi.org/10.1007/s11630-020-1273-7
Keywords: organic-inorganic PCM, form-stable PCM, thermal property, energy storage
Abstract: Organic and inorganic phase change materials (PCMs) are considered potential materials for thermal energy storage (TES) with different phase change characteristics. In this study, a novel organic-inorganic composite phase change material (PCM) called disodium hydrogen phosphate dodecahydrate-lauric-palmitic acid (D-LA-PACM) was prepared. Expanded graphite (EG) was selected as the support material, and the novel organic-inorganic form-stable PCM called D-LA-PAPCM/EG was prepared using the vacuum adsorption method. Differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, leakage testing, melting and solidification cycle testing, thermal conductivity testing, scanning electron microscopy observation of the micromorphology, and other characterization methods were used to study the microstructure and morphology, thermal physical parameters, thermal conductivity, stability of the PCMs, and the comprehensive material properties of D-LA-PAPCM under the composite action of EG. Results indicated that the melting and freezing temperatures and latent heats of D-LA-PAPCM/EG were measured to be 31.6°C and 34.3°C and 142.9 and 142.8 J/g, respectively. Although some of the lauric-palmitic acid (LA-PA) and disodium hydrogen phosphate dodecahydrate (DHPD) separated in the multiple porous structures of EG after 1000 cycles, they could still absorb and release latent heats independently, with D-LA-PAPCM/EG still exhibiting good thermal stability. The thermal conductivity of D-LA-PAPCM/EG was 1.361 W/(m?K). Therefore, the material and thermal properties of the prepared D-LA-PAPCM/EG indicate that it could be well used as a feasible material for energy-saving phase change floor units in indoor TES systems.
17. Experimental Study on Hybrid Organic Phase Change Materials Used for Solar Energy Storage
WANG Zanshe, LI Ran, HU Juntao, HU Xianwei, GU Zhaolin
Corresponding author: GU Zhaolin
E-mail: guzhaoln@mail.xjtu.edu.cn
Journal of Thermal Science, 2020, 29(2): 486-491.
https://doi.org/10.1007/s11630-020-1224-3
Keywords: lauric acid, stearic acid, expanded graphite, phase change material, solar energy
Abstract: The solar energy utilization in built environment has been limited due to its low heat flux, uneven distribution in time and space and temporal difference in day and night. The phase change materials have been used to collect the fluctuant solar energy to form a stable energy source for the terminal equipment of the buildings. In this study, the hybrid organic phase change materials was prepared for the capillary radiant heating system which formed a cascade utilization of solar energy. Firstly, lauric acid and stearic acid were selected as the basic organic phase change materials and the binary equilibrium phase diagram was completed based on the method of step cooling curve according to the experimental tests data. The results showed that the phase transition temperature of the mixed acid at the lowest eutectic point was 31.2°C and the latent heat value was 264.3 kJ/kg when the mass mixing ratio was 70% for lauric acid and 30% for stearic acid. Secondly, the expanded graphite was used as an additive to enwrap the mixed acid and enhance the heat conductivity. The experimental results showed that when the mass proportion of expanded graphite in the mixed acid was 10%, the mixed acid could be completely enclosed by expanded graphite and the stability of melting and solidification was optimal. Additionally, the phase transition temperature of the hybrid phase change material was 31.5°C and the latent heat value was 217.4 kJ/kg. The novel hybrid phase change material has a lower eutectic point and a higher latent heat of phase change, so it has a large application space and is quite suitable for the cascade utilization of solar energy with capillary network heating system.
18. Stearic Acid/Copper Foam as Composite Phase Change Materials for Thermal Energy Storage
LI Chuanchang, ZHAO Xinbo, ZHANG Bo, XIE Baoshan, HE Zhangxing, CHEN Jian, HE Jianjun
Corresponding author: LI Chuanchang
E-mail: chuanchangli@csust.edu.cn; chuanchangli@126.com
Journal of Thermal Science, 2020, 29(2): 1-12.
https://doi.org/10.1007/s11630-020-1272-8
Keywords: stearic acid, latent thermal energy storage, copper foam
Abstract: The application of stearic acid in the latent thermal energy storage (LTES) systems is hindered due to its lower heat transfer rate. Stearic acid (SA) was blended with copper foam (CF) of pore numbers per inch (PPI) of 5, 20, and 40 to prepare composite phase change materials via a molten impregnation method. The thermal physical properties including latent heat, phase change temperature, and thermal energy storage density of composites were characterized. The thermogravimetric analysis indicated that the loadages of SA of SA/CF(5 PPI), SA/CF(20 PPI), and SA/CF(40 PPI) were 74.69%, 71.03%, and 63.54%, respectively; The latent heat of SA/CF(5 PPI), SA/CF(20 PPI), and SA/CF(40 PPI) were determined to 139.9 J?g-1, 132.7 J?g-1, and 117.8 J?g-1, respectively. Meanwhile, the infrared thermal images of SA and SA/CF composites were provided to demonstrate the thermal energy storage and dissipation capability intuitively by the temperature response and surface temperature distribution. The infrared thermal images indicated the addition of CF also reduced the fluidity of liquid SA, and the SA/CF(40 PPI) had better internal heat transfer uniformity and thermal diffusion performance than SA/CF(5 PPI) and SA/CF(20 PPI). All these thermal properties suggested SA/CF(40 PPI) has the potential application in the latent thermal energy storage.
19. Experimental Investigation of Heat Storage and Heat Transfer Rates during Melting of Nano-Enhanced Phase Change Materials (NePCM) in a Differentially-Heated Rectangular Cavity
LI Zirui, HU Nan, TU Jing, FAN Liwu
Corresponding author: HU Nan, E-mail: zju_hunan@zju.edu.cn;
FAN Liwu, liwufan@zju.edu.cn
Journal of Thermal Science, 2020, 29(2): 503-511.
https://doi.org/10.1007/s11630-020-1225-2
Keywords: aspect ratio, graphene nanoplatelets, latent heat storage, melting heat transfer, phase change material, rectangular cavity
Abstract: In this work, an experimental study of melting heat transfer of nano-enhanced phase change materials (NePCM) in a differentially-heated rectangular cavity was performed. Two height-to-width aspect ratios of the cavity, i.e., 0.9 and 1.5, were investigated. The model NePCM samples were prepared by dispersing graphene nanoplatelets (GNP) into 1-tetradecanol, having a nominal melting point of 37?C, at loadings up to 3 wt.%. The viscosity was found to have a more than 10-fold increase at the highest loading of GNP. During the melting experiments, the wall superheat at the heating boundary was set to be 10?C or 30?C. It was shown that with increasing the loading of GNP, both the heat storage and heat transfer rates during melting decelerate to some extent, at all geometrical and thermal configurations. This suggested that the use of NePCM in such cavity may not be able to enhance the heat storage rate due to the dramatic growth in viscosity, which deteriorates significantly natural convective heat transfer during melting to overweigh the enhanced heat conduction by only a decent increase in thermal conductivity. This also suggested that the numerically predicted melting accelerations and heat transfer enhancements, as a result of the increased thermal conductivity, in the literature are likely overestimated because the negative effects due to viscosity growth are underestimated.
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