CONTENTS-Volume 29, Issue 5, September-October 2020
Springer Link: https://link.springer.com/journal/11630/volumes-and-issues/29-5
1. Special Column for the Distributed Energy System with Renewable Energy and Natural Gas
Guest Editors:
Prof. HAN Wei
Institute of Engineering Thermophysics, CAS, Beijing, China
E-mail: hanwei@iet.cn
Prof. ZHU Tong
School of Mechanical Engineering, Tongji University, Shanghai, China
E-mail: zhu_tong@tongji.edu.cn
Prof. GAN Zhongxue
ENN Science and Technology Development Co., Ltd., Hebei, China
E-mail: ganzhongxue@fudan.edu.cn
Journal of Thermal Science, 2020, 29(5): 1095-1096.
https://doi.org/10.1007/s11630-020-1368-1
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1368-1
2. Comprehensive Review of Line-Focus Concentrating Solar Thermal Technologies: Parabolic Trough Collector (PTC) vs Linear Fresnel Reflector (LFR)
SUN Jie, ZHANG Zhi, WANG Li, ZHANG Zhenwen, WEI Jinjia
Corresponding author: SUN Jie
E-mail: sunjie@xjtu.edu.cn
Journal of Thermal Science, 2020, 29(5): 1097-1124.
https://doi.org/10.1007/s11630-020-1365-4
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1365-4
Keywords: concentrating solar thermal (CST), concentrating solar power (CSP), line-focus, parabolic trough collect (PTC), linear Fresnel reflector (LFR)
Abstract: In the present review, parabolic trough collector (PTC) and linear Fresnel reflector (LFR) are comprehensively and comparatively reviewed in terms of historical background, technological features, recent advancement, economic analysis and application areas. It is found that although PTC and LFR are both classified as mainstream line-focus concentrating solar thermal (CST) technologies, they are now standing at different stages of development and facing their individual opportunities and challenges. For PTC, the development is commercially mature with steady and reliable performance; therefore, extension of application is the main future demand. For LFR, the development is still in rapid progress to commercial maturity, yet indicating very promising potentials with high flexibility in novel designs and remarkable reduction in capital and operational costs. The question, which has to be answered in order to estimate the future perspectives of these two line-focus CST technologies, becomes which of these characteristics carries more weight or how to reach an optimal trade-off between them.
3. A Deep Reinforcement Learning Bidding Algorithm on Electricity Market
JIA Shuai, GAN Zhongxue, XI Yugeng, LI Dewei, XUE Shibei, WANG Limin
Corresponding author: JIA Shuai;
E-mail: liu2596615@sjtu.edu.cn
GAN Zhongxue;
ganzhongxue@fudan.edu.cn
Journal of Thermal Science, 2020, 29(5): 1125-1134.
https://doi.org/10.1007/s11630-020-1308-0
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1308-0
Keywords: electricity market, reinforcement learning, energy efficiency, conjectural variation, bidding strategy
Abstract: In this paper, we design a new bidding algorithm by employing a deep reinforcement learning approach. Firms use the proposed algorithm to estimate conjectural variation of the other firms and then employ this variable to generate the optimal bidding strategy so as to pursue maximal profits. With this algorithm, electricity generation firms can improve the accuracy of conjectural variations of competitors by dynamically learning in an electricity market with incomplete information. Electricity market will reach an equilibrium point when electricity firms adopt the proposed bidding algorithm for a repeated game of power trading. The simulation examples illustrate the overall energy efficiency of power network will increase by 9.90% as the market clearing price decreasing when all companies use the algorithm. The simulation examples also show that the power demand elasticity has a positive effect on the convergence of learning process.
4. Optimization of Operation Strategies for a Combined Cooling, Heating and Power System based on Adiabatic Compressed Air Energy Storage
CHEN Shang, ZHU Tong, GAN Zhongxue, ZHU Xiaojun, LIU Liuchen
Corresponding author: ZHU Tong
E-mail: ztcfd@163.com; zhu_tong@tongji.edu.cn
Journal of Thermal Science, 2020, 29(5): 1135-1148.
https://doi.org/10.1007/s11630-020-1170-0
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1170-0
Keywords: combined cooling, heating and power (CCHP) system, advanced adiabatic compressed air energy storage (AA-CAES), optimization
Abstract: The fluctuations of renewable energy and various energy demands are crucial issues for the optimal design and operation of combined cooling, heating and power (CCHP) system. In this paper, a novel CCHP system is simulated with advanced adiabatic compressed air energy storage (AA-CAES) technology as a join to connect with wind energy generation and an internal-combustion engine (ICE). The capital cost of utilities, energy cost, environmental protection cost and primary energy savings ratio (PESR) are used as system performance indicators. To fulfill the cooling, heating and power requirements of a district and consider the thermal-electric coupling of ICE and AA-CAES in CCHP system, three operation strategies are established to schedule the dispatch of AA-CAES and ICE: ICE priority operation strategy, CAES priority operation strategy and simultaneous operation strategy. Each strategy leads the operation load of AA-CAES or ICE to improve the energy supply efficiency of the system. Moreover, to minimize comprehensive costs and maximize the PESR, a novel optimization algorithm based on intelligent updating multi-objective differential evolution (MODE) is proposed to solve the optimization model. Considering the multi-interface characteristic and active management ability of the ICE and AA-CAES, the economic benefits and energy efficiency of the three operation strategies are compared by the simulation with the same system configuration. On a typical summer day, the simultaneous strategy is the best solution as the total cost is 3643 USD and the PESR is 66.1%, while on a typical winter day, the ICE priority strategy is the best solution as the total cost is 4529 USD and the PESR is 64.4%. The proposed methodology provides the CCHP based AA-CAES system with a better optimized operation.
5. Feasibility Analysis of the Operation Strategies for Combined Cooling, Heating and Power Systems (CCHP) based on the Energy-Matching Regime
FENG Lejun, DAI Xiaoye, MO Junrong, SHI Lin*
Corresponding author: SHI Lin
E-mail: rnxsl@mail.tsinghua.edu.cn
Journal of Thermal Science, 2020, 29(5): 1149-1164.
https://doi.org/10.1007/s11630-020-1314-2
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1314-2
Keywords: combined cooling, heating and power systems (CCHP), energy-matching performance, operation strategies, comprehensive parameter, energy saving performance
Abstract: Although numerous studies have considered the two traditional operation strategies: following the electric load (FEL) and following the thermal load (FTL), for combined cooling, heating, and power (CCHP) systems in different case studies, there are limited theoretical studies on the quantification methods to assess the feasibility of these two strategies in different load demands scenarios. Therefore, instead of a case study, we have undertaken a theoretical analysis of the suitable application scenarios for FEL and FTL strategies based on the energy-matching performance between systems’ provision and users’ demands. To compare the calculation models of energy saving rate (ESR) for FEL and FTL strategies in the left and right sub-regions of the energy-supply curve, a comprehensive parameter (?) that combines three inherently influential factors (off-design operation parameter, energy-matching parameter, and install capacity coefficient) is defined to determine the optimal installed capacity and feasibility of FEL or FTL strategies quantitatively. The results indicate that greater value of ? will contribute to a better energy saving performance, and FEL strategy shows better performance than FTL in most load demands scenarios, and the optimal installed capacity occurs when the load demand points were located in different regions of the energy-supply curve. Finally, taking a hotel in Beijing as an example, the value of the optimal install capacity coefficient is 0.845 and the FEL strategy is also suggested, and compared to the maximum install capacity, the average values of the ESR on a typical summer day, transition season, and winter can be enhanced by 3.9%, 8.8%, and 1.89%, respectively.
6. Proposal and Assessment of an Engine-Based Distributed Steam and Power Cogeneration System Integrated with an Absorption-Compression Heat Pump
LIU Changchun, HAN Wei, WANG Zefeng, ZHANG Na
Corresponding author: HAN Wei
E-mail: hanwei@iet.cn
Journal of Thermal Science, 2020, 29(5): 1165-1179.
https://doi.org/10.1007/s11630-020-1302-6
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1302-6
Keywords: steam and power cogeneration, HACHP, ICE, high-temperature heat pump
Abstract: Internal combustion engine-based poly-generation systems have been widely used for energy savings and emissions reductions. To maximize their thermodynamic and environmental performance potentials, the efficient recovery of flue gas and jacket water heat is essential. In a conventional internal combustion engine-based steam and power cogeneration system, the low-temperature (less than 170°C) heat from flue gas and jacket water is usually directly discharged to the environment, which dramatically reduces the thermal and economic performance. In this work, a high-temperature heat pump is employed to recover this part of low-temperature heat for steam generation. The sensible heat of the flue gas and jacket water is cascade utilized in a steam generator and a heat pump. Simulation results show that the process steam yield of the proposed system is almost doubled (increased by 703 kg/h) compared to that of an engine-based cogeneration system without a heat pump. The proposed system can reduce natural gas consumption, CO2 and NOx emissions by approximately 199 069 m3, 372.64 tons and 3.02 tons per year, respectively, with a primary energy ratio and exergy efficiency of 72.52% and 46.28%, respectively. Moreover, the proposed system has a lower payback period with a value of 5.11 years, and the determining factors that affect the payback period are natural gas and electricity prices. The total net present value of the proposed system within its lifespan is 2 441 581 USD, and an extra profit of 785 748 USD can be obtained compared to the reference system. This is a promising approach for replacing gas boilers for process steam production in industrial sectors.
7. Experimental Study on Long Cycling Performance of NCM523 Lithium-Ion Batteries and Optimization of Charge-Discharge Strategy
ZHU Xiaojun, ZHU Jianhua, WANG Junming, GAN Zhongxue, LI Guoxian, MENG Chuizhou
Corresponding author: WANG Junming;
E-mail: wangjunming@enn.cn;
MENG Chuizhou
2018108@hebut.edu.cn
Journal of Thermal Science, 2020, 29(5): 1180-1192.
https://doi.org/10.1007/s11630-020-1174-9
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1174-9
Keywords: lithium-ion batteries, NCM523, long cycling performance, charge-discharge strategy, prismatic cell
Abstract: With the increasing demand for clean renewable energy and electric cars, people have put forward higher requirement for the energy storage system. One of the most successful lithium-ion batteries with a cathode combination of lithium nickel manganese cobalt oxide (also called NCM lithium-ion battery), has been playing an increasingly important role. So far, numerous research has been done on the fabrication of cathode material with optimization of its composition, design, and assembly of the battery system in order to improve the energy storage performance. However, most of the previous studies were conducted based on relatively short cycling time of testing, with limited charge-discharge cycles of no more than 1000. Thus the conclusions were insufficient to be applied in the practical working condition. In this work, by using the developed NCM523 lithium-ion batteries, we have performed a series of ultra-long cycling tests on the individual cell and its module, with a comprehensive study on the relationship between the retained capacity after long cycling time and the depth of discharge (DOD), charge-discharge rate and operating temperature. Optimization of the charge-discharge strategies on a single cell and the whole module was also made to effectively improve the overall energy storage efficiency. This experimental study offers a guideline for the efficient use of similar types of lithium-ion batteries in the practical working condition. The developed batteries together with the optimized charge-discharge strategy proposed here are promising to meet the requirements for applications of stationary energy storage and electric cars.
8. Performance Analysis of a Combined Absorption Refrigeration-Liquid Desiccant Dehumidification THIC System Driven by Low-Grade Heat Source
XU Cong, SUI Jun, DAI Yuze, LIU Feng, LIU Hao
Corresponding author: SUI Jun
E-mail: suijun@iet.cn
Journal of Thermal Science, 2020, 29(5): 1193-1205.
https://doi.org/10.1007/s11630-020-1363-6
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1363-6
Keywords: temperature and humidity independent control (THIC), low-grade heat source, cascade utilization, heat utilization rate
Abstract: Traditional condensing air-conditioning systems consume large amounts of energy in hot and humid areas, and it is difficult to achieve simultaneous control of temperature and humidity. A combined absorption refrigeration (AR) and liquid desiccant dehumidification (LDD) air-conditioning system based on cascade utilization of low-grade heat source is proposed. The system can realize independent control of temperature and humidity and carry out profound recovery of low-grade heat sources. Under the design conditions, the heat utilization rate ζ reaches 21.05%, which is 2.73 times that of the conventional absorption refrigeration reference system. A parametric sensitivity analysis is performed to optimize the system. The ζ increases from 9.79% to 18.55% and the coefficient of performance COPt increases from 0.33 to 0.35 with an increase in chilled water temperature from 7°C to 15°C. With an increase in regenerant solution temperature from 60°C to 70°C, the ζ achieves the optimal value of 21.05% at 68°C. ζ decreases from 21.05% to 15.05% as the concentration of the regenerant solution increases from 36% to 40%. Under variable environmental temperature and humidity, the ζ of the proposed system changes within a small range and stays much higher than that of the reference system with the same quality heat source, which indicates that the proposed system has a better adaptability to changing environmental parameters.
9. Influence of Fill Point in Multiple-Heat-Sources Looped District Heating System with Distributed Variable-Speed Pumps
XU Tong, YAN Jing, WANG Xinlei, WANG Hai, ZHU Tong, WANG Haiying
Corresponding author: WANG Xinlei;
E-mail: wangxinlei@chinasperi.sgcc.com.cn
WANG Haiying
haiyingw@tongji.edu.cn
Journal of Thermal Science, 2020, 29(5): 1206-1222.
https://doi.org/10.1007/s11630-020-1307-1
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1307-1
Keywords: district heating, central circulating pump, distributed variable-speed pumps, fill point, energy saving
Abstract: When regulating a pipe network according to user demand, hydraulic balance and power consumption are crucial factors for a multi-source looped-pipe network applying distributed variable-speed pumps compared to the conventional central circulating pump system. In this paper, the influence of the fill point on power consumption and hydraulic balance of the multi-source looped-pipe network was studied. A mathematical model for electricity energy consumption analysis was built and calculated for a large sized looped-pipe network with multiple heat sources and distributed variable-speed pumps. The hydraulic calculation models of each single element, such as pipe, distribution pump, valve, replenishment pump, heat source and substation, were built. A case located in Dezhou city, China was analyzed. The results showed that: the maximum power saving (39.2%) could be achieved when each heat source had its own fill point, but the heat sources would not meet their design flows; to meet the design flows of all the heat sources, only one fill point should be necessarily located near the heat source with the lowest flow rate to get the expected hydraulic stability and energy saving.
10. Flue Gas Water Recovery by Indirect Cooling Technology for Large-Scale Applications: A Review
ZHONG Wei, JI Wenhui, CAO Xiaoling, YUAN Yanping
Corresponding author: YUAN Yanping
E-mail: ypyuan@home.swjtu.edu.cn
Journal of Thermal Science, 2020, 29(5): 1223-1241.
https://doi.org/10.1007/s11630-020-1360-9
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1360-9
Keywords: flue gas, condensation, water recovery, heat exchanger, power plants
Abstract: With social development and economic enhancement, energy is facing significant worldwide demand, and fossil fuels are the prime energy sources for various energy systems over past decades. Furthermore, among fuel-consumed applications, power plants are the primary source of energy consumption. There is a lot of waste heat and steam accompanied by the latent heat produced in the exhaust flue gas. Therefore, the latent heat recovery from the flue gas plays an important role in increasing the efficiency of the system and saving water. To recover the heat and mass in power plants, three primary methods are proposed to condense the vapor based on previous studies: (1) flue gas condensation technology, (2) liquid desiccant-based dehydration (LDD) technology and (3) membrane technology. This paper mainly reviews and summaries the indirect cooling technology in flue gas condensation technology. The numerical simulation and theory of flue gas condensation are introduced. Different heat exchanger types and conducted experiments are also summarized. The performance of the indirect cooling technology is affected not only by its own configuration and design but also by the flue gas inlet temperature, velocity, water vapor mass fraction, etc. The major concerns and outlook of practical applications for further study are attributed to the heat exchanger size and cost, acid corrosion, ash accumulation in flue gas, etc.
11. NOx Emission Reduction Technology for Marine Engine Based on Tier-III: A Review
LU Xiuwei, GENG Peng, CHEN Yunyue
Corresponding authors: GENG Peng;
E-mail: penggeng@shmtu.edu.cn
CHEN Yunyue
yunyuechen123@126.com
Journal of Thermal Science, 2020, 29(5): 1242-1268.
https://doi.org/10.1007/s11630-020-1342-y
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1342-y
Keywords: marine engine, NOx emission, Tier-III, exhaust gas recirculation (EGR), selective catalytic reduction (SCR), dual-fuel
Abstract: The development of maritime trade has greatly promoted the development of diesel engines. However, with the increasingly serious environmental problems, more and more attention has been paid to the exhaust emissions of high-power marine diesel engines. The restrictions on SOx have been implemented globally, and the limitation of the NOx will be the next priority. This paper illustrates (a) Principle and research progress of NOx emissions-reduction technology of marine diesel engine; (b) Summary of advantages and disadvantages among various reduction technologies and their reduction effects; (c) The application effect of mainstream technology on board. Firstly, since exhaust gas recirculation (EGR) can achieve Tier-III directly from Tier-I without considering the increased fuel consumption. It is deemed as the most promising technology to reduce emissions by controlling combustion condition. However, EGR has shortcomings of excessive increase in fuel consumption and generation of waste water, which need to be solved immediately. Secondly, selective catalytic reduction (SCR) is the most effective and straightforward means to achieve Tier-III. Despite of the continuous optimization of SCR unit volume, the problem of scrap catalyst seriously limits its wide application. How to match the supercharger more efficiently is a key factor in choosing between high and low pressure SCR. Thirdly, nature gas (NG) engines are capable of achieving a reduction in NOx, but in order to meet the requirements of Tier-III, it still needs to be assisted by other technologies. The emissions of hydrocarbon (HC) and CO in NG engines are huge defects that must be solved. Lastly, technologies such as the Miller cycle, Two-stage supercharging and mixed-water combustion can also reduce emissions but were rarely used alone. These technologies can be combined with EGR, SCR and NG engines to optimize the engines’ economy and emission characteristics.
12. Comparative Study on Soot Reduction, Soot Nanostructure and Oxidation Reactivity of n-heptane/DMC and Isooctane/DMC Inverse Diffusion Flames
JIANG Bo, PALADPOKKRONG Chutikarn, LIU Dong
Corresponding author: LIU Dong
E-mail: dongliu@njust.edu.cn
Journal of Thermal Science, 2020, 29(5): 1269-1281.
https://doi.org/10.1007/s11630-020-1298-y
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1298-y
Keywords: inverse diffusion flame, n-heptane/DMC, isooctane/DMC, soot reduction, soot nanostructure, oxidation reactivity
Abstract: Dimethyl carbonate (DMC) is an environmentally oxygenated compound which can be used efficiently for soot reduction. This paper compared the soot reduction, soot nanostructure and oxidation reactivity from inverse diffusion flames (IDFs) of the hydrocarbon fuels, namely n-heptane and isooctane doped with DMC. Effects of DMC additions on soot reduction were discussed. DMC addition is more effective for the soot reduction of n-heptane/DMC IDF than isooctane/DMC IDF. The morphology and nanostructures of soot particles were investigated by Transmission Electron Microscopy (TEM) and High Resolution TEM (HRTEM), and the soot graphitization and oxidation reactivity were analyzed by X-ray Diffraction (XRD) and Thermogravimetric Analyzer (TGA), respectively. The results of HRTEM images showed that many larger aggregates were observed for the structures of soot particles from IDFs with DMC additions. The soot particles exhibited more liquid-like material, more amorphous, higher disorganized layers, and less graphitic than that of IDFs without DMC additions. With increasing of DMC blending rate, soot particles changed younger to have shorter fringe length, higher tortuosity, and greater fringe separation. Based on the XRD and TGA results, the degree of the soot graphitization level decreased; the soot mass lost significantly faster, and the soot become more reactive.
13. Experimental Investigation on the Development Process of Large-Scale Low-Speed Stall Disturbance in Contra-Rotating Compressor
YUE Shaoyuan, WANG Yan’gang, WEI Liguo, WANG Hao
Corresponding author: WANG Yan’gang;
E-mail: wyg704@nwpu.edu.cn
WANG Hao
wanghao@nwpu.edu.cn
Journal of Thermal Science, 2020, 29(5): 1282-1291.
https://doi.org/10.1007/s11630-020-1341-z
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1341-z
Keywords: contra-rotating, abrupt, large scale, stall
Abstract: In order to better understand the stall process of a contra-rotating compressor, the detailed characteristic and multi-channel unsteady pressure signals have been achieved by a special layout of high-frequency response pressure sensors. The array consists of thirty-one high-frequency response dynamic sensors coupled with two optical fiber sensors that were installed on the compressor casing in the direction of circumferential and chordwise of the upstream and downstream of the contra-rotating rotors. A significant hysteresis loop during the stall-recovery process of the contra-rotating compressor was captured successfully. The time series of unsteady signals when the compressor was working on the point of stall occurrence, the period of fully stall, and recovery stall were studied and discussed. Results show a large scale, and low-speed disturbance occurred abruptly at the leading-edge plane of the rear rotor and expands until it passes through both rotors. The single stall cell occupied a circumferential range of 135° and moved in the direction of the rear rotor with an 8.3% shaft speed. As the mass flow rate dropped, the stall cell speed decreases. During the stall recovery process, the rotational speed of disturbance suddenly increased from 7.5% to 18% and even increased to 47% just before the moment when flow recovered axisymmetric. Compared with the rear rotor, the front one dropped out unstable conditions earlier.
14. Optimization of Flow Matching Schemes for a Heavy Gas Turbine Burning Syngas
GUO Lei, LI Guoqing, HU Chunyan, LEI Zhijun, HUANG Enliang, GONG Jianbo, XU Gang
Corresponding author: HU Chunyan
E-mail: huchunyan@iet.cn
Journal of Thermal Science, 2020, 29(5): 1292-1299.
https://doi.org/10.1007/s11630-020-1359-2
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1359-2
Keywords: gas turbine, flow matching, syngas
Abstract: A heavy-duty gas turbine, designed for natural gas, was used to burn the syngas with two different calorific values. This study was mainly to optimize the flow matching scheme for the gas turbine. Two models of gas turbine burning syngas with different calorific values were established and the calculation models of different flow matching schemes were provided. The optimum scheme was obtained by evaluating thermal efficiency and work output under different operating conditions. The results showed that the highest unit efficiency was achieved by, without significant drop in work output, increasing the throat area of the turbine nozzle and reducing the initial temperature of the gas. On the premise of ensuring the safety of the gas turbine unit, increasing the pressure ratio of the compressor could further improve the unit efficiency and the work output. Simply adjusting the angle of the inlet guide vane fails to match the flow of compressor and turbine. The measures such as reducing inlet temperature of turbine or air bleed still need to be adopted, but the thermal efficiency dropped significantly in this process.
15. A New Hybrid System Design for Thermal Energy Storage
CEYLAN ?lhan, ALI Ismail Hamad Guma, ERGüN Alper, GüREL Ali Etem, ACAR Bahad?r, ?SLAM Nursel
Corresponding author: ERGüN Alper
E-mail: alperergun@karabuk.edu.tr
Journal of Thermal Science, 2020, 29(5): 1300-1308.
https://doi.org/10.1007/s11630-020-1292-4
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1292-4
Keywords: heat storage, phase change material, concentrated solar air collector
Abstract: Due to some serious environmental problems like global warming and greenhouse effect, studies on solar energy systems are being conducted all over the world. The studies conducted in recent years are on hybrid designs in which solar energy systems can realize both electricity and heat production at the same time. In this way, both electrical energy and heat energy can be generated from the same system. In this study, the design and analysis of a concentrated solar air collector with a heat storage unit were carried out. In the solar air collector, heat energy was depot in paraffin wax, and the electrical energy which was stored in the battery using the PV (photovoltaic) modules in the system enabled the operation of the system fan. The experiments which aimed at determining system performance were carried out in winter when the ambient temperature was low. The experiments were performed with or without a heat storage unit, and a comparative analysis was made. It was found that the temperature of the air released from the collector ranged from 15°C to 40°C when the exterior temperature was ?5°C. The average efficiency of the concentrated system without the heat storage unit was calculated as 67%. The average efficiency of the concentrated system with the heat storage unit was calculated as 96%.
16. Enhancing Thermal Performance of a Parabolic Trough Collector with Inserting Longitudinal Fins in the Down Half of the Receiver Tube
LAARABA Adel, MEBARKI Ghazali
Corresponding author: LAARABA Adel
E-mail: Laaraba_adel_83@yahoo.fr
Journal of Thermal Science, 2020, 29(5): 1309-1321.
https://doi.org/10.1007/s11630-020-1256-8
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1256-8
Keywords: solar energy, Nusselt number, thermal efficiency, parabolic trough collector, forced convection
Abstract: Heat transfer in a finned absorber of a parabolic trough collector was studied numerically. The main aim of this work was to study the effect of attached fins on the enhancement of the thermal performance of a parabolic trough collector. The values of the fin’s length varied from 0 to 20 mm; their thicknesses varied from 0 to 8 mm and their number was 5. The parameters used in the current study are: the thermal and dynamic field, friction coefficient, Nusselt number, the thermal efficiency and thermal enhancement index. Obtained results show that inclusion of fins to the lower half of the absorber tube can enhance the heat transfer between the absorber tube and working fluid. The increase of the fin’s length increases the friction factor, Nusselt number and thermal efficiency, and the increase of fin’s thickness also increases the previous parameters. Starting the value 6 mm of thickness, its effect remains the same, but thickness is less effective than length. The values 15 mm of length and 6 mm of thickness are selected as optimal values. Results show that the inclusion of the fins enhances the thermal performance of the parabolic collector by 8.45%.
17. Enhancement of Photo-Thermal Conversion Performance of the Nanofluids Through Spectral Complementarity between Silver and Cesium Tungstate Oxide Nanoparticles
LIU Changqing, ZHANG Liye, HE Yan, YU Wei
Corresponding author: HE Yan;
E-mail: heyan_sd@163.com
YU Wei;
yuwei@sspu.edu.cn
Journal of Thermal Science, 2020, 29(5): 1322-1332.
https://doi.org/10.1007/s11630-020-1306-2
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1306-2
Keywords: photo-thermal conversion, nanofluids, Ag, cesium tungsten oxide, near-infrared
Abstract: Nanofluids with full-spectrum absorption properties are highly desirable for direct solar thermal energy conversion applications. In this work, Ag and CsWO3 nanofluids, which exhibit absorption both in the visible and near-infrared (NIR) region, are integrated to obtain two-component hybrid nanofluids. The hybrid nanofluids show broad band absorption with a solar weighted absorption fraction of 99.6%, compared to 18% and 54% for the base liquid (ethylene glycol) and CsWO3 nanofluids, respectively. The highest photo-thermal conversion performance for the hybrid nanofluids is obtained with Ag/CsWO3 weight ratio of 3/7. The solar thermal conversion efficiency of the optimum hybrid nanofluids is 67%, 10% and 15% higher than single Ag and CsWO3 nanofluids. The two-component hybrid nanofluid provides an alternative for making the best use of solar energy.
18. Flow Boiling of Ammonia in a Diamond-Made Microchannel Heat Sink for High Heat Flux Hotspots
YANG Qi, MIAO Jianyin, ZHAO Jingquan, HUANG Yanpei, FU Weichun, SHEN Xiaobin
Corresponding author: SHEN Xiaobin
E-mail: shenxiaobin@buaa.edu.cn
Journal of Thermal Science, 2020, 29(5): 1333-1344.
https://doi.org/10.1007/s11630-019-1208-3
Springer Link: https://link.springer.com/article/10.1007/s11630-019-1208-3
Keywords: high heat flux, flow boiling, microchannel, ammonia, multipoint heat sources
Abstract: To solve the heat dissipation problem of electronic devices with high heat flux hotspots, a diamond microchannel heat sink consisting of 37 parallel triangular microchannels with channel lengths of 45 mm and hydraulic diameters of 280 μm was designed. The flow boiling heat transfer characteristics of ammonia in the microchannels were investigated under high heat fluxes of 473.9–1000.4 W/cm2. Saturated flow boiling experi- ments with saturation temperatures of 25°C, 30°C, and 35°C and mass fluxes of 98–1200 kg/m2s were conducted, as well as subcooled flow boiling with inlet subcooling of 5°C as a comparison. The temperature and pressure drop measurements were analyzed. The main conclusions below can be drawn. (1) At a given heat flux, the heat source temperature first decreased and then increased with the mass flux, and there existed an optimum mass flux to optimize the cooling performance of the heat sink. (2) The heat transfer performance under the saturated inlet condition was obviously better than that under the subcooled inlet condition. (3) A larger saturation temperature leaded to weakening of both the heat transfer capacity and the stability of the microchannel heat sink. Notably, with the high heat diffusion ability of the diamond substrate and the great heat transfer capacity of ammonia flow boiling in microchannels, the heat sink can achieve a heat removal capacity of up to 1000.4 W/cm2.
19. Numerical Study and Optimization of a Combined Thermoelectric Assisted Indirect Evaporative Cooling System
ZHOU Yuanyuan, ZHANG Tao, WANG Fang, YU Yanshun
Corresponding author: ZHOU Yuanyuan
E-mail: zhouyy@njust.edu.cn
Journal of Thermal Science, 2020, 29(5): 1345-1354.
https://doi.org/10.1007/s11630-020-1362-7
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1362-7
Keywords: indirect evaporative cooling, thermoelectric, regenerative, cross flow, heat and mass transfer, optimization
Abstract: This paper numerically investigates the performance of a novel combined cross-regenerative cross flow (C-RC) thermoelectric assisted indirect evaporative cooling (TIEC) system. This C-RC TIEC system combines the indirect evaporative cooling and thermoelectric cooling technologies. A heat and mass transfer model is developed to perform the performance analysis and optimization of this novel system. Performance comparison between the novel C-RC TIEC system and a regenerative cross flow TIEC system is conducted under various operating conditions. It is found that the novel system provides better performance with higher coefficient of performance (COP) and higher dew point effectiveness than the regenerative cross flow TIEC system, especially under smaller working current and smaller number of thermoelectric cooling modules. The performance optimization of the novel system is also made by investigating the influences of primary air parameters, three different mass flow rate ratios, as well as the length ratio of the left wet channel to the whole wet channel. The results show that there exist optimal mass flow rate ratios and wet channel length ratio resulting in the maximum COP.
20. Theoretical Analysis of Annular Elliptic Finned Tube Evaporative Condenser Based on Field Measurement
GU Yaxiu, WANG Junwei, WANG Xinru, LI Mohua, PAN Song, LIU Guangdong, WANG Wentao, GONG Zexiang
Corresponding author: WANG Xinru;
E-mail: saxxw1@nottingham.edu.cn;
PAN Song
pansong@bjut.edu.cn
Journal of Thermal Science, 2020, 29(5): 1355-1369.
https://doi.org/10.1007/s11630-020-1354-7
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1354-7
Keywords: evaporative condenser, finned tube heat exchanger, annular elliptic tube, heat transfer enhancement, air-conditioning system, metro station
Abstract: In this article, a new evaporative condenser with an annular elliptic finned tube heat exchanger that includes a round inner tube and elliptic outer finned tube was designed and analyzed. The refrigerant flows between the round inner tube and the elliptic outer tube, and it simultaneously exchanges heat with the cooling water in the inner tube, the spray water, and the cooling air flowing past the outer tube. Using field measurement for the traditional round finned tube evaporative condenser in the Futong Metro Station of Line 14 in Beijing, China, the theoretical heat transfer performance of the annular elliptic finned tube evaporative condenser was analyzed and simulated. Compared with a round finned tube heat exchanger, the heat exchange capacity of the annular elliptic finned tube increased by 2.34% to 9.28%; the total heat transfer coefficient increased by 47.42%, and the power consumption of the fan in the air-conditioning system with an annular elliptic finned tube heat exchanger decreased by 11.18% to 14.65%. Therefore, the energy-saving performance and the heat transfer performance of the new annular elliptic finned tube heat exchanger were enhanced compared to the round finned tube heat exchanger.
21. A New Algorithm for a Condenser Design for Large-Scale Nuclear Power Plants in Tropical Region
KHAN Abid Hossain, ISLAM Md. Shafiqul
Corresponding author: ISLAM Md. Shafiqul
E-mail: msislam@du.ac.bd
Journal of Thermal Science, 2020, 29(5): 1370-1389.
https://doi.org/10.1007/s11630-020-1270-x
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1270-x
Keywords: nuclear power plant, vacuum condenser, velocity-search algorithm, tropical region
Abstract: This work presents a new velocity search algorithm for designing a condenser of a 1200 MWe large-scale nuclear power plant situated in tropical region. For this, the condenser pressure was considered in the range of 7.5–15 kPa while its tube inner diameter was taken as 28 mm with 1 mm tube wall thickness. Both longitudinal and transverse condensers with multiple shell tanks and varied shell tank lengths from 8–14 m have been considered in this work. Three different tertiary coolant temperature rises were chosen as 4°C, 8°C and 12°C by considering tropical region average reservoir water temperature range of 28°C to 32°C during summer. Velocity of tertiary coolant was kept within 0.75–1.5 m/s to ensure sufficient turbulence to avoid erosion-corrosion of the tubes. Numerical simulation has been employed to obtain tube-side pressure drop and convection heat transfer coefficient directly from tertiary coolant inlet velocity using κ-ω turbulent flow model. A new iterative “velocity-search algorithm” has been developed that focuses on finding the correct tertiary coolant velocity instead of overall heat transfer coefficient. Results revealed that velocity-search algorithm yielded very close to the important physical and thermal parameters of condenser compared to the existing design data in large scale nuclear power plants. Velocity-search algorithm has given less number of condenser design physical parameters that meets the velocity acceptance criteria for longitudinal condenser compared to the transverse condenser. Finally, velocity-search algorithm is found to be more reliable, robust, and consistent for condenser design compared to the conventional design algorithm used in Log-Mean Temperature Difference method.
Download the attachment
Journal of Thermal Science