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Table of Content
05 June 2023, Volume 74 Issue S1
    Reviews and monographs
    Review on greenhouse gas reduction related to refrigerants in cold chain
    Runmiao GAO, Mengjie SONG, Enyuan GAO, Long ZHANG, Xuan ZHANG, Keke SHAO, Zekang ZHEN, Zhengyong JIANG
    2023, 74(S1):  1-7.  doi:10.11949/0438-1157.20221644
    Abstract ( 211 )   HTML ( 20)   PDF (1002KB) ( 128 )  
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    To promote sustainable development and energy saving and emission reduction of cold chain equipment, based on freezing equipment, refrigerating equipment, refrigeration transportation equipment, refrigeration sales equipment, and domestic refrigerator, combined with the refrigerant charge volume, leakage rate, and recovery rate, the development history of refrigerants was summarized, and the influence of refrigerant replacement on related greenhouse gas emissions was summed up. The results show that natural refrigerants, HCs, and HFOs have broad application prospects in cold chain equipment. The implementation of the three types of refrigerant alternatives can achieve about 5%, 20%, and 10% improvement in energy saving and emission reduction, respectively. In terms of refrigerant charging, leakage and recovery, there are still many gaps in existing research, such as unclear mechanisms and unverified effects. Research and development of efficient and environmentally friendly refrigerants and improvement of refrigerant recovery systems of cold chain equipment have become the focus of current research.

    Recent progress and development trend of mechanical vapor compression evaporation technology
    Huafu ZHANG, Lige TONG, Zhentao ZHANG, Junling YANG, Li WANG, Junhao ZHANG
    2023, 74(S1):  8-24.  doi:10.11949/0438-1157.20230077
    Abstract ( 197 )   HTML ( 5)   PDF (1025KB) ( 183 )  
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    At present, the research on mechanical vapor compression(MVC) evaporation system has the following three problems: (1) For the working principle, no more in-depth descriptions of the thermodynamic process is proposed; (2) For the process types, no more comprehensive classification methods is established; (3) For the application cases, more systematic design and operation rules are not summarized. Therefore, the principle and system composition, classification and process type, application and engineering cases of MVC evaporation system are introduced emphatically, the research status, existing problems and future development trend of MVC technology are reviewed deeply, comprehensively and systematically.

    A review of coupling PCM modules with heat pipes for electronic thermal management
    Yanpeng WU, Qianlong LIU, Dongmin TIAN, Fengjun CHEN
    2023, 74(S1):  25-31.  doi:10.11949/0438-1157.20230069
    Abstract ( 190 )   HTML ( 11)   PDF (622KB) ( 234 )  
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    The miniaturization of electronic devices creates problems of high heat flux and uneven temperature distribution. The coupling of heat pipe and phase change material (PCM) combines the high thermal conductivity of heat pipe with the high latent heat of PCM, so as to better control the temperature in the evaporation section of heat pipe, ensure the stability and uniformity of the internal temperature field of electronic devices, effectively improve the heat dissipation capacity of electronic devices, and reduce the energy consumption of cooling system. In this paper, the research progress of thermal management of electronic devices coupled with heat pipe and PCM is reviewed, the coupling mode of heat pipe and PCM and the coupling heat transfer method of PCM and heat pipe are introduced, and the existing problems and possible solutions of the coupling module are put forward.

    Progress in infrared imaging detection technology and domestic equipment for industrial gas leakage in chemical industry parks
    Weiqi JIN, Yuerong WU, Xia WANG, Li LI, Su QIU, Pan YUAN, Minghe WANG
    2023, 74(S1):  32-44.  doi:10.11949/0438-1157.20230835
    Abstract ( 208 )   HTML ( 3)   PDF (9377KB) ( 471 )  
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    The prevention and early warning of industrial gas leakage in chemical parks is an important part of the current production process, which is not only a matter of life and property safety, but also a project of vital and lasting importance for dual-carbon compliance and environmental protection. On the basis of introducing the basic principles and typical products of advanced technologies such as conventional single-point detection, laser detection and infrared imaging detection of industrial gas leakage, this paper analyzes the infrared imaging detection technology of gas cloud suitable for on-site leakage and its characteristics of localized equipment, and analyzes the key technologies that need to be solved to further realize engineering application after breakthroughs in laboratory theory and key technologies, which is of significance for promoting the development of gas leakage prevention technology and equipment promotion in domestic chemical parks.

    Thermodynamics
    Performance analysis of water vapor quasi-saturated compression high temperature heat pump system
    Di WU, Bin HU, Ruzhu WANG, Junyu LIANG
    2023, 74(S1):  45-52.  doi:10.11949/0438-1157.20221619
    Abstract ( 117 )   HTML ( 6)   PDF (942KB) ( 212 )  
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    The water vapor high temperature heat pump (HTHP) combines the environmental protection of natural working medium water and the energy saving of heat pump, and gives full play to the performance advantages of water working medium in the field of HTHP. The water-injection cooling effectively ensures the long-term safety, stability and efficient operation of the unit. In this paper, the possibility and the main problem of constructing reverse Carnot cycle in the heat pump system are analyzed. It is proved theoretically that continuous injection of low enthalpy water working medium into the working chamber during the process of water vapor compression can not only effectively reduce the exhaust superheat at the end of compression, but also improve the overall performance of the system. The influence of suction superheat and water-injection cooling times on system performance was theoretically analyzed, and it was concluded that the existence of suction superheat was not conducive to the improvement of system performance, while the increase of water-injection times was beneficial to system performance. However, when the water-injection times exceeded 5 times, the improvement of system performance was very slow. When the suction superheat was 20℃, COP decreased by 1.45%—1.54% compared with non-suction superheat. When the water-injection cooling times reached 30, COP increased by 3.10%—3.73% compared with one water-injection.

    Energy and exergy analysis of a solution cross-type absorption-resorption heat pump using NH3/H2O as working fluid
    Zhenghao JIN, Lijie FENG, Shuhong LI
    2023, 74(S1):  53-63.  doi:10.11949/0438-1157.20221586
    Abstract ( 94 )   HTML ( 7)   PDF (2608KB) ( 88 )  
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    Ammonia water absorption-reabsorption heat pump (ARHP) is a special kind of absorption heat pump (AHP), which can reduce the working pressure and the temperature of the driving heat source. However, the COP of traditional ARHP is lower than the AHP. This paper proposed a cross-type ARHP, which optimized the pipelines to improve the COP. The thermodynamic model of the ARHP was established by MATLAB software, and energy and exergy analyses were carried out. The results show that the COP of the system can reach 1.564, which is 8.1% higher than that of the traditional system. The exergy loss of the system mainly comes from the generator and the resorber. The influence of generation temperature, absorption temperature and exergy temperature on exergy efficiency was further analyzed. The exergy efficiency of the ARHP increased by up to 6.9% compared with that of the AHP. The proposed system provides an essential reference for the advancement of absorption-reabsorption technology.

    Thermodynamic performance analysis of combined cooling and heating system based on combination of CO2 with the zeotropic refrigerant assisted subcooled
    Baomin DAI, Qilong WANG, Shengchun LIU, Jianing ZHANG, Xinhai LI, Fandi ZONG
    2023, 74(S1):  64-73.  doi:10.11949/0438-1157.20221670
    Abstract ( 102 )   HTML ( 3)   PDF (2888KB) ( 64 )  
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    In order to meet the requirements of uperization and freezing in the field of food processing, two-stage compression transcritical CO2 cooling and heating system with dedicated mechanical subcooling using zeotropic refrigerant is proposed. The subcooling cycle that uses low global warming potential (GWP) zeotropic refrigerant makes full use of the heat of the condenser and gas cooler to produce hot water. Additionally, cooling capacity is also generated for food freezing. Setting the coefficient of performance (COP) as the objective function, the component, mass fraction, discharge pressure and subcooling degree of the system are analyzed and optimized. The results show that the system has optimal discharge pressure and subcooling degree. The large temperature glide working fluid can significantly improve the system performance and reduce the discharge pressure comparing with the small temperature glide and pure working fluid. The highest COP of 3.45 is achieved when R32/R1234ze(Z) (0.4/0.6) is utilized, which is 4.77% and 5.15% higher than that of pure R32 and R1234ze(Z), and the discharge pressure drops by 0.958 MPa and 0.910 MPa, respectively. The CO2 cycle plays a dominant role for the overall system. The system exergy efficiency can also be improved by using zeotropic refrigerant. This study can provide a theoretical reference to widen the application of CO2 refrigeration and heat pump technology.

    Fluid dynamics and transport phenomena
    Lattice Boltzmann simulation of surface microstructure effect on crystallization fouling
    Cheng CHENG, Zhongdi DUAN, Haoran SUN, Haitao HU, Hongxiang XUE
    2023, 74(S1):  74-86.  doi:10.11949/0438-1157.20221605
    Abstract ( 70 )   HTML ( 1)   PDF (2903KB) ( 166 )  
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    Crystallization fouling is a type of harmful crystals that commonly exists in heat exchange equipment, which deteriorates heat transfer performance. Setting rough microstructures on the heat exchange surface has a significant impact on the flow and heat transfer, and also makes the deposition mechanism of crystallization fouling on the surface complicated. In this paper, a finite difference-lattice dynamic coupling model is established to analyze the deposition characteristics of calcium carbonate on the heat exchange surface of microchannels based on the theory of crystallization deposition kinetics. The influence of the microstructure spacing and height on the fouling behavior is discussed. The results show that the finite difference-lattice dynamic coupling model proposed can effectively simulate the local eddy current on the leeward side of the microstructure and scaling process of heat exchange surface. The decrease of the spacing and the increase of the height of the microstructure will obviously alter the domination of crystallization deposition process from surface reaction to mass transfer in the high-temperature wall area. Compared with the case of the smooth surface, the presence and increasing height of the microstructure facilitates the fouling deposition on the heat exchange surface, and the vortex between adjacent microstructures decreases gradually with the deposition time.

    Numerical study on bubble dynamics of liquid oxygen at a submerged orifice
    Mingkun XIAO, Guang YANG, Yonghua HUANG, Jingyi WU
    2023, 74(S1):  87-95.  doi:10.11949/0438-1157.20221610
    Abstract ( 69 )   HTML ( 0)   PDF (1150KB) ( 141 )  
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    Liquid oxygen is an essential component of high-specific-impulse cryogenic propellant in deep space exploration. Thus it is necessary to study the bubble dynamics of liquid oxygen. In this paper, based on the open source computational fluid dynamics (CFD) software OpenFOAM, the coupled level set and volume of fluid (CLSVoF) method is adopted and the liquid oxygen bubbles growing from a submerged orifice under different gravity levels are numerically investigated. The results show that the lower the gravity level, the larger the bubble volume at the same dimensionless time, and the closer the bubble to sphere. The change of bubble center of gravity in axial direction will go through three stages: fast-slow-fast, but the first stage is not obvious at high gravity levels. The change of wall contact angle is greater at low gravity levels than that at high gravity levels. Moreover, there is a conspicuous power law between bubble detachment parameters and gravity levels.

    Numerical simulation of flow boiling heat transfer in pipe arrays of carbon dioxide direct evaporation ice field
    Ruitao SONG, Pai WANG, Yunpeng WANG, Minxia LI, Chaobin DANG, Zhenguo CHEN, Huan TONG, Jiaqi ZHOU
    2023, 74(S1):  96-103.  doi:10.11949/0438-1157.20221580
    Abstract ( 67 )   HTML ( 2)   PDF (1260KB) ( 71 )  
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    In order to investigate the heat transfer characteristics of the direct evaporation of carbon dioxide indoor ice rink, the computational fluid dynamics simulation of carbon dioxide in horizontal smooth tubes with inner diameters of 11.00 mm and 13.47 mm was carried out. The effects of mass flow rate, heat flux, pipe diameter and dryness on the flow boiling heat transfer characteristics of carbon dioxide in horizontal smooth tubes were analyzed. The calculation results show that under the working condition of CO2 indoor ice rink, the improvement of mass flow rate, heat flow density and other parameters can enhance the heat transfer performance. The existing heat transfer correlation was modified to make it suitable for large pipe diameter conditions. The results calcalated by the new correlation was compared with experimental data from literatures, and the results showed that the new heat exchange correlation had good correlation. The influence factors of refrigerant oil content on heat transfer coefficient under the condition of large pipe diameter are analyzed. This paper has reference value for the optimization design of indoor ice rink for direct evaporation of carbon dioxide.

    Study on the transportation characteristics of droplets on the aluminium surface under ultrasonic excitation
    Xin WU, Jianying GONG, Long JIN, Yutao WANG, Ruining HUANG
    2023, 74(S1):  104-112.  doi:10.11949/0438-1157.20221593
    Abstract ( 79 )   HTML ( 2)   PDF (2075KB) ( 82 )  
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    The transportation characteristics of droplets on the horizontal aluminum surface under ultrasonic excitation are experimentally studied. In this study, the effects of ultrasonic power, initial droplet volume, and hydrophobicity on the movement process of droplets are explored. The research results indicate that the motion coalescence time and evaporation time of droplets are negatively correlated with ultrasonic power, but positively correlated with initial droplet volume and surface contact angle. With the increase of ultrasonic power, the particle size distribution uniformity of droplets increases, and the minimum motion coalescence time is 12 s, and the evaporation time can be shortened by 46 s at most. With the increase of the initial droplet volume, the particle size distribution uniformity of droplets weakens but the motion coalescence phenomenon increases. The hydrophobic surface can not only optimize the particle size distribution of droplets, but also enhance the motion coalescence process. Compared with the bare aluminum surface, the motion coalescence time of droplets on hydrophobic surface increases by about 17 s, and the evaporation time of droplets on hydrophobic surface can be extended by 62 s. This study confirms that ultrasound is feasible to inhibit frost formation.

    Experimental study of flow noise in short tube throttle valve and noise reduction measures
    Shaohua ZHOU, Feilong ZHAN, Guoliang DING, Hao ZHANG, Yanpo SHAO, Yantao LIU, Zheming GAO
    2023, 74(S1):  113-121.  doi:10.11949/0438-1157.20221529
    Abstract ( 109 )   HTML ( 1)   PDF (1581KB) ( 62 )  
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    Short tube throttle valve as a throttling device is widely used in household air conditioners because of its simple structure. When the refrigerant in two-phase state flows through the short tube throttle valve, serious noise is generated. In this paper, we designed and built a test bench for flow noise of short tube throttle valve, and experimentally studied the effect of refrigerant flow pattern, refrigerant mass flow rate and refrigerant quality on the frequency and sound pressure level of flow noise. The experimental results show that the sound pressure level of the flow noise is the largest when the valve inlet flow pattern is churn flow, and the flow noise is smaller when the valve inlet flow pattern is bubble flow and annular flow. The peak frequency of flow noise increases with the increase of mass flow rate. When the mass flow rate increases from 20 kg/h to 80 kg/h, the peak frequency of flow noise increases by 38.6%; when the refrigerant quality increases from 0.05 to 0.4, the average sound pressure level of flow noise firstly increases by 7 dB and then decreases by 3 dB. The optimized structural solution is proposed to reduce the average sound pressure level of flow noise by 2 dB by replacing the sudden contraction structure at the spool inlet with a flared and tapering structure.

    Visual experimental study on effect of surface wettability on frost propagation characteristics
    Wei SU, Dongxu MA, Xu JIN, Zhongyan LIU, Xiaosong ZHANG
    2023, 74(S1):  122-131.  doi:10.11949/0438-1157.20221567
    Abstract ( 79 )   HTML ( 4)   PDF (2074KB) ( 142 )  
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    Frost layer propagation is a key in the early stage of surface frosting, and it is very important in the whole surface condensation frosting process. In order to research the relationship between surface wettability and frost crystal propagation process and velocity in the process of condensation frosting, a micro-visual frosting experimental test platform was built, and three kinds of high reflectivity surfaces with different wettability were prepared according to the experimental requirements. The surface frost layer propagation process can be divided into two stages: frost crystal propagation within droplet and ice bridge propagation between droplets. It is found that the distance between the ice bridge and the droplet is the main element affecting the ice bridge propagation speed. When the distance between ice bridge and droplet decreases from 16 μm to 2 μm, the ice bridge propagation velocity increases rapidly from 2 μm/s to 12 μm/s. Besides, the distribution characteristics of condensation droplets on superhydrophobic surfaces and the obvious difference of ice bridge propagation element are the main reasons for the slow frost propagation on superhydrophobic surfaces. The key elements affecting frost transfer and inhibiting frost formation were revealed, that is, droplet size distribution characteristics of superhydrophobic surface. Present investigation may provide ideas and basis for the design and optimization of anti-frost surface.

    Performance simulation of paper folding-like evaporator for solar evaporation systems
    Zhanyu YE, He SHAN, Zhenyuan XU
    2023, 74(S1):  132-140.  doi:10.11949/0438-1157.20221538
    Abstract ( 86 )   HTML ( 8)   PDF (1411KB) ( 337 )  
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    Solar vapor generation, as a carbon-free and sustainable freshwater production approach, exhibits considerable potential for alleviating the global freshwater crisis. However, the conventional evaporators that adopt the one-dimensional structure have faced a theoretical upper limit evaporation rate of 1.47 kg·m-2·h-1 for solar evaporation due to the solar energy conversion efficiency. Differently, the three-dimensional evaporator can surpass the evaporation limit by exploiting environmental heat and enhancing solar capture, realizing a higher evaporation rate and energy efficiency. Herein, we explore the performance and advantages of the three-dimensional (3D) paper folding-like evaporator in comparison with one-dimensional flat evaporator enabled by the multiphysics simulation method via COMSOL software. Meanwhile, we study the influences of ambient air speed, relative humidity, and solar incident angle on the overall evaporation performance. The results show that the evaporation rate of the paper folding-like 3D evaporator is averagely increased by 1.20 times in comparison with the flat evaporator, reaching 1.53 kg·m-2·h-1, meanwhile the dynamic solar energy capture performance is improved by 32.07%. The ambient with high wind speeds and low relative humidity can increase the overall evaporation rate, finally reaching the calculated evaporation rate of 3.07 kg·m-2·h-1 at the relative humidity of 20% and the airflow rate of 1.0 m·s-1. We anticipate that our designed structure and simulation results could provide design ideas for the subsequent three-dimensional evaporator and its practical applications.

    Icing kinetics and mechanism of droplet impinging on supercooled corrugated plates with different curvature
    Xiaoqing ZHOU, Chunyu LI, Guang YANG, Aifeng CAI, Jingyi WU
    2023, 74(S1):  141-153.  doi:10.11949/0438-1157.20221591
    Abstract ( 94 )   HTML ( 1)   PDF (3815KB) ( 142 )  
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    CLSVOF method and enthalpy-porosity method were coupled to carry out a parametric analysis on icing behaviors of single droplet impinging on supercooled corrugated plates with different curvature and various Weber number. The inner mechanism of differences among kinetic behaviors of droplet contraction, oscillation and fragmentation during droplet impaction was focused on, considering two substrates: single-row corrugated plate and double-row corrugated plate with different curvature. The influence law of supercooling and impingement on freezing interface evolution rate was explored. Simulation results showing: droplet impact icing dynamics was the results coupled of fluid disorder characteristics and time-varying characteristics of heat transfer boundary. The Rayleigh-Taylor instability appears in the droplet spreading leading edge can accelerate droplet freezing during high velocity impaction, interfacial energy transformation caused by droplet breakage can bring up freezing rate decrease. Increasing of supercooling can lead to liquid film fracture obstruction and reduction of droplet circumferential capillary climbing area. Results can supply theoretical reference for microscopic droplet capillarity icing dynamics and its application to anti-icing engineering.

    Research on the performance of liquid cooling system for UVLED optical components
    Yifan JIANG, Lei LIU, Yao ZHAO, Yanjun DAI
    2023, 74(S1):  154-160.  doi:10.11949/0438-1157.20221634
    Abstract ( 77 )   HTML ( 0)   PDF (1843KB) ( 70 )  
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    With the development of light source technology, UVLED optical components are widely used in various fields. It is very important to ensure the temperature of UVLED optical components within a safe range. In this paper, the liquid cooling system for UVLED was studied by experiment and simulation, and four kinds of liquid cooling plates with different flow channels were designed. In the case of heat flux of 2.2 W/cm2, the surface temperature and inlet and outlet pressure drop of the liquid cooling plate were tested experimentally, and the heat transfer and flow performance of the liquid cooling plate were studied by numerical simulation. The results show that the relative error between the experimental and simulation results is 3%. When the liquid cooling working medium is heat conduction oil, the temperature distribution of the six-sided flow channel liquid cooling plate is the most uniform and the temperature control effect is the best. When the flow rate is 2.5 L/min, the highest temperature is 49.7℃, and the DC flow channel plate surface temperature difference is the largest, but the lowest pressure drop is only 5.34 kPa.

    Experimental study on the formation and distribution of trapped air bubbles in horizontal ice slice
    Keke SHAO, Mengjie SONG, Zhengyong JIANG, Xuan ZHANG, Long ZHANG, Runmiao GAO, Zekang ZHEN
    2023, 74(S1):  161-164.  doi:10.11949/0438-1157.20221643
    Abstract ( 94 )   HTML ( 6)   PDF (606KB) ( 172 )  
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    To investigate the formation and distribution characteristics of trapped air bubble during freezing process of water, a water slice freezing experiment is conducted in a horizontal Hele-Shaw cell. Results show two types of bubbles in ice, egg-shaped and needle-shaped, and their behavior is affected by the ice growth rate. When the rate is less than 20.6 μm/s and 9.4 μm/s, needle-shaped bubbles appear and egg-shaped bubbles disappear, respectively. When it is less than 3.1 μm/s, no bubble appears. As the ice grows, the bubble size increases first and then be constant. These results may help to optimize anti-icing/deicing technology.

    Experimental study on phase change heat storage and release performance of R-134a pulsating heat pipe
    Shuangxing ZHANG, Fangchen LIU, Yifei ZHANG, Wenjing DU
    2023, 74(S1):  165-171.  doi:10.11949/0438-1157.20230172
    Abstract ( 256 )   HTML ( 4)   PDF (1094KB) ( 83 )  
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    In order to study the influence of low temperature working medium on the pulsating heat pipe phase change heat accumulator, a test bed for pulsating heat pipe phase change heat storage and release was built. The cryogenic working medium selected in the experiment is R-134a, the phase change material is paraffin, and the heat accumulator is composed of a group of self-designed pulsating heat pipes. The experimental results show that the normal heat storage and heat release of pulsating heat pipe accumulator can be realized by using R-134a as working medium. In the process of heat storage, the increase of heating power will reduce the heat storage time, but also increase the maximum temperature difference in the heat storage. In the process of heat release, the decrease of cooling water temperature can reduce the solidification time of paraffin. When the water temperature changes from 20℃ to 5℃, the solidification time of paraffin is shortened by 34.8%. The increase of cooling water flow also reduces the setting time of paraffin wax. The water flow is changed from 10 L/h to 40 L/h, and the setting time is shortened by 9.5%. After about three hours of exothermic experiment, the temperature of the phase change material was close to room temperature.

    Molecular dynamics study on evaporation modes of nanodroplets at rough interfaces
    Lisen BI, Bin LIU, Hengxiang HU, Tao ZENG, Zhuorui LI, Jianfei SONG, Hanming WU
    2023, 74(S1):  172-178.  doi:10.11949/0438-1157.20221554
    Abstract ( 102 )   HTML ( 6)   PDF (1091KB) ( 269 )  
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    In this paper, the evaporation modes of nanodroplet on rough substrates are studied by molecular dynamics method, and the influence of ratio of contact area (RCA) between the nanodroplets and the rough interfaces on the contact radius and contact angle during the evaporation process of nanodroplets is discussed. The roughness of the interfaces is achieved by textured patterns based on the Wenzel wetting model. The results show that, in equilibrium, compared with the ideal smooth substrate, when the contact area ratio is smaller, the contact angle of the nanodroplet increases significantly (RCA = 33.3%, θ = 106°), while when the roughness of the substrates is larger, this phenomenon is not obvious (RCA = 50%, θ = 81°; RCA = 66.6%, θ = 85°). In the evaporation process, when RCA = 33.3%, the evaporation mode of nanodroplet is mixed mode, when RCA = 50%, the evaporation mode of nanodroplet is constant contact radius mode (CCR mode), and when RCA = 66.6%, the evaporation mode of nanodroplet is constant contact angle mode (CCA mode).

    Simulation study on frosting at windward fin end of heat exchanger
    Long ZHANG, Mengjie SONG, Keke SHAO, Xuan ZHANG, Jun SHEN, Runmiao GAO, Zekang ZHEN, Zhengyong JIANG
    2023, 74(S1):  179-182.  doi:10.11949/0438-1157.20221641
    Abstract ( 86 )   HTML ( 6)   PDF (514KB) ( 100 )  
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    In terms of the phenomenon of frost growth on the windward fin end of a heat exchanger, in this paper, a frosting model on the windward fin end is established. The numerical results show that the frost on the windward fin end of a heat exchanger grows the fastest along the opposite direction of the airflow, and its growth rate gradually decreases with an increase of the angle θ. Besides, frost density and frost surface temperature also decrease with an increase of θ, and the frost layer is streamlined. After 3600 s, frost layer thickness and density at θ=0° are 1.47 times and 1.23 times larger than those at θ=90°, respectively. Besides, the surface temperature of the frost layer is 2.2℃ higher than later one. The results of this paper may help to provide theoretical guidance for delaying or avoiding frosting.

    Performance analysis of printed circuit heat exchanger for supercritical carbon dioxide
    Yifei ZHANG, Fangchen LIU, Shuangxing ZHANG, Wenjing DU
    2023, 74(S1):  183-190.  doi:10.11949/0438-1157.20230171
    Abstract ( 184 )   HTML ( 4)   PDF (1291KB) ( 281 )  
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    Printed circuit heat exchanger (PCHE), as a new micro-channel heat exchanger with high efficiency and compactness, has very high potential to be applied to supercritical CO2 Brayton cycle. Based on the principle of heat transfer enhancement, the straight channel of PCHE is improved and the PCHE with variable diameter is proposed. This kind of channel can adapt to the change of fluid physical properties and obtain better comprehensive performance. The thermal-hydraulic performance of supercritical CO2 in PCHE channel with variable diameter is analyzed by numerical simulation. The results show that with the decrease of width, convective heat transfer coefficient increases, and the more it increases than corresponding PCHE with constant diameter. The structure of variable diameter has little influence on the pressure drop of cold fluid, and the application of structure of variable diameter to PCHE with larger width can reduce the increase of CO2 pressure drop. The structure of variable diameter will improve the comprehensive performance more obviously for PCHE with smaller width. For PCHE whose width is 1.6 mm, the comprehensive performance of PCHE with variable diameter is 1.81 times that of PCHE with constant diameter at 1.2 g/s. Convective heat transfer coefficient increases with the augment of changing ratio of width. When the changing ratio of width changes from 2 mm/m to 2.75 mm/m, the peak value of convective heat transfer coefficient increases by 2.9%. Arranging the variable diameter section at the back end of PCHE has better heat transfer characteristics, and its peak of convective heat transfer coefficient is increased by 23% compared with other forms. Analysis of thermal-hydraulic performance of PCHE with different structures can provide reference for theoretical research of supercritical CO2 cooling and typical engineering application of PCHE.

    Influence of substrate temperature on HFE7100 droplet evaporation process
    Aiqiang CHEN, Yanqi DAI, Yue LIU, Bin LIU, Hanming WU
    2023, 74(S1):  191-197.  doi:10.11949/0438-1157.20221633
    Abstract ( 85 )   HTML ( 0)   PDF (1092KB) ( 50 )  
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    In order to investigate the effect of substrate temperature on evaporation model, morphology parameters and evaporation rate of droplet of butane,1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxy (HFE7100), and to promote its application in microscale heat transfer. Three kinds of glass materials with different surface temperatures (20, 30, 40℃) were selected as substrates, the contact angle, contact diameter, wetting area, droplet residual volume and mass loss rate during droplet evaporation were recorded. The results show that the contact angle and contact diameter of HFE7100 decrease at the same time until the end of evaporation at different substrate temperatures, the droplet evaporation model is not a mixed evaporation model. The substrate temperature has a significant effect on the morphological parameters of HFE7100 during the initial evaporation stage, the higher the substrate temperature, the larger the initial contact angle, the smaller the initial contact diameter and wetting area, and the larger the change rate of initial morphological parameters. The evaporation process of HFE7100 droplets can be divided into three stages, in the first and the third stages, the evaporation rate is higher, and in the middle stage, the evaporation rate is lower, the maximum amount of evaporation occurs at the initial stage. And the higher the substrate temperature, the higher the evaporation rate is.

    Experimental study on heat transfer performance of ultra-thin flat heat pipe
    Limei SHEN, Boxing HU, Yufei XIE, Weihao ZENG, Xiaoyu ZHANG
    2023, 74(S1):  198-205.  doi:10.11949/0438-1157.20221590
    Abstract ( 76 )   HTML ( 5)   PDF (2611KB) ( 128 )  
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    With the gradual improvement of the integration of electronic devices, ultra-thin flat heat pipe has attracted more and more attention as an efficient radiator suitable for confined space. In this paper, the heat transfer performance of ultra-thin flat heat pipe with thickness of 0.27 mm is tested. Taking the heat transfer temperature difference, heat transfer and thermal resistance as indicators, the heat transfer characteristics under the influence of heating power, cooling mode and gravity are systematically studied. It is found that gravity has a slight effect on the heat transfer performance of ultra-thin flat heat pipe. The maximum heat dissipation in vertical state is 5%—10% higher than that in horizontal state, and 2%—10% higher than that in vertical anti-gravity state. The cooling mode has a great influence on its heat transfer performance. At lower power, compared with natural cooling, forced cooling can make electronic components work at lower temperature, but the temperature difference and thermal resistance at the cold and hot ends of the heat pipe are greater than those under natural cooling. After exceeding a certain power (about 1.2 W), the temperature difference and thermal resistance increase sharply and the heat transfer effect is poor.

    Simulation analysis of effect of diameter and length of light pipes on heat transfer
    Mingxi LIU, Yanpeng WU
    2023, 74(S1):  206-212.  doi:10.11949/0438-1157.20230078
    Abstract ( 70 )   HTML ( 3)   PDF (1116KB) ( 31 )  
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    Light pipes can improve indoor luminous environment and are increasingly used in large space buildings. The use of light pipes leads to heat gain in summer and heat loss in winter, heat transfer must be considered in buildings with a large number of light pipes installed. In this paper, CFD simulation was used to analyze the heat transfer characteristics of light pipes in Beijing under summer and winter conditions. The results showed that, in summer, the air inside the tube is more evenly distributed, and the average temperature varies between 20℃ and 32℃. As the diameter of the light pipe increased, the average temperature of the air inside the tube first decreased and then tended to be stable, and the total heat loss gradually increased. As the length of the light pipe increased, the average temperature showed a decreasing trend, and the total heat transfer did not have a significant trend, but finally remained unchanged. In winter, the air inside the tube is divided into two zones and the average temperature varies between 0℃ and 25℃. As the diameter of the light pipe increased, the average temperature rose and the total heat transfer increased; as the length of the light pipe increased, the average temperature first rose and then tended to be smooth, and the total heat transfer first increased and then remained unchanged.

    Experimental study on startup dynamic characteristics of R1150/R600a auto-cascade refrigeration cycle
    Yingying TAN, Xiaoqing LIU, Lin WANG, Lisheng HUANG, Xiuzhen LI, Zhanwei WANG
    2023, 74(S1):  213-222.  doi:10.11949/0438-1157.20221631
    Abstract ( 91 )   HTML ( 6)   PDF (1284KB) ( 39 )  
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    An experimental bench of auto-cascade refrigeration cycle with dephlegmator was set up. The startup dynamic characteristics of the auto-cascade refrigeration cycle with dephlegmator and that of the traditional auto-cascade refrigeration cycle under different evaporation pressure and composition ratio were analyzed experimentally using the environment-friendly non-azeotropic mixed refrigerant R1150/R600a. The results showed that the refrigeration temperatures of both cycles decreased and the compressor exhaust pressures increased with the decrease of evaporative pressure, and the temperature drop of auto-cascade refrigeration cycle with dephlegmator was larger, the lowest evaporator inlet temperature reached -73.8℃ while the evaporation pressure was 280 kPa. After startup, the auto-cascade refrigeration cycle with dephlegmator can reach stable refrigeration temperature faster, the temperature drop rate of cryogenic chamber was faster, and the refrigeration temperature was lower. When the R1150/R600a mass fraction ratio was 0.3∶0.7, the evaporator inlet temperature reached -77.2℃, 5.6℃ lower than the traditional auto-cascade refrigeration cycle. With the increase of the mass fraction of low boiling point component, the cooling rates of both cycles were faster. However, the compressor exhaust temperature increased. The compressor discharge temperature of the conventional auto-cascade refrigeration cycle was 25.0—36.0℃ lower than that of the auto-cascade refrigeration cycle with dephlegmator.

    Numerical simulation and analysis of geothermal rock mass heat flow coupling based on fracture roughness characterization method
    Zhiguo WANG, Meng XUE, Yushuang DONG, Tianzhen ZHANG, Xiaokai QIN, Qiang HAN
    2023, 74(S1):  223-234.  doi:10.11949/0438-1157.20221552
    Abstract ( 74 )   HTML ( 3)   PDF (2334KB) ( 243 )  
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    With the transformation of energy structure, geothermal energy like dry hot rock has been rapidly developed. As the complex composite of the internal structure of the geothermal rock, as well as the changeable transfusion and heat transfer process, further discussion is needed as to how to establish a more accurate representation model and conduct multi-physical fields coupling analysis aiming at the distribution characteristics of rock fracture. Based on the description method of joint roughness coefficient (JRC), the representative elementary volume (REV) was introduced into the JRC size selection and it was applied into the geothermal rock physical model. The coupling analysis was conducted on the temperature field of geothermal rock and transfusion field by adopting numerical simulation method. It was found that the distribution of temperature field near the fracture was basically consistent with the fracture's morphology, showing a fluctuation law of the temperature field of bedrock with the change of the fracture morphology. There was a negative correlation between fluid injection speed and temperature on the time when the system reached steady state; both lower injection speed and higher injection temperature could effectively prolong the production life of the system; in addition, through the analysis of the outlet normal heat flux, it was concluded that the optimal injection velocity in this paper.

    Experimental study on the effect of flow sharing cavity structure on phase change flow characteristics in microchannels
    He JIANG, Junfei YUAN, Lin WANG, Guyu XING
    2023, 74(S1):  235-244.  doi:10.11949/0438-1157.20221614
    Abstract ( 87 )   HTML ( 5)   PDF (1631KB) ( 188 )  
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    In order to make the heat dissipation system run more safely and reliably, and improve the instability and heat transfer performance of two-phase flow and heat transfer in microchannels, R134a refrigerant is used as the working fluid, and the boiling flow characteristics of microchannels with square flow sharing cavity and microchannels with circular-arc flow sharing cavity are compared. The experiment was carried out in 9 parallel microchannels arrays, with a base area of 136 mm2 and a hydraulic diameter of 400 μm. Under the conditions of mass flow rate of 416—728 kg/(m2·s) and base heat flux of 36.7—242.6 kW/m2, the variation of two-phase flow pattern in the microchannels was studied by experiment and simulation, and the pressure drop, pressure fluctuation and heat transfer characteristics of microchannels under different conditions were studied by experiment. The results show that the simulation results are in good agreement with the experimental results. The flow patterns in the microchannels of the two kinds of flow sharing cavities are similar, and the flow reversal phenomenon is observed in the slug flow pattern. Compared with the square flow sharing cavity microchannels, the circular-arc microchannels have lower pressure drop, smaller pressure fluctuation and higher heat transfer coefficient. When the heat flux density is 242.6 kW/m2 and the mass flux density is 416 kg/(m2·s), the pressure drop is reduced by 51%. When the heat flux is 154.4 kW/m2 and the mass flux is 416 kg/(m2·s), the fluctuation of outlet pressure decreases by 35%. When the heat flux is 242.6 kW/m2 and the mass flow rate is 728 kg/(m2·s), the corresponding heat transfer coefficient is increased by 9.7%.

    Catalysis, kinetics and reactors
    Synthesis of isoxepac and 2-ethylanthraquinone catalyzed by chloroaluminate-triethylamine ionic liquid/P2O5
    Qi WANG, Bin ZHANG, Xiaoxin ZHANG, Hujian WU, Haitao ZHAN, Tao WANG
    2023, 74(S1):  245-249.  doi:10.11949/0438-1157.20230045
    Abstract ( 82 )   HTML ( 2)   PDF (677KB) ( 62 )  
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    To develop a novel acidic catalytic system suitable for intramolecular acylation of carboxylic acid molecules, this research system examines the catalytic efficacy of an acidic system composed of chloroaluminate-triethylamine ionic liquid and phosphorus pentoxide (P2O5) in the synthesis of isoxepac and 2-ethylanthraquinone, and performs condition optimization experiments. This study found that this catalytic system could effectively catalyze the synthesis of isoxepac and 2-ethylanthraquinone with the highest yield of 82.6% of isoxepac, as an alternative to polyphosphoric acid and fuming sulfuric acid, and this new process could effectively reduce industrial waste acid wastewater and reduce production cost, and the mechanism of P2O5 in the modification reaction was speculated.

    Separation engineering
    Simulation analysis of water crystallization process
    Hongxin YU, Shuangquan SHAO
    2023, 74(S1):  250-258.  doi:10.11949/0438-1157.20221608
    Abstract ( 123 )   HTML ( 7)   PDF (1771KB) ( 195 )  
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    In this paper, molecular dynamics was used to explore the effect of different temperatures and pressures on the crystallization process of water. The TIP4P/ICE four-point water model was used to build a three-layer (ice-water-ice) three-layer crystallization template. In the temperature part, molecular dynamics simulation was carried out under six temperature conditions, respectively. As the temperature of the box increased from 210 K to 250 K, the time of complete crystallization of the box was extended from 78 ns to 147 ns, and the density decreased. Therefore, as the temperature decreases and the degree of supercooling increases, the crystallization rate and the density of ice formation also increase. In the pressure part, the molecular dynamics simulation of the water crystallization process was carried out under six pressure conditions, respectively. It was found that with the increase of pressure, the crystallization time increased first and then decreased, and the crystallization time was the longest (115 ns) at 200 MPa. This was because the change of pressure would lead to the change of the freezing point of water. In addition, it was found that pressure has a direct effect on the water crystallization rate, and high pressure can directly promote the water crystallization. Ice forms were denser under high pressure.

    Experimental analysis on filtration performance of electrospun nanofibers with amphiphobic membrane of oily fine particles
    Yanpeng WU, Xiaoyu LI, Qiaoyang ZHONG
    2023, 74(S1):  259-264.  doi:10.11949/0438-1157.20230013
    Abstract ( 100 )   HTML ( 7)   PDF (1038KB) ( 72 )  
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    The pollution of oily fine particles has increasingly become an important issue in the field of air quality research in China, which has aroused widespread concern. Polyacrylonitrile (PAN), polyurethane (PU) and fluorine-containing polyurethane (FPU) were selected as raw materials, N,N-dimethylformamide (DMF) was selected as solvent, and the content of fluorine-containing polyurethane was changed by using electrostatic spinning technology to prepare oleophobic and hydrophobic properties of nanofiber membrane. The water contact angle and oil contact angle of the nanofiber membrane reached 153.24° and 132.45° respectively. Set up an air filtration performance test device to test the filtration efficiency of the nanofiber membrane for conventional particles and oily particles. The results show that they were all above 98.7%. Finally, the filtration durability of the nanofiber bicophobic membrane was investigated. By testing the change of its filtration efficiency, it was found that the nanofiber membrane had certain filtration durability.

    Energy and environmental engineering
    Experimental study of two-stage parallel desiccant coated heat pump system based on multi-objectives
    Qihong ZOU, Qian LI, Tianshu GE
    2023, 74(S1):  265-271.  doi:10.11949/0438-1157.20221521
    Abstract ( 62 )   HTML ( 3)   PDF (1228KB) ( 80 )  
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    A novel two-stage parallel desiccant coated heat pump system is proposed, the system performance is experimentally studied under air typical conditions. The experiments show that the system can effectively solve the problem of insufficient handling capacity of the sensible heat load of the solid desiccant coated heat pump(SDHP), the sensible and latent heat load can be flexibly deployed in different ratio: it can provide 19.0℃ and 8.81 g/kg of air supply in the comfort zone under typical air conditions, the average COP reached 3.92 under the condensing temperature of 50℃. The COP risen from 3.39 to 5.81 when the condensing temperature changed from 55℃ to 35℃, the sensible heat load ratio is always maintained above 16∶1. The latent load ratio of the system in different environments can reach 7%—60%, which can meet the requirements of temperature and humidity decoupling in most air supply conditions.

    Experimental investigation on heating performance of vapor-injection CO2 heat pump for electric vehicles at -30℃
    Tianyang YANG, Huiming ZOU, Hui ZHOU, Chunlei WANG, Changqing TIAN
    2023, 74(S1):  272-279.  doi:10.11949/0438-1157.20221508
    Abstract ( 84 )   HTML ( 4)   PDF (1771KB) ( 141 )  
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    To improve the heating performance of electric vehicle heat pumps in extremely cold environments, an experimental bench of the vapor-injection CO2 heat pump with a flash tank was built and the heating performance under the working conditions of -30℃ was studied in this paper. The experimental results show that when the inlet air temperature is 20℃, the discharge temperature of the no vapor-injection system reaches 176.1℃, and the discharge temperature is reduced by 30.7℃ through the injected refrigerant vapor, and the increase in the total refrigerant flow rate and the pressure of the gas cooler increase the heating capacity and coefficient of performance (COP) by 74.1% and 43.9%, respectively. The inlet air temperature is controlled to increase from 0℃ to 20℃, and the outlet air temperature of the vapor-injection system is increased from 11.9℃ to 32.7℃, but the heating capacity is reduced by 3%, the energy consumption is increased by 43.2%, and the COP is reduced from 2.14 to 1.45. With the increase of the inlet air temperature, the vapor-injection heat pump cycle gradually changes from subcritical to transcritical, and the discharge temperature and pressure increase, but the discharge enthalpy is unchanged.

    Simulation analysis of temperature characteristics of the high-pressure hydrogen refueling process
    Xin YANG, Wen WANG, Kai XU, Fanhua MA
    2023, 74(S1):  280-286.  doi:10.11949/0438-1157.20221624
    Abstract ( 121 )   HTML ( 4)   PDF (537KB) ( 182 )  
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    The reliability and efficiency in the operating process of the high-pressure hydrogen refueling station (HRS) is the prerequisite for promoting the broad application of hydrogen fuel power. Temperature control during the refueling process is crucial to the safety of the vehicle tank. This paper displays a simulation of the complete thermodynamics process of the high-pressure hydrogen refueling process by developing a dynamic model, which is combined with the mass equation, energy equation, and heat transfer equation. The transient temperature, pressure, mass flow rate of hydrogen, and cooling demand during the refueling process are discussed. Aiming at higher efficiency and less energy consumption, the optimization strategies of operation in HRS are proposed. Under the target of 95% state of charge (SOC) and 80℃ final gas temperature in the vehicle tank, the effects of ambient temperature, the initial pressure of the vehicle tank, and refueling time on the pre-cooling temperature are analyzed. Moreover, the effects of nozzle diameter on the temperature rise of the vehicle tank, the cooling load, and the total cooling capacity of the heat exchanger are discussed. The results show that in most cases, the pre-cooling temperature can be increased by 5℃ with the ambient temperature decreasing by 5℃, the charging pressure increasing by 4 MPa, and the refueling time extending by one minute. The nozzle diameter has little influence on the final temperature of the vehicle tank and the refueling time but has a great influence on the cooling load of the heat exchanger. When the nozzle diameter is reduced from 8 mm to 5 mm, the final temperature in the tank is only increased by 6%, the refueling time is only extended by 5 s, but the peak cooling load and total cooling capacity of the heat exchanger are reduced by 25% and 7.3%, respectively.

    Study on coupling operation characteristics of Stirling engine and high temperature heat pipe
    Jiahao SONG, Wen WANG
    2023, 74(S1):  287-294.  doi:10.11949/0438-1157.20221632
    Abstract ( 91 )   HTML ( 1)   PDF (903KB) ( 155 )  
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    As a closed cycle engine heated with external heat source, Stirling engine coupled with high-temperature heat pipe could provide power output resulted from heat energy in certain cases. In this paper, the method of the thermal resistance network and adiabatic analysis method are used to analyze the high temperature heat pipe and Stirling engine respectively. Through the calculation of the heat flow between the heat pipe and the engine, the coupling operation characteristics of the two are studied. With the group of a stirling engine and a liquid metal heat pipe which could meet the input requirements of the Stirling engine, the operating characteristics of coupled Stirling engine system are analyzed, and the starting characteristics and the change of output power with the temperature of heat source are studied. The results show that at a heat source temperature of 1000 K, the Stirling system studied in this paper reaches a steady state after 400 s and can provide output power about 101 W. As the heat source temperature increases, the power loss in the engine will increase accordingly, making the growth of the engine output power slower. When the heat pipe wall thickness is changed, the engine output power first increases and then decreases. The optimal heat pipe wall thickness under this working condition is 7 mm.

    Study on seasonal thermal energy storage characteristics of double U-shaped buried pipe group
    Siyu ZHANG, Yonggao YIN, Pengqi JIA, Wei YE
    2023, 74(S1):  295-301.  doi:10.11949/0438-1157.20221623
    Abstract ( 94 )   HTML ( 1)   PDF (1518KB) ( 57 )  
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    Borehole thermal energy storage (BTES) can solve the contradiction between energy supply and demand in time and space, which is an important means to improve energy utilization efficiency. In this paper, the three-dimensional transient numerical model of the buried pipe thermal storage is established to realize the full-cycle dynamic monitoring of the three types of characteristic temperatures of the buried pipe thermal storage and the boundary heat flow, as well as to evaluate the thermal characteristics of the system under long-cycle operation. The results show that after the full-cycle operation, the average soil volume temperature increases by 10% compared with the initial state, and the lateral heat loss of the heat storage body accounts for 66%—90% of the total heat loss. The BTES efficiency of the system increases year by year, and basically reaches stability in the 7th year, when the efficiency can reach 55.2%. This research aims to provide a certain reference for the actual engineering design and application of BTES system.

    Investigation on the heating performance of the tube-free-evaporation based sorption thermal battery
    Jingwei CHAO, Jiaxing XU, Tingxian LI
    2023, 74(S1):  302-310.  doi:10.11949/0438-1157.20221544
    Abstract ( 53 )   HTML ( 2)   PDF (1276KB) ( 47 )  
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    To improve the heat and mass transfer of the sorption thermal battery (STB) for a higher energy/power density of STB, the strategy of tube-free-evaporation is proposed, and then verified by the theoretical analysis. Adopting the proposed strategy, a 30 kWh STB is established. The result demonstrates that the proposed strategy can reduce the thermal resistance of the conventional evaporator with tubes by 94.9% and increases the sorption-evaporation rate of the STB by 24.2%. Thus, the STB employing the proposed tube-free-evaporator can supply the thermal energy with 3℃ higher temperature over the STB adopting the evaporator with tubes, confirming the effectiveness of the strategy in facilitating the heat and mass transfer of STB. Meanwhile, it is also found that increasing desorption temperature and decreasing condensation pressure can also promote the energy/power density of the STB. With the desorption temperature of 170℃ and condensation pressure of 7.5 kPa, the energy density and power density of the designed STB have reached 113.21 Wh/kg and 149.45 W/kg, respectively. More importantly, the supplied hot water temperature and the hot water flow have reached 55℃ and 1980.2 L/h, which demonstrates the feasibility of the designed STB on supplying hot water to multi-users or supplying hot water to single users for longer duration. So, the proposed tube-free-evaporation is expected to be enlightening in the future scalable deployment of STB with a higher energy/power density.

    Heating performance of air preheated integrated ground water heat pump air-conditioning system
    Mengya LIAN, Yingying TAN, Lin WANG, Feng CHEN, Yifei CAO
    2023, 74(S1):  311-319.  doi:10.11949/0438-1157.20221600
    Abstract ( 89 )   HTML ( 0)   PDF (1277KB) ( 162 )  
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    An integrated ground water heat pump air-conditioning (IGWHP) system is proposed to solve the problem of limited utilization of ground water thermal storage in conventional ground water source heat pump air-conditioning (CGWHP) system. Based on distributed parameter method and lumped parameter method, a steady-state simulation model of IGWHP system is developed, and the heating performance of the proposed system is simulated. The influence of hot water on the performance of IGWHP system is analyzed, and the heating performance of IGWHP system is compared with CGWHP system. The results show that IGWHP system has good energy saving advantages over CGWHP system. As heating temperature of the hot water increases from 40℃ to 55℃, the energy consumption of IGWHP system decreases by 36.12% on average compared with CGWHP system. Moreover, the simulation results are in good agreement with the experimental results, and the error is with in ±10%.

    Simulation study of thermal management system of alkaline water electrolysis device for hydrogen production
    Congqi HUANG, Yimei WU, Jianye CHEN, Shuangquan SHAO
    2023, 74(S1):  320-328.  doi:10.11949/0438-1157.20221598
    Abstract ( 278 )   HTML ( 10)   PDF (1061KB) ( 319 )  
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    Renewable energy power generation coupling alkaline water electrolysis for hydrogen production technology is one of the ideal ways to product green hydrogen, however, which is limited probably due to the volatility of electrolytic power that affects the stability of the operating temperature of the electrolytic cell, which influences the electrolytic efficiency. For the problem mentioned, this paper constructs a thermal management system of alkaline water electrolysis device for hydrogen production based on the design of an absorption heat transformer. Through the analysis of the operating parameters of the absorption heat transformer under different condensing temperatures, the characteristics of best operating performance are summarized. Through the analysis of the operating condition under different loads, as the heat released from the electrolytic cell drops from 32.28 kW to 25.08 kW, the recovery heat serving users decreases from 8.31 kW to 4.17 kW and the total cooling consumption of the system decreases by 44.55% when the temperature of the regurgitant lye increases from 58℃ to 70℃. The results above show that the system effectively regulates the operating temperature of electrolytic cell, at the same time decreases the cooling consumption and achieves heat recovery, which improves the comprehensive energy utilization efficiency.

    Study on the cycle performance of salt solution-storage-based heat pump
    Minghui CHANG, Lin WANG, Jiajia YUAN, Yifei CAO
    2023, 74(S1):  329-337.  doi:10.11949/0438-1157.20221620
    Abstract ( 65 )   HTML ( 0)   PDF (865KB) ( 49 )  
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    In order to solve the problem of electricity demand peak and valley in heating period, a solution-based energy-stored heat pump (SEHP) is proposed, which is composed of compression heat pump subsystem and salt solution subsystem with energy storage and release to realize thermal storage and thermal grade improvement. The multi-layer liquid storage units are used to optimize the design of salt solution storage tank to improve the energy storage density. Based on the thermodynamic model of the new cycle, the effect of key operating parameters on the performance of SEHP are studied, and its economy makes comparisons with that of the air-source energy-stored heat pump (AEHP) and the air-source heat pump (ASHP). The results show that the comprehensive heating coefficient of performance (CCOP) of the new cycle is lower than that of AEHP and ASHP, but its energy storage density (ESD) and economy are better than those of the two conventional heat pumps. At 300 kW heating load, although CCOP of SEHP is 4.76% lower than that of AEHP, ESD of SEHP is 2.2 times higher than that of AEHP, while the annual cost of AEHP is 1.46% and 29.00% lower than that of AEHP and ASHP respectively.

    Material science and engineering, nanotechnology
    Preparation of high-concentration positive electrolyte of vanadium redox flow battery by activating vanadium pentoxide with highly concentrated sulfuric acid
    Chao HU, Yuming DONG, Wei ZHANG, Hongling ZHANG, Peng ZHOU, Hongbin XU
    2023, 74(S1):  338-345.  doi:10.11949/0438-1157.20221541
    Abstract ( 272 )   HTML ( 10)   PDF (1173KB) ( 218 )  
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    Vanadium redox flow battery (VRFB) is one of the most promising chemical electric source technologies for large scale stationary energy storage. Currently, since a large share of the VRFB costs is attributed to the cost of the electrolyte, vanadium pentoxide was usually chosen as the raw materials of vanadium. However, due to the low solubility of vanadium pentoxide in sulfuric acid, the direct dissolution of vanadium pentoxide in sulfuric acid is unable to prepare an electrolyte with high vanadium concentration. In this study, pentavalent vanadium electrolyte is directly prepared from vanadium pentoxide solid by activating vanadium pentoxide with sulfuric acid at elevated temperatures. The composition, structure, and dissolution processes of the activated solid mixture are analyzed by XRD, Raman, and FT-IR. The results indicate that when the activating temperature is 180°C and the molar ratio of sulfuric acid to vanadium pentoxide of 4, the dissolution performance of vanadium pentoxide after activation is greatly enhanced, and its dissolution mass percentage is up to 98.5%. And the vanadium ion concentration can be dissolved successfully up to 3 mol·L-1. After activation, sulfuric acid and vanadium pentoxide form V2O3(SO4)2. The original structure of vanadium pentoxide is changed and the solubility of the substance is increased. At the same time, it is found that V(Ⅴ) ions with high concentration will react with SO42- to produce VO2SO4-, while VO2+ in solution would also polymerize to form polymers such as V2O34+ and V2O42+.

    Process safety
    Experimental study on the flammability of HFO-1243zf
    Xi WU, Zudi OU, Xinjie ZHANG, Shiming XU, Xiaojing ZHU
    2023, 74(S1):  346-352.  doi:10.11949/0438-1157.20221576
    Abstract ( 116 )   HTML ( 2)   PDF (1064KB) ( 187 )  
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    3,3,3-Trifluoropropene (HFO-1243zf) is a kind of synthetic environmentally friendly refrigerants that has applicable thermophysical property. The flammability of HFO-1243zf should be ascertained before extending its usage. The flammability limits and burning velocity of HFO-1243zf are tested as per the ASHRAE 34 and ISO— 817 standards, respectively. The tested flammability limit range is 4.45%±0.05%~15.8%±0.2% in volume fraction, which is enlarged with the increase of the environmental temperature but slightly lessened with the increase of relative humidity. The burning velocity of HFO-1243zf is increased by increasing the equivalence ratio, until which increases to a peak value and then gradually decreases on a further increase of the fuel concentration.