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CONTENTS-Volume 28, Issue 2, March-April 2019

Sept. 11, 2019

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Springer Link: https://link.springer.com/journal/11630/28/2

 

1. Dual-Wavelength Laser Flash Raman Spectroscopy Method for In-Situ Measurements of the Thermal Diffusivity: Principle and Experimental Verification

FAN Aoran, HU Yudong, MA Weigang, WANG Haidong, ZHANG Xing

Journal of Thermal Science, 2019, 28(2): 159-168

DOI: https://doi.org/10.1007/s11630-019-1084-x

Keywords: dual-wavelength laser flash Raman spectroscopy method, thermal diffusivity, Raman spectroscopy, nanomaterials, bulk materials

Abstract: This paper presents an in-situ, non-contact, non-destructive “dual-wavelength laser flash Raman spectroscopy method” for measuring the thermal diffusivity. In this method, a heating pulse is used to heat the sample and another pulsed laser with a different wavelength and negligible heating effect is used as a probe to measure the sample temperature changes during the heating and cooling periods from the Raman peak shifts. The sample temperature rise and fall curves are measured by changing the delay between the heating pulse and the probing pulse with the thermal diffusivity then characterized by fitting the temperature curves. The time delay between the heating and probing pulses can be precisely controlled with a minimum step of 100 ps. Hence, the temperature variation can be scanned with an ultra-high temporal resolution of up to 100 ps, which significantly improves the measurement accuracy of transient thermal parameters. The measurement accuracy of this method has been verified using a bulk material model and experiments. The measured thermal diffusivity of a silicon sample has been obtained to be 8.8×10-5 m2/s with a 3% difference between the measured value and the average result for bulk silicon in the literature which verifies the reliability and accuracy of this method.

 

2. A Review about Thermal Comfort in Aircraft

FAN Juli, ZHOU Qiongyao

Journal of Thermal Science, 2019, 28(2): 169-183

DOI: https://doi.org/10.1007/s11630-018-1073-5

Keywords: aircraft, thermal comfort, energy efficient, ventilation system, numerical simulation

Abstract: Thermal comfort is an important factor which affects both work efficiency and life quality. On the basis of satisfying the normal life of the crew and reliable work of equipment, the thermal comfort is increasingly pursued through the design of the environmental control system of modern craft. Thus, a comprehensive survey of the thermal comfort in the cockpit is carried out. First of all, factors affecting the thermal comfort in aircraft cabin are summarized, including low relative humidity, meanradiant temperature, colored light, human metabolic rate and gender, among which the first three factors are environmental factors and the other two are human factors. Although noise is not a factor affecting thermal comfort, it is an important factor in the overall satisfaction of the aircraft cabin environment. Then the thermal comfort prediction models are introduced, including thermal comfort models suitable for steady state uniform environment and thermal comfort models suitable for transient non-uniform environment. Then the limitations of the typical thermal comfort models applied to aircraft are discussed. Since the concept of thermal adaptation has been gradually accepted in recent years, many field studies on thermal adaptation have been carried out. Therefore, the adaptive thermal comfort models are summarized and analyzed systematically in this paper. At present, mixing ventilation (MV) system is widely used in most commercial aircraft. However, the air quality under the MV system is very poor, and contaminants cannot be effectively eliminated. So a noticeable shift is the design of ventilation system for cabin drawing lessons from the surface buildings. Currently, the most interesting questionis that whether the traditional mixing ventilation (MV) system in an aircraft can be replaced by or combined with displacement ventilation (DV) system without decreasing thermal comfort. A reduction of energy consumption is avaluable gain. Additionally, various seat personalized ventilation systems have also been proposed which could effectively reduce the risk of infectious diseases. At present, optimal design of airflow in aircraft cabin is the most commonly used method to enhance thermal comfort and save energy. The optimal design of the aircraft cabin colored lighting system, however, is also worth trying.

 

3. Multi-Objective Optimizationfor China's Power Carbon Emission Reduction by 2035

WU Jianjun, TANG Guihua, WANG Run, SUN Yanwei

Journal of Thermal Science, 2019, 28(2): 184-194

DOI: https://doi.org/10.1007/s11630-019-1108-6

Keywords: power sector, carbon emission reduction optimization, energyoutlook, comprehensive evaluation

Abstract: Low carbon transformation plays an important role in promoting the energy production and consumption revolution. Currently, the power sector of China still faces aseries of challenges, such as the overcapacity of coal-fired power, there newable energy consumption, the new constraints of carbon-emissions, and fragmented power planning. This study develops a multi-objective optimization model to predict the future trend of China power structure by 2035. The key factors such as network, power, load and storage are taken into account. Besides, the technical feasibility, economic rationality and social acceptable constraints are also fully considered. Through planning and optimization, the premise of low carbon transformation is to ensure the continuity of existing policies for removing inefficient assets, and the core is to develop and utilize non-fossil energy on a large scale. Specifically, the capacity ofcoal-fired power will be attained in the peak in 2025, and the factor will also transfer from main power supplier to main power and energy supplier. Before 2025, the clean replacement of incremental power installation will becompleted. In 2035, 92% of new investment comes from non-fossil energy. The economy and competitiveness of wind power and PV (Photovoltaic) power generation are continuously increasing. By 2020, the coal-fired power and the wind power in eastern of China will be parity firstly. In 2025, the cost of PV and wind power will be the same. Furthermore, the evaluation dimension of modern power system with clean, low-carbon, safety and high efficiency are innovatively constructed, and the index system target of 2035 is quantitatively analyzed and prospected.

 

4. Energy Storage Performance of a PCM in the Solar Storage Tank

MAO Qianjun, CHEN Hongzhang, YANG Yizhi

Journal of Thermal Science, 2019, 28(2): 195-203

DOI: https://doi.org/10.1007/s11630-019-1076-x

Keywords: solar phase change materials, energy storage performance, sensible heat, latent heat

Abstract: High-temperature solar thermal power station with solar energy storage is one of the effective ways to solve energy shortage and environmental pollution. The heat storage characteristics of phase change materials in solar energy storage tanks directly affect the performance of the system and its future promotion and utilization. Based on the knowledge of heat transfer, fluid mechanics and engineering thermodynamics, this paper uses MATLAB software to compile the dynamic heat storage characteristics calculation program of phase change materials in energy storage tanks, and verify the results. This paper analyzes the phase change heat storage process with three PCM initial temperatures and three HTF speeds. The results show that when the initial temperature of the PCM changes from 185°C to 210°C, the latent heat storage heat increases by 21.8%, and thetotal heat storage decreases. Increasing the HTF speed from 1.8 m/s to 2.2 m/s, the melting time was reduced from 414 minutes to 390 minutes, and the total heat storage and sensible heat storage were also increased. The results also show that changing the initial temperature of the PCM and the flow rate of the HTF will change the thermal storage performance of the system. The research has certain reference significance for mastering the basic principle of high temperature solar thermal power generation system and promoting the application of the system.

 

5. Design and Operational Strategy Research for Temperature Control Systems of Isothermal Compressed Air Energy Storage Power Plants

FU Hao, JIANG Tong, CUI Yan, LI Bin

Journal of Thermal Science, 2019, 28(2): 204-217

DOI: https://doi.org/10.1007/s11630-019-1089-5

Keywords: hierarchical relay operation, isothermal compression, compressed air energy storage power plant, energy storage

Abstract: Energy storage technology is critical for intelligent power grids. It has great significance for the large-scale integration of new energy sources into the power grid and the transition of the energy structure. Based on the existing technology of isothermal compressed air energy storage, this paper presents a design scheme of isothermal compressed air energy storage power station, which uses liquid to compress air, hydraulic piston to transfer potential energy, hydraulic turbine to generate electricity at constant pressure, and liquid occupancy to store the gas at constant pressure. Then the technical features and control strategies of its internal temperature controlsubsystem are studied, and the mathematical model is constructed. A hierarchical relay operation is put forward to address the actual construction and operational requirements of compressed air energy storage power plants. Finally, through physical platform experiments and MATLAB simulation, the feasibility of the design is validated.

 

6. Evaluation of Electricity Generating System’s Technology Mix Using 3E Indicator

GRKOVIĆ Vojin

Journal of Thermal Science, 2019, 28(2): 218-224

DOI: https://doi.org/10.1007/s11630-019-1095-7

Keywords: 3E indicator, technology matrix, energy technologies, carbon-free, despatchable

Abstract: For the purpose of the research, the technologies for electricity generation are classified in four categories: CO2-free-desspatchable (hydro, nuclear, and biomass fired), CO2-free-non-desspatchable (wind generators and photo voltaic), CO2-dependent-despatchable and CO2-dependent-non-despatchable ones. 3E indicator is introduced purposely to enable quantitative evaluation of the considered complex technology structures, as well as to provide support for decision making during the design and operation procedures of electricity generating systems. The application of the indicator is demonstrated with appropriate model numerical simulations for the general European conditions. In the model calculations are analyzed simplified technology mixes with CO2 free, non-despatchable technologies in overall load, two technologies in base part of the residual load (lignite fired and nuclear), one technology in intermediate part of the residual load and one in the pick part of the residual load both CO2 dependent, despatchable ones. The results show that the introduced 3E indicator is suitable for analysis of the technological combinations for electricity generation within considered countries. The results also show that increase participation of nuclear power plants in residual load domain contribute to better (lower) value of 3E indicator. The results obtained for technology structures in nine analyzed European countries (Germany, France, Austria, Greece, Serbia, Hungary, Bulgaria, Belgium and Netherlands) point out that the country with higher participation of CO2 free despatchable and lower participation of CO2 free non-despatchable technologies in electricity generation has tendency toward better i.e. lower value of 3E indicator. On the other hand the country with the higher participation of CO2 free non-despatchableand lower to moderate participation of CO2 free despatchable technologies has tendency toward the higher value of 3E indicator. These results are in accordance with the results obtained by numerical simulations with simplified technology mixes.

 

7. Cu-Promoted Cobalt Oxide Film Catalyst for Efficient Gas Emissions Abatement

ELKASMI Achraf, WAQAS Muhammad, MOUNTAPMBEME KOUTOU Patrick, TIAN Zhenyu

Journal of Thermal Science, 2019, 28(2): 225-231

DOI: https://doi.org/10.1007/s11630-019-1093-9

Keywords: low Cu-doping, PSE-CVD technique, thin film catalysts, complete catalytic oxidation, VOCs

Abstract: Thin film catalysts have been recently reported as promising catalysts owing to their good catalytic activity and reduced material amount, leading to low-cost efficient catalysts for gaseous emissions control. Here, we report the slight loading of Cu in cobalt spinel using a one-step pulsed-spray evaporation chemical vapor deposition (PSE-CVD) synthesis technique for efficient short-chain volatile organic compounds (VOCs) emissions treatment. Crystalline structure and morphology analyses revealed nano-crystallite sizes and open-like morphology. The catalytic performance was evaluated through the complete oxidation of C3H6, as a short-chain representative model of VOCs, at a high gas hourly space velocity (GHSV). Very good activity was obtained towards the complete abatement of C3H6at low temperature and no carbon monoxide (CO) was formed during the oxidation process. Slightly-promoted Co3O4 catalyst with Cu introduction resulted in high catalytic activity comparing to the performance of the catalysts in the literature, due to the high dispersion of Cu and high active surface oxygen amount. Moreover, to evaluate the capability of the used catalysts under near realistic reaction conditions, CO2 effect on the catalytic activity was performed and the catalyst exhibited very good results. Thus, the adopted slightly-doping strategy to tailor a high active catalyst at low temperature could establish a very promising route to strongly enhance the activity of such other catalysts towards gas emissions abatement at low temperature.

 

8. Study on Laminar Natural Convection Heat Transfer from a Hemisphere with Uniform Heat Flux Surface

ZHANG Jian, LIU Jie, LU Wenqiang

Journal of Thermal Science, 2019, 28(2): 232-245

DOI: https://doi.org/10.1007/s11630-018-1051-y 

Keywords: numerical simulation, natural convection, hemisphere, uniform heat flux, heat transfer correlations

Abstract: By employing the modified model based on Bejan et al., laminar natural convection heat transfer from a hemisphere with uniform heat flux surface has been numerically investigated. Extensive results of two different surface boundary conditions are obtained for a wide range of Grashof numbers (10 ≤ Gr ≤ 107) and Prandlt number of 0.72. The characteristics of heat transfer and fluid flow are analyzed in terms of isotherm contours and streamline patterns, radial and tangential velocities, dimensionless temperature profiles, local friction and pressure drag coefficients, as well as local and average Nusselt numbers. Meanwhile, the effects of Grashof number and adiabatic surface on flow motion and heat transfer have been studied. No recirculation zone or flow separation generates over the top of the hemisphere compared to the isothermal sphere. Owing to the curvature effect, the maximum values of local friction and pressure drag coefficients appear at the corner point B. Comparisons with the previous results are also reported in detail. All the results are in good agreement with the numerical data. Moreover, both local and average Nusselt numbers show a positive dependence on Grashof number. The values of the non-adiabatic case are smaller than that of the adiabatic case due to the preheating effect. Finally, two precise and general correlations of average Nusselt number varying with Grashof numbers have been presented, which can provide an effective prediction for the heat transfer rate in engineering applications, and offer academic values for the future research.

 

9. Experimental Investigation on the Temperature Distribution Characteristics of the Evaporation Section in a Pulsating Heat Pipe

WANG Xuehui, GAO Xu, BAO Kangli, HUA Chao, HAN Xiaohong, CHEN Guangming

Journal of Thermal Science, 2019, 28(2): 246-251

DOI: https://doi.org/10.1007/s11630-019-1065-0

Keywords: temperature distribution, pulsating heat pipe, oscillation motions, heat transfer

Abstract: With the increasing demand for heat dissipation in the electronics industry, pulsating heat pipe (PHP) has attracted wide attention due to its simple structure and excellent heat transfer ability. However, due to the unique operational mechanism of PHP, the temperature distribution in the evaporation section is obviously not even during the operational process of PHP. When the PHP is used as a heat dissipater, the evaporation section of the PHP directly contacts with the chips and has great influence on the performance of the chips, so it is very important to investigate the temperature distribution characteristics in the evaporation section. In this paper, both the effects of the filling ratio and heat flux on these characteristics were investigated. The experimental results indicated that the temperatures of the middle “U” turn were the highest. When the heat flux and the filling ratio were 364 W/cm2 and 36.3%, respectively, the maximum temperature difference between the middle “U” turn and the other “U” turns could be as high as 18.92 K. Furthermore, the temperature differences between the middle “U” turn and the other “U” turns firstly increased and then decreased with the increase of heat flux and filling ratio.

 

10. Thermal-Hydraulic-Structural Analysis and Design Optimization for Micron-Sized Printed Circuit Heat Exchanger

HOU Yaqiong, TANG Guihua

Journal of Thermal Science, 2019, 28(2): 252-261

DOI: https://doi.org/10.1007/s11630-018-1062-8

Keywords: computational fluid dynamics (CFD), Printed Circuit Heat Exchanger, thermal-hydraulic-structural performance, channel arrangement, channel aspect ratio

Abstract: The Printed Circuit Heat Exchanger (PCHE) is one of the most promising heat exchangers for Synergetic Air-breathing and Rocket Engine (SABRE). To reduce pressure drop and improve compactness, themicron-sized PCHE made up of rectangular channels of tens of microns in size, is used in SABRE. In present work, we focus on thermal-hydraulic-structural characteristics of micron-sized PCHE by conducting three-dimensional (3-D) numerical simulation. Helium and hydrogen are employed as the working fluids and the Stainless Steel 316 (SS316) as the solid substrate. The thermal-hydraulic performance of the micron-sized PCHE is discussed by using the commercial Computational Fluid Dynamics (CFD) software of Fluent. ANSYS- Mechanical is also employed to simulate stress field of representative PCHE channels. The mechanical stress induced by pressure loading and the thermal stress induced by temperature gradient are found to be equally important sources of stress. To improve comprehensive performances of micron-sized PCHE, two types of channel arrangements and different channel aspect ratios are studied. The double banking is of higher thermal-hydraulic performance compared to the single banking while the stress performance is identical for the two modes. Meanwhile, the effect of channel aspect ratio is investigated by comparing thermal-hydraulic characteristics and structural stress of the model. The rectangular channel with w/h=2 achieves the most balanced stress characteristic and higher thermal-hydraulic performance.

 

11. Effect of Cooling Water Flow Path on the Flow and Heat Transfer in a 660 MW PowerPlant Condenser

ZHONG Dawen, MENG Ji’an, QIN Peng, QIU Xiaolong, JIANG Ping, LI Zhixin, YUAN Fang

Journal of Thermal Science, 2019, 28(2): 262-270

DOI: https://doi.org/10.1007/s11630-018-1063-7

Keywords: steam surface condenser, porous media, cooling water flow path, condensation, computational fluid dynamics

Abstract: The effect of the cooling water flow path on the flow and heat transfer in a double tube-pass condenser for a 660 MW power plant unit was numerically investigated based on a porous medium model. The results were used to analyze the streamline, velocity, air mass fraction and heat transfer coefficient distributions. The simulations indicate that the cooling water flow path is important in large condensers. For the original tube arrangement, the heat transfer with the lower-upper cooling water flow path is better than that with the upper-lower cooling water flow path. The reason is that the steam cannot flow into the internal of upper tube bundle and the air fractions are higher in the upper tube bundle with the upper-lower cooling water flow path. An improvement tube arrangement was developed for the upper-lower cooling water flow path which reduced the back pressure by 0.47 kPa compared to the original scheme. Thus, the results show that the tube arrangements should differ for different cooling water flow paths and the condenser heat transfer can be improved for the upper-lower cooling water flow path by modifying the tube arrangement.

 

12. Thermal Performance and Mechanics Characteristic for Double Layer Microchannel Heat Sink

XU Yupeng, GONG Liang, LI Yongtong, BAI Zhang, XU Minghai

Journal of Thermal Science, 2019, 28(2): 271-282

DOI: https://doi.org/10.1007/s11630-019-1078-8

Keywords: double layer micro-channel heat sink, thermal strain, thermal performance, optimized design

Abstract: Double layer micro-channel heat sink (DLMCHS) has been widely used in various electronic devices; however, the existence of the non-uniform thermal strain distribution in actual operation has adverse effect on the overall stability. In this paper, two optimized designs of DLMCHS with cutting baffles on top and bottom layers are presented based on the traditional DLMCHS. The heat transfer and thermal stress performance are numerically analyzed and compared with the traditional DLMCHS. The results indicate that cutting baffles of micro-channels remarkably improves heat transfer and thermal stress performance. The optimized design with cutting baffles on the bottom layer decreases thermal strain but deteriorates heat transfer performance. The model with cutting baffles on the top layer has better combined thermal strain and heat transfer performance, which reduces thermal strain by about 1.5 times and enhances heat transfer by about 26.5%. For the design with cutting baffles on the top board, adding metal foam in the inlet collector can decrease the total minimum thermal strain by 51.4% and maximum temperature by 1.4 K, and increase the Nusselt number by 15%. These results indicate that DLMCHS with cutting baffles on the top layer has great potential for thermal managements on electronic devices with high power density.

 

13. Optimization Potentials for the Waste Heat Recovery of a Gas-Steam Combined Cycle Power Plant Based on Absorption Heat Pump

ZHANG Hongsheng, ZHAO Hongbin, LI Zhenlin, HU Eric

Journal of Thermal Science, 2019, 28(2): 283-292

DOI: https://doi.org/10.1007/s11630-018-1055-7

Keywords: combined cycle power plant, absorption heat pump, waste heat recovery, evaluation criteria, exergy analysis

Abstract: A new waste heat recovery system is presented to recover exhausted steam waste heat from the steam turbine by absorption heat pump (AHP) in a gas-steam combined cycle (GSCC) power plant. The system can decrease energy consumption and further improve the energy utilization. The performance evaluation criteria are calculated, and exergy analysis for key components are implemented in terms of the energy and exergy analysis theory. Besides, the change of these criteria is also revealed before and after modification. The net power output approximately increases by 21738 kW, and equivalent coal consumption decreases by 5.58 g/kWh. A 1.81% and 1.92% increase in the thermal and exergy efficiency is respectively obtained in the new integrated system as the heating load is 401095 kJ at 100% condition. Meanwhile, the appropriate extraction parameters for heating have been also analyzed in the two systems. The proposed scheme can not only save energy consumption but   also reduce emission and gain great economic benefit, which is proven to be a huge potential for practical application.

 

14. Investigation on the Influence of Refrigerant Charge Amount on the Cooling Performance of Air Conditioning Heat Pump System for Electric Vehicles

LI Kang, LAN Jiao, ZHOU Guoliang, TANG Qitian, CHENG Qia, FANG Yidong, SU Lin

Journal of Thermal Science, 2019, 28(2): 294-305

DOI: https://doi.org/10.1007/s11630-018-1056-6

Keywords: air conditioning heat pump, electric vehicle, critical refrigerant charge, cooling performance

Abstract: The application of air conditioning heat pump (ACHP) in electric vehicles could lead to significant electrical power saving effect. As for an air conditioning heat pump system for electric vehicles, the influence of refrigerant charge amount should be investigated during the design phase. In this study, experimental method was employed to investigate the influence of the refrigerant charge amount on the performance of the ACHP system. The results showed that there frigerant charge amount had different influence on the refrigerant properties at various locations within the system. The coefficient of performance and pressure-enthalpy diagram were calculated, and showed a close relationship with refrigerant charge amount under different compressor speeds. The degree of subcooling and the degree of superheating were recorded and the critical charge amount was determined by a typical practical test method. In addition, the critical refrigerant charge amount determined by the experimental method was also compared with two typical void fraction correlation models, and the model with consideration of two phase stream reaction of the refrigerant showed a good estimation accuracy on the critical charge amount.

 

15. Energy Loss Analysis of Novel Self-Priming Pump Based on the Entropy Production Theory

CHANG Hao, SHI Weidong, LI Wei, LIU Jianrui

Journal of Thermal Science, 2019, 28(2): 306-318

DOI: https://doi.org/10.1007/s11630-018-1057-5

Keywords: entropy production, energy loss, thickness distribution, pressure pulsation

Abstract: The conventional method cannot explicitly confirm the location and type of the energy loss, therefore this paper employs the entropy production theory to systematically analyze the category, magnitude and location of hydraulic loss under different blade thickness distribution. Based on the analysis, the turbulent entropy and viscosity entropy produced by the separation of boundary layer at the trialing edge are major factors leading to the hydraulic loss. In addition, the separation of the boundary layer can not only cause the energy loss, but also block the passage of the impeller and reduce the expelling coefficient of the blade. Therefore, the hydraulic performance of the blades with increment thickness distribution is obviously better than the decrement one. Further, the flow rate has different influence on the three types of entropy production. Meanwhile, the pressure pulsation on the working surface was investigated. It was concluded that with flow rates increasing, the amplitude of pressure pulsation firstly decreases and then smoothly improves, and reaches the minimum under design flow rate. Finally, the optimal blade was obtained, and the relevant hydraulic performance test was performed to benchmark the simulation result. This research can provide the theoretical reference for designing the reasonable thickness distribution of the blades.

 

16. Influences of Reservoir Heterogeneity and Anisotropy on CO2 Sequestration and Heat Extraction for CO2-Based Enhanced Geothermal System

WANG Changlong, HUANG Zhijia, LU Yuehong, TANG Gang, LI Huan

Journal of Thermal Science, 2019, 28(2): 319-325

DOI: https://doi.org/10.1007/s11630-019-1064-1

Keywords: enhanced geothermal system, CO2 sequestration, heat extraction, reservoir heterogeneity, reservoir anisotropy

Abstract: Enhanced geothermal systems (EGS) have a great potential to extract geothermal energy and have attracted much interest. In this paper, based on a 3D thermal-hydrologic model considering CO2 sequestration, the influences of reservoir heterogeneity and anisotropy on CO2 sequestration and heat extraction in CO2-based EGS are investigated. Different heterogeneous reservoirs and homogeneous reservoir are compared, and different ratios among reservoir permeability components are compared. The results show that greater reservoir heterogeneity enhances CO2 sequestration and restrains heat extraction. Higher ratio between horizontal (x and y directions) and vertical permeability components enhances CO2 sequestration and heat extraction, and vertical permeability component has a little effect. With the increasing ratio between x-directional (perpendicular to the line of the injection well and the production well) and y-directional (perpendicular to x direction) reservoir permeability components (i.e. kx:ky), both CO2 sequestration amount and steady-state heat extraction rate first increase and then decrease, and thermal breakthrough time increases, showing that there exists an optimum kx:ky, which is about 1:1. The results of this paper indicate that reservoir heterogeneity and anisotropy have important influences on CO2 sequestration and heat extraction.

 

17. Effects of Offset Blade on Aerodynamic Characteristics of Small-scale Vertical Axis Wind Turbine

LI Yan, ZHAO Shouyang, QU Chunming, FENG Fang, KOTARO Tagawa

Journal of Thermal Science, 2019, 28(2): 326-339

DOI: https://doi.org/10.1007/s11630-018-1058-4

Keywords: vertical axis wind turbine (VAWT), offset blade, airfoil, numerical simulations, wind tunnel tests

Abstract: A new way of connecting blade to rotor shaft named offset blade method was proposed for straight-bladed vertical axis wind turbine (SB-VAWT) in this study. In order to invest the efficiency of this method and effects of main parameters including offset length and blade airfoil on improving the output power performance and static starting characteristics, numerical simulations and wind tunnel tests were carried out. Four kinds of blade airfoil including NACA0012, NACA0018, NACA0024 and S809 were selected to analyze the influence of blade thickness and symmetry on SB-VAWT with offset blade. Numerical simulations were firstly carried out on output power for the rotor with 6 kinds of offset length for each airfoil. Wind tunnel tests were also carried out to compare with the results of simulations. The flow fields of rotor with different offset lengths were simulated and the effects of offset blade were analyzed. The optimum offset length among all studied for output power performance was found. Furthermore, the static starting torque and aerodynamic force characteristics of the rotor with optimum offset length were researched. According to the results, appropriate offset length can improve the output power characteristics and smooth the fluctuations of the static torque during one rotational period. The best offset length varies with the airfoil.

 

18. Effect of Different Trench Lips on Downstream Film Cooling Effectiveness and Flow Fields

HOU Rui, WEN Fengbo, CUI Tao, TANG Xiaolei, WANG Songtao

Journal of Thermal Science, 2019, 28(2): 340-353

DOI: https://doi.org/10.1007/s11630-018-1061-9 

Keywords: gas turbine, film cooling, trench hole, cooling effectiveness

Abstract: In the present study, the trenched configurations, including traditional trench (TT), fillet trench (FT) and varying-radius trench (VRT), are numerically investigated at different conditions in terms of downstream cooling effectiveness and flow fields. Different trench width and fillet radii are discussed at different blowing ratios and density ratios. Results show that the downstream lips mainly change the downstream pressure distributions and then change the lateral coolant distribution. The downstream fillet can reduce the penetration of coolant and improve laterally averaged effectiveness in the configurations with the narrow trench at modest blowing ratios. The enhancement of cooling effectiveness near the centerline plane is the positive effect of downstream fillet. This enhancement becomes more obvious with the increase of fillet radius, except for high blowing ratio. The fillet lip, compared with TT cases, also leads to a decline of coolant lateral spread for configurations with the wide trench and large radius, and more decline in the lateral direction deteriorates downstream overall cooling performance. Besides, the increase of density ratio contributes to a higher cooling effectiveness for fillet trench configurations. VRT cases guarantee the stream wise extension and lateral spread of coolant, therefore improving downstream cooling effectiveness further at blowing ratio M=1.0 and 1.5.

 

19. Experimental Study of Rotor Flow Separation Control using a New Type of Dielectric Barrier Discharge Plasma Actuator

HU Xu, GAO Chao, HAO Jiangnan, ZHANG Zhengke, XUE Ming, YAN Rihua

Journal of Thermal Science, 2019, 28(2): 354-359

DOI: https://doi.org/10.1007/s11630-019-1088-6

Keywords: rotor, flow separation control, DBD, plasma, PIV

Abstract: Flow separation occurring on rotor blades is an important limiting factor for helicopter performance. This paper presents a new type of dielectric barrier discharge (DBD) plasma actuator for rotor blade flow separation control called bipolar DBD plasma actuator. The bipolar DBD plasma actuator's connection mode differs from traditional plasma actuators and eliminates reverse discharge between electrodes. The experiments in this work were carried out by smoke-wire flow visualization and PIV technology in the open test section of a low speed wind tunnel, and solved the problem of high voltage electricity supplied to the plasma actuator while the rotor rotated. In this experiment, the rotor, camera, and laser were synchronized to obtain results. Smoke-wire results and PIV results illustrated that the flow separation weakened with increasing rotor speed; the separated flow area was large at a rotating speed of 300 r/min and gradually became smaller at the rotating speed of 600 r/min, the flow separation disappeared at the rotating speed of 1200 r/min. When the plasma was active, both smoke-wire results and PIV results showed the flow separation area was greatly reduced at the rotating speed of 300 r/min and disappeared at the rotating speeds of 600 r/min and 1200 r/min, the rotor flow separation at high angles of attack could be effectively controlled by the new DBD plasma actuator.

 

20. An Experimental Study on the Effects of a Film Cooling Configuration and Mainstream Temperature on Depositing

LIU Zhengang, LIU Zhenxia, ZHANG Fei, LIU Yanan

Journal of Thermal Science, 2019, 28(2): 360-369

DOI: https://doi.org/10.1007/s11630-019-1087-7

Keywords: depositing, film cooling, dilute multiphase flow

Abstract: The effects of a film cooling configuration and mainstream temperature on the depositing of particles are experimentally studied by using plate models. The particles are generated by melting wax and atomizing it. One model has a film cooling configuration and the other does not. The experimental results show that the film cooling configuration does not influence the depositing on the leading edge of the model very significantly. However, the film cooling configuration could increase the depositing on the upper surface of the model dramatically since the flow structure on the upper surface is changed due to the film cooling configuration. The effect of the mainstream temperature on the depositing is studied by using the model with film cooling configuration. The lower and higher mainstream temperature both could reduce the depositing. However, the mechanisms are different. The lower mainstream temperature could make more molten particles become solid particles, which could rebound from the surface of the model, reducing the depositing. The higher mainstream temperature could make all particles remain molten with higher temperature. In this case, more particles could splash from the surface of the model. Therefore, there may be a mainstream temperature at which the depositing mass is maximum.

 

21. Numerical Investigation of Transient Temperature Distribution during Ti-6Al-4V Selective Laser Melting

XING Xiaodong, ZHOU Qiuyu, WANG Shiyuan, WANG Liquan, JIANG Fengchun

Journal of Thermal Science, 2019, 28(2): 370-377

DOI: https://doi.org/10.1007/s11630-019-1082-z   

Keywords: Selective Laser Melting, transient temperature field, process parameters, melt pool

Abstract: The transient temperature field in the powder bed has a crucial effect on the quality of parts fabricated using Selective Laser Melting (SLM). In this study, a finite element model is established regarding the variance of temperature-dependent thermal properties and transformation latent heat. The temperature distribution and melt pool dimensions of a laser scan track were obtained by varying multiple parameters (layer thickness, laser power and scan speed). The effects of transition of material state and heat source model are also analyzed in this paper. The finite element simulation results show that an increased laser power and/or decreased scan speed results in an elevated maximum temperature of the powder layer and a larger melt pool size. Furthermore, it is found that the maximum temperature is significantly lowered due to the heat diffusion into the previous sintered zone. The heat source model has to be selected properly according to the element size.

 

22. An Improved Enthalpy-Based Lattice Boltzmann 3D Model with Added Probability Function for the Growth Characteristics of Frost Layer

CUI Jing, YANG Tinghao, YANG Fan, YANG Guangfeng

Journal of Thermal Science, 2019, 28(2): 378-392

DOI: https://doi.org/10.1007/s11630-018-1066-4

Keywords: lattice Boltzmann model, improved enthalpy model, nucleation probability model, three-dimensional, frost, surface wettability

Abstract: In this paper, the effects of different surface properties on the growth of frost layer were numerically studied from the mesoscopic scale using the lattice Boltzmann method. The improved enthalpy method and nucleation probability model were combined to establish a three-dimensional lattice Boltzmann model based on nucleation probability theory. The model was used to carry out numerical research on frost layer formation and growth process on cold wall surface. The model could not only simulate the gradual densification and thickening process of frost layer growth from the macro scale, but also describe the change process of the frost layer structure caused by ice branch growth on the micro scale. The average thickness, average density and the amount of the frost layer could be obtained. Through this model, the temporal and spatial evolution characteristics of the topography of the frost layer were obtained. The model was used to analyze the effects of cold wall surface temperature, relative humidity and cold surface wettability on the frosting characteristics. The average thickness, frost average density, frost quality and average solid volume fraction of frost at different times were obtained by calculation.