Volume 29, Issue 4, July-August 2020

CONTENTS-Volume 29, Issue 4, July-August 2020

Springer Link: https://link.springer.com/journal/11630/29/4

1. Review on Large Eddy Simulation of Turbulent Premixed Combustion in Tubes

LUO Gang, DAI Haidong, DAI Lingpeng, QIAN Yunlou, SHA Ce, ZHANG Yuxiang, WU Bingxin

Corresponding author: LUO Gang; WU Bingxin

E-mail: luogang3615@163.com; bxys11@163.com

Journal of Thermal Science, 2020, 29(4): 853-867.

https://doi.org/10.1007/s11630-020-1311-5

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1311-5

Keywords: LES, turbulent premixed combustion, SGS models, empty tube, obstructed tube

Abstract: This paper reviews the existing knowledge on the large eddy simulation (LES) of turbulent premixed combustion in empty tubes and obstructed tubes. From the view of model development in LES, this review comprehensively analyzes the development history and applicability of the important Sub-Grid Scale (SGS) viscosity models and SGS combustion models. LES is also used to combine flow and combustion models to reproduce industrial explosion including deflagration and detonation and the transition from deflagration to detonation (DDT). The discussion about models and applications presented here leads readers to understand the progress of LES in the explosion of tube and reveals the deficiencies in this area.

2. Characteristics of Nitric-Oxide Emissions from Traditional Flame and MILD Combustion Operating in a Laboratory-Scale Furnace

SHU Ziyun, WANG Feifei, DAI Chong, SI Jicang, WANG Bo, MI Jianchun

Corresponding author: MI Jianchun

E-mail: jmi@pku.edu.cn

Journal of Thermal Science, 2020, 29(4): 868-883.

https://doi.org/10.1007/s11630-020-1235-0

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1235-0

Keywords: MILD (moderate or intensive low-oxygen dilution) combustion, traditional combustion, NO emission

Abstract: This study investigated the formation and emission characteristics of nitric oxide (NO) from flameless MILD (moderate or intensive low-oxygen dilution) combustion (MILDC) versus traditional visible-flame combustion (TC) in a 30-kW furnace. Both combustion processes were experimentally operated successively in the same furnace, burning natural gas at a fixed rate of 19 kW and the equivalence ratio of 0.86. Numerical simulations of TC and MILDC were carried out to explain their distinction in the measured furnace temperature and exhaust NO emissions. Present measurements of the NO emission (XNO) versus a varying furnace wall temperature (Tw) have revealed, at the first time, that the relationship of XNO ~ Tw was exponential in both TC and MILDC. By analyzing the simulated results, the average temperature over the reaction zone was identified to be the common characteristic temperature for scaling NO emissions of both cases. Moreover, relative to TC, MILDC had a fairly uniform temperature distribution and low peak temperature, thus reducing the NO emission by over 90%. The thermal-NO formation was found to contribute more than 70%?80% to the total XNO from TC while the N2O-intermediate route dominated the NO emission from MILDC.

3. Experimental Study of Influence of Fuel Ratio on Combustion Characteristics of Diesel-Wetted Wood Powder

CHEN Changkun, LEI Peng, ZHANG Yulun, XIAO Huang, XU Tong, JIAO Weibing

Corresponding author: CHEN Changkun; LEI Peng

E-mail: cckchen@csu.edu.cn; leipeng2015@csu.edu.cn

Journal of Thermal Science, 2020, 29(4): 884-892.

https://doi.org/10.1007/s11630-020-1259-5

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1259-5

Keywords: diesel-wetted wood powder, fuel ratio, flammability, combustion characteristics

Abstract: In this study, experiments were conducted to examine the influence of the fuel ratio (i.e., the ratio of diesel mass to wood powder mass) on the combustion characteristics of diesel-wetted wood powder, in which 0# diesel and poplar wood powder were used and well mixed. The fuel ratios were set to 0, 0.5, 1.0, 1.5, and 2.0. Fire behaviors, temperature distributions, mass loss rates, and CO concentrations were measured and analyzed. The results showed that because of the coupled effect of evaporation and the capillary force, the ignition point of diesel-wetted wood powder (less than 3°C) dropped dramatically as compared with that of pure wood powder (higher than 280°C) and pure diesel (higher than 107°C). At the early stage of combustion, diesel is lifted upwards by the capillary force, increasing both the concentration of diesel vapor and the temperature at the surface. When the surface temperature reaches that of the pyrolysis of wood powder, considerable pyrolysis gas emerges and combusts. As the flammable gas is consumed gradually, carbon combusts prominently when plenty of oxygen diffuses to its surface. Regarding the influence of the fuel ratio, the results showed that in cases with lower fuel ratios, the combustion was not self-sustainable. When the fuel ratio was relatively high, the temperature at the flame center was lower owing to incomplete combustion. More CO could be found in cases with higher fuel ratios in the early and late stages of combustion. The results could help to improve knowledge regarding combustion of fuel-wetted wood powder.

4. Numerical Research on Inlet Total Pressure Distortion in a Transonic Compressor with Non-Axisymmetric Stator Clearance

XU Wenfeng, SUN Peng, YANG Guogang, HUANG Longsheng, FU Wenguang

Corresponding author: XU Wenfeng; SUN Peng

E-mail: xuwf789@163.com; sp_hit@hotmail.com

Journal of Thermal Science, 2020, 29(4): 893-905.

https://doi.org/10.1007/s11630-020-1289-z

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1289-z

Keywords: total pressure distortion, non-axisymmetric stator clearance, transonic compressor, numerical simulation

Abstract: Inlet total pressure distortion has great adverse effects on the aero-engine performance. The distorted flow passes through the compressor and becomes non-uniform in the downstream blade rows. Different from previous studies based on the assumption of circumferential uniformity, this study aims to improve circumferential non-uniform flow with the non-axisymmetric structure. Non-axisymmetric stator clearance was adopted to resolve the effects of non-uniform flow caused by inlet total pressure distortion in this paper. The 9 stators with tip clearance were installed in the distorted region and the flow field structure and performance under different operating conditions was studied. The study finds that the non-axisymmetric compressor with 9 tip clearance stators can ensure compressor efficiency while improving compressor stability margin. What’s more, the separation range and strength in the distorted region can be reduced significantly and the anti-distortion capability of compressor can be enhanced.

5. Flow Regulation and Heat Transfer Characteristics in a Novel Turbine Shroud with Internal Asymmetric Throttle Chamber

ZHANG Wei, ZHU Huiren, LI Guangchao

Corresponding author: ZHANG Wei

E-mail: emma7691@163.com

Journal of Thermal Science, 2020, 29(4): 906-915.

https://doi.org/10.1007/s11630-020-1229-y

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1229-y

Keywords: turbine shroud, throttle chamber, mass flow rate regulation, heat transfer

Abstract: Flow and heat transfer of a novel turbine shroud with throttle chamber under two kinds of orifice arrangements were numerically studied. The original shroud model composed of the impingement holes, film holes and jet channel. The two modified models have identical geometrical spacing except for the number and location of the orifices in the upper plate of the throttle chamber added in the jet channel. Different pressure values were set at the outlets of different row film holes simulating the mainstream favorable pressure gradient. The ratios of inlet total pressures of impingement holes to outlet static pressures of the third row film holes ranged from 1.6 to 3.6. The Nusselt number distributions were validated by the experimental data. The main target of this study was to quantify the impact of the throttle chamber on the flow regulation and internal heat transfer characteristics. The flow factor, relative mass flow rate, the Nusselt number and the heat transfer factors on the target walls were presented. It is found that the mass flow rate distributions in the film hole rows become more reasonable by the modification of location and number of the orifices on the throttle chamber. The throttle chamber decreases the heat transfer on the target walls.

6. Numerical Investigation of Circumferential Groove Casing Treatment in a Highly-Loaded Low-Reaction Transonic Compressor Rotor

ZHU Wei, CAI Le, WANG Songtao, WANG Zhongqi

Corresponding author: CAI Le

E-mail: caile_lele@163.com

Journal of Thermal Science, 2020, 29(4): 916-927.

https://doi.org/10.1007/s11630-019-1180-y

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1180-y

Keywords: low-reaction transonic compressor, circumferential casing groove, vortex breakdown, stall margin

Abstract: In this paper, a computational investigation of circumferential groove casing treatment in a highly-loaded low-reaction transonic compressor rotor is conducted, in which the stage reaction is significantly reduced due to a larger meridional contraction with respect to conventional transonic compressors. Steady computation at near-stall point is performed first to capture the stall inception of the rotor with smooth casing. Detailed observations, which mainly focus on the tip leakage flow behavior, obstruction and vortical structures in the tip region, determine the reason for the compressor stall. There is tip leakage vortex breakdown in the tip region. Moreover, it yields passage obstruction, and finally leads to the compressor stall. Then, attempts are made to investigate how the circumferential grooves can be applied for the compressor’s stall margin enhancement without compromising efficiency. Three configurations are obtained and analyzed by changing axial position and the number of the circumferential grooves. The results of computational parametric study indicate the optimal location of the groove is near the leading edge and the downstream grooves combine their influence on the compressor’s stabilization and performance in a cumulative manner. The optimal circumferential groove configuration produces an increase of 1% in total pressure ratio at the near-stall point and a gain of 3.7% in stall margin, without any penalty in efficiency. Furthermore, the impact the grooves will exert on the flow mechanisms between the grooves and the main flow is also considered.

7. Inducer/Exducer Matching Characteristics inside Tandem Impellers of a Highly Loaded Centrifugal Compressor

LI Ziliang, ZHAO Shengfeng, LU Xin’gen, HAN Ge, YANG Chengwu, ZHU Junqiang

Corresponding author: ZHAO Shengfeng

E-mail: zhaoshengfeng@iet.cn

Journal of Thermal Science, 2020, 29(4): 928-944.

https://doi.org/10.1007/s11630-020-1191-8

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1191-8

Keywords: highly loaded centrifugal compressor, tandem impeller, inducer/exducer matching, flow mechanism, Kutta condition

Abstract: A centrifugal compressor usually operates with low isentropic efficiency and a terrible stable operating range, resulting from the complex impeller flow structure companied with the intense interaction among the impeller and the diffuser downstream. In many studies, the potential of centrifugal compressor tandem-impeller configurations for improving the compressor has been demonstrated. Whereas, compared with the convincing results on the tandem-designed axial compressors, the results on tandem impellers are limited and contradictory. Very little insight has been provided into the flow mechanisms inside tandem impellers, which is considered to be the primary reason for the confusion in tandem impeller design and application. Tandem impellers are expected to exhibit a totally different behavior due to the intense aerodynamic interaction between the inducer and the exducer, which substantially contributes to the flow structure and the compressor performance change. In the present study, a numerical study of a highly-loaded centrifugal compressor with various tandem designs was conducted to explore the inducer/exducer matching characteristics and the underlying flow mechanism inside tandem impellers. Two tandem impeller design parameters, namely, the inducer/exducer clocking fraction and the axial gap (overlap), were considered in the tandem impeller design process. The tandem impeller was also compared to the existing conventional impeller which the tandem impeller was redesigned for. The results demonstrated that the tandem-designed impeller can improve the centrifugal compressor stage performance and intense inducer/exducer interaction can be observed with changes in the clocking fraction and the axial gap (overlap). The tandem impeller performance is sensitive to changes in axial gap (overlap) when the suction side of the exducer blade is circumferentially close to the inducer blade. The fundamental reason for the performance variation in the inducer and the exducer lies in the inducer pressure change in the blade trailing edge that is determined by the Kutta condition. Additionally, the correlation between the tandem impeller slip effect and the discharge flow quality should be emphasized in the inducer/exducer gap jet analysis, in which the jet injection angle and the Coanda effect of the exducer suction surface critically affect the discharge flow characteristics.

8. Numerical Investigation of a Centrifugal Compressor with a Pre-Compression Wedge Diffuser under High Subsonic Conditions

WANG Yi, LI Qingkuo, BAI Huan, ZHOU Xueqi, LU Xin’gen

Corresponding author: LI Qingkuo

E-mail: liqingkuo@iet.cn

Journal of Thermal Science, 2020, 29(4): 945-954.

https://doi.org/10.1007/s11630-020-1332-0

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1332-0

Keywords: wedge diffuser, pre-compression, high Subsonic, centrifugal compressor

Abstract: As the total pressure ratio of centrifugal compressors increases, the diffuser inlet flow becomes highly subsonic or even supersonic, which causes additional shock loss. The shock loss leads the stage performance to drop greatly. Pre-compression is an efficient method for reducing shock loss and improving the stage performance. To study the effect of wedge diffusers with pre-compression blades on centrifugal compressor performance, wedge diffusers with various pre-compression angles, divergence angles and numbers of blades were designed and investigated via a numerical method. As a result, it is found that the compressor stage achieves high peak efficiency when the pre-compression angle ranges from 2.5° to 5.5° and when the divergence angle ranges from 7° to 9°. As the number of blades increases, the total pressure ratio and adiabatic efficiency of the compressor stage increase slightly, whereas the surge margin of the stage decreases.

9. Investigation of the Conjugate Heat Transfer and Flow Field for a Flat Plate with Combined Film and Impingement Cooling

FU Jinglun, CAO Ying, ZHANG Chao, ZHU Junqiang

Corresponding author: FU Jinglun; ZHANG Chao

E-mail: fujl@iet.cn; czhangxj@163.com

Journal of Thermal Science, 2020, 29(4): 955-971.

https://doi.org/10.1007/s11630-020-1233-2

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1233-2

Keywords: conjugate heat transfer, combined film and impingement cooling, overall cooling effectiveness, Biot number, blowing ratio

Abstract: Film cooling combined with internal impingement cooling is one of the most effective technologies to protect the gas turbine vanes and blades from the hot gas. In this study, conjugate heat transfer CFD study was undertaken for a flat plate with combined film cooling and impingement cooling. An experiment on conjugate heat transfer of a flat plate with combined film and impingement cooling was performed to validate the code. Then the effects of several parameters including Biot number, blowing ratio, film hole shape and impingement hole diameter on the overall cooling effectiveness were numerically studied. The results show that for a specific combined cooling scheme and a given blowing ratio, the coolant potential can be reasonably allocated to the internal and the external cooling to achieve the overall cooling effectiveness. As the blowing ratio increases, the overall cooling effectiveness trends to reach a maximum value. For different film hole geometrical, the maximum values of the overall cooling effectiveness at high blowing ratio approximate to the same value. At a given mass flow rate of coolant, the increase of the impingement hole diameter leads to the reduction of the overall cooling effectiveness.

10. Numerical Research on the Influence of Deborah Number on Flow and Heat Transfer of Maxwell Fluid in a Tube with Laminar Pulsating Flow

WANG Zhipeng, CHENG Shuhao, ZHUO Yuqun

Corresponding author: WANG Zhipeng; ZHUO Yuqun

E-mail: wzp13@mails.tsinghua.edu.cn; zhuoyq@mail.tsinghua.edu.cn

Journal of Thermal Science, 2020, 29(4): 972-981.

https://doi.org/10.1007/s11630-019-1157-x

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1157-x

Keywords: Maxwell fluid, pulsating flow, Hagen-Poiseuille law, Deborah number, start-up flow

Abstract: The flow and heat transfer characteristics of Maxwell fluid in a pipe under pulsating pressure gradient were studied. The governing equations were made dimensionless. The Rubin boundary condition was adopted. The flow field was solved theoretically and the temperature field was obtained using finite volume method. A general model suitable for various fluctuating characteristics and physical parameters was established. The Deborah number (De) was used to characterize the fluidity of the fluid. The influence of De on flow and temperature fields was evaluated. The Nusselt number and start-up process of Maxwell fluid were studied. Results showed that the influence of De on flow field was greater than that on temperature field. The effect of De on Nusselt number was irregular and related to the oscillation parameters. The over-shooting amplitude and oscillation time of axis center velocity in start-up flow grow larger with De.

11. Heat Transfer Performance of Microgroove Back Plate Heat Pipes with Working Fluid and Heating Power

WU Yanpeng, JIA Jie, TIAN Dongmin, CHUAH Yew Khoy

Corresponding author: WU Yanpeng;

E-mail: wuyanpeng@126.com

Journal of Thermal Science, 2020, 29(4): 982-991.

https://doi.org/10.1007/s11630-020-1336-9

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1336-9

Keywords: microgroove back plate heat pipes, working fluids, filling ratio, heat power

Abstract: Micro heat pipes (MHP) cooling is one of the most efficient solutions to radiate heat for high heat flux electronic components in data centers. It is necessary to improve heat transfer performance of microgroove back plate heat pipes. This paper discusses about influence on thermal resistance through experiments and numerical simulation with different working fluids, filling ratio and heat power. Thermal resistance of the CO2 filled heat pipe is 14.8% lower than the acetone filled heat pipe. In the meantime, at the best filling ratio of 40%, the CO2 filled heat pipe has the optimal heat transfer behavior with the smallest thermal resistance of 0.123 K/W. The thermal resistance continues to decline but the magnitude of decreases is going to be minor. In addition, this paper illustrates methods about how to enhance heat pipe performance from working fluids, filling ratio and heat power, which provides a theoretical basis for practical applications.

12. Thermal Analysis and Validation of GF-4 Remote Sensing Camera

LI Shiqi, WANG Yue, ZHANG Heng, YU Feng

Corresponding author: ZHANG Heng;

E-mail: zh20061100068@163.com

Journal of Thermal Science, 2020, 29(4): 992-1000.

https://doi.org/10.1007/s11630-020-1230-5

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1230-5

Keywords: thermal control system, geostationary orbit, thermal design, optical remote sensor

Abstract: The Chinese GF-4 satellite remote sensor is the highest spatial resolution among the civil satellite on the geosynchronous orbit, which carries on a camera with spatial resolution of 50 meter in the bands of visible and near infrared red and 400 meter in middle infrared red band. The thermal design of the spacecraft was challenging because the high resolution and the sensitivity requirement to achieve the desired scientific objectives. This paper presents the thermal analysis and test of the GF-4 in GEO orbit. The major findings of the analyses are the following. The GF-4 experiences complex, alternating external heat flux and faces direct sunlight in most of the orbital period. By applying a finite element model, the predicted temperature variation of the components remains in the desired temperature regime even in the extreme conditions. Comparing the thermal analysis results, the difference between the predicted and measured temperatures was less than 3°C for most of the components. The thermal control system functioned properly and the thermal model simulated the actual thermal design of GF-4. This thermal design method realizes the high efficiency and precision thermal control of the first high resolution geostationary orbit camera in China, which can provide reference for the high precision and stability thermal control of large aperture optical camera.

13. Experimental Study on Thermal Management of Cylindrical Li-ion Battery with Flexible Microchannel Plates

WEI Liting, JIA Li, AN Zhoujian, DANG Chao

Corresponding author: JIA Li

E-mail: ljia@bjtu.edu.cn

Journal of Thermal Science, 2020, 29(4): 1001-1009.

https://doi.org/10.1007/s11630-020-1331-1

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1331-1

Keywords: thermal management, Li-ion battery, flexible microchannels, contact area

Abstract: A novel thermal management system of cylindrical Li-ion battery with the liquid cooling in flexible microchannel plate was established in the study. The experiments were conducted with R141b in flexible microchannel plates. The cooling system with the flexible aluminum microchannels can effectively transfer heat from battery to the cooling refrigerant R141b based on flow boiling. A battery module with five cells along flow channel was chosen to study the effects of contact surface area and mass flux on the thermal performance and electrochemical characteristics in the experiments. Three types of structure with different contact areas were studied and their performances were compared with the experiments without cooling structures. The experiments were carried out at the same discharge rate with the inlet mass flow rates of 0–10 kg/h. For the inlet mass flow rate of 5.98 kg/h, the surface temperature and temperature uniformity of battery were the best, and the output voltage and capacity of batteries were higher than those under other mass flow rates. With given inlet mass flow rates, the five series cells exhibited different electrochemical performances, including output voltage and discharge capacity, due to the different refrigerant flow states in the microchannels. Finally, an optimal design was presented with thermal performances, macroscopic electrochemical characteristics, inlet mass flow rates and cooling performance taken into consideration.

14. Heat Transfer Enhancement of an Automobile Engine Radiator using ZnO Water Base Nanofluids

Muhammad QASIM, Muhammad SAJID KAMRAN, Muhammad AMMAR, Muhammad ALI JAMAL, Muhammad YASAR JAVAID 

Corresponding author: Muhammad AMMAR

E-mail: mammar@gcuf.edu.pk

Journal of Thermal Science, 2020, 29(4): 1010-1024

https://doi.org/10.1007/s11630-020-1263-9

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1263-9

Keywords: ZnO, nanoparticles, heat transfer enhancement, thermal efficiency, automobile radiator

Abstract: In this research paper, the forced convective heat transfer enhancement of a Suzuki Mehran (VXR) 2016 radiator (heat exchanger) along with pressure drop and friction factor by utilizing Zinc oxide (ZnO) water based nanofluids has been experimentally studied. Three types of nanofluids with different volumetric concentrations of ZnO nanoparticles (0–0.3%) were employed in order to understand its effect on heat transfer enhancement. The experimental setup was completely designed as closely as possible to the car cooling system. The experimentation has been done under laminar flow conditions (186≤Re≤1127) at different fluid volume flow rates (2–12 L/min) and constant fluid inlet temperature (70°C) to the automobile radiator. A maximum enhancement in heat transfer rate, overall heat transfer coefficient and Nusselt number was obtained up to 41%, 50% and 31% by using nanofluid with 0.2% volumetric concentration of nanoparticles respectively. On the other hand, the mean enhancement in pressure drop and friction factor was obtained up to 47% and 46% by using nanofluid with the same volumetric concentration of nanoparticles i.e. 0.2% respectively. The experimental results also revealed that the heat transfer rate, overall heat transfer coefficient and Nusselt number of nanofluids increases by increasing the volume flow rates and volumetric concentration of nanoparticles. However, these thermal performance parameters of nanofluids started to decline when the volumetric concentration of nanoparticles was increased from 0.2% to 0.3%. Furthermore, pressure drop and friction factor of nanofluids increase by increasing the volumetric concentration of nanoparticles, while pressure drop increases and friction factor decreases by increasing the volume flow rate of nanofluids respectively. At the end, the thermal efficiency of automobile radiator with high cooling rates was obtained by using nanofluid with 0.2% volumetric concentration of nanoparticles.

15. Modeling and Energy Efficiency Analysis of Thermal Power Plant with High Temperature Thermal Energy        Storage (HTTES)

ZHANG Hongwei, LIANG Wenbin, LIU Junqing, WANG Jie

Corresponding author: ZHANG Hongwei

E-mail: hongwei19851215@126.com

Journal of Thermal Science, 2020, 29(4): 1025-1035.

https://doi.org/10.1007/s11630-020-1310-6

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1310-6

Keywords: thermal power plant, peak shaving, high temperature thermal energy storage, wind power accumulation

Abstract: This paper presents the recent research on the study of the strategies for the flexible operation of the thermal power plant to meet the requirement of load balance. The study aimed to investigate the feasibility of bringing the High Temperature Thermal Energy Storage (HTTES) to the thermal power plant steam-water cycle, to identify the suitable HTTES in the cold (hot) section of the reheating pipeline and to test the efficiency of the HTTES integration to increase the flexibility of peak shaving and energy efficiency via thermal power plant with HTTTES modelling and simulation. Thermoflex was adopted to perform the simulation and a 300 MW subcritical coal-fired power plant model was implemented onto the software platform. The simulation results show that it is feasible to extract steam from the steam turbine to charge the HTTES, and to discharge the stored thermal energy back to the power generation process, and to analyse the improved capability of the plant flexible operation with HTTES. Then the study was extended to analyse the effect of thermal energy temperature, the opening of the regulating valve, and the pipeline pressure loss aspects on thermal efficiency of the whole plant. The study is beneficial to achieve more economic operation of the thermal power plant with HTTES integration. It is concluded that the introduction of the HTTES can improve the consumption of wind power, and these ideas and methods for solving the energy consumption of the renewable energy and reducing the peak energy consumption are provided.

16. Performance Analysis and Evaluation of a Supercritical CO2 Rankine Cycle Coupled with an Absorption Refrigeration Cycle

CHEN Yi, XU Dongjie, CHEN Zheng, GAO Xiang, REN Fukang, HAN Wei

Corresponding author: CHEN Yi; CHEN Zheng

E-mail: yichen@eppei.com; zchen@eppei.com

Journal of Thermal Science, 2020, 29(4): 1036-1052.

https://doi.org/10.1007/s11630-020-1166-9

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1166-9

Keywords: supercritical CO2 cycle, absorption refrigeration cycle, sensible heat source, solar energy, thermodynamic analysis

Abstract: The utilization of sensible waste heat such as flue gas and industrial surplus heat is essential for energy saving. Supercritical CO2 power generation cycle is a promising way to be used in this field. In this paper, a new supercritical CO2 Rankine cycle coupled with an absorption refrigeration cycle is proposed, which consists of a reheating supercritical CO2 cycle, a mixed-effect LiBr-H2O absorption refrigeration cycle and solar subsystem including evacuated-tube collector and a hot water storage tank. The system has four variants according to the presence or absence of solar subsystem and net cooling energy output. The thermodynamic model of the proposed system was established and its performance was evaluated. The proposed system is able to realize cascade utilization of flue gas waste heat and efficient conversion of solar energy. It has much higher thermodynamic efficiency than the reference system (i.e., the conventional supercritical CO2 Brayton cycle). Taking combined power and cooling system driven by flue gas waste heat and solar energy as an example, its thermal efficiency and exergy efficiency are 20.37% and 54.18% respectively, compared with the 14.74% and 35.96% of the reference system. Energy Utilization Diagrams (EUD) are implemented to investigate the irreversible losses and variation of the exergy destruction in the energy conversion process. Parametric analysis in two key parameters is conducted to provide guidance for the system optimal design.

17. Equivalent Cycle and Optimization of Auto-Cascade Absorption Refrigeration Systems

HE Yijian, CHEN Guangming

Corresponding author: CHEN Guangming

E-mail: gmchen@zju.edu.cn

Journal of Thermal Science, 2020, 29(4): 1053-1062.

https://doi.org/10.1007/s11630-020-1333-z

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1333-z

Keywords: auto-cascade absorption refrigeration, equivalent cycle, thermodynamic perfect degree, entropy generation, optimizing

Abstract: Auto-cascade absorption refrigeration (ACAR) systems are a class of new cycles that can achieve low refrigeration temperatures by utilizing low-quality thermal energy. In this study, the equivalent thermodynamic processes of a reversible ACAR system are established, and illustrated in a T-s diagram. The formula of the coefficient of performance for the reversible ACAR system is derived from the first and second thermodynamic laws. And then, the equivalent cycle of an irreversible ACAR system is established. The irreversible ACAR system is optimized by minimizing entropy generation of the thermodynamic processes. As a result, the optimum distribution ratio of heat fluxes at cascade process, which is defined as a ratio of heat fluxes between a condensing reservoir and cascade reservoir, and the optimum cascade temperature are obtained. Finally, its coefficient of performance and thermodynamic perfect degree are determined with minimum entropy generation.

18. Operation Optimization of Liquid Cooling Systems in Data Centers by the Heat Current Method and Artificial Neural Network

SHAO Wei, CHEN Qun, HE Kelun, ZHANG Mengqi

Corresponding author: CHEN Qun

E-mail: chenqun@tsinghua.edu.cn

Journal of Thermal Science, 2020, 29(4): 1063-1075.

https://doi.org/10.1007/s11630-020-1283-5

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1283-5

Keywords: liquid cooling system, energy conservation, heat current method, global heat transfer constraints, artificial neural network

Abstract: Liquid cooling systems in data centers have been attracting more attentions due to its better cooling capability and less energy consumption. In order to propose an effective optimization method for the operation of indirect liquid cooling systems, this paper first constructs an experiment platform and applies the heat current method to build the global heat transfer constraints of the whole system. Particularly, the thermal conductance of each heat exchanger under different working conditions is predicted by the Artificial Neural Networks (ANN) trained by the historical data. On this basis, combining the heat transfer and fluid flow constraints together with the Lagrange multiplier method builds the optimization model with the objective of minimum pumping power consumption (PPC), solving which by the solution strategy designed obtains the optimal frequencies of the variable frequency pumps (VFPs). Operating with the optimal and other feasible operating conditions validates the optimization model. Meanwhile, the experiments with variable heat loads and flow resistances provide some guidelines for the optimal system operation. For instance, to address heat load increase of a branch, it needs to increase the frequencies of the VFPs, not only the corresponding hot loop but also the whole cold loop.

19. Molecular Dynamics Simulations of the Effects of Surface Sinusoidal Nanostructures on Nanoscale Liquid Film Phase-Change

CAO Qun, CUI Zheng

Corresponding author: CUI Zheng

E-mail: zhengc@sdu.edu.cn

Journal of Thermal Science, 2020, 29(4): 1076-1084.

https://doi.org/10.1007/s11630-019-1152-2

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1152-2

Keywords: molecular dynamics simulation, sinusoidal surface, phase-change, interfacial thermal resistance, nanoscale

Abstract: Nanostructures on heat transfer surfaces can enhance micro/nanoscale phase-change heat transfer processes. To understand the enhancement mechanisms provided by nanostructures, evaporation processes of nanoscale liquid films on periodic sinusoidal-shaped surfaces were investigated via molecular dynamics simulations. By changing the amplitudes (A) and periods (T) of the curves describing the sinusoidal shapes, which possess shapes similar to f(x)=h0+Asin(2πx/T), sinusoidal surfaces of different sizes were constructed. An unevaporated region always existed on the copper plate for all surfaces during phase-change processes. Moreover, we calculated the interfacial thermal resistances and the mismatches between the vibrational density of states of the solid and liquid for different surfaces. The results show that the argon temperature changes and evaporation rates during the phase-change process on sinusoidal surfaces are higher than those on flat surfaces, and these results increase with the increase in amplitudes and the decrease in periods within certain limits mainly because of the thermal resistance decrease at the solid-liquid interface. Furthermore, the corresponding mismatches between the vibrational density of states of the solid and liquid also decrease, which indicates that the existence of sinusoidal nanostructures enhances the heat transfer of the phase-change process.

20. Experimental Characterization of the Supersonic Transitional Wake Downstream of a Single Roughness Element

BOTTINI Henny, SARACOGLU Bayindir H., PANIAGUA Guillermo

Corresponding author: BOTTINI Henny

E-mail: henny.bottini@email.it

Journal of Thermal Science, 2020, 29(4): 1085-1093.

https://doi.org/10.1007/s11630-019-1198-1

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1198-1

Keywords: supersonic boundary layer, roughness wake, steady measurements, unsteady measurements, heat transfer

Abstract: An experimental campaign was carried out to investigate the characteristics of the transitional supersonic wake downstream of a single roughness element. Two Mach numbers were tested, 1.6 and 2.3, and two roughness heights, 0.1 mm and 1 mm. Unsteady and steady wall temperature measurements were taken along and across the roughness wake. The spatial trends of adiabatic wall temperature and heat flux, and the spectral time evolution of temperature were documented in this paper. The initial wall temperature was varied during the temperature measurements, and the resulting steady and unsteady effects on the roughness wake were investi- gated. The streamwise trends of heat-?ux and adiabatic-wall temperature con?rmed the transitional nature of the roughness wake. Spectral analysis showed that roughness height and initial wall temperature had the same type of effect on the wake wall-temperature ?uctuations. The effect of roughness height was more sensible at Mach 2.3, and that of the initial wall temperature was more evident with the smallest roughness also tested at Mach 2.3.