CONTENTS-Volume 30, Issue 2, March-April 2021
Springer Link: https://link.springer.com/journal/11630/volumes-and-issues/30-2
1. Forced Convection Heat Transfer in Porous Structure: Effect of Morphology on Pressure Drop and Heat Transfer Coefficient
ZHAO Jiafei, SUN Mingrui, ZHANG Lunxiang, HU Chengzhi, TANG Dawei, YANG Lei, SONG Yongchen
Corresponding author: YANG Lei
E-mail: leiyang@dlut.edu.cn
Journal of Thermal Science, 2021, 30(2): 363-393.
https://doi.org/10.1007/s11630-021-1403-x
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1403-x
Abstract: A light-weight structure with sufficient mechanical strength and heat transfer performance is increasingly required for some thermal management issues. The porous structure with the skeleton supporting the ambient stress and the pores holding the flowing fluid is considered very promising, attracting significant scientific and industrial interest over the past few decades. However, due to complicated morphology of the porous matrices and thereby various performance of the pressure drop and heat transfer coefficients (HTC), the comprehensive comparison and evaluation between different structures are largely unclear. In this work, recent researches on the efforts of forced convection heat transfer in light-weight porous structure are reviewed; special interest is placed in the open-cell foam, lattice-frame, structured packed bed, and wire-woven structures. Their experimental apparatus, morphological of the porous structures, effect of morphology on pressure drop and HTC, and further applications are discussed. The new method which measure morphology accurately should be paid more attention to develop more accuracy correlation. Also, the most research focused on low Reynolds number and existing structure, while very few researchers investigated the property of forced convection heat transfer in high velocity region and developed new porous structure.
Keywords: forced convection, heat transfer, heat transfer coefficient, pressure drop, morphological characteristics, porous structure
2. A Review on Thermal Design of Liquid Droplet Radiator System
CHONG Daotong, ZHU Maoguo, ZHAO Quanbin, CHEN Weixiong, YAN Junjie
Corresponding author: YAN Junjie
E-mail: yanjj@mail.xjtu.edu.cn
Journal of Thermal Science, 2021, 30(2): 394-417.
https://doi.org/10.1007/s11630-021-1419-2
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1419-2
Abstract: Liquid Droplet Radiator (LDR) system is regarded as a quite promising waste heat rejection system for aerospace engineering. A comprehensive review on the state-of-the-art of LDR system was carried out. The thermal design considerations of crucial components such as working fluid, droplet generator and collector, intermediate heat exchanger, circulating pump and return pipe were reviewed. The state-of-the-art of existing mathematical models of radiation and evaporation characteristics of droplet layer from literatures were summarized. Furthermore, thermal designs of three LDR systems were completed. The weight and required planform area between the rectangular and triangular LDR systems were respectively compared and the evaporation models for calculating the mass loss were evaluated. Based on the review, some prospective studies of LDR system were put forward in this paper.
Keywords: Liquid Droplet Radiator (LDR) system, thermal design considerations, radiative heat transfer, evaporation loss
3. A Review on Thermophysical Properties and Nusselt Number Behavior of Al2O3 Nanofluids in Heat Exchangers
ISSA Roy Jean
Corresponding author: ISSA Roy Jean
E-mail: rissa@wtamu.edu
Journal of Thermal Science, 2021, 30(2): 418-431.
https://doi.org/10.1007/s11630-021-1266-1
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1266-1
Abstract: During the last several years, the increase in cooling power requirements for heat exchangers have led to an escalation in heat transfer studies being performed on the use of nanofluids as heat transfer fluids. However, limited effort has been attempted to relate and interpret these findings or the anomalies associated with them. The paper compiles test data from several studies conducted on different types of heat exchangers. In this review, a concentrated effort is spent to clarify the ambiguities regarding the effect of nanoparticle size on the nanofluid thermal conductivity and Nusselt number. Results show that the nanofluid thermal conductivity is not influenced by the nanoparticle size, but by the clustering of the particles themselves. The less compact the structure of the nanoparticle clustering is, the greater the enhancement in the nanofluid thermal conductivity is. Data were also compiled to interpret the relation between the nanofluid flow pattern, nanoparticles volume fraction in the base fluid, and the convective heat transfer. The results from the majority of the heat exchanger studies show an increase in the heat transfer coefficient with the increase in nanoparticle volume fraction. However, studies conducted on plate heat exchanges display some inconsistencies. In the majority of the heat exchanger studies with the exception of few, the decrease in the nanoparticle size is shown to result in an enhancement of the bulk fluid Nusselt number. Compiled test data also reveal that the effectiveness of the alumina nanoparticles is dependent on the flow pattern. The increase in the nanoparticles concentration is shown to result in an increase in the nanofluid heat transfer enhancement as the fluid is transitioning from laminar to turbulent flow. In general, the smaller the nanoparticle size is, the greater the enhancement in the fluid Nusselt number is.
Keywords: heat exchanger, Nusselt number, alumina, nanofluid
4. Experimental Study on Condensation Heat Transfer Characteristics inside an Inclined Wave-Finned Flat Tube of Direct Air-Cooling System
WANG Haitao, TAO Tao, MEI Xuesong, WANG Haijun, GU Hongfang
Corresponding author: WANG Haitao; TAO Tao
E-mail: wanghaitao@mail.xjtu.edu.cn; taotao@mail.xjtu.edu.cn
Journal of Thermal Science, 2021, 30(2): 432-440.
https://doi.org/10.1007/s11630-020-1353-8
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1353-8
Abstract: In this paper, the condensation heat transfer characteristics of parallel flow and counter flow inside an inclined wave-finned flat tube is investigated experimentally. The condensation heat transfer coef?cients are analyzed based on the experimental results. Results of experiments show that condensation heat transfer coefficient decreases as the temperature difference ?t=ts?tw increases and mass flow rate decreases. The parallel flow has a similar development with the counter flow, and the condensation heat transfer coefficient of counter flow is less than that of parallel flow under the same air cooling conditions. In addition, condensation heat transfer coefficient correlations are also obtained under experimental ranges. The calculations agree well with the measured data and the agreement is seen to be within ±4% for the parallel flow and ±5% for the counter flow.
Keywords: condensation heat transfer, wave-finned flat tube, modified model, parallel flow, counter flow
5. Comparison of Heat Transfer in Gravity-Driven Granular Flow near Different Surfaces
GUO Zhigang, TIAN Xing, YANG Jian, SHI Tuo, WANG Qiuwang
Corresponding author: WANG Qiuwang
E-mail: wangqw@mail.xjtu.edu.cn
Journal of Thermal Science, 2021, 30(2): 441-450.
https://doi.org/10.1007/s11630-020-1357-4
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1357-4
Abstract: Heat transfer in gravity-driven granular flow has been encountered in many industrial processes, such as waste heat recovery and concentrated solar power. To understand more about Moving Bed Heat Exchanger (MBHE) applied in this field, numerical simulation was carried out for the characteristics of granular flow near different surfaces through discrete element method (DEM). In this paper, both the performances of particles motion and heat transfer were investigated. It’s found that, even though the macroscopic granular flow is similar to fluid, there is still obvious discrete nature partly. The fluctuations of parameters in granular flow are inevitable which is more obvious in the circular tube cases. A special phenomenon, where competition motion is found, is resulted from discrete nature of particles. In terms of heat transfer, overall heat transfer coefficients for plate are higher than that of tube owing to better contact between particles and wall. However, due to competition motion, particles in high temperature tend to contact the tube, which is beneficial to heat transfer in some local zones. The heat transfer characteristics above will also affect the temperature distribution near the outlet of different geometries.
Keywords: gravity-driven granular flow, discrete element method (DEM), heat transfer, numerical simulation
6. A New Nodes-Based Model for Optimization of Heat Exchanger Network Synthesis
XU Yue, HERI Ambonisye Kayange, XIAO Yuan, CUI Guomin
Corresponding author: CUI Guomin
E-mail: cgm@usst.edu.cn
Journal of Thermal Science, 2021, 30(2): 451-464.
https://doi.org/10.1007/s11630-020-1313-3
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1313-3
Abstract: Searching the global optimal value in heat exchanger network synthesis (HENS) becomes more difficult along with the increasing scale of cases. In structural optimization model, such as stage-wise superstructure, solution domain can be enlarged by adding the stages of network, which would involve multiple integer and continuous variables in optimization and result in a decreasing computational efficiency. Thus, a new nodes-based model with stream splits is proposed, which can promote the quality of result and decrease time consumption at the same time. The characteristic of this model is that it changes the matching mode of heat exchangers by setting the number of nodes on streams to quantify the positions of heat exchangers. The proposed nodes-based model has more flexibility in generating and eliminating the heat exchangers and strong ductility in exploring the solution domain. The random walk with compulsive evolution is modified for enhancing its searching ability and applying modified random walk algorithm with compulsive evolution (RWCE) into the new proposed model. The obtained results of Case 1, Case 2 and Case 3 are superior to those reported in the literature, which decreases 106 USD?a–1, 1253 USD?a–1, 23 444 USD?a–1, respectively, verifying the robust effectiveness of this new model in solving HENS problem.
Keywords: HENS, nodes-based model, stream splits, random walk with compulsive evolution, efficiency
7. Experimental Characterization and Model Verification of Thermal Conductivity from Mesoporous to Macroporous SiOC Ceramics
QIU Lin, DU Yanbo, BAI Yangyang, FENG Yanhui, ZHANG Xinxin, WU Jin, WANG Xiaotian, XU Caihong
Corresponding author: FENG Yanhui; WU Jin
E-mail: yhfeng@me.ustb.edu.cn; wujin8@mail.sysu.edu.cn
Journal of Thermal Science, 2021, 30(2): 465-476.
https://doi.org/10.1007/s11630-021-1422-7
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1422-7
Abstract: Based on the chemical cross-linking method, this paper uses polydimethylsiloxane with various viscosities of 10 cSt, 20 cSt, 50 cSt, and 100 cSt to synthesize mesoporous and macroporous SiOC ceramics. Their thermal conductivities are measured by using 3ω method with high accuracy. Three typical models for their thermal conductivities, i.e., series model (SM), maxwell-Eucken 1 model (ME1), and effective medium theory (EMT) model, are utilized to derive the empirical formula through the multi-parameter linear optimization algorithm, which agrees well with the experimental results. The effects of pore size and specific surface area on the overall thermal conductivity of the porous structure are explored. Interestingly, it is found that the thermal conductivities of both gas phase and solid phase inside the porous structure increase with the increasing pore size at the nanometer scale, but the overall thermal conductivity of the porous structure decreases with the increasing pore size. Scanning electron microscopy graphs corroborate that the extension of the heat transfer route and the barrier of more pores between the solid phases together cause the reduction of the gas-solid coupling thermal conductivity of SiOC ceramics with larger pore size. On the contrary, the miniaturization of individual particles through modulating the synthesis parameters can increase the number of small pores in the sample itself to meet the pseudo-lattice vibration conditions, which results in the increment of the gas-solid coupling thermal conductivity and the overall thermal conductivity of the porous structure. These findings would provide meaningful guidance for designing SiOC porous ceramic super-insulation materials with extremely low thermal conductivity.
Keywords: SiOC ceramics, macroporous media, 3ω method, thermal conductivity
8. Thermal Property Measurements of a Large Prismatic Lithium-ion Battery for Electric Vehicles
CHENG Ximing, TANG Yu, WANG Zhenpo
Corresponding author: CHENG Ximing; WANG Zhenpo
E-mail: cxm2004@bit.edu.cn; wangzhenpo@bit.edu.cn
Journal of Thermal Science, 2021, 30(2): 477-492.
https://doi.org/10.1007/s11630-021-1398-3
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1398-3
Abstract: Because of the high cost of measuring the specific heat capacity and the difficulty in measuring the thermal conductivity of prismatic lithium-ion batteries, two devices with a sandwiched core of the sample-electric heating film-sample were designed and developed to measure the thermal properties of the batteries based on Fourier’s thermal equation. Similar to electrical circuit modeling, two equivalent thermal circuits were constructed to model the heat loss of the self-made devices, one thermal-resistance steady circuit for the purpose of measuring the thermal conductivity, the other thermal-resistance-capacitance dynamic circuit for the purpose of measuring the specific heat capacity. Using the analytic method and recursive least squares, the lumped model parameters of these two thermal circuits were extracted to estimate the heat loss and correct the measured values of the self-made devices. Compared to the standard values of the reference samples of the glass and steel plates, the measured values were corrected to improve the measurement accuracies beyond 95% through steady thermal-circuit modeling. Compared to the measured value of the specific heat capacity of the battery sample at 50% state of charge using the calorimeter, the measured value using the self-made device was corrected in order to elevate the measurement accuracy by about 90% through dynamic thermal-circuit modeling. As verified through the experiments, it was reliable, convenient, and low cost for the proposed methodology to measure the thermal properties of prismatic lithium-ion batteries.
Keywords: lithium-ion battery, specific heat capacity, thermal conductivity, equivalent thermal circuit, measurement
9. Heat Transfer Characteristics outside the Condenser of a Rotating Heat Pipe Grinding Wheel with a Lateral Air Impinging Jet
CHEN Jiajia, ZHANG Liyong, FU Yucan, QIAN Ning, JIANG Huafei, YANG Lin
Corresponding authors: CHEN Jiajia; FU Yucan
E-mail: Jiajiachen@njfu.edu.cn; yucanfu@nuaa.edu.cn
Journal of Thermal Science, 2021, 30(2): 493-503.
https://doi.org/10.1007/s11630-021-1415-6
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1415-6
Abstract: This study numerically analyzed the heat transfer characteristics outside the condenser of a rotating heat pipe grinding wheel (RHP-GW). The goal of this investigation is to determine the optimal structure and parameters for the condenser section of RHP-GW. Different fin height (f=0–7 mm), rotational Reynolds number (Rer=1602–6408) and jet Reynolds number (Rej=42 379–108 302) were analyzed under input heat flux of 4000 W/m2. A fully developed flow was imposed at the outlet of the nozzles. Results showed that the optimal heat transfer rate was obtained for fin height of 5 mm, which improved the average Nusselt number by 84% compared to the structure without fins. A critical Rej for each Rer that the impinging jet can reach the condenser section was found. The critical Rej value increases with Rer, which is in the range from 42 379 to 61 215 and 61 215 to 80 050 for Rer=6408 and Rer=9610, respectively.
Keywords: rotating heat pipe grinding wheel, impinging jet, heat transfer, numerical analysis
10. Numerical Investigation of Boundary Grid Effect on Heat Transfer Computation of RP-3 at Supercritical Temperature of Helical Tube Wall
LIU Shaobei, BAO Zewei, HUANG Weixing, ZENG Tao, QIAO Min, MENG Jiancheng
Corresponding author: HUANG Weixing
E-mail: hwx@scu.edu.cn
Journal of Thermal Science, 2021, 30(2): 504-516.
https://doi.org/10.1007/s11630-021-1355-1
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1355-1
Abstract: To get reliable computational results, the RNG k-ε turbulence model with enhanced wall treatment was validated to solve the heat transfer of supercritical RP-3 in a helically coiled tube, and models of the thermo-physical properties of RP-3 were optimally chosen. Most significantly, the grid independence was validated by two-step procedure, and the effect of boundary grids of the supercritical-temperature wall on the computational accuracy was well studied. Through adjusting boundary-layer girds’ size, four regions (increased, pseudo-convergence, decreased and convergence) of the outlet temperature Tout were obtained and analyzed. The results showed that the maximum computation errors of Tout and the pressure differential between the inlet and outlet ΔP reached 20.65% and 98.15%, respectively, indicating that boundary grids have a significant influence on computation of flow and heat transfer. Based on this, a dimensionless distance from the wall-adjacent cell to the wall (Prw denotes Wall Prandtl number) was recommended as a convergence point. The variation laws of viscous length scale y* were discussed under different structural parameters, operation parameters, and helical lengths. An explicit model of y* was proposed to calculate the height (y) of the first boundary layer grids and refine boundary grids efficiently. A modified model for coefficient of friction factor Cf was proposed based on Rogers’s, and Nusselt number Nu was proposed based on an analogy of momentum and heat transfer. The above models about y*, Cf and Nu could apply to both the entrance region and the whole tube length, and showed good performance when Reynolds number was extended to above 70 000, or whenever the outlet temperature is below or above the critical point.
Keywords: supercritical heat transfer, helically coiled tube, aviation kerosene, dimensionless wall distance, viscous length scale
11. Effect of Inlet and Outlet Manifolds on Regenerative Cooling in LOX/Methane Thrust Chambers
ZHANG Meng, SUN Bing, SONG Jiawen
Corresponding author: SUN Bing
E-mail: sunbing@buaa.edu.cn
Journal of Thermal Science, 2021, 30(2): 517-529.
https://doi.org/10.1007/s11630-020-1312-4
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1312-4
Abstract: Regenerative cooling is considered one of the most effective cooling methods used in liquid rocket engines and has been widely studied in recent years. But the effect of the non-uniform flow in cooling channels caused by inlet and outlet manifolds did not attract much attention. In this paper, we carried out the coupled flow and heat transfer of combustion and regenerative cooling in a LOX/Methane (LOX means liquid oxygen) engine and compared the results with and without manifolds. Then, three different configurations of the inlet and outlet manifolds were also discussed. The results show that the parameters averaged in the circumferential direction are less affected by the manifolds. However, the existence of the manifolds will make the distribution of mass flow rate as well as wall temperature non-uniform along the circumferential direction. In addition, when the angles between inlet and outlet are 0o, 90o and 180o, the maximum temperature difference along the circumference of throat increases by 90.1%, 151.2% and 229.5%, respectively, compared with that without manifolds. This indicates that the larger the angle between inlet and outlet, the greater the non-uniformity of mass flow rate and wall temperature along the circumferential direction. As a result, extra thermal stress will be generated which could cause some negative effects on the rocket engines.
Keywords: regenerative cooling, conjugate heat transfer, inlet and outlet manifolds, non-uniform flow
12. Thermal Contact Resistance between Aero Engine Compressor Blade and Flexible Fixture
DAI Shijie, WANG Dong, ZHANG Huibo, LI Shibo, WANG Zhiping
Corresponding author: ZHANG Huibo
E-mail: zhanghb@hebut.edu.cn
Journal of Thermal Science, 2021, 30(2): 530-539.
https://doi.org/10.1007/s11630-020-1316-0
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1316-0
Abstract: In the process of two-pass micro plasma arc welding of titanium alloy sheet, based on the thermal contact resistance theory, a three-dimensional transient heat transfer finite element model of contact heat transfer between titanium alloy sheet and flexible fixture was established. The effects of contact upper surface temperature, micro-contact thermal resistance, micro-gap thermal resistance, DC and pulse welding on thermal contact resistance were investigated, and the simulation and experimental results were compared. The results show that the thermal contact resistance increases as the temperature increases when the temperature of the contact upper surface (titanium alloy sheet) is in the range of 290?350 K. The effect of micro-contact thermal resistance on the thermal contact resistance is 26.1%?46.3% larger than the micro-gap thermal resistance. The thermal contact resistance of pulse welding is 3.1%?3.5% larger than DC welding. The error of simulation and experimental results of weld pool depth is 8.6%, which verifies the reliability of the model.
Keywords: titanium alloy, micro plasma arc welding, thermal contact resistance, micro-contact thermal resistance, micro-gap thermal resistance, finite element model
13. Experimental Analysis and Evaluation of Thermostat Effects on Engine Cooling System
GHASEMI ZAVARAGH Hadi, KALELI Alir?za, SOLMU? ?smail, AFSHARI Faraz
Corresponding author: GHASEMI ZAVARAGH Hadi
E-mail: haghasemi@tvu.ac.ir
Journal of Thermal Science, 2021, 30(2): 540-550.
https://doi.org/10.1007/s11630-020-1264-8
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1264-8
Abstract: Thermostat as a part of engine cooling system has a significant role in the shortening warm-up time and regulating the engine in proper temperature to approach optimal performance. Whereas, there is not adequate research on this part of the cooling system and its responsibility. Considering this gap and also being used in large scale, this study is intended to evaluate performance and reflex of the wax type thermostat in different engine working conditions. In this regard, performance of engine cooling system was investigated in various engine speeds and loads to reveal positive and negative influences of thermostat on engine cooling efficiency and engine performance. According to observed results, warm-up period and fuel consumption decrease by using a thermostat. On the other hand, however, the temperature oscillation of coolant fluid passing through engine increases sharply, which causes a disruption in the regulating engine temperature and also a possibility of the fluid boiling rises in some regions of the engine that increases the risk of damage in the engine parts. Engine temperature, fuel consumption, warm-up duration and emissions were provided and compared in two operation modes, with and without thermostat.
Keywords: engine cooling system, wax type thermostat, warm-up, radiator, emissions, fuel consumption
14. Moisture and Temperature Response of Structural and Lithology based Thermophysical and Energy Saving Traits of Limestone using Experimental and Least-Square Fitting Methods
Farah Anjum, Muhammad Yasin Naz, Abdul Ghaffar, Shazia Shukrullah, Nasser M AbdEl-Salam, Khalid Aref Ibrahim
Journal of Thermal Science, 2021, 30(2): 551-561.
https://doi.org/10.1007/s11630-021-1416-5
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1416-5
Abstract: Thermophysical analysis of the crustal rocks is important for heat transfer determination and insulation purposes to save energy in buildings. In the presented work, thermophysical properties of four limestones were investigated in dry and moist state under ambient conditions by using a transient plane source method. A thermal constant analyzer was used to raise the sample temperature and to measure the thermal properties in the temperature range of 300 K to 433 K. Thermal conductivity and diffusivity were measured by developing a linear relationship between temperature response of TPS (transient plane source) sensor and dimensionless time function through least-square fitting method. The experimental observations and predicted thermal conductivity of samples have shown that in-situ observations are important to determine the thermal properties accurately. The effect of temperature on thermal properties of limestone was defined by considering the chemical composition of the samples and associated heat transfer mechanism. Both thermal conductivity and diffusivity of limestone decreased while specific heat capacity increased with a rise in temperature. The overall findings indicate that the spinoff of this research is useful in studying the reliance of thermophysical properties of rocks on their structures and lithology.
Keywords: limestone, thermophysical properties, transient plane source (TPS), thermal conductivity
15. Numerical Investigation of the Transient Flow and Frequency Characteristic in a Centrifugal Pump with Splitter Blades
LI Guidong, ZHANG Jinfeng, MAO Jieyun, YUAN Shouqi, JIA Jing
Corresponding author: ZHANG Jinfeng
E-mail: zhangjinfeng@ujs.edu.cn
Journal of Thermal Science, 2021, 30(2): 562-573.
https://doi.org/10.1007/s11630-020-1391-2
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1391-2
Abstract: To analyze the internal flow characteristics of each subchannel in a low-specific-speed centrifugal pump with splitter blades, the time histories and frequency spectra of pressure fluctuations and the distributions of the corresponding flow states in one impeller channel were investigated through the numerical analysis. Performance experiments and particle image velocimetry (PIV) tests were carried out to verify the results of the numerical calculations. The results suggested that the simulation analysis agreed well with the test results. The time histories and frequency spectra of pressure fluctuations depending on its location (close to or away from the volute tongue) present different changes. The predominant frequency of each monitor point equals to five or ten times shaft frequency. The jet-wake flow pattern at each subchannel separated by splitter blade in one impeller channel is not circumferentially uniform. For the channel away from volute tongue, the magnitude of turbulence kinetic energy in pressure side subchannel is well larger than that in suction side subchannel. With the increase in flow rate, the region close to the elbow of the volute outlet emerges a large-scale vortex.
Keywords: centrifugal pump, splitter blades, frequency characteristics, transient analysis, turbulence kinetic energy
16. Experimental Investigation on an Absorption Heat Transformer for Production of Hot Water or Steam Generation
LIU Feng, JING Yang, LIU Taixiu, SUI Jun, XU Yujie
Corresponding author: SUI Jun
E-mail: suijun@iet.cn
Journal of Thermal Science, 2021, 30(2): 574-584.
https://doi.org/10.1007/s11630-020-1406-z
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1406-z
Abstract: The absorption heat transformer is widely used to utilize low-temperature waste heat in the field of distributed energy, industrial processing, and long-distance indoor heating, because it can upgrade energy level and deliver heat to heated medium. In this work, an experimental system of a vertical single-stage LiBr/H2O absorption heat transformer was established to study its performance in the case of producing high-temperature water or low-pressure steam generation under different heating water flow rates. The useful output heat, coefficient of performance, exergy coefficient of performance, and gross temperature lift of the single-stage heat transformer have all been tested. The results show that the absorber cannot directly generate low-pressure steam under the condition of counter-flow heat exchange but can obtain more useful output heat. The largest useful output heat is 20.3 kW, which is higher than that in the case of parallel-flow heat exchange. The generation of low-pressure steam has certain requirements on the mode of heat transfer. The largest internal gross temperature lift of 28.1°C corresponds to the smallest coefficient of performance of 0.22 when the heating water flow rate is 2.1 m3/h. The performance of the single-stage absorption heat transformer can be improved to some extent by increasing the heating water flow rate.
Keywords: vertical falling film absorber, counter flow and parallel flow, high-temperature water, low-pressure steam, exergy coefficient of performance
17. Study on the Control Strategy of Free Piston Expander-Linear Generator Used for Organic Rankine Cycle Waste Heat Recovery
HOU Xiaochen, ZHANG Hongguang, ZHAO Tenglong, SHI Xin, XU Yonghong, LI Jian, GE Zhong, ZHANG Jun, WU Yuting
Corresponding author: HOU Xiaochen
E-mail: houxiaochenlove@126.com
Journal of Thermal Science, 2021, 30(2): 585-597.
https://doi.org/10.1007/s11630-021-1221-1
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1221-1
Abstract: This study presents a free piston expander-linear generator (FPE-LG) for engine waste heat recovery. The control strategies based on displacement (control strategy A) and valve timings (control strategy B) are proposed. The operation and output characteristics with different control strategies are conducted. The results show that control strategy has significant effect on the FPE-LG performance. When FPE-LG operates with control strategy A, the operation frequency is determined by the intake pressure, advanced exhaust duration, fixed position point and external load resistance, whereas it is only related with the intake/exhaust time and advanced exhaust duration (ta) for control strategy B. The external load resistance has slight influence on the stroke length for these two control strategies. For control strategy A, when advanced exhaust duration is more than 40 ms, the stroke length rises with the intake pressure, whereas it first rises and then reduces when advanced exhaust duration is less than 40 ms. There exist the optimal external load resistance and advanced exhaust duration to achieve the maximum power output with control strategy A, whereas the average power output reduces with the increasing advanced exhaust duration when using control strategy B. Stable operation and high power output can be obtained by using different control strategies and adjusting relevant operation parameters.
Keywords: free piston expander-linear generator, advanced exhaust duration, control strategy, operation frequency, power output
18. Start-up Characteristics of Linear Compressors in a Refrigeration System
ZOU Huiming, LI Xuan, TANG Mingsheng, TIAN Changqing
Corresponding author: TANG Mingsheng
E-mail: tangmingsheng@mail.ipc.ac.cn
Journal of Thermal Science, 2021, 30(2): 598-609.
https://doi.org/10.1007/s11630-020-1325-z
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1325-z
Abstract: This work investigates the start-up characteristics of linear compressors in a refrigeration system through experiment and simulation. Experiments are carried out by a refrigeration test system with a linear compressor controlled by a LabVIEW platform. A simulation model that considers the nonlinear process of gas force is set up on the basis of Runge-Kutta method for linear compressors. Compared with the experimental results, the simulation errors are within 15%, including the unstable state. The influences of ambient temperature and power frequency on linear compressors are studied through experiments. Unstable phenomena exist at 25°C ambient temperature compared with the designed ambient temperature of 35°C. The unsteadiness mechanism is analyzed by simulation. Simulation analysis indicated that two sensitive stages of linear compressors, namely, starting to pump and touching top dead center, are unstable. Furthermore, properly increasing equivalent mass (approximately 3%) or spring stiffness during the design stage can be a practical method to improve the stability of linear compressors.
Keywords: linear compressor, start-up, dynamic characteristics, unsteadiness
19. Reduced Methane Combustion Mechanism and Verification, Validation, and Accreditation (VV&A) in CFD for NO Emission Prediction
SUN Jihao, ZHANG Zhihao, LIU Xiao, ZHENG Hongtao
Corresponding author: LIU Xiao
E-mail: liuxiao_heu@163.com
Journal of Thermal Science, 2021, 30(2): 610-623.
https://doi.org/10.1007/s11630-020-1321-3
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1321-3
Abstract: In order to obtain a reduced methane combustion mechanism for predicting combustion field and pollutants accurately in CFD simulations with a lower computational cost, a reduced mechanism with 22 species and 65 steps of reactions from GRI-Mech 3.0 was obtained by direct relation graph method and sensitivity analysis. The ideal reactor calculation and VV&A (Verification, Validation, and Accreditation) in CFD were carried out using the proposed mechanism. The results showed that the proposed mechanism agrees well with the detailed mechanism in a wide range of operating conditions; the temperature field and species can be predicted accurately in CFD simulations (RANS and LES models), and the NO prediction error of an industrial gas turbine combustor outlet is less than 2?10–6. The proposed mechanism has high engineering values.
Keywords: mechanism reduction, pollutant emissions, direct relation graph method, sensitivity analysis, numerical simulation
20. Group Contribution based Flammability Limit Estimation of Hydrocarbon- Inert Gas Mixture
TIAN Hua, HUO Xu, LIU Yuewei, CAI Jinwen, SUN Rui, SHU Gequn
Corresponding author: HUO Xu; SHU Gequn
E-mail: xuhuo@tju.edu.cn; sgq@tju.edu.cn
Journal of Thermal Science, 2021, 30(2): 624-635.
https://doi.org/10.1007/s11630-021-1399-2
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1399-2
Abstract: As group contribution method is easy to apply and has a wide application range, current study has developed this model to predict flammability limit of hydrocarbons mixed with inert gas using the Marrero/Gani group contribution method, which is significative to the safe application of hydrocarbons in the ORC system. The whole modeling process is divided into two parts: pure compound prediction and mixture prediction. The contribution factors of inert gases and dilute concentration were first introduced in the group contribution method. Moreover, the respective 95%-confidence interval of the mixture based on linear superposition method has been proposed in the developed group contribution model to improve the safety coefficient. For CO2 as inert gas, the average relative error and correlation coefficient are 5.34% and 0.88 for lower flammability limit while 6.99% and 0.95 for upper flammability limit. For N2 as inert gas, the average relative error and correlation coefficient are 7.47% and 0.84 for lower flammability limit while 6.68% and 0.97 for upper flammability limit. Most importantly, this group contribution method has extended the application range to make up the shortcomings of other flammability limit prediction methods aiming at hydrocarbon and inert gas mixtures and proposed the uncertainty analysis to provide reliable prediction range.
Keywords: group contribution, flammability limit, uncertainty analysis, hydrocarbon and inert gas mixture
21. Modeling De-NOx by Injection Ammonia in High Temperature Zone of Cement Precalciner
ZHANG Leyu, WEI Xiaolin, ZHANG Zhongxiao, LI Sen
Corresponding author: WEI xiaolin; ZHANG zhongxiao
E-mail: xlwei@imech.ac.cn; zhzhx222@163.com
Journal of Thermal Science, 2021, 30(2): 636-643.
https://doi.org/10.1007/s11630-020-1324-0
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1324-0
Abstract: The quantity of NOx emission from cement production is second only to thermal power generation and vehicle exhaust. In this paper, a phenomenon found by Taniguchi is used to achieve NOx reduction in the cement precalciner. Based on his results, it is proposed to reduce NOx that ammonia is injected in the high-temperature and lean-oxygen zone (HT-DeNOx) during pulverized coal combustion. For a large cement precalciner (3200 t/d), numerical simulation is used to evaluate the technology of HT-DeNOx combined with the traditional selective non-catalytic reduction (SNCR) method. The results indicate that NH3 and HCN in HT-DeNOx can reduce NO during the reaction process. With very little ammonia injection (normalized stoichiometric ratio NSR=0.1, the normalized stoichiometric ratio), the efficiency of NO reduction by HT-DeNOx is 27.72%. Combining SNCR (NSR=1.1) and HT-DeNOx (NSR=0.1), the reduction efficiency will be improved to 60.05%, compared with 50.83% efficiency when using only SNCR at NSR=1.2.
Keywords: cement precalciner, coal combustion, CaCO3 decomposition, high temperature zone, SNCR
22. Slagging Characteristics and Optimization of Operating Temperature on High-Alkali Coal Gasification
FAN Yanqi, ZHANG Haixia, ZHU Zhiping, LYU Qinggang
Corresponding author: ZHANG haixia
E-mail: zhanghaixia@iet.cn
Journal of Thermal Science, 2021, 30(2): 644-655.
https://doi.org/10.1007/s11630-021-1410-y
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1410-y
Abstract: In order to mitigate the slagging risks of high-alkali coal (HAC) gasification while optimizing the operating temperatures for practical application, the experimental and calculational works were performed on the horizontal tubular furnace system and the FactSage 7.2 software, respectively. The slagging tendencies of three HACs were anticipated by applying different indexes of ash chemistry characteristics prior to experiments, but the determined results were found inconsistent. The relationship between Na retained ratio (RNa) and the ash fusion temperatures (AFTs) of gasification residues demonstrated that the AFTs of coal with high RNa are low, while AFTs of coal with low RNa are high. Nevertheless, when the residues contained a large number of calcium-containing silicates and aluminosilicates, the ATFs were reduced significantly even if its RNa stayed at a low level. Furthermore, the operating temperatures of the three coals (in order of Mulei coal, Shaerhu coal, and Tietou coal) were suggested to be controlled below 1150°C, 1100°C, and 950°C, respectively.
Keywords: high-alkali coal, slagging, gasification, FactSage, ash fusion temperatures
23. Experimental and Numerical Study of the Effect of Fuel/Air Mixing Modes on NOx and CO Emissions of MILD Combustion in a Boiler Burner
ZHU Ziru, XIONG Yan, ZHENG Xianglong, CHEN Weijie, REN Baohe, XIAO Yunhan
Corresponding author: XIONG Yan
E-mail: xiongyan@iet.cn
Journal of Thermal Science, 2021, 30(2): 656-667.
https://doi.org/10.1007/s11630-020-1323-1
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1323-1
Abstract: The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emissions, stable combustion and low noise for various kinds of fuel, which has great potential in the industry. The aim of this study is to investigate the effect of fuel/air mixing modes on NOx and CO emissions of MILD combustion in a boiler burner by experiments and numerical simulations. Three types of fuel/air mixing modes (premixing mode, diffusion mode and hybrid mode) have been considered in this study. The realizable k-ε turbulent model and the Eddy Dissipation Concept (EDC) combustion model were used in numerical simulations. In addition to the temperature near the burner head, the calculation results match very well with the axial temperature distribution at the furnace center. The flow pattern under different mixing modes is similar, while the hybrid mode has a higher OH concentration near the diffusive fuel nozzle than the premixing mode, and the corresponding position of the peak OH concentration is closer to the rear half of the furnace. The distribution of temperature is extremely uniform for the premixing mode in the main reactive zone, which is typical for MILD combustion. There is a distinct area where the reaction temperature is higher than 1600 K for the hybrid mode. Moreover, in the main reactive zone, the gas recirculation ratio is high enough to ensure flue gas recirculation, which is beneficial to achieve MILD combustion at local areas. At the location where the axial distance is greater than 0.2 m, the gas recirculation ratio of the premixing mode is larger than that of the hybrid mode, which strengthens the entrainment of hot flue gas into the recirculated gas. The experimental results show that when the thermal intensity is less than 1.67 MW?m–3, the NOx emissions are less than 15×10–6@3.5%O2 in near stoichiometric ratio in the premixing mode, and the CO emissions are less than 10×10–6@3.5%O2 under the same conditions. In the diffusion mode, the NOx emissions are less than 30×10–6@3.5%O2. In order to keep NOx and CO emissions low, the hybrid modes with optimized fuel distribution ratio are found under different thermal intensities.
Keywords: MILD combustion, boiler burner, fuel/air mixing, NOx emissions, CFD
24. Numerical Investigation on the Flow Mechanism of Multi-Peak Frequency Feature of Rotating Instability
WANG Hao, WU Yadong, YUE Shaoyuan, WANG Yan’gang
Corresponding author: WU Yadong; WANG Hao
E-mail: yadongwu@sjtu.edu.cn; wanghao@nwpu.edu.cn
Journal of Thermal Science, 2021, 30(2): 668-681.
https://doi.org/10.1007/s11630-020-1349-4
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1349-4
Abstract: In this paper, the rotating instability (RI) in an axial compressor has been investigated numerically in order to examine the capability of URANS method to simulate its typical characteristics of RI broadband humps with multi-peak frequencies (MPFs) and further to uncover the underlying flow mechanism. A full-annulus modeling solution has been adopted to fully capture the wide range of different length-scale flow disturbances that circumferentially propagating around the compressor rotor. During the transient computing process, long-term monitoring up to 50 revolutions has been carried out to achieve a fine frequency resolution, and that would be essential for resolving the MPFs with small frequency interval. It is shown that the MPFs feature of RI has been successfully captured by the full-annulus URANS approach, and also its frequency range and spectral feature agree well with the experimental results. Further, with a circumferential mode decomposition on the MPFs characteristics of RI, it has been found that the MPFs result from the interaction between long- and short-scale flow disturbances which circumferentially propagate around the compressor rotor near the clearance region. Detailed examination on the numerical three dimensional flow field indicates that the short-scale disturbance is induced by the unsteady oscillation of tip clearance vortexes with inter-passage phase delay. The long-scale disturbance is caused by the mistuning of the wave number of the short-scale disturbance and the blade number within the whole annulus.
Keywords: axial compressor, rotating instability, multiple frequency peaks, URANS, tip leakage vortex
25. Experimental Investigation of a Linear Cascade with Large Solidity Using Pressure Sensitive Paint and Dual-Camera System
GAO Limin, YANG Guanhua, GAO Tianyu, LI Ruiyu, HU Xiaoquan
Corresponding author: GAO Limin
E-mail: gaolm@nwpu.edu.cn
Journal of Thermal Science, 2021, 30(2): 682-695.
https://doi.org/10.1007/s11630-021-1425-4
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1425-4
Abstract: Pressure Sensitive Paint (PSP) technique has been increasingly applied to the experimental research of aerodynamics and thermodynamics due to its strengths of non-contact, high resolution results and large coverage area, etc. However, rarely has this technique been successfully used to the study of internal flow such as compressor cascade, since narrow flow passages would heavily restrict the acquisition of PSP images. In this paper, PSP technique was used to study the pressure distribution on a linear compressor cascade with large solidity of 2.3, where the view of recording camera can be heavily blocked due to adjacent blade surfaces. To help get integrated PSP images of the internal flow passage, dual camera system along with image processing tools like 3D reconstruction and image integration were adopted. The results showed that with the aid of such assistance, image results with good quality and readability could be obtained. Meanwhile, pressure data given by PSP were compared with data from traditional way of pressure taps and showed good consistency. Massive results of the entire cascade passage surface were given with different inlet Mach numbers and incidence angles. The results showed that PSP technique can integrally measure cascade tunnel of large solidity with the help of dual-camera system.
Keywords: pressure sensitive paint, compressor cascade, dual-camera system, large solidity, full channel measurement
26. Numerical Investigation of the Centrifugal Compressor Stability Improvement by Half Vaned Low Solidity Diffusers
CHEN Siyue, ZUO Shuguang, WEI Kaijun
Corresponding author: ZUO Shuguang
E-mail: sgzuo@tongji.edu.cn
Journal of Thermal Science, 2021, 30(2): 696-706.
https://doi.org/10.1007/s11630-021-1318-6
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1318-6
Abstract: Centrifugal compressors for the fuel cell vehicles often operate near the surge line compared with the turbocharger compressors. Low solidity and half vaned diffusers are recognized as good ways to improve the stability of the centrifugal compressor. The presented work investigated four diffuser configurations (i.e., the vaneless diffuser (VLD), full-height low solidity vaned diffuser (LSVD), hub-side half vaned diffuser (HVD) and shroud-side half vaned diffuser (SVD)) through steady-state and unsteady numerical simulations. The results show that the best performance is achieved by the LSVD, HVD and SVD at the design, surge and choke conditions. The flow rate at the surge operating point of the HVD has decreased by 15.53% compared with the LSVD, and 9.21% compared with the VLD. At near surge operating point, a longitudinal suction side passage vortex is formed on the hub of the LSVD and rotates as circumferential stall cells. A hairpin vortex is formed along the leading edge and is dragged by the main flow along the suction side as a local vortex shedding. The mechanism of the stability improvement by half vaned diffusers is that the tip leakage vortex migrates from the clearance side to the vane mounting side and replenishes the low-momentum zone on the mounting side. The best position where the half vaned diffuser should be mounted is based on the impeller outlet flow conditions, namely, the location of the wake region, where the meridional velocity and relative stagnation pressure is low.
Keywords: centrifugal compressor, low solidity diffuser, half vaned diffuser, flow control, numerical simulation
27. Rotation Effect on Flow and Heat Transfer for High-Temperature Rotor Blade in a Heavy Gas Turbine
DONG Aihua, YAN Peigang, QIAN Xiaoru, HAN Wanjin, WANG Qingchao
Corresponding author: YAN Peigang
E-mail: peigang_y@163.com
Journal of Thermal Science, 2021, 30(2): 707-715.
https://doi.org/10.1007/s11630-020-1319-x
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1319-x
Abstract: In this paper, the composite inner cooling structures of the rotating blade in the first stage heavy gas turbine were modeled and simulated by coupling heat transfer (CHT). The flow characteristics and heat transfer performances were comparatively analyzed under two operations of the stationary and the rotational states. The results show that the turbulence intensity, the flow resistance and the heat transfer level of the rotating coolant are significantly increased compared with the stationary state, which is considered to be obtained by the combined effects of the Coriolis force, the centrifugal force and their derived buoyancy forces. It is pointed out that the rotation leads to the non-uniform flow of film holes at the leading edge of the pressure surface along blade height. In addition, it increases the slope of the limiting streamline, which has a decisive influence on the heat transfer of both the pressure and suction surfaces. The paper provides guidance for the design of a rotating composite cooling structure based on the relations between the stationary and rotational conditions.
Keywords: heavy gas turbine, composite cooling structure, coupled heat transfer, rotation effect, simulation
28. Effects of Injection Angles and Aperture Ratios on Film Cooling Performance of Sister Holes
LI Mingchun, HE Yeguang, LI Rundong, YANG Tianhua
Corresponding author: LI Rundong
E-mail: leerd@sau.edu.cn
Journal of Thermal Science, 2021, 30(2): 716-728.
https://doi.org/10.1007/s11630-020-1315-1
Springer Link: https://link.springer.com/article/10.1007/s11630-020-1315-1
Abstract: In this paper, to analyze the influences of the injection angles and aperture ratios (AR) of the primary hole and the side hole on the film cooling performance of a flat plate model, pressure sensitive paint (PSP) technology was used to study the forward and backward jet of a single hole and four sister holes, and a numerical simulation was supplemented to explore the flow structure of the sister holes. The sister holes had a better film cooling performance than the cylindrical hole at all blowing ratios (BR). The backward jet of the primary hole or the side hole could increase the spanwise film coverage of the sister hole. In this study, with the primary hole featuring a backward jet and the side hole featuring a forward jet, the film cooling performance was the best, 11.9 times higher than the areal mean film cooling efficiency of the cylindrical hole when AR=1 and BR=1.5. At a low blowing ratio, the counter-rotating vortex pair (CRVP) of the side hole could suppress the strength of the CRVP of the primary hole. At a high blowing ratio, when the primary hole featured a backward jet and the side hole featured a forward jet, the CRVP of the side hole had the optimal performance for suppressing the CRVP of the primary hole.
Keywords: sister hole, injection angle, aperture ratio, film cooling effectiveness, vorticity distribution
29. Experimental Studies on Fuel Spray Characteristics of Pressure-Swirl Atomizer and Air-Blast Atomizer
WANG Kaixing, FAN Xiongjie, LIU Fuqiang, LIU Cunxi, LU Haitao, XU Gang
Corresponding author: LIU Fuqiang; XU Gang
E-mail: liufuqiang@iet.cn; xugang@iet.cn
Journal of Thermal Science, 2021, 30(2): 729-741.
https://doi.org/10.1007/s11630-021-1320-z
Springer Link: https://link.springer.com/article/10.1007/s11630-021-1320-z
Abstract: In this work, the effects of fuel temperatures and pressure drops on the flow field and spray characteristics of a pressure-swirl atomizer were discussed using the Particle Imaging Velocimetry (PIV), Planar Laser Induced Fluorescence (PLIF) and Laser Particle Size Analyzer (LPSA) methods. Then the air-blast atomizer was selected to study the interaction of initial atomization and flow field. The effect of fuel-air ratio on the air-blast atomizer were also considered, where the fuel-air ratio was varied by adjusting mass flow rate of the air and fuel respectively. The results show that the spray angle of the pressure-swirl atomizer increases first and changes a little after the pressure drop higher than 0.5 MPa. However, more fuel concentrate on the central region, which is mainly caused by the increase of the proportion of small droplets with lower centrifugal force. The fuel temperature can improve the spray angle only in lower pressure drop, and it has a little effect under higher pressure drops. In addition, the fuel pressure drop has an obvious influence on the fuel distribution and flow field near the nozzle exit compared with the downstream. For the air-blast atomizer, the spray angle increases compared with the pressure-swirl atomizer for the introduction of swirl air. Furthermore, the spray angle decreases with the air mass rate increasing, and it increases with the fuel mass rate increasing. The distribution of velocity and droplet near the nozzle exit is influenced by the air mass rate, and the fuel mass rate mainly affects the distribution in the downstream. The fuel accumulates in the annular area below the nozzle, and the distribution of it changes little with the development along the axial direction.
Keywords: pressure-swirl atomizer, air-blast atomizer, spray characteristic, Particle Imaging Velocimetry (PIV), Planar Laser Induced Fluorescence (PLIF)
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