Volume 29, Issue 3, May-June 2020

CONTENTS-Volume 29, Issue 3, May-June 2020

Springer Link: https://link.springer.com/journal/11630/29/3

1. On the Use of Nanofluids in Solar Energy Applications

CUCE Erdem, CUCE Pinar Mert, GUCLU Tamer, BESIR Ahmet Burhaneddin

Corresponding author: CUCE Erdem

E-mail: erdem.cuce@erdogan.edu.tr

Journal of Thermal Science, 2020, 29(3): 513-534.

https://doi.org/10.1007/s11630-020-1269-3

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1269-3

Keywords: nanofluids, solar energy applications, thermal and electrical performance, COP, cost

Abstract: Renewable energy technologies are in the centre of interest to narrow the gap between fossil fuels and clean energy systems. The dominant role of solar energy systems among the alternatives is beyond question owing to being associated with an infinite energy source, well-documented theory, simplicity, eco-friendly structure and notably higher energy and exergy efficiency range compared to other renewables. However, in solar energy systems, conventional working fluids with poor thermophysical properties are still utilised. In other words, further improvements are still available in the said systems by the use of unique nanoparticles with superior thermal, electrical, optical and mechanical properties. Within the scope of this research, the applications of nanofluids in various solar energy systems such as tracking and non-tracking solar collectors, photovoltaic/thermal systems, solar thermoelectric devices, solar stills, solar thermal energy storage systems, solar greenhouses and solar ponds are comprehensively analysed. Relevant comparisons and discussions are proposed for the potential impacts of various nanofluids on coefficient of performance (COP) and thermodynamic performance figures of solar energy systems such as energy and exergy efficiency, effectiveness and productivity. Some challenges of nanofluids are also addressed which need to be resolved in further works.

2. Field and CFD Study of Fuel Distribution in Pulverized Fuel (PF) Boilers

CIUKAJ Szymon, HERNIK Bart?omiej

Corresponding author: CIUKAJ Szymon

E-mail: szymon.ciukaj@polsl.pl

Journal of Thermal Science, 2020, 29(3): 535-545.

https://doi.org/10.1007/s11630-020-1199-0

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1199-0

Keywords: pulverized fuel (PF) boiler, NOx reduction, biomass co-firing, fuel distribution

Abstract: The article presents both field and CFD results of a new concept of a mechanical pulverized fuel (PF) distributor. The goal of the study was to improve the pulverized coal-air mixture separation in PF boilers where the fuel preparation and feeding system was operated in a combined coal and biomass grinding conditions. The numerical analysis was preceded after a field study, where measurements were carried out in a pulverized coal-fired (PC) boiler equipped with a technology of NOx reduction by means of primary methods. Proper distribution of a pulverized coal-air mixture to the individual burners is one of the fundamental tasks of the combustion systems where the primary methods are implemented to control the NOx emission. Problems maintaining the proper distribution of fuel to the burners related primarily to the boilers where the coal and biomass co-grinding is used. Changing the load of coal-mills and fuel type at the same time (i.e., different types of biomass) could result in less effective separation of pulverized fuel particles in PF distributors. Selection of an appropriate construction of a distributor will allow the better control of the combustion process which results in decreased NOx emission while keeping the proper combustion efficiency, i.e., less unburned carbon (UBC) in the fly ash. The results of the field measurements made it possible to create a CFD distribution base model, which was used for the analysis of a new splitter construction to be used in a PF distributor. Subsequent analysis of the numerical splitter enables precise analysis of its construction, including the efficiency of separation and the prediction of conveying of the coal and biomass particles.

3. Research and Development of Supercritical Carbon Dioxide Coal-Fired Power Systems

LI Zhaozhi, LIU Xuejiao, SHAO Yingjuan, ZHONG Wenqi

Corresponding author: ZHONG Wenqi

E-mail: wqzhong@seu.edu.cn

Journal of Thermal Science, 2020, 29(3): 546-575.

https://doi.org/10.1007/s11630-020-1282-6

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1282-6

Keywords: S-CO2 cycle, coal-fired power plant, thermal efficiency, boiler

Abstract: Using supercritical carbon dioxide (S-CO2) Brayton cycle instead of the traditional steam Rankine cycle is a promising technique to enhance the coal-fired power generation efficiency. Researchers from all over the world are actively designing and exploring efficient S-CO2 coal-fired power plants in recent years with great efforts made to overcome the significant technical challenges in the cycle layouts of S-CO2 and its specific thermal integration with coal-fired heat resources. This paper provides a detailed review of the research progress on the coal-fired power generation using S-CO2 Brayton cycles. The basic knowledge of S-CO2 properties, the promising S-CO2 power cycles and the conceptual designs for S-CO2 coal-fired power plants are comprehensively summarized, with some key issues in the constructing process and the corresponding engineering solutions being emphatically discussed. Based on the current achievements, the overall technical and economic evaluations on the S-CO2 coal-fired power system are figured out. Furthermore, the specific integration applications of S-CO2 cycles with different coal firing devices and modes including pulverized coal combustion, circulating fluidized bed combustion, oxy-coal combustion, pressurized fluidized bed combustion, chemical looping combustion are discussed. Finally, the main challenges requiring further studies are highlighted.

4. Primary Frequency Control Ability Evaluation of Valve Opening in Thermal Power Units Based on Artificial Neural Network

LIAO Jinlong, LUO Zhihao, YIN Feng, CHEN Bo, SHENG Deren, LI Wei, YU Zitao

Corresponding author: YU Zitao

E-mail: yuzitao@zju.edu.cn

Journal of Thermal Science, 2020, 29(3): 576-586.

https://doi.org/10.1007/s11630-019-1203-8

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1203-8

Keywords: primary frequency control, valve opening, main steam pressure, thermal power unit, artificial neural network, evaluation

Abstract: With the development of new energy, the primary frequency control (PFC) is becoming more and more important and complicated. To improve the reliability of the PFC, an evaluation method of primary frequency control ability (PFCA) was proposed. First, based on the coupling model of the coordinated control system (CCS) and digital electro-hydraulic control system (DEH), principle and control mode of the PFC were introduced in detail. The simulation results showed that the PFC of the CCS and DEH was the most effective control mode. Then, the analysis of the CCS model and variable condition revealed the internal relationship among main steam pressure, valve opening and power. In term of this, the radial basis function (RBF) neural network was established to estimate the PFCA. Because the simulation curves fit well with the actual curves, the accuracy of the coupling model was verified. On this basis, simulation data was produced by coupling model to verify the proposed evaluation method. The low predication error of main steam pressure, power and the PFCA indicated that the method was effective. In addition, the actual data obtained from historical operation data were used to estimate the PFCA accurately, which was the strongest evidence for this method.

5. Design and Optimization of a Full-Generation System for Marine LNG Cold Energy Cascade Utilization

SUN Xiaofei, YAO Shouguang, XU Jinjin, FENG Guozeng, YAN Likun

Corresponding author: YAO Shouguang

E-mail: zjyaosg@126.com

Journal of Thermal Science, 2020, 29(3): 587-596.

https://doi.org/10.1007/s11630-019-1161-1

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1161-1

Keywords: LNG, cold energy utilization, CO2, transcritical, Rankine cycle, genetic algorithm

Abstract: This paper took a 100,000 DWT LNG fuel powered ship as the research object. Based on the idea of “temperature matching, cascade utilization” and combined with the application conditions of the ship, a horizontal three-level nested Rankine cycle full-generation system which combined the high-temperature waste heat of the main engine flue gas with the low-temperature cold energy of LNG was proposed in this paper. Furthermore, based on the analysis and selection of the parameters which had high sensitivity to the system performance, the parameters of the proposed system were optimized by using the genetic algorithm. After optimization, the exergy efficiency of the marine LNG gasification cold energy cascade utilization power generation system can reach 48.06%, and the thermal efficiency can reach 35.56%. In addition, this paper took LNG net power generation as the performance index, and compared it with the typical LNG cold energy utilization power generation system in this field. The results showed that the unit mass flow LNG power generation of the system proposed in this paper was the largest, reaching 457.41 kW.

6. Quantification on the Effects of Liquid-Vapor Separation in Air-Conditioning System by using Advanced Exergy Analysis

LI Yunhai, CHEN Jianyong, LIN Xu, YANG Zhi, CHEN Ying, LUO Xianglong

Corresponding author: YANG Zhi

E-mail: yangzhi@gdut.edu.cn

Journal of Thermal Science, 2020, 29(3): 597-608.

https://doi.org/10.1007/s11630-020-1295-1

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1295-1

Keywords: air-conditioning system, liquid-vapor separation, advanced exergy analysis, avoidable exergy destruction

Abstract: Air-conditioning system consumes a large amount of electricity in residential sections, and its efficiency has drawn extensive concerns in energy-conscious era. Liquid-vapor separation is a heat transfer enhancement technology that can effectively improve the performance of the heat exchanger as well as the system. In this paper, a regular air-conditioning system as the baseline (system-A) and other two air-conditioning systems with liquid-vapor separation heat exchanger (system-B and system-C) are comparatively studied. The component behaviors and system performances are deeply explored by using advanced exergy analysis with a focus on quantifying how much consequences come from the variants, i.e. liquid-vapor separation. The results indicate that the system-B has large reduced exergy destruction from the compressor and condenser at cooling mode relative to the system-A. The system-C has mainly diminished exergy destruction in the compressor caused by other components relative to the system-B. At heating mode, the system-C has an enhanced system exergy efficiency of 9.6% over the system-A, and it also has the decreased avoidable exergy destruction which is dominantly contributed by the compressor and evaporator. Furthermore, it is found that liquid-vapor separation mainly benefits the compressor and outdoor heat exchanger where it locates, leading to the system performance improvements.

7. A Multiple-Relaxation-Time Lattice Boltzmann Model for Natural Convection in a Hydrodynamically and Thermally Anisotropic Porous Medium under Local Thermal Non-Equilibrium Conditions

YANG Bo, WU Wei, LI Maodong, ZHAI Wei

Corresponding author: WU Wei

E-mail: dawuweijun@163.com

Journal of Thermal Science, 2020, 29(3): 609-622.

https://doi.org/10.1007/s11630-020-1169-6

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1169-6

Keywords: lattice Boltzmann method, natural convection in anisotropic porous medium, local thermal non-equilibrium

Abstract: To investigate the natural convective process in a hydrodynamically and thermally anisotropic porous medium at the representative elementary volume (REV) scale, the present work presented a multiple- relaxation-time lattice Boltzmann method (MRT-LBM) based on the assumption of local thermal non-equilibrium conditions (LTNE). Three sets of distribution function were used to solve the coupled momentum and heat transfer equations. One set was used to compute the flow field based on the generalized non-Darcy model; the other two sets were used to solve the temperature fields of fluid and solid under the LTNE. To describe the anisotropy of flow field of the porous media, a permeability tensor and a Forchheimer coefficient tensor were introduced into the model. Additionally, a heat conductivity tensor and a special relaxation matrix with some off-diagonal elements were selected for the thermal anisotropy. Furthermore, by selecting an appropriate equilibrium moments and discrete source terms accounting for the local thermal non-equilibrium effect, as well as choosing an off-diagonal relaxation matrix with some specific elements, the presented model can recover the exact governing equations for natural convection under LTNE with anisotropic permeability and thermal conductivity with no deviation terms through the Chapman-Enskog procedure. Finally, the proposed model was adopted to simulate several benchmark problems. Good agreements with results in the available literatures can be achieved, which indicate the wide practicability and the good accuracy of the present model.

8. A Method to Measure Thermal Conductivity of Vacuum Insulation Panel Using Enhanced Extreme Learning Machine Model

XIA Rongfei, CHEN Yifei, FENG Yongjian

Corresponding author: FEGN Yongjian

E-mail: yjfeng@xmu.edu.cn

Journal of Thermal Science, 2020, 29(3): 623-631.

https://doi.org/10.1007/s11630-020-1213-6

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1213-6

Keywords: vacuum insulation panel, thermal conductivity, extreme learning machine, ridge regression

Abstract: Thermal conductivity is an important quantity which represents the characteristic of Vacuum Insulation Panel’s (VIP’s) performance. Precise measurement of thermal conductivity provides better quality assurance for the users. In this paper, we presented a novel embedded sensor method to measure the thermal conductivity of VIP. The proposed method evaluated the quality of VIP primarily based on the relationship between thermal conductivity and frequency characteristic of the output signal. In addition, we presented a new mean ridge regression extreme leaning machine (M-RRELM) model via improving extreme learning machine (ELM) by ridge regression to modify the relationship between the thermal conductivity and the output signal frequency characteristic. Experiments have shown that the M-RRELM model has higher precision compared with the traditional ELM. The proposed method achieved good performance and was faster than the well known methods.

9. Numerical Simulation of Dual-Phase-Lag Model and Inverse Fractional Single-Phase-Lag Problem for the Non-Fourier Heat Conduction in a Straight Fin

MOZAFARIFARD Milad, AZIMI Aziz, MEHRZAD Salem

Corresponding author: AZIMI Aziz

E-mail: a.azimi@scu.ac.ir;aazimi@asme.org

Journal of Thermal Science, 2020, 29(3): 632-646.

https://doi.org/10.1007/s11630-019-1137-1

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1137-1

Keywords: non-Fourier heat transfer, fractional calculus, inverse heat transfer, Levenberg-Marquardt, straight fin, unsteady boundary condition

Abstract: In recent years, many studies have been done on heat transfer in the fin under unsteady boundary conditions using Fourier and non-Fourier models. In this paper, unsteady non-Fourier heat transfer in a straight fin having an internal heat source under periodic temperature at the base was investigated by solving numerically Dual-Phase-Lag and Fractional Single-Phase-Lag models. In this way, the governing equations of these models were presented for heat conduction analysis in the fin, and their results of the temperature distribution were validated using the theoretical results of Single and Dual-Phase-Lag models. After that, for the first time the order of fractional derivation and heat flux relaxation time of the fractional model were obtained for the straight fin problem under periodic temperature at the base using Levenberg-Marquardt parameter estimation method. To solve the inverse fractional heat conduction problem, the numerical results of Dual-Phase-Lag model were used as the inputs. The results obtained from Fractional Single-Phase-Lag model could predict the fin temperature distribution at unsteady boundary condition at the base as well as the Dual-Phase-Lag model could.

10. Investigation of Heat Transfer Augmentation between the Ribbed Plates via Taguchi Approach and Computational Fluid Dynamics

GOKTEPELI Ilker, ATMACA Ulas, CAKAN Abdullah

Corresponding author: GOKTEPELI Ilker

E-mail: igoktepeli@ktun.edu.tr

Journal of Thermal Science, 2020, 29(3): 647-666.

https://doi.org/10.1007/s11630-019-1155-z

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1155-z

Keywords: CFD, heat transfer, Nusselt number, parallel plate, Reynolds number, rib, Taguchi approach, turbulent flow

Abstract: Heat transfer and turbulent flow characteristics between the ribbed plates have been numerically studied in the present paper. The ribs with the rectangular cross-section have been placed on the top and the bottom plates of the duct, symmetrically. It is assumed that the fluid at 300 K has entered the system while the walls kept at 400 K. All numerical analyses have been performed by k-ω Shear Stress Transport (SST) turbulence model for Re = 10000, 15000 and 20000. For the fixed rib width, the dimensionless height and the dimensionless spacing have been respectively varied as 0.1 ≤ h' ≤ 0.3 and 0.5 ≤ S' ≤ 1, and the results have been compared with the ones of the smooth plate. Even though there are twenty-seven cases obtained as a result of parametric combinations, the number of various cases has been reduced from twenty-seven to only nine different variations by applying the Taguchi method. Furthermore, the effects of all the considered parameters on the heat transfer and flow characteristics have been determined in terms of the influence degree. The optimum parameters for Nusselt number and pressure loss have been ascertained individually. What is more, the almost exact values for Nusselt number and pressure loss have also been attained by the confirmation test having an error percentage of 6%. The most dominant factor has been determined as the rib height due to its effect on both heat transfer and flow characteristics. Similarly, with respect to the numerical results, increasing the rib height, the rib spacing and Reynolds number has separately increased Nusselt number. Nevertheless, symmetrical flow structure has been disturbed as a result of ascending the rib height as clearly seen for h' = 0.3 from the charts. In the meantime, pressure loss has been augmented owing to the increment of the geometrical parameters and also Reynolds number. h' = 0.1 with S' = 0.5 at Re = 10000, h' = 0.2 with S' = 0.5 at Re = 15000 and h' = 0.1 with S' = 0.75 at Re = 15000 can be suggested for the heat transfer enhancement since the pressure loss of the system is tolerated.

11. Experimental Analysis of Atypically Long Finned Oscillating Heat Pipe for Ventilation Waste Heat Recovery Application

MAHAJAN Govinda, CHO Heejin, SMITH Aaron, THOMPSON Scott M.

Corresponding author: CHO Heejin

E-mail: cho@me.msstate.edu

Journal of Thermal Science, 2020, 29(3): 667-675.

https://doi.org/10.1007/s11630-019-1178-5

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1178-5

Keywords: oscillating heat pipe, waste heat recovery, ventilation

Abstract: Oscillating heat pipes (OHP) which are constructed from a serpentine-arranged capillary tube possess a desirable aerodynamic form factor and provide for relatively high heat transfer rates via cyclic evaporation and condensation of an encapsulated working fluid with no internal wicking structure required. In last two decades, OHP has been extensively investigated for its potential application in thermal management of various applications. This study presents an experimental investigation on the heat transfer performance of an atypically long finned OHP. The heat transfer performance of the proposed OHP was analyzed and compared with a bare tube OHP with similar overall dimensions. Results show that a unit row of finned OHP filled with n-pentane with fill ratio of 70% can recover up to (400±40) W of heat from a typical waste exhaust air stream. The additional pressure drop due to fins was estimated to be (6.8±2) Pa resulting in an increase of 1–2 W of fan power consumption. The average heat recovery rate via finned OHP was found to be almost 80% more than bare tube OHP filled with same working fluid with same fill ratio.

12. Enhancement of Thermo-Flow Performances by Windbreakers for Two-Tower Indirect Dry Cooling System

YAN Jingbo, WANG Weijia, CHEN Lei, YANG Lijun, DU Xiaoze

Corresponding author: YANG Lijun

E-mail: yanglj@ncepu.edu.cn

Journal of Thermal Science, 2020, 29(3): 676-686.

https://doi.org/10.1007/s11630-020-1294-2

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1294-2

Keywords: indirect dry cooling system, twin towers, windbreakers, wind directions, flow and heat transfer performances

Abstract: The winds will greatly weaken the cooling performance of indirect dry cooling system with twin towers. The exterior windbreakers are recommended to restrain the wind adverse effects in this paper. The macro heat exchanger model was adopted to simulate the heat exchange between circulating water and ambient air. The performances of natural draft dry cooling system (NDDCS) with and without exterior windbreakers were numerically studied. The pressure, velocity and temperature distribution of cooling air in wind angles of 0°, 45° and 90° was obtained and presented. The results show that in all wind directions, the performances for lateral sector of towers with windbreakers are significantly improved, but the low-pressure zone appears unexpectedly for the rear sectors, which reduces the air flow rate. The cooling performances of the twin towers with or without windbreakers decrease at first but then recover with the wind velocity increasing. Besides, the optimal flow and heat transfer performances appear in the wind angle of 0°. The cooling performances can be significantly improved in all three wind directions due to windbreaker configuration.

13. Research on an Arc Air-Lubricating Oil Radiator Equipped in Internal Surface of Air Intake for the Aero Engine

CAI Huikun, WENG Zeju, LIAO Yidai, GU Kaixuan, WANG Junjie

Corresponding author: CAI Huikun

E-mail: caihuikun@xmu.edu.cn

Journal of Thermal Science, 2020, 29(3): 687-696.

https://doi.org/10.1007/s11630-019-1121-9

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1121-9

Keywords: aero engine, air-lubricating oil radiator, arc plate-fin radiator, oil flowing path, internal surface of air intake

Abstract: Due to huge-power aircraft development and more electronic devices applied onboard, high heat flow density and uneven thermal distribution are becoming new problems. One new try is adding an air-lubricating oil radiator as the secondary cooling component but there are still few reports on its research. Therefore, this paper proposes a newly-design plate-fin air-lubricating oil radiator different from tube-fin or shell-tube conventionally used in previous engine system. This radiator is arc, and equipped in internal surface of air intake. Numerical and experimental analyses were carried out on fin performance. Their results agreed well with average error of 13% on thermal resistance. Then heat and flow behaviors of oil side were presented with different structures and sizes of flowing passage. According to all research, optimized radiator is gained with fin spacing of 3.76 mm, fin thickness of 2 mm, single flowing path with width of 13 mm and gradient inlet and outlet. Its heat dissipation of 28.35 kW and pressure loss of 2.2 MPa can meet actual working requirements. The research proves an air-lubricating oil radiator with arc structure and layout mode of internal surface to be feasible, which is a new but efficient cooling scheme and can lead to an innovative but wide use in modern aircrafts.

14. Analysis of Heat and Mass Transfer for a Single-Planar-Anode-Supported Solid Oxide Fuel Cell Considering Internal Reforming

ZHANG Zhuqian, WANG Yulei, BA Liming

Corresponding author: ZHANG Zhuqian

E-mail: zhqzhang@bjtu.edu.cn

Journal of Thermal Science, 2020, 29(3): 697-707.

https://doi.org/10.1007/s11630-019-1210-9

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1210-9

Keywords: three-dimensional numerical simulation, internal reforming reaction, solid oxide fuel cell, temperature gradient, fuel utilization

Abstract: The temperature uniformity and component concentration distributions in solid oxide fuel cells during operating processes can influence the cell electrochemical and thermal characteristics. A three-dimensional thermal-fluid numerical model including electrochemical reactions and water-gas-shift (WGS) reaction for a single channel solid oxide fuel cell was developed to study the steady-state characteristics, which include distributions of the temperature (T), temperature gradient, and fuel utilization. It was shown that the maximum temperature changed with operating voltage and the maximum temperature gradient occurred at the inlet of the channel of a solid oxide fuel cell by simulation. Moreover, the natural convection condition had a great influence on T and T/x. The thermal stress generated by temperature differences was the key parameter and increasing the convection heat-transfer coefficient can greatly reduce the thermal stress. In addition, the results also showed that there were lower temperature gradients and lower current density at high working voltage; therefore, choosing the proper operating voltage can obtain better cell performance.

15. Effect of Nanoparticle Type and Surfactant on Heat Transfer Enhancement in Spray Cooling

WANG Bingxing, LIU Zhixue, ZHANG Bo, XIA Yue, WANG Zhaodong, WANG Guodong

Corresponding author: LIU Zhixue

E-mail: a947437732@163.com

Journal of Thermal Science, 2020, 29(3): 708-717.

https://doi.org/10.1007/s11630-020-1212-7

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1212-7

Keywords: spray cooling, nanofluids, surfactant, wettability, heat flux

Abstract: In this study, the heat transfer characteristics of nanofluids used in spray cooling systems were examined. Three nanofluids, i.e., Cu, CuO, and Al2O3, respectively, with volume fractions ranging from 0.1% to 0.5%, as well as different volume fractions of a surfactant Tween 20, were used. In addition, their contact angles were measured to examine the heat-transfer characteristics. Under the same experimental conditions, with the increase in the volume fraction of the Cu nanoparticles from 0.1% to 0.5%, the maximum heat flux qmax increased from 3.36 MW/m2 to 3.48 MW/m2 from the impinging central point to r=30 mm (r is the distance from the impingement point), and the corresponding temperature of qmax increased from 400°C to 420°C. Results revealed that with increasing Tween 20 concentrations, the contact angle decreased because of the decrease in the surface tension of nanofluids and improvement of the wetting ability, and the corresponding qmax increased from 3.48 MW/m2 to 3.94 MW/m2 at the impact central point.

16. Experimental Study on Jet Impingement Boiling Heat Transfer in Brass Beads Packed Porous Layer

ZHANG Yunsong, CHEN Wei

Corresponding author: ZHANG Yunsong; CHEN Wei

E-mail: zhangyunsong@stu.shmtu.edu.cn; weichen@shmtu.edu.cn

Journal of Thermal Science, 2020, 29(3): 718-729.

https://doi.org/10.1007/s11630-019-1148-y

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1148-y

Keywords: jet impingement, nucleate boiling, beads packed porous layer, heat transfer coefficient, critical heat flux

Abstract: Jet impingement boiling has been widely used in industrial facilities as its higher heat transfer coefficient (HTC) and critical heat flux (CHF) can be achieved in comparison with the pool boiling. By covering beads packed porous layer on the heated wall surface, the enlarged heat transfer area and rise of nucleation sites for boiling occur, thus, the heat transfer performance of boiling can be enhanced. For the jet impingement boiling with brass bead packed porous layers, the heat transfer performance is crucially influenced by the characteristics of porous layer and working fluid flow, so the experiments were conducted to investigate the effects of the jet flow rate, fluid inlet subcooling, number of porous layer and brass bead diameter of porous layer. Comparison study shows that impingement boiling promotes the HTC and CHF as 1.5 times and 2.5 times respectively as pool boiling at similar conditions. Higher heat transfer performance can be obtained in the cases of a higher jet flow rate and a higher fluid inlet subcooling, and there exist the optimal layer number and bead diameter for heat transfer. Particularly, a double-layer porous layer results in an increase of 39% in heat flux at superheat of 30 K compared with a single-layer case; a single porous layer at d=8 mm brings an increase of 23% in heat flux at superheat of 30 K compared with that of bare plain surface. Besides, the actual scene of jet impingement boiling was recorded with a camera to investigate the behavior evolution of vapor bubbles which is highly correlated to the heat transfer process.

17. Synergy Methodology for Internal Flow of Turbomachinery

ZHOU Xin, ZUO Zhitao, LIANG Qi, HOU Hucan, TANG Hongtao, CHEN Haisheng

Corresponding author: ZUO Zhitao

E-mail: zuozhitao@iet.cn

Journal of Thermal Science, 2020, 29(3): 730-742.

https://doi.org/10.1007/s11630-019-1205-6

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1205-6

Keywords: thermal-fluid interaction, internal flow, turbomachinery, energy losses, numerical simulation

Abstract: The complex curvature of turbomachinery rotor blade channels combined with strong rotational effect and clearance leakage brings on intricate internal flow phenomenon. It is necessary to study the internal flow and energy loss mechanism to reveal the influence law of the key parameters and to achieve its optimal design. Considering features of flow and temperature fields in rotor passage, the concept of synergy analysis derived from equation of energy conservation was put forward. Typical NASA low-speed centrifugal compressor (LSCC) rotor was chosen for analysis using CFD. Numerical results showed remarkable agreement with experiment datum in both the tendency of the performance characteristics and quantitative pressure values. Under different flow rates and inlet total temperatures conditions, thermal-fluid interaction effect and losses were studied by synergy analysis. Results showed that peak synergy positive value zones located around blade leading edge, across the shroud wall and hub wall, and at the position where tip-leakage flow was mixing with the bulk flow and high entropy zones existed. Increasing flow rate from design condition, positive and negative synergy areas both changed tiny around leading edge and trailing edge. Reducing flow rate, positive synergy areas tended to increase and negative areas decreased at same positions. The relationship between flow separation, heat transfer and losses in turbomachinery rotor can be revealed based on synergy analyses.

18. Study of Rotating Stall in a Centrifugal Compressor with Wide Vaneless Diffuser

ZHANG Lei, ZHENG Zhi, ZHANG Qian, ZHANG Liang, LI Kang

Corresponding author: ZHANG Qian

E-mail: zhangqian@ncepu.edu.cn

Journal of Thermal Science, 2020, 29(3): 743-752.

https://doi.org/10.1007/s11630-020-1214-5

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1214-5

Keywords: centrifugal compressor, wide vaneless diffuser, rotating stall, numerical simulation

Abstract: To study the stall mechanism in a wide vaneless diffuser, a three-dimensional centrifugal compressor model was established. The numerical simulation method was used to study the fluid characteristics in a centrifugal compressor with a wide vaneless diffuser under stall conditions. The simulated results showed that the wide vaneless diffuser stall was related to the instability of the core flow. Due to the influence of the reflow, the core flows moved between the hub and shroud side and the directions were not consistent. This was called core flow distortion, which triggered the rotating stall. The reflow first appeared at the outlet boundary of the diffuser, and the reflux gradually expanded to the inside of the diffuser as the impeller rotated. Eventually, the reflux zones grew and merged, forming a stable low-speed fluid regiment, which produced a stall cell. The stall cells rotated around themselves with an opposite direction with impeller.

19. Effect of Meridional Characteristic Angle on Aerodynamic Performance of Ram-Rotor

HAN Ji’ang, GUAN Jian, ZHONG Jingjun, CHEN Luting

Corresponding author: HAN Ji’ang

E-mail: hja@dlmu.edu.cn

Journal of Thermal Science, 2020, 29(3): 753-762.

https://doi.org/10.1007/s11630-019-1211-8

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1211-8

Keywords: ram-rotor, meridional shape, contracting angle, expanding angle, numerical simulation

Abstract: A kind of meridional concept which has a shape of contraction-expansion (Con-Exp) was applied to the ram-rotor in the paper, and detailed numerical simulation to understand the impact of meridional shape and geometric characteristic angle on the aerodynamic behavior of ram-rotors has been undertaken. Compared to baseline, there was a positive effect in intensifying shock train and suppressing low momentum fluid in Con-Exp scheme, and the pressure ratio and efficiency of Con-Exp scheme increased by 2.075% and 3.160%, respectively. When the contracting angle was increasing, supersonic flow at and after throat region accelerated remarkably, and the static pressure rise was decreased gradually. The terminating shock train was transformed to terminating shock, and the efficiency of ram-rotor was unfavorable to improve due to low throttle extent. As expanding angle rose, the terminating shock moved forward and turned to shock train gradually. The pressure rise capacity and throttling ability of ram-rotor were raised. More low momentum fluid was accumulated near the middle and upper flow-path, yielding greater flow loss at large expanding angle.

20. Efficient Determination of Turbomachinery Blade Aero-Damping Curves for Flutter Assessment via Trigonometric Interpolation

HUANG Xiuquan, WANG Dingxi

Corresponding author: WANG Dingxi

E-mail: dingxi_wang@nwpu.edu.cn

Journal of Thermal Science, 2020, 29(3): 763-771.

https://doi.org/10.1007/s11630-020-1286-2

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1286-2

Keywords: trigonometric interpolation, influence coefficient method, travelling wave method, blade flutter, aero-damping, turbomachinery

Abstract: Proposed in the paper is a trigonometric interpolation method for efficient determination of turbomachinery blade aero-damping curves which are required in a flutter assessment. The trigonometric interpolation method was proposed to be incorporated with the widely used travelling wave method to replace the influence coefficient method. Through analyzing aero-damping/worksum at a few carefully chosen nodal diameters, trigonometric interpolation was applied through existing data points to get aero-damping/worksum at the rest nodal diameters. The proposed approach is much more efficient than the travelling wave method for determining the aero-damping curve of a blade. In principle, the method can be as efficient as the influence coefficient method. Unlike the influence coefficient method, the trigonometric interpolation method does not involve linear superposition, and it can include nonlinear effect and is expected to be more accurate. Two test cases were provided to validate the proposed method and demonstrate its effectiveness. The method is not only effective, but also very easy to be incorporated into existing widely used aero-damping/worksum analysis system using the travelling wave method.

21. Experimental Investigation on the Adiabatic Film Effectiveness for Counter- Inclined Simple and Laid-Back Film-Holes of Leading Edge

YE Lin, LIU Cunliang, XU Zhipeng, ZHU Huiren, LIU Haiyong, ZHAI Yingni

Corresponding author: LIU Cunliang; ZHAI Yingni

E-mail: liucunliang@nwpu.edu.cn; ynzhai2013@163.com

Journal of Thermal Science, 2020, 29(3): 772-783. https://doi.org/10.1007/s11630-020-1287-1

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1287-1

Keywords: turbine blade leading edge, adiabatic film effectiveness, counter-inclined holes, impingement, thermochromic liquid crystal, transient measurement

Abstract: The adiabatic film effectiveness η of the counter-inclined film-holes fed by varying internal coolant intake on the turbine vane leading edge model was experimentally investigated. A semi-cylinder model was adopted to model the vane leading edge which was arranged with two-row holes, which located at ±15° on both sides. The four Leading edge model with the combinations of hole-shape (simple holes and laid-back holes) and intake structure (plenum and impingement) were tested under four blowing ratios M of 0.5, 1.0, 1.5, and 2.0. The η contours were obtained by the transient measurement technique based on double thermochromic liquid-crystals. The results present that the η is sensitive to the M for the four studied leading edge cases. The addition of impingement enhances the η for the two studied holes. The film jets make the coolant-flow closed to the target surface, resulting in higher η under lower M. The core with higher η appears in the downstream area of hole-exit. The η enhancement can be provided to almost the identical level by adding the impingement-holes and improving the hole-exit shaping in most areas. With increasing M, the jets with stronger exit normal momentum penetrate into the main-flow. The impingement addition may be a more effective program to upgrade the η relatively to the exit shaping under larger M. Besides, the laid-back holes with impingement case produce the highest film cooling performance among the four cases, providing great potential in the leading edge especially under larger M.

22. Application of Phase-Locked PIV Technique to the Measurements of Flow Field in a Turbine Stage

ZHANG Zhenyang, MA Hongwei

Corresponding author: MA Hongwei

E-mail: mahw@buaa.edu.cn

Journal of Thermal Science, 2020, 29(3): 784-792.

https://doi.org/10.1007/s11630-020-1215-4

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1215-4

Keywords: flow field measurement, PIV (particle image velocimetry), phase-locking technique, turbine inter-stage

Abstract: For the purpose of improving turbine efficiency, a detailed investigation of flow field near rim seal region in the main annulus is absolutely essential. Purge flow egressed from the seal gap penetrates the hub boundary layer and travels along with the secondary flow in the main path. The propagation of the purge flow and its influence on the turbine performance are crucial and cannot be neglected in the aerodynamic and thermal design. In addition, the interaction of vane wake and blade potential field also has a significant impact on the turbine stage performance. In this study, flow field between inlet guide vanes (IGV) and rotor blades was experimentally investigated at specific positions with the help of a two-dimensional particle image velocimetry (2-D PIV). A phase-locking technique was also employed to capture the images of flow field at different rotor blade positions. Data acquired characterizes the impact of emergent purge flow on the flow structures within the main annulus. The impacts of vane wake and blade potential field on the flow fields were analyzed through characterizations provided by the time-averaged field results. Finally, flow fields at different main flow rates and under different seal gap widths were also presented and assessed.

23. The Effect of Different Reaction Mechanisms on Combustion Simulation of a Reverse-Flow Combustor

LU Haitao, LIU Fuqiang, WANG Yulan, FAN Xiongjie, LIU Cunxi, XU Gang

Corresponding author: LIU Fuqiang

E-mail: liufuqiang@iet.cn

Journal of Thermal Science, 2020, 29(3): 793-812.

https://doi.org/10.1007/s11630-019-1184-7

Springer Link: https://link.springer.com/article/10.1007/s11630-019-1184-7

Keywords: reaction mechanisms, reverse-flow combustor, flamelet models, combustion simulation

Abstract: Three different reaction mechanisms of kerosene and flamelet models were used to simulate combustion in a reverse-flow combustor. By comparing the effects of different mechanisms on the flow field characteristics, components and temperature distribution of the combustion chamber, the results showed that: Under different reaction mechanisms, there was a strong similarity between flow filed and temperature field, but the penetration depth and temperature distribution of local jets were affected by the mechanism. Due to the different reaction paths and reaction rates, the distribution of major components had a great degree of similarity, but the concentration of intermediate components varied greatly. Comprehensive analysis, the 16 species and 17 species reaction mechanisms can simulate the flow field and outlet temperature distribution of the combustor well.

24. Experimental Investigations of the Flow Field Structure and Interactions between Sectors of a Double-Swirl Low-Emission Combustor: Effects of Main Stage Swirl Intensity and Venturi Angle

FAN Xiongjie, XU Gang, LIU Cunxi, ZHANG Chi, WANG Jianchen, LIN Yuzhen

Corresponding author: LIU Cunxi

E-mail: liucunxi@iet.cn

Journal of Thermal Science, 2020, 29(3): 813-819.

https://doi.org/10.1007/s11630-020-1228-z

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1228-z

Keywords: combustor, recirculation zone, PIV, swirl intensity, venturi angle

Abstract: Effect of venturi angle and main stage swirl intensity on flow field and interactions were investigated using PIV. The results showed the difference between the side sector and the middle sector was caused by interactions. The interactions were stronger with the rise of the main stage swirl intensity. When the swirl intensity was 0.7 and 0.9, there was little difference of the width of the recirculation zone. But the flow field had a great difference when the swirl intensity was 0.5 and 0.7, which means that when the swirl intensity was small, the swirl intensity had a great influence on the flow field. Venturi angle had a great influence on the flow field structure and interactions when the venturi angle was big, such as 90°. The venturi angle just had a small influence on the width of the recirculation zone when the venturi angle was relatively small, such as 28° and 52°. The velocity of the center plane between two sectors (plane 3) was small. There was a recirculation zone at upstream of the center plane between two sectors (plane 3) when the swirl intensity was 0.7 and 0.9, whereas not one when the swirl intensity was 0.5. The above was induced by interactions. In addition, the velocity of plane 1, plane 3, and plane 5 when the venturi angle was 52° was smaller than that of 28° and 90°.

25. Effects of Magnetic Fields on Morphology and Nanostructure Evolution of Incipient Soot Particles from n-heptane/2,5-dimethylfuran Inverse Diffusion Flames

JIANG Bo, WANG Pengfei, LIU Dong

Corresponding author: LIU Dong

E-mail: dongliu@njust.edu.cn

Journal of Thermal Science, 2020, 29(3): 820-839.

https://doi.org/10.1007/s11630-020-1262-x

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1262-x

Keywords: magnetic fields, incipient soot particle, n-heptane/DMF, morphology, nanostructure, evolution

Abstract: Differences of the morphology and nanostructure evolution of incipient soot particles generated in n-heptane/2,5-dimethylfuran (DMF) inverse diffusion flames (IDFs) with/without magnetic fields were investigated. Utilizing a high resolution transmission electron spectroscopy, the morphology and nanostructures of soot sampled from spatial locations at different heights in IDFs were analyzed. The graphitization and the oxidation reactivity of soot were tested by an X-ray diffraction and a thermogravimetric analyzer, respectively. Results demonstrated that the magnetic force on paramagnetic species, such as oxygen molecules, can modify the soot formation and oxidation. More incipient soot particles with larger diameters appeared in chains or branches or tufted forms on the flame wing region and the higher position than that on the flame centerline region and the lower position. With magnetic fields, greater amounts of clustered soot particles displayed more crowded distribution and larger diameters. Soot particles with typical structures of the core-shell were promoted to own more orderly bordered lamellae with longer fringe length and smaller fringe tortuosity by the magnetic force acting on oxygen at the same sample position. These modifications resulted in relatively larger diffraction angle of the peak, higher graphitization degree and slightly lower oxidation reactivity of soot.

26. Influence of Secondary Sealing Flow on Performance of Turbine Axial Rim Seals

WANG Ruonan, DU Qiang, LIU Guang, LIAN Zengyan, XIE Lei, ZHU Junqiang

Corresponding authors: DU Qiang; LIU Guang

E-mail: duqiang@iet.cn; liuguang@iet.cn

Journal of Thermal Science, 2020, 29(3): 840-851.

https://doi.org/10.1007/s11630-020-1317-z

Springer Link: https://link.springer.com/article/10.1007/s11630-020-1317-z

Keywords: rim seal, sealing efficiency, secondary sealing flow, sealing flowrate ratio, swirled flow

Abstract: Purge flow is of great importance in cooling turbine disks and sealing rotor-stator disc cavity to reduce hot gas ingestion in gas turbines. The amount of cooling air extracted from the compressor is crucial to engine efficiency. Excessive sealing air will cause not only a reduction in work transfer but also an increase in aerodynamic losses caused by the mixing of main and sealing flow. In order to simplify rim seal structure while ensuring high sealing efficiency, the current paper optimizes the flow path of the secondary air system and presents a new rim seal structure with auxiliary sealing holes transporting a certain amount of secondary sealing flow. The new structure was compared with the conventional counterpart using validated CFD methods, showing that the additional secondary sealing flow is possible to improve sealing efficiency in disk cavity. The current paper investigates the secondary sealing flow with and without swirl (the angle of auxiliary sealing hole inclination is 0° and 45° respectively), while maintaining the total amount of the sealing flow, flow rate ratio of sealing air (main sealing flow rate versus secondary sealing flow rate=1:1, 2:1, 3:1, 4:1), found that both two parameters have essential impacts on sealing efficiency. The relationship between these two parameters and sealing efficiency was obtained, and it provides a new philosophy for the design of rim seal in gas turbines.