Sept. 14, 2019
Springer Link: https://link.springer.com/journal/11630/28/5
1. Special column for the memory of Professor CHEN Naixing
NIE Chaoqun, E-mail: email@example.com
ZHANG Hongwu, E-mail: firstname.lastname@example.org
DU Juan, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 835‒836
2. Application of Fast Wavelet Analysis on Early Stall Warning in Axial Compressors
LIU Yang1,2, LI Jichao1,2*, DU Juan1,2, LI Fan1,2, ZHANG Hongwu1,2
Corresponding author: LI Jichao, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 837-849
Keywords: axial compressor, stall inception, pre-stall inception, stall warning, fast wavelet
Abstract: The timely detection of stall inception is of great significance for safe operation and stability control of axial compressor. In the current study, a fast wavelet tool was selected to predict stall precursor in axial compressors with spike-type and modal-wave stall inception. Dynamic pressure was measured in the casing wall by using a collection of time-resolved pressure transducers with circumferential and chord-wise spatial resolution. Fast wavelet analysis with low frequency reconstruction results demonstrate that the initial inception can be detected 110 rotor revolutions prior to stall for modal-wave stall inception in a 1.5 stage axial compressor. For spike-type stall inception, despite the failure of early stall warning via low frequency reconstruction, an increase amplitude frequency band of 0.2–0.8 blade passing frequency was identified using high frequency reconstruction in an isolated-rotor axial compressor. Fast wavelet method can predict two kinds of stall inceptions simultaneously in advance and realize the early stall warning in axial compressors through a reasonable selection of reconstructed frequency.
3. Adjoint-Based Geometrically Constrained Aerodynamic Optimization of a Transonic Compressor Stage
SU Xinrong1*, MA Can2, YUAN Xin1
Corresponding author: SU Xinrong, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 850-861
Keywords: aerodynamic optimization, compressor stage, discrete adjoint method, geometric constraint
Abstract: Efficient method to handle the geometric constraints in the optimization of turbomachinery blade profile is required. Without constraints on the blade thickness, optimal designs typically yield thinner blade to reduce the friction loss, however, at the risk of degraded strength and stiffness. This issue is seldom discussed and existing literature always treat the blade thickness constraint in an indirect manner. In this work, two different geometric constraints on the blade thickness are proposed and applied in the adjoint optimization: one is on the maximum blade thickness and the other is on the blade area. Methods to compute sensitivities of both constraints are proposed and they are integrated into an optimization system based on a finite volume code and a solver for the discrete adjoint equation. Adjoint optimization is conducted to minimize the entropy production in a transonic compressor stage. Results for the adjoint optimization without geometry constraint and two comparative cases are detailed. It is indicated that three cases yield similar performance improvement; however, if geometry constraints are properly handled, the optimal designs have almost the same maximum thickness as the original design, compared to a thinner blade profile with 14% reduction of maximum thickness in the case without geometry constraint. The cases considering geometry constraints also consume slightly reduced Central Processing Unit (CPU) cost. Result of this work verifies the effectiveness of the proposed method to treat geometric constraints in adjoint optimization.
4. Application of Stall Warning Approach with Stall Precursor-Suppressed Casing Treatment on a Two-Stage Compressor
XU Ruize, SUN Dakun, DONG Xu*, LI Fanyu, SUN Xiaofeng, LI Jia
Corresponding author: DONG Xu, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 862-874
Keywords: axial compressor, stall warning, casing treatment
Abstract: A stall warning approach based on aero-acoustic theory is studied in this paper. For this stall warning approach, a parameter Rc is defined to measure the periodicity of the blade-passing signal. Signal simulation is used to investigate the mechanism of the stall warning approach. The results suggest that the value of Rc is influenced by the power of the perturbations. The experiments on a two-stage compressor indicate this stall warning approach can generate a warning signal several seconds before the stall. It is demonstrated in this paper that the stall warning approach can detect the distribution and evolution of stall precursors. According to the distribution of the stall precursors, the partial stall precursor-suppressed casing treatment is applied and realized a stabilization of compressor.
5. A Robust Blade Design Method based on Non-Intrusive Polynomial Chaos Considering Profile Error
GAO Linmin1, 2*, MA Chi1, 2, CAI Yutong1, 2
Corresponding author: GAO Limin, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 875-885
Keywords: robust design, non-intrusive polynomial chaos, aerodynamic performance, random profile error, uncertainty quantification
Abstract: To weaken the influence of profile error on compressor aerodynamic performance, especially on pressure ratio and efficiency, a robust design method considering profile error is built to improve the robustness of aerodynamic performance of the blade. The characteristics of profile error are random and small-scaled, which means that to evaluate the influence of profile error on blade aerodynamic performance is a time-intensive and high-precision work. For this reason, non-intrusive polynomial chaos (NIPC) and Kriging surrogate model are introduced in this robust design method to improve the efficiency of uncertainty quantification (UQ) and ensure the evaluate accuracy. The profile error satisfies the Gaussian distribution, and NIPC is carried out to do uncertainty quantification since it has advantages in prediction accuracy and efficiency to get statistical behavior of random profile error. In the integrand points of NIPC, several surrogate models are established based on Latin hypercube sampling (LHS) + Kriging, which further reduces the costs of optimization design by replacing calling computational fluid dynamic (CFD) repeatedly. The results show that this robust design method can significantly improve the performance robustness in shorter time (40 times faster) without losing accuracy, which is meaningful in engineering application to reduce manufacturing cost in the premise of ensuring the aerodynamic performance. Mechanism analysis of the robustness improvement samples carried out in current work can help find out the key parameter dominating the robustness under the disturbance of profile error, which is meaningful to further improvement of compressor robustness.
6．Effect of Leading-Edge Optimization on the Loss Characteristics in a Low-Pressure Turbine Linear Cascade
CUI Tao, WANG Songtao*, TANG Xiaolei, WEN Fengbo*, WANG Zhongqi
Corresponding author: WANG Songtao, E-mail: firstname.lastname@example.org; WEN Fengbo, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 886-904
Keywords: low pressure turbine, leading edge, loss breakdown, loss audit, boundary layer, entropy production rates
Abstract: This paper presents a numerical study on the aerodynamics loss reduction characteristics after the leading-edge (LE) optimization in a low-pressure turbine linear cascade. The LE was optimized with a simple and practical method of “Class Function/Shape Function Transformation Technique” (CST). The simulation conditions, covering the whole working range, were independently determined by incidence, Reynolds number and Mach number. Quantitative loss analyses were carried out with a loss breakdown method based on volumetric integration of entropy production rates. To understand the reason of loss reduction, the local sources at different operating points were identified with entropy production rates. The results showed that LE optimization with the CST method played a positive role in decreasing the total losses, and the working range with lower loss was extended. The profile loss and the endwall loss were significantly reduced by the LE optimization, which were also verified to be the major causes of the total loss reduction by loss breakdown. The decrease of profile loss can be attributed to the boundary layer near the LE region and the boundary layer of downstream at off-design incidence. The reduction mostly came from the pressure side at negative incidence, while came from the suction side at the positive incidence. The endwall loss was decreased markedly about 2.5%–5% by the LE optimization at the incidence of ‒12°, which was 1% at the incidence of 12°. The mechanism for the endwall loss reduction at different incidences was different from each other. At negative incidence, the LE optimization diminished the corner separation vortex on the pressure side. While at positive incidence, the benefits came from three aspects, i.e., reduced suction LE separation bubbles close to the endwall, reduced passage vortex strength, and weakened shear process between passage vortex and trailing shed vortex. The loss of the downstream zone was relatively lower than that of the profile losses and the endwall losses. The effect of LE optimization on the loss of the downstream zone at different conditions was complex and it depended both on the profile boundary layer behavior at the suction trailing edge and on the passage vortex strength.
7．Effects of Trenched Film Hole Configurations on the Endwall Film Cooling and Suction Side Phantom Cooling
DU Kun1,3, LI Zhigang1, LI Jun1,2*
Corresponding author: LI Jun, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 905-914
Keywords: gas turbine, turbine endwall cooling, trenched film holes, phantom cooling, numerical simulations
Abstract: To maximize the turbine thermal efficiency, modern gas turbine’s inlet temperature is significantly augmented within the past few decades. To prolong the lifespan of gas turbines, many efficient cooling techniques have been proposed and applied in the endwall cooling schemes. However, conventional discrete film hole does not take effect at the leading edge nearby region. In this research, how the trenched film hole configurations affects the endwall cooling and phantom cooling characteristics were deeply studied by using a verified approach. Steady 3D Reynolds-averaged Navier-Stokes (RANS) governing equations together with the shear stress transport (SST) k-w turbulence model have been solved. Firstly, results indicate that trenched film holes greatly influence the cooling effectiveness at leading edge nearby region compared to normal case. Nevertheless, suction side phantom cooling is hardly influenced by the trenched film holes. Secondly, the case with a smaller trench width obtains higher endwall cooling effectiveness, particularly at upstream region. More importantly, the cases with W=3D achieve large cooling effectiveness at leading edge nearby region with little influence by trench depth. Additionally, majority of trenched film holes coolant flow is driven towards middle passage. Therefore, the suction side phantom cooling is unaffected by the trenched film holes.
8. Entropy Generation Analysis in a Mixed-Flow Compressor with Casing Treatment
ZHANG Qianfeng1,2, DU Juan1,2,*, LI Zhihui1,2, LI Jichao1,2, ZHANG Hongwu1,2
Corresponding author: DU Juan, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 915-928
Keywords: numerical simulation, mixed-flow compressor, loss mechanism, casing treatment
Abstract: Casing treatments (CT) can effectively extend compressors flow ranges with the expense of efficiency penalty. Compressor efficiency is closely linked to loss. Only revealing the mechanisms of loss generation can design a CT with high aerodynamic performance. In the paper, a highly-loaded mixed-flow compressor with tip clearance of 0.4 mm was numerically studied at a rotational speed of 30,000 r/min to reveal the effects of axial slot casing treatment (ASCT) on the loss mechanisms in the compressor. The results showed that both isentropic efficiency and stall margin were improved significantly by the ASCT. The local entropy generation method was used to analyze the loss mechanisms and to quantify the loss distributions in the blade passage. Based on the axial distributions of entropy generation rate, for both the cases with and without ASCT, the peak entropy generation rate increased in the rotor domain and decreased in the stator domain during throttling the compressor. The peak entropy generation in rotor was mainly caused by the tip leakage flow and flow separations near the rotor leading edge for the mixed-flow compressor no matter which casing was applied. The radial distributions of entropy generation rate showed that the reduction of loss in the rotor domain from 0.4 span to the rotor casing was the major reason for the efficiency improved by ASCT. The addition of ASCT exerted two opposite effects on the losses generated in the compressor. On the one hand, the intensity of tip leakage flow was weakened by the suction effect of slots, which alleviated the mixing effect between the tip leakage flow and main flow, and thus reduced the flow losses; On the other hand, the extra losses upstream the rotor leading edge were produced due to the shear effect and to the heat transfer. The aforementioned shear effect was caused by the different velocity magnitudes and directions, and the heat transfer was caused by temperature gradient between the injected flow and the incoming flow. For case with smooth casing (SC), 61.61% of the overall loss arose from tip leakage flow and casing boundary layer. When the ASCT was applied, that decreased to 55.34%. The loss generated by tip leakage flow and casing boundary layer decreased 20.54% relatively by ASCT.
9. Review on Development of Small Point-Focusing Solar Concentrators
WANG Lu, YUAN Zhongxian*, ZHAO Yan, GUO Zhanquan
Corresponding author: YUAN Zhongxian, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 929-947
Keywords: point-focusing concentrator, Scheffler, dish, Fresnel, application
Abstract: The technology of small point-focusing concentrator of solar energy has been developing rapidly in recent years owing to its compact structure and high collecting efficiency. This report presents important developments of small point-focusing concentrator in the past decade. This kind of solar concentrator refers to the parabolic dish concentrator, the point-focusing Fresnel lens, and the Scheffler reflector. Technological advances of these concentrators and the related performances have been presented. There are three main mirror fabrication technologies for dish concentrator, which are high polishing metal, silver-glass mirror and vacuum-membrane. Polymethyl methacrylate is widely used as material in Fresnel lens. Many scholars have proposed new lens shape to improve the uniformity of focusing. The Scheffler reflector has a characteristic of fixed focus, but its design parameters are not perfect so current research focuses on the theoretical calculation of the mirror. In addition, typical applications of the small point-focusing concentrator in photovoltaic system, solar thermal system, solar chemical system, and day-lighting system are summarized. Upon listing the important publications in open literature, a category of main applications of such kind of solar collector is provided based on the working characteristics of the system.
10. Effect of Nanobubble Evolution on Hydrate Process: A Review
ZHANG Yue1,3, ZHAO Li1,3*, DENG Shuai1,3, ZHAO Ruikai2, NIE Xianhua1,3, LIU Yinan1
Corresponding author: ZHAO Li, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 948-961
Keywords: gas hydrates, nanobubbles, memory effect, hydrate process
Abstract: As a huge reserve for potential energy, natural gas hydrates (NGHs) are attracting increasingly extra attentions, and a series of researches on gas recovery from NGHs sediments have been carried out. But the slow formation and dissociation kinetics of NGHs is a major bottleneck in the applications of NGHs technology. Previous studies have shown that nanobubbles, which formed from melt hydrates, have significant promotion effects on dissociation and reformation dynamics of gas hydrates. Nanobubbles can persist for a long time in liquids, disaccording with the standpoint of classical thermodynamic theories, thus they can participate in the hydrate process. Based on different types of hydrate systems (gas + water, gas +water +inhibitors/promoters, gas + water + hydrophilic/hydrophobic surface), the effects of nanobubble evolution on nucleation, dissociation, reformation process and “memory effect” of gas hydrates are discussed in this paper. Researches on the nanobubbles in hydrate process are also summarized and prospected in this study.
11. Investigation of the Unsteady Disturbance in Tip Region of a Contra-Rotating Compressor near Stall
CHEN Weixiong, WANG Yangang*, WANG Hao
Corresponding author: WANG Yangang, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 962-974
Keywords: contra-rotating axial compressor, blade passing frequency, tip leakage flow, unsteady disturbance source, phase-locked RMS
Abstract: The present study investigated the spectrum characteristics of unsteady disturbance and the tip leakage vortex evolution during pre-stall process for a contra-rotating axial compressor (CRAC). Transient numerical simulation was carried out in a single passage of the CRAC. The original transient fluctuation and oscillation of the tip leakage vortex structure with varying flow capacity of the CRAC were revealed using circle-like pattern figure and phase-locked root mean square (PLRMS). Additionally, the tip leakage flow in terms of vortex structure evolution was visualized for the sake of revealing the flow mechanism during pre-stall process. Results show that the unsteady fluctuation first appears at φ=0.3622, and the fluctuation frequency is 2.86 BPF. Unsteady disturbance source is mainly located at the tip side of the downstream rotor leading edge. From the choking point to the near stall condition, tip leakage vortex is always found in the tip leading edge of the upstream rotor. In addition, the tip leakage vortex of upstream rotor remains in the same place over time, i.e., no fluctuation, even when the downstream rotor entered into stall state. Such a phenomenon indicates that the stall point of the contra-rotating compressor is determined by the downstream rotor. Moreover, the maximum fluctuation position is mainly concentrated on the interface between the mainstream and the tip leakage vortex of the downstream rotor. By throttling the compressor, the angle between the main leakage vortex and the circumferential direction decreases gradually. When the main leakage vortex touches and continuously impacts on the leading edge of the adjacent blade, the unsteady disturbance, which is different from that of BPF, appears firstly.
12. The Development of Top-Hat Flow Field in a Circular Symmetrical Subsonic Nozzle
ZHANG Han1, JIA Li1*, CUI Lishui2*, LI Chunhui2
Corresponding author: JIA Li, E-mail: email@example.com; CUI Lishui, firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 975-983
Keywords: top-hat flow field, jet flow, formation process, inlet condition
Abstract: In this work, the numerical analysis and experimental measurements were made to investigate the development of top-hat flow field at atmospheric pressure in a circular symmetrical subsonic nozzle. Measurements were carried out over a range of inlet velocities (about 0.07–7 m/s) based on a nozzle with constant geometric parameters, which also provided verification for the numerical simulation. The objective of this study was to determine the change of top-hat flow field from the well-known pipe velocity profile to the saddle-back distribution as well as the key behaviours for the process. Results revealed a close coupling relationship between the process and the pressure gradient inside nozzle. It was concluded that the local flow direction of fluid near the edge of cross section was changed by static pressure gradient and overlapped with the mainstream. The increase in kinetic energy of each gas particle on the cross section was different contributed to the formation of top-hat flow field. The saddle-back distribution seems to occur after the appearance of the critical position. In addition, the influence of inlet velocity on the location of critical position as well as the degree of saddle-back distribution was also concerned.
13. Three-Dimensional Numerical Simulation of Ice Crystal Melting in Jet Engine
ZHU Pengfei1, ZHANG Jiachen1, HAN Bingbing2, ZHANG Lifen1, LIU Zhenxia1*
Corresponding author: LIU Zhenxia, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 984-992
Keywords: ice crystals, three-dimensional simulation, melting process, liquid fraction
Abstract: A method was presented for calculating the melting rate of ice crystals in different axial positions in a compressor. The volume of fluid model and enthalpy-porosity model were used to simulate the melting process of single ice crystal. The result was validated by experimental data from literature. The change of the liquid fraction of the ice crystals with the axial position was obtained when the temperature distribution inside the compressor was introduced into the melting process. The liquid fraction of the spherical ice crystals was fitted with the ice crystal diameter as a variable, and the general distribution function for computing liquid fraction in any axial position in the compressor was obtained. The function of axial position as a variable for non-spherical ice crystal was also got.
14. Performance Assessment of Air-Cooled Steam Condenser with Guide Vane Cascade
ZHANG Xuelei*, LI Yunpeng, CHEN Haiping
Corresponding author: ZHANG Xuelei, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 993-1003
Keywords: air-cooled steam condenser, ambient wind, guide vane cascade, heat transfer
Abstract: Ambient wind has an unfavourable impact on air-cooled steam condenser (ACSC) performance. A new measure to improve ACSC performance is proposed by setting a diffusion type guide vane cascade beneath the ACSC platform. The numerical models are developed to illustrate the effects of diffusion type guide vane cascade on ACSC performance. The simulation results show that this vane cascade can cause the increases in coolant flows across almost all fans due to its diffusion function and lower flow resistance. Meanwhile, the guide vane cascade also decreases the fan inlet temperatures because of the uniform flow field around the condenser cells. Comparing with the case without guide device, the overall heat transfer efficiency is increased by 11.2% for guide vane cascade case under the condition of 9 m/s. The heat transfer efficiency firstly enhances and then decreases with decreasing stagger angle of guide vane under a certain wind speed. The optimum stagger angle corresponding to the maximum heat transfer efficiency is about 65.5°. The heat transfer efficiency always enhances as increasing vane cascade height, and a vane cascade with 20 m to 30 m height may be suitable to the ACSC as considering the cost.
15. Study on Working Pairs of Sorption Type Air Conditioner for Electric Vehicles under Different Temperature Zones
AN Guoliang, WANG Liwei*, WANG Zixuan, GAO Jiao
Corresponding author: WANG Liwei, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 1004-1014
Keywords: electric vehicle, automobile air conditioning, solid sorption, energy density, continue voyage course
Abstract: The air conditioning (AC) system of electric vehicles (EVs) consumes a large part of electricity of on-board batteries and influences the continue voyage course seriously. The feasibility of sorption type AC for EVs has been verified theoretically to decrease this part of energy consumption. However, the choice of optimal working pairs based on local working conditions is not considered before, which can realize not only high efficiency but also the steady and reliable operation. Thus in this paper, different solid sorption working pairs used in sorption type AC under different temperature zones are studied. We utilized Rubotherm balance test unit to study the sorption properties of various working pairs (halide-ammonia) and selected candidate working pairs by Clapeyron equation and energy analysis. Results show that MnCl2 is the only choice for cold temperate zone (CTZ) and CaCl2 is optimal for warm temperate zone (WTZ), while the mixed double halide (MnCl2 and CaCl2) is recommended in other zones. In middle temperate zone (MTZ), the probability for performance dropping down is relatively large, thus the ratio (CaCl2:MnCl2) is recommended as 0.33–1 to take advantage of the stability property of MnCl2. While in Qinghai-Tibet plateau cold area (QTPCA, the special temperature zone in China), the ratio is chosen as 2–3 because only under the limiting condition reaction is invalid. Because the continued high environmental temperature will increase the probability of limiting condition, ratio of subtropical zone (STZ) is still selected as 2–3 while that of tropical Zone (TZ) is 1–2. Taking WTZ under summer condition as example, by using sorption type AC with CaCl2 as sorbent, the increment voyage course (IVC) over the practical voyage course with conventional compression AC system (PVC) ranges from 9.4% to 37.7% for different type of EVs, i.e. the continue voyage course is increased effectively. This work provides the guidance for choosing optimal working pairs for actual utilization.
16. Experimental Study on Performance of a Closed Wet Cooling Tower for Air Wet-Bulb Temperature near 0°C
ZHOU Yasu, ZHANG Pan, ZHAO Jingde*, YANG Honghai, BAI Yufeng
Corresponding author: ZHAO Jingde, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 1015-1023
Keywords: closed wet cooling tower, performance of cooling tower, low air wet-bulb temperature, rated operating parameters, evaluation index
Abstract: Closed wet cooling towers (CWCTs) are used widely because of their better water quality and smaller water consumption. However, the operating parameters shown in the technical documents are only for rated conditions in summer, not for any other conditions, especially in low air wet-bulb temperature areas such as those near 0°C. In addition, CWCTs often fail to achieve the designed cooling effect at low air wet-bulb temperatures. A experiment set of CWCT was built, and the performance of the CWCT at low air wet-bulb temperature near 0°C was investigated. The impact of the operating parameters (air flow rate, cooling water flow rate, and spray water flow rate) on the heat and mass transfer performance of the CWCT was measured and analyzed. The results show the cooling performance of the CWCT at an air wet-bulb temperature 0°C, 2°C, and 4°C is about 47%–63% of the rated operating condition; the optimal operating parameters of these conditions for the CWCT are just the same as those of the rated operating condition in summer. According to the experimental results, some operating advices are given.
17. Numerical Simulation and Optimization of Staged Combustion and NOx Release Characteristics in Precalciner
WANG Weishu, LIAO Yihan, LIU Jun*, HUANG Zhihao, TIAN Miao
Corresponding author: LIU Jun, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 1024-1034
Keywords: TTF precalciner, staged combustion, NOx emission characteristics, optimization
Abstract: In order to study the combustion characteristics in a precalciner, the temperature and composition field in a typical Trinal-sprayed calciner were numerically analysed. The results obtained by simulation were compared to actual measurements and the simulated results were in good agreement with the measured ones. The results indicated that the aerodynamic flow field in the precalciner is satisfactory, and a symmetrical reflux occurs in the shrinkage zone of the precalciner because of air staging, which can increase the residence time of the solid particles. The temperature distribution in the furnace is uniform, and the average temperature is greater than 1200 K, which can satisfy the conditions for the pulverised coal combustion and raw material decomposition. The mass fraction distribution of oxygen, carbon monoxide, and carbon dioxide in the precalciner is closely related to the temperature distribution. The concentration of nitrogen oxides (NOx) exhibits a trend of increasing, decreasing and then increasing, and finally tending to a stable level. Within a certain velocity range, the average temperature in the precalciner and the decomposition efficiency of the raw material increase as the flue gas velocity increases. When the flue gas velocity is 24 m/s, the overall performance of the precalciner is optimal.
18. Effects of Dielectric Barrier Discharge Plasma on the Combustion Performances of Reverse-Flow Combustor in an Aero-Engine
DENG Jun1*, PENG Changxin2, HE Liming1, WANG Shuai2, YU Jinlu1, ZHAO Bingbing1
Corresponding author: DENG Jun, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 1035-1041
Keywords: aero-engine, reverse-flow combustor, double dielectric barrier discharge, plasma assisted combustion
Abstract: In order to apply plasma assisted combustion (PAC) into a reverse-flow aero-engine and verify the improvement of combustion performance, a feasible approach was proposed in this work. In this approach, based on the structure characteristics of the reverse-flow combustor, a parallel plate double dielectric barrier discharge (DBD) PAC actuator was designed to generate plasma. It was installed at the front of combustor. When the actuator is driven, the original air flow is not disturbed for the device’s structure and installation. Using aviation kerosene as fuel, the effects of plasma on ignition boundary and outlet temperature of the combustor were experimentally investigated at atmosphere pressures. Through the dual high voltage differential power supply, the large gap, large area and uniform plasma discharge was achieved. The results of PAC actuator discharge indicate that inlet air temperature has a small increase of 4–9 K. After PAC is applied, the combustion performances of reverse-flow combustor in an aero-engine are remarkably improved. Experimental results indicate that ignition boundary is widened by 3.7%–12.5% because of the impact of plasma. Outlet highest temperature of combustor is raised by 19–75 K; outlet temperature distribution coefficient is reduced by 11.1%–26.6%. This research provides an effective and practicable way to implement the application of PAC in aero-engine combustor and has some engineering application significance.
19. Experimental Study on Thermal Performance of FLNG Spiral Wound Heat Exchanger under Sloshing Conditions
YAN Yan, SUN Chongzheng, HAN Hui, LI Yuxing*
Corresponding author: LI Yuxing, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 1042-1053
Keywords: spiral wound heat exchanger, FLNG, experimental, sloshing
Abstract: The FLNG spiral wound heat exchanger (SWHE) is affected by the sea conditions, which leads to more complex flow process and decrease the heat transfer performance of the heat exchanger. In order to study the thermal performance of FLNG SWHE under heaving and swaying conditions, the experimental devices of FLNG SWHE and six-DOF (degree of freedom) sloshing platform were built. The effects of heaving and swaying motions on the pressure drop and heat transfer characteristics were analyzed at different sloshing amplitudes. The results showed that the heaving and swaying motions can cause the temperature rise and pressure fluctuation of SWHE, especially for swaying. The effect of sloshing on the heat transfer performance at the top of SWHE was greater than bottom. The pressure fluctuation percentage was within 7% and the amount of temperature change was less than 2°C, under the sloshing displacement among 120–255 mm.
20. Experimental Study of the Particulate Dirt Characteristics on Pipe Heat Transfer Surface
YANG Qirong, ZHANG Zhenglin, YAO Erren*, ZHANG Ning, LI Nan
Corresponding author: YAO Erren, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 1054-1064
Keywords: particulate fouling, growth rule, fouling thermal resistance, fouling rate, synergistic fouling
Abstract: The systematic study of the particulate dirt characteristics on heat exchanging surface can provide theoretical guidance for defouling. In this paper, four main compositions of particulate dirt in the treated city sewage (i.e., CaCO3, MgO, CaSO4 and SiO2) are selected as the research objects. The effects of different working conditions, characteristics of particles on the growth rules of particulate dirt and the synergistic fouling by different particles are researched by thermal resistance method experimentally, while the microstructures of the dirt are observed by Scanning Electron Microscope (SEM). The asymptotic values of both dirt thermal resistance and the scaling rate decrease with the increasing of working fluid velocity, while the two asymptotic values increase with the increasing particle size and particle concentration. Although the working fluid import temperature shows a weaker influence on the thermal resistance, but the increase of working fluid import temperature can retard the fouling rate. Among the stable values of the thermal resistances of four types of fouling, SiO2 is the largest and MgO is the smallest. The synergistic fouling by different types of particles results in the denser structure of mixed fouling.
21. Study on the Performance of Organic Rankine Cycle-Heat Pump (ORC-HP) Combined System Powered by Diesel Engine Exhaust
ZHAO Tenglong1,2, YU Fei1,2, ZHANG Hongguang1,2,* , WU Yuting1,2, WANG Yan1,2
Corresponding author: ZHANG Hongguang, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 1065-1077
Keywords: organic Rankine cycle, heat pump, combined system, total efficiency, COPh
Abstract: This study presents an ORC-HP combined system driven by diesel engine exhaust. This paper focuses on the feasibility and performance of the combined system under heating mode to heat a coach. The performances of the combined system with different parameters, including condensation temperature and evaporation pressure in ORC system, gas cooler outlet pressure, gas cooler outlet temperature and evaporation temperature in HP system, have been analyzed. The results show that the combined system can fully meet the demand of heat production. The optimal flow division ratio (rp) of 0.32 is selected by analyzing the system performance. Low condensation temperature is beneficial to the combined system performance. There exists a suitable range of evaporation temperature, gas cooler outlet pressure and gas cooler outlet temperature to achieve excellent performance. The heating coefficient of performance (COPh) shows a first increasing and then decreasing trend with gas cooler outlet pressure, namely there exists an optimal gas cooler outlet pressure that achieves the maxi- mum COPh. The maximum total efficiency, COPh and heating capacity can reach up to 48.44%, 4.78 and 176.56 kW, respectively. These results show significant energy savings by applying the ORC-HP combined system.
22. Coupling Effect of Heat Transfer and Flow Resistance in the Rifled Tube Water Wall of a Ultra-Supercritical CFB Boiler
LI Yaode1,2, YANG Dong1,*, OUYANG Shijie1, LIU Dan1, WANG Wenyu1
Corresponding author: YANG Dong, E-mail: firstname.lastname@example.org
Journal of Thermal Science, 2019, 28(5): 1078-1088
Keywords: supercritical pressure, heat transfer, frictional resistance, coupling effect
Abstract: The coupling factor is used in this study to characterise the combined effect of the heat transfer and resistance characteristics of a rifled tube. Boundary layer theory is utilised to investigate the relationship between the comprehensive coefficient and Reynolds number in two regions, namely, higher and lower than pseudo-critical enthalpy. Results indicate that mass flux exerts a decisive negative influence on the coupling effect, and the impacts of pressure and heat flux are weak. The overall effect decreases rapidly as the mass flux increases, but it increases in the area behind the quasi-critical enthalpy. The coupling effect is also affected by specific heat ratio, thermal acceleration and buoyancy. The correlations of heat transfer and friction resistance are deduced with high precision according to experimental data.
23. Ventilation Optimization for Reduction of Indoor Air Temperature of Main Transformer Room in Urban Indoor Substation by the Variational Method
LIU Yun1*, YE Wenjie1, LI Yonghua1, CHEN Tiantian1, HU Kang2
Corresponding author: LIU Yun, E-mail: email@example.com
Journal of Thermal Science, 2019, 28(5): 1089-1101
Keywords: urban indoor substation, main transformer room, ventilation optimization, variational principle, average temperature of indoor air
Abstract: Urban indoor substations are widely used for electrical power distribution in urban networks. However, they have the problems of heat dissipation and ventilation in main transformer room, which not only influence the thermal behavior of main transformer, but also decrease the lifetime, reliability, and precision of other electronic equipment. In this contribution, we developed a new ventilation optimization method based on the variational method to solve the aforementioned problems. First, we applied the minimum average temperature of indoor air as the optimization objective combined with some constrains to establish a Lagrange function, and employed the variational method to deduce some optimized governing equations that the optimum indoor patterns should meet the minimum indoor air average temperature. Finally, a typical main transformer room model was taken as an example to demonstrate the applications of the newly developed ventilation optimization method. It was concluded that the inflowing fresh air needed to sweep more area of heating walls to take away more heat, and reduce the average temperature of indoor air. Furthermore, based on the optimized air velocity distribution, we redesigned the ventilation arrangements and reduced the indoor average temperature prominently (from 337.44 K to 314.82 K), which can provide the guidance to design the ventilation of main transformer room to improve the reliability of electronic equipment in main transformer room.