Springer Link: https://link.springer.com/journal/11630/28/1
1. Review of Molecular Simulation Method for Gas Adsorption/desorption and Diffusion in Shale Matrix
WANG Hui, QU Zhiguo, YIN Ying, BAI Junqiang, YU Bo
Journal of Thermal Science, 2019, 28(1): 1-16
DOI: https://doi.org/10.1007/s11630-018-1053-9
Keywords: shale gas, molecular simulation, adsorption/desorption, diffusion
Abstract: Shale gas is becoming an increasingly promising alternative energy resource because of its high efficiency and environment-friendly characteristic. The amount of adsorbed gas on the shale matrix surfaces and dissolved gas in the shale matrix bulk is the dominant factor in the long-term productivity of shale reservoir. Although experimental measurements have been extensively carried out to investigate the gas adsorption and diffusion properties in the shale matrix, they cannot provide the detailed information on the microscopic transport mechanism of shale gas during the gas production process. Molecular simulation can accurately visualize the gas adsorption/desorption and diffusion processes in the shale matrix. In the present study, the recent research advances of molecular simulation on gas adsorption/desorption and diffusion in the shale matrix are reviewed. Firstly, the density functional theory (DFT) for shale gas molecule desorption/adsorption on the surface of the matrix crystal is illustrated. Then, the grand canonical Monte Carlo (GCMC) method predicting the amount of shale gas desorption/adsorption in the shale matrix crystal is introduced. Finally, molecular dynamics simulation (MD) for gas diffusion in the shale matrix is elucidated. Further developments of the molecular simulation method in shalegas production are also discussed.
2. Design and Development of a Lens-walled Compound Parabolic Concentrator- A Review
LI Guiqiang
Journal of Thermal Science, 2019, 28(1): 17-29
DOI: https://doi.org/10.1007/s11630-019-1083-3
Keywords: compound parabolic concentrator, lens-walled, optical, uniform flux distribution
Abstract: Compound parabolic concentrator (CPC) is a representative among solar concentrators, one of whose disadvantage is that the concentration ratio limits the half acceptance angle. Based on this, researchers put forward a novel structure, named the lens-walled CPC. This paper reviews the design and development of lens-walled CPC. The structure of the symmetric and asymmetric lens-walled CPC and the improved ones are presented, and their indoor and outdoor performances are also illustrated. The lens-walled CPC has a larger half acceptance angle and a more uniform flux distribution that is suitable for PV application. Furthermore, the life-cycle assessment for building integrated with PV is performed and it shows that the energy payback time of such integrated system has a significant advantage. In addition, future research areas are also indicated that may provide more functions and more stable performance. The design methods and developmental directions given in this study would provide many references in solar optical research and solar concentrator optimization.
3. An Improved Modeling Method of Water-side Fouling in Enhanced Tubes of Condensers in Application of Cooling Water Tower
SHEN Chao, WANG Yuan, GAO Rong, YAO Yang, WANG Xinlei
Journal of Thermal Science, 2019, 28(1): 30-39
DOI: https://doi.org/10.1007/s11630-018-1021-4
Keywords: fouling, enhanced tubes, sticking probability, thermal resistance, cooling water
Abstract: Kern-Seaton fouling model of enhanced tubes and two parameters that foulant sticking probability (P) and deposit bond strength factor (ξ) in that model are analyzed theoretically. A new modeling method of fouling in enhanced tubes is proposed, which has physical meaning and a higher accuracy in comparison to traditional ones. A semi-theoretical model of fouling in internal helical-rib tubes is developed in this paper based on the long-term fouling data, targeting to improve previous fouling models. This new fouling model has three variables: area index, j-factor ratio and friction factor ratio. This triple-variable model has a maximum deviation of 5.20% and an average deviation of 1.87%, indicating a higher accuracy than previous ones. The mathematical type of this new model is in accordance with the theoretic deduction, thus makes sense in theory compared with old ones. It is also found that all current fouling models without the correction of heat transfer area index (β) have the biggest deviation when predicting the fouling resistance of enhanced tubes with p/e around 3.5, but which can be reduced by introducing the area index into the model. The new modeling method presented in this paper has outstanding advantages in modeling fouling of enhanced tubes, thus can be used in future fouling research.
4. Effects of High-temperature Char Layer and Pyrolysis Gas on NOx Reduction in a Typical Decoupling Combustion Coal-fired Stove
LI Honglin, HAN Jian, ZHANG Nan, LIU Xinhua, HE Jingdong, DU Wei
Journal of Thermal Science, 2019, 28(1): 40-50
DOI: https://doi.org/10.1007/s11630-018-1022-3
Keywords: decoupling combustion, low NOx emission, domestic stove, numerical simulation, bituminous briquette, thermal efficiency
Abstract: The suppression of nitrogen oxides (NOx) is the key to reducing pollutant emission of a domestic coal-fired stove due to the limitation of technology condition and economic cost. The decoupling combustion (DC) technology invented by Institute of Process Engineering (IPE), Chinese Academy of Sciences (CAS) is characterized by that a traditional stove is separated into a pyrolysis and a combustion chamber as well as a bottom passage between them. In this study, the combustion of briquette from bituminous coal in different operation modes in a typical decoupling stove is tested and simulated to validate the advantage of DC technology over so-called reverse combustion. The smokeless and high-efficiency combustion of bituminous briquette with low emissions of NOx and CO can be implemented by utilizing low NOx combustion under low temperature and reduction atmosphere in the pyrolysis chamber as well as after-combustion of char and pyrolysis gas under high temperature and oxidation atmosphere in the combustion chamber. The effects of the main reducing components in pyrolysis gas as well as char on NOx reduction were numerically investigated in this study, which shows that the reducing ability increases gradually from CH4, CO to char, but the combined reducing ability of them cannot be determined by a simple addition.
5. Investigation of the Vortex Dynamic Mechanism of the Flow Losses on a Transonic Compressor Stator
KAN Xiaoxu, WANG Songtao, LUO Lei, SU Jiexian
Journal of Thermal Science, 2019, 28(1): 51-60
DOI: https://doi.org/10.1007/s11630-018-1029-9
Keywords: transonic compressor stator, throttling process, vortex structure, flow losses, topological analysis
Abstract: For a transonic axial-flow compressor, the numerical simulations, verified against experimental data, were used to study the inherent correlation between the evolutionary process of the vortex structures and the flow loss in a compressor stator passage during the throttling process. The flow loss was divided accurately and quantitatively, based on the evolutionary process of the vortex structures. According to the position of the singular points of the vortex structures, the influence of the evolution of the vortex structures on the generation and development of the flow loss was analyzed on a microscale scale. Thereafter, this paper provided the vortex dynamic mechanism of the flow loss, which was important to enrich the theoretical system of the flow field in the compressor. The results show that: the flow loss at the top of the stator tip is caused by the low-energy fluid clusters, which are transported and accumulated by the vortices from the endwall; the transport effect of the pressure separation vortex at the upper half-height only migrates the position of the flow losses, but there is new flow loss generated by its shear action to the endwall. The dominant flow loss during the throttling process concentrates upon the closed separation bubble around the middle of the suction side of the stator.
6. Investigation of Vapor-liquid Ejector with Organic Working Fluids
CHEN Jianyong, HUANG Yisheng, NIU Zhiting, LUO Xianglong, CHEN Ying, YANG Zhi
Journal of Thermal Science, 2019, 28(1): 61-71
DOI: https://doi.org/10.1007/s11630-018-1031-2
Keywords: vapor-liquid ejector, modelling, organic fluids, pressurelifting
Abstract: The vapor-liquid ejector is a simply flow device and driven by thermal energy. In this paper, a modified mathematical model of the vapor-liquid ejector is proposed, and the validation shows good agreements with the experimental data. A study is carried out with six organic working fluids, namely R1233zd(E), R1336mzz(Z), R236ea, R245ca, R245fa and R365mfc. The influences of the entrainment ratio, the area ratio, the superheating at the vapor nozzle inlet, the subcooling at the liquid nozzle inlet, and the pressures at these inlets on the pressure lifting are parametrically investigated. An increase in the subcooling leads to the great increasing of pressure lifting and the superheating has slight effect on the pressure lifting, whereas others have the opposite tendency. The studies of the pressures and temperatures at the typical locations inside the vapor-liquid ejector are further conducted by using R1336mzz(Z). The results show that the above parameters have great influence on these pressures and temperatures inside except that the pressures are insignificantly impacted by the superheating, and the temperatures are negligibly affected by the area ratio. R1336mzz(Z) is recommended as a good working fluid for the vapor-liquid ejector.
7. Testing and Modeling of the Dynamic Response Characteristics of Pulsating Heat Pipes during the Start-up Process
XU Rongji, CHEN Hao, WU Qingping, XU Shuhui, WANG Ruixiang
Journal of Thermal Science, 2019, 28(1): 72-81
DOI: https://doi.org/10.1007/s11630-018-1032-1
Keywords: pulsating heat pipe, heating power, dynamic response characteristic, time constant, amplification factor
Abstract: Pulsating heat pipes (PHPs) are two-phase heat transfer heat pipes with high heat transfer capability and simple structure. Heating power is an important factor that affects the start-up response characteristics of PHPs. The operational characteristics during the start-up and stable operating stages were studied through experiments, and the corresponding dynamic response model under a specified heating power was established based on experimental data and flow pattern in the tube. The starting time, starting temperature, and dynamic response characteristic parameters at a certain heating power were calculated by the dynamic response model. The response characteristics of working fluid during the stable operation of PHPs were deduced based on the dynamic response curve of PHPs during the non-operational and stable operation stages. The response characteristics of PHPs for the step effect (given heating power) were quantitatively described by amplification factor K and time constant τ, thereby presenting the basis for the study on heat and mass transfer mechanisms of PHPs from non-operational to steady operation stage. Results showed that the minimum thermal resistance and the minimum time constant of the PHP are approximately 0.28 °C/W and 75, respectively, obtained at a heating power of 160 W. Moreover, these results indicated that the dynamic response of PHPs demonstrates a favourable performance and rapidly reaches another stable working state when their heat transfer performance is stable. However, the dynamic response time constant of pure fluids decreases when the quantity of the liquid working fluid in the PHP decreases with the increase in heating power.
8. Experimental Study on the Characteristics of Water Vapor Generation from Gas-washing Bottle and Injector
WANG Zhipeng, WANG Lang, ZHAO Angran, CHENG Shuhao, YANG Ruiming, ZHUO Yuqun, TONG Huiling
Journal of Thermal Science, 2019, 28(1): 82-87
DOI: https://doi.org/10.1007/s11630-018-1050-z
Keywords: water vapor, FTIR, gas-washing bottle, injector, temperature and humidity recorder
Abstract: Gas-washing and water injection are two commonly used methods in generating certain moisture content in gas flow stream, but the control accuracy of these methods remains uncertain. The purpose of the study is to investigate the characteristic of water vapor generation of the two methods. The temperature and humidity recorder and FTIR gas analyzer have been adopted to monitor the moisture content in tests. It has been revealed that, in gas-washing process, the moisture content in gas stream is well below saturation, and long time is required before moisture content stabilized after water bath temperature or carrier gas flow rate changed. Water injection pump could directly control the amount of water injected into gas stream. However, the moisture content generated in this way is not stable but oscillates in cycles, whose frequency and magnitude are closely related to water injection amount.
9. Thermal Analysis and Identification of Potential Fire-proof Energy Building Material Based on Artificial Leather
MA Yujie, DANG Xugang, SHAN Zhihua
Journal of Thermal Science, 2019, 28(1): 88-96
DOI: https://doi.org/10.1007/s11630-018-1054-8
Keywords: polyvinyl chloride, polyurethane, artificial leather, identification, ATR-FTIR
Abstract: Artificial leather fire-proof materials have obtained a good market due to stable production quality and low production price. Three kinds of artificial leather materials (polyvinyl chloride artificial leather (PVC), polyurethane artificial leather (PU) and polyurethane/polyvinyl chloride artificial leather (PU/PVC) have been investigated, and then seven analysis methods were introduced to identify the materials. Thermo-gravimetric analysis indicated the materials had fine thermal stability. Fire-proof testing revealed the artificial leather materials had good flame retardancy, which could improve the applicability of fire-proof building materials. Tearing examination results indicated that there was a clear distinction between PVC and PU. The PU displayed significant differences compared with PVC or PVC/PU through pH indicator to observe the color of the pyrolysis gas aqueous solution. The dissolution tests results showed that cyclohexanone, dichloromethane and dimethylformamide(DMF) were efficient solvents that could be used for identifying PVC, PU and PU/PVC. The ATR-FTIR, a way to provide the high discriminating ability for identifying artificial leathers, indicated that the artificial leathers had different infrared characteristic peaks. In addition, the main compositive materials of the artificial leathers could be inferred by the relative contents analysis of N and Cl in artificial leathers.
10. Influence of Solids Circulation Flux on Coal Gasification Process in a Pressurized High-density Circulating Fluidized Bed
ZHANG Yawen, LEI Fulin, XIAO Yunhan
Journal of Thermal Science, 2019, 28(1): 97-105
DOI: https://doi.org/10.1007/s11630-018-1059-3
Keywords: CFD, two-fluid model, gasification, high-density CFB
Abstract: The coal gasification behaviors in the pressurized high-density circulating fluidized bed under various solids circulation fluxes were studied with the CFD method, which combines the two-fluid model and coal gasification reactions represented by the chemical percolation devolatilization and the MGAS models. The numerical method was validated with two experimental cases, and detailed distributions of gas species and temperature in the riser were illustrated to understand the gasification process. To fully understand the influence of solids circulation flux on the gasification behavior, a series of cases were simulated with the solids flux varying gradually from 260 to 1010 kg/m2s, and the composition and quality of syngas were compared between various cases. The higher heating value of syngas firstly increased and then decreased with the increase of solids flux, and it reached the highest value around 480 kg/m2s. The influence of solids flux on gasification process was further analyzed through the contours of temperature, solids concentration, and gas composition in the riser.
11. Numerical Study of Pressure Pulsation of Centrifugal Pumps with the Compressible Mode
YANG Jun, LIU Jun, LIU Xiaohua, XIE Tian
Journal of Thermal Science, 2019, 28(1): 106-114
DOI: https://doi.org/10.1007/s11630-018-1071-7
Keywords: water compressibility, Tait equation, unsteady flow, pressure pulsations, centrifugal pump
Abstract: The compressible effect of wateris often neglected in the simulation of hydraulic machinery. However, based on experimental and numerical study, it is found that the compressibility of water could influence the magnitude of the pressure pulsation at some frequency in the pump. Therefore, in order to investigate the influence of water compressibility, compressible model is established by using Tait equation. The internal flow of centrifugal pump under different conditions is calculated by this model. The calculated results are compared with the incompressible results, and it is indicated that the compressibility of water has little effect on the performance parameters. But it affects the amplitude of pressure fluctuations at some discrete frequency, especially at the outlet of impeller and volute tongue where significant jet-wake and rotor/stator interaction appears respectively. Meanwhile, water compressibility makes greater influence on the flow pulsation under off-design condition. Therefore, it is necessary to consider the compressibility of working medium in the numerical simulation of unsteady flow in centrifugal pumps, especially in area with strong unsteady flow and at off-design condition.
12. MWCNTs/SWCNTs Nanofluid Thin Film Flow over a Nonlinear Extending Disc: OHAM Solution
GOHAR, TAZA Gul, WARIS Khan, MUHAMMAD Shuaib, MUHAMMAD Altaf Khan, EBENEZER Bonyah
Journal of Thermal Science, 2019, 28(1): 115-122
DOI: https://doi.org/10.1007/s11630-018-1075-3
Keywords: CNTs-H2O based nanofluid, variable thin layer, nonlinear radially stretching disc, magnetic field, skin friction and Nusselt number, OHAM & numerical method
Abstract: The aim of this research is the improvement towards the consumption of energy in the field of engineering and industry. The efforts have been paid to the enhancement of heat transmission and cooling process through a nanofluid coating of a nonlinear stretching disc. The combination of Water (H2O) and multiple walled carbon nanotubes (MWCNT) / single walled carbon nanotubes (SWCNT) have been used as a nanofluid. The spreading of a thin nano-layer with variable thickness over a nonlinear and radially stretching surface has been considered. The estimated results of the problem have been accomplished using the Optimal Homotopy Analysis Method (OHAM). The residual errors of the OHAM method have been shown physically and numerically. The important physical parameters of skin friction and Nusselt number have been calculated and discussed. The other embedding parameters like generalized magnetic parameter, Prantl number, nanofluid volume fraction and Eckert number have been intended and discussed.
The obtained results have been compared with the Numerical(ND-Solve) method for both sorts of CNTs. The closed agreement of both methods has been achieved.
13. Thermal and Electrical Modelling of a CPV/T System Varying Its Configuration
RENNO Carlo
Journal of Thermal Science, 2019, 28(1): 123-132
DOI: https://doi.org/10.1007/s11630-018-1082-4
Keywords: CPV/T system, point-focus configuration, linear focus configuration, thermal analysis, electrical analysis, primary energy saving, economic analysis
Abstract: In this paper, the main aim is the performances modelling from the electrical and thermal point of view of a concentrating photovoltaic and thermal (CPV/T) system in order to evaluate the primary energy and economic savings respect to a traditional system, when the same energy loads are satisfied. This study is realized by both varying the CPV/T system configuration and considering two different users. In particular, the point-focus (PF), and linear focus (LF) configurations of the CPV/T system are considered in order to match the residential user and hotel energy loads. The CPV/T system is sized adopting as input data: the Direct Normal Irradiance (DNI) modelled by an artificial neural network and the users’ energy demands. In these hypotheses, the performances of the PF and LF systems are evaluated and then compared for the two users located in Southern Italy, in terms of electrical and thermal energy production, cells number, space occupied, energy and economic savings and CO2 emissions avoided. Finally, the PF system shows a lower simple pay-back and a higher primary energy saving, while the space occupied by a LF system results to be lower respect to the PF configuration.
14. Effect of Bowed/Leaned Vane on the Unsteady Aerodynamic Excitation in Transonic Turbine
LIU Jian, QIAO Weiyang, DUAN Wenhua
Journal of Thermal Science, 2019, 28(1): 133-144
DOI: https://doi.org/10.1007/s11630-018-1084-2
Keywords: transonic turbine, leaned, bowed, aerodynamic performance, aerodynamic excitation, numerical simulation
Abstract: To investigate the effect of bowed/leaned vane configurations on the aerodynamic performance and aerodynamic excitation in transonic high-pressure turbine, the full three-dimensional viscous unsteady numerical simulation was performed by solving N-S equations based on SAS SST method．The influence of bowed /leaned vanes on turbine efficiency and efficiency fluctuation was investigated. The action of vane modelling to the overall aerodynamic fluctuation level and the amplitude of each vane passing frequency were analyzed. By comparing instantaneous pressure fluctuation contours in the blade passage with space-time maps, the link of the pressure fluctuation on blade surface with flow distortions was achieved, which can reveal the mechanism of the impact of the vane modelling. As the results suggest, the turbine efficiency is promoted with positively leaned and bowed vane modelling, and the fluctuation of stage turbine efficiency is repressed, which contributes to the smooth running of the turbine stage. The blade aerodynamic excitation on the rotor blade is characterized by the motion of vane trailing edge shock system, and the vane configurations can reduce the fluctuation level on the rotor blade surface effectively. For the positively leaned vane configuration, the aerodynamic excitations at the root and tip region are affected by the impact of the amplitude of the first harmonic, where as they are reduced with the decrease of the amplitude of the second and higher harmonics at midspan. For the positively bowed vane, aerodynamic excitation is repressed by reducing the amplitude of the third harmonic at the root region, and the first harmonic at the tip region, and the amplitude of each harmonic is reduced at the middle region.
15. Experimental Investigation on the Effect of Mainstream Turbulence on Full Coverage Film Cooling Effectiveness for a Turbine Guide Vane
FU Zhongyi, ZHU Huiren, CHENG Lijian, JIANG Ru
Journal of Thermal Science, 2019, 28(1): 145-157
DOI: https://doi.org/10.1007/s11630-019-1085-9
Keywords: film cooling effectiveness, turbulence intensity, mass flow rate ratio, turbine guide vane
Abstract: Experiments have been performed to investigate the effect of mainstream turbulence on the three-dimensional distribution of the full coverage film cooling effectiveness for two enlarged actual twisted vanes with cylindrical or shaped holes. The film cooling effectiveness was measured by transient liquid crystal technique at mainstream turbulence intensities of 2%, 9% and 15%. The mass flow rate ratios range from 5.5% to 12.5%. There are 3, 8 and 7 rows of film holes on the suction side, leading edge and pressure side, respectively. Results show that for the cylindrical hole vane the high mainstream turbulence intensity decreases the film cooling effectiveness in the top region and down region of pressure side in the low mass flow rate ratio of 5.5%, while the effect is opposite in the high mass flow rate ratio of 12.5%. The film cooling effectiveness in the middle region of pressure side decreases obviously with the increase of the turbulence at the low mass flow rate ratio of 5.5%, while the influence of increasing turbulence weakens gradually with the increase of mass flow rate ratio. Moreover, the high mainstream turbulence improves the film cooling effectiveness in the further downstream of the holes on suction side at the high mass flow rate ratio of 12.5%. For the shaped hole vane, the increase of mainstream turbulence decreases the film cooling effectiveness at all mass flow rate ratios. This study reveals the influence rule of the mainstream turbulence on the film cooling effectiveness in the different regions of the three-dimensional vane surface. The results would guide the designs of engineering heat transfer with application in gas turbine blade/vane cooling.
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