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Journal of Thermal Science
Journal Prestige (SJR): 0.316  Citation Impact (citeScore): 1 Number of Followers: 21  Hybrid journal (It can contain Open Access articles)ISSN (Print) 1993-033X - ISSN (Online) 1003-2169 Published by Springer-Verlag  [2468 journals]
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- Experimental and Numerical Investigations of Shock-Wave Boundary Layer
Interactions in a Highly Loaded Transonic Compressor Cascade-
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Abstract: Abstract Experimental and numerical investigations were conducted to investigate the variations of shock-wave boundary layer interaction (SBLI) phenomena in a highly loaded transonic compressor cascade with Mach numbers. The schlieren technique was used to observe the shock structure in the cascade and the pressure tap method to measure the pressure distribution on the blade surface. The unsteady pressure distribution on blade surface was measured with the fast-response pressure-sensitive paint (PSP) technique to obtain the unsteady pressure distribution on the whole blade surface and to capture the shock oscillation characteristics caused by SBLI. In addition, the Reynolds Averaged Navier Stokes simulations were used to compute the three-dimensional steady flow field in the transonic cascade. It was found that the shock wave patterns and behaviors are affected evidently with the increase in incoming Mach number at the design flow angle, especially with the presence of the separation bubble caused by SBLI. The time-averaged pressure distribution on the blade surface measured by PSP technique showed a symmetric pressure filed at Mach numbers of 0.85, while the pressure field on the blade surface was an asymmetric one at Mach numbers of 0.90 and 0.95. The oscillation of the shock wave was closely with the flow separation bubble on the blade surface and could transverse over nearly one interval of the pressure taps. The oscillation of the shock wave may smear the pressure jump phenomenon measured by the pressure taps.
PubDate: 2023-12-06
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- Exergy Analysis of Charge and Discharge Processes of Thermal Energy
Storage System with Various Phase Change Materials: A Comprehensive
Comparison-
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Abstract: Abstract Thermal energy storage (TES) is of great importance in solving the mismatch between energy production and consumption. In this regard, choosing type of Phase Change Materials (PCMs) that are widely used to control heat in latent thermal energy storage systems, plays a vital role as a means of TES efficiency. However, this field suffers from lack of a comprehensive investigation on the impact of various PCMs in terms of exergy. To address this issue, in this study, in addition to indicating the melting temperature and latent heat of various PCMs, the exergy destruction and exergy efficiency of each material are estimated and compared with each other. Moreover, in the present work the impact of PCMs mass and ambient temperature on the exergy efficiency is evaluated. The results proved that higher latent heat does not necessarily lead to higher exergy efficiency. Furthermore, to obtain a suitable exergy efficiency, the specific heat capacity and melting temperature of the PCMs must also be considered. According to the results, LiF-CaF2 (80.5 wt%:19.5 wt%) mixture led to better performance with satisfactory exergy efficiency (98.84%) and notably lower required mass compared to other PCMs. Additionally, the highest and lowest exergy destruction are belonged to GR25 and LiF-CaF2 (80.5:19.5) mixture, respectively.
PubDate: 2023-12-01
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- Numerical Investigation of Zigzag Bending-Angle Channel Effects on Thermal
Hydraulic Performance of Printed Circuit Heat Exchanger-
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Abstract: Abstract This study investigated the effects of zigzag-flow channel bending angle in printed circuit heat exchangers (PCHEs) using a computational fluid dynamics method with ANSYS-FLUENT simulation. The three-dimensional model of PCHE with a 15° curved, zigzag channel was conducted for preliminary validation. The comparisons between the CFD simulation results and the experimental data showed good agreement with some discrepancies in the heat transfer and pressure drop results. In addition, different bending angle configurations (0°, 3° to 30°) of zigzag channels were analyzed to obtain better thermal-hydraulic performance of the zigzag channel PCHE under different inlet mass flow rates. The criteria of heat transfer and frictional factor were applied to evaluate the thermal-hydraulic performance of the PCHE. The results showed that the 6° and 9° bending channel provided good thermal-hydraulic performance. New correlations were developed using the 6° and 9° bending channel angles in PCHE designs to predict the Nusselt number and friction factor.
PubDate: 2023-11-24
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- Experimental and Numerical Analysis of a PCM-Integrated Roof for Higher
Thermal Performance of Buildings-
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Abstract: Abstract Phase change materials (PCMs) designate materials able to store latent heat. PCMs change state from solid to liquid over a defined temperature range. This process is reversible and can be used for thermo-technical purposes. The present paper aims to study the thermal performance of an inorganic eutectic PCM integrated into the rooftop slab of a test room and analyze its potential for building thermal management. The experiment is conducted in two test rooms in Antofagasta (Chile) during summer, fall, and winter. The PCM is integrated into the rooftop of the first test room, while the roof panel of the second room is a sealed air cavity. The work introduces a numerical model, which is built using the finite difference method and used to simulate the rooms’ thermal behavior. Several thermal simulations of the PCM room are performed for other Chilean locations to evaluate and compare the capability of the PCM panel to store latent heat thermal energy in different climates. Results show that the indoor temperature of the PCM room in Antofagasta varies only 21.1°C±10.6°C, while the one of the air-panel room varies 28.3°C±18.5°C. Under the experiment’s conditions, the PCM room’s indoor temperature observes smoother diurnal fluctuations, with lower maximum and higher minimum indoor temperatures than that of the air-panel room. Thermal simulations in other cities show that the PCM panel has a better thermal performance during winter, as it helps to maintain or increase the room temperature by some degrees to reach comfort temperatures. This demonstrates that the implementation of such PCM in the building envelope can effectively reduce space heating and cooling needs, and improve indoor thermal comfort in different climates of Chile.
PubDate: 2023-11-13
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- Comparative Experimental Study on Heat Transfer Characteristics of
Building Exterior Surface at High and Low Altitudes-
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Abstract: Abstract The external surface heat transfer coefficient of building envelope is one of the important parameters necessary for building energy saving design, but the basic data in high-altitude area are scarce. Therefore, the authors propose a modified measurement method based on the heat balance of a model building, and use the same model building to measure its external surface heat transfer coefficient under outdoor conditions in Chengdu city, China at an altitude of 520 m and Daocheng city at an altitude of 3750 m respectively. The results show that the total heat transfer coefficient (ht) of building surface in high-altitude area is reduced by 34.48%. The influence of outdoor wind speed on the convective heat transfer coefficient (hc) in high-altitude area is not as significant as that in low-altitude area. The fitting relation between convection heat transfer coefficient and outdoor wind speed is also obtained. Under the same heating power, the average temperature rise of indoor and outdoor air at high-altitude is 41.9% higher than that at low altitude, and the average temperature rise of inner wall is 25.8% higher than that at low altitude. It shows that high-altitude area can create a more comfortable indoor thermal environment than low-altitude area under the same energy consumption condition. It is not appropriate to use the heat transfer characteristics of the exterior surface of buildings in low-altitude area for building energy saving design and related heating equipment selection and system terminal matching design in high-altitude area.
PubDate: 2023-11-13
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- Numerical Study on Local Flow and Heat Transfer Characteristics of
Supercritical CO2 in PCHE with Sinusoidal Channels-
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Abstract: Abstract Local heat transfer and flow characteristics, which is crucial to the overall performance of supercritical CO2 recuperators, is rarely examined in details in reported studies. In this paper, the local heat transfer and flow characteristics of supercritical CO2 in sinusoidal channel printed circuit heat exchangers are numerically investigated under the working conditions of recuperators. Based on the simplified physical model constituted by 10 pitches, the variations of Re, heat flux, Nu, secondary flow and other relevant parameters along the flow direction are analyzed firstly. Comparison is further made between the high and low temperature recuperators (HTR and LTR). It’s observed that the local heat transfer and flow characteristics vary greatly from the inlet to the outlet, especially in the LTR. Differences of 127.5% and 61.7% can be observed on the cold side of the LTR for Re and heat transfer coefficient h, respectively. Results indicate that the temperature difference and heat transfer coefficient h should not be regarded as constant and the distribution of h should be carefully considered in the design of the LTR. The complicated interactions among the varying thermophysical properties, buoyancy and the periodically changed centrifugal force are believed to be the key that shapes the flow fields. Furthermore, the changes of the wavy angle θ are found to have greater influence than the changes of mass flow rate in reshaping the flow field when θ>25°. Though gravity direction strongly affects the local heat transfer and flow characteristics, it’s also found that the effects on the overall thermal-hydraulic performance are relatively minor. Yet the installation direction that yields αy=g should better be avoided for the sinusoidal channel printed circuit heat exchanger.
PubDate: 2023-11-10
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- Flame Structure of Methane and Kerosene Combustion with A Compact Concave
Flame-Holder using the LES-pdf Method-
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Abstract: Abstract Compact flame-holders for afterburners are an increasing requirement for modern aero engines. However, flame-holder design is non-trivial since high inlet temperatures, velocities, and elaborate structures induce complex turbulence, combustion, and spray coupling in modern afterburners. In this work, the LES-pdf and stochastic fields-Lagrangian particle spray methods are used to investigate methane and aviation kerosene combustion structures formed by new-type concave flame-holders. The flow pattern, combustion mode, and flame structure of gaseous and liquid fuel around a concave flame-holder are analyzed, discussed, and compared with experimental results. Results reveal that the flame stability of a concave flame-holder is better than that of the non-concave one. Furthermore, when using liquid fuel, the concave flame-holder forms a stable and compact flame. These results suggest concave flame-holders are a promising design for compact afterburners.
PubDate: 2023-11-07
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- Effect of CO2 Opposing Multiple Jets on Thermoacoustic Instability and NOx
Emissions in a Lean-Premixed Model Combustor-
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Abstract: Abstract This paper experimentally studied the effect of CO2 opposing multiple jets on the thermoacoustic instability and NOx emissions in a lean-premixed model combustor. The feasibility was verified from three variables: the CO2 jet flow rate, hole numbers, and hole diameters of the nozzles. Results indicate that the control effect of thermoacoustic instability and NOx emissions show a reverse trend with the increase of open area ratio on the whole, and the optimal jet flow rate range is 1ȃ1 L/min with CO2 opposing multiple jets. In this flow rate range, the amplitude and frequency of the dynamic pressure and heat release signals CH* basically decrease as the CO2 flow rate increases, which avoids high-frequency and high-amplitude thermoacoustic instability. The amplitude-damped ratio of dynamic pressure and CH* can reach as high as 98.75% and 93.64% with an optimal open area ratio of 3.72%. NOx emissions also decrease as the jet flow rate increases, and the maximum suppression ratio can reach 68.14%. Besides, the flame shape changes from a steep inverted “V” to a more flat “M”, and the flame length will become shorter with CO2 opposing multiple jets. This research achieved the synchronous control of thermoacoustic instability and NOx emissions, which could be a design reference for constructing a safer and cleaner combustor.
PubDate: 2023-11-06
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- Special Column on Convergence of Carbon Neutral Transition via Energy
Storage Technologies-
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PubDate: 2023-11-01
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- Brief Information for Authors
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PubDate: 2023-11-01
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- A Review on SOM-LES of Turbulent Two-Phase Combustion
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Abstract: Abstract Turbulent two-phase combustion is widely encountered in spray and pulverized-coal combustors, and large-eddy simulation (LES) becomes a powerful CFD method for its simulation, because LES can give unsteady flame structures and more reasonable statistical results than Reynolds-averaged modeling. Present combustion models in LES either lack of generality or are computationally too expensive. A statistical moment model based on the idea of turbulence modeling called “second-order moment (SOM) combustion model” was developed by the present authors for LES of two-phase combustion. In this paper, a review is given on our published research results for SOM-LES of two-phase combustion, including the description of the SOM-LES model, its application, validation of statistical results by experiments, as well as the phenomena obtained by instantaneous results.
PubDate: 2023-11-01
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- Thermodynamics of Cascaded Waste Heat Utilization from Flue Gas and
Circulating Cooling Water-
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Abstract: Abstract A detailed thermal power plant model was developed to evaluate power plant waste heat usage in terms of the operating parameters, energy consumption, water consumption, and pollutant emissions. This model was used to analyze the bypass flue gas energy cascade utilization design which provides excellent energy savings and emission reductions. This paper then presents a design to use the low-temperature waste heat and to extract water from the flue gas. The low-grade heat can be recovered from a coal-fired unit using absorption heat pumps to increase the air preheating. This method significantly reduces the turbine steam extraction in the low pressure stages which increases the turbine power and reduces the coal consumption. This design has a small heat transfer temperature difference between the air preheater and the air warmer, resulting in a smaller exergy loss. The power output of the present design was 1024.28 MW with a coal consumption savings of 3.69 g·(kWh)−1. In addition, the present design extracts moisture out of the flue gas to produce 46.48 t·h−1 of water. The main goal of this work is to provide a theoretical analysis for studying complex thermal power plant systems and various energy conservation and CO2 reduction options for conventional power plants.
PubDate: 2023-11-01
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- Enhancing Heat Transfer and Energy Storage Performance of Shell-and-Tube
Latent Heat Thermal Energy Storage Unit with Unequal-Length Fins-
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Abstract: Abstract Previous studies in literatures adequately emphasized that inserting fins into phase change material is among the most promising techniques to augment thermal performance of shell-and-tube latent heat thermal energy storage unit. In this study, the novel unequal-length fins are designed from the perspective of synergistic benefits of heat transfer and energy storage performance, and the effects of arrangement, number and total length of unequal-length fins are numerically investigated. Results show that utilization of fins with ascending length, when short and long fins are located in the inlet and outlet of heat transfer fluid respectively, can further promote the heat transfer and energy storage performance compared with equal length fins, and a maximum 6.17% and 0.43% increment of heat transfer performance and stored energy is achieved in full melting time, respectively. The number of unequal-length fins plays a major role in the energy storage, and 18.95% and 0.91% improvement of heat transfer performance and stored energy is realized when equipped with 2 unequal-length fins. A 21.17% improvement of the heat transfer performance is obtained when the total length of unequal-length fins is 18 mm. The present study is helpful to make further efforts to enhance heat transfer and energy storage of shell-and-tube latent heat thermal energy storage unit with unequal-length fins.
PubDate: 2023-11-01
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- Numerical Evaluation on the Thermal Performance of the Solar External
Cylinder Receiver using Monte Carlo Ray-Tracing Algorithm-
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Abstract: Abstract The heat receiver is an essential part of the Concentrating Solar Power plant, directly affecting its operation and safety. In this paper, the Monte Carlo ray-tracing algorithm was introduced to evaluate a 50 MW (e) external cylindrical receiver’s thermal performance. The radiation heat flux concentrated from the heliostats field and the view factors between grids divided from the tubes were both calculated using Monte Carlo ray-tracing algorithm. Besides, an in-house code was developed and verified, including three modules of the view-factor calculation, thermal performance calculation, and thermal stress calculation. It was also employed to investigate the 50 MW (e) receiver, and the detailed 3D profiles of temperature and thermal stress in the receiver were analyzed. It was found that the molten salt was heated from 298°C to 565°C and the tube at the 50 MW (e) receiver’s outlet had a high temperature, while the high thermal stress came out at the receiver’s entrance. Finally, the over-temperature of the receiver was discussed, and an optimization algorithm was introduced. The tube wall temperature and film temperature at the overheated area matched the safety criteria, and the outlet molten salt temperature still reached 563°C after the optimization process, with only 2°C dropped.
PubDate: 2023-11-01
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- Increasing Coal-Fired Power Plant Operational Flexibility by Integrating
Solar Thermal Energy and Compressed Air Energy Storage System-
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Abstract: Abstract This paper proposed a novel integrated system with solar energy, thermal energy storage (TES), coal-fired power plant (CFPP), and compressed air energy storage (CAES) system to improve the operational flexibility of the CFPP. A portion of the solar energy is adopted for preheating the boiler’s feedwater, and another portion is stored in the TES for the CAES discharging process. Condensate water from the CFPP condenser is used for cooling compressed air during the CAES charging process. The thermodynamic performance of the integrated system under different load conditions is studied. The system operations in a typical day are simulated with EBSILON software. The system enables daily coal saving of 9.88 t and reduces CO2 emission by 27.95 t compared with the original CFPP at 100% load. Under partial load conditions, the system enables maximum coal saving of 10.29 t and maximum CO2 emission reduction of 29.11 t at 75% load. The system has maximum peak shaving depth of 9.42% under 40% load condition. The potential of the system participating ancillary service is also discussed. It is found that the integration of solar thermal system and CAES system can bring significant ancillary service revenue to a conventional CFPP.
PubDate: 2023-11-01
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- Parametric Study of Operating Conditions on Performances of a Solid Oxide
Electrolysis Cell-
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Abstract: Abstract The operating conditions greatly affect the electrolysis performance and temperature distribution of solid oxide electrolysis cells (SOECs). However, the temperature distribution in a cell is hard to determine by experiments due to the limitations of in-situ measurement methods. In this study, an electrochemical-flow-thermal coupling numerical cell model is established and verified by both current-voltage curves and electrochemical impedance spectroscopy (EIS) results. The electrolysis performance and temperature distribution under different working conditions are numerically analyzed, including operating temperature, steam and hydrogen partial pressures in the fuel gas, inlet flow rate and inlet temperature of fuel gas. The results show that the electrolysis performance improves with increasing operating temperature. Increasing steam partial pressure improves electrolysis performance and temperature distribution uniformity, but decreases steam conversion rate. An inappropriately low hydrogen partial pressure reduces the diffusion ability of fuel gas mixture and increases concentration impedance. Although increasing the flow rate of fuel gas improves electrolysis performance, it also reduces temperature distribution uniformity. A lower airflow rate benefits temperature distribution uniformity. The inlet temperature of fuel gas has little influence on electrolysis performance. In order to obtain a more uniform temperature distribution, it is more important to preheat the air than the fuel gas.
PubDate: 2023-11-01
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- Experimental Investigation on Liner Cooling Characteristics of a
Mixed-Flow Trapped Vortex Combustor-
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Abstract: Abstract The mixed-flow trapped vortex combustor (TVC) is a new type of combustor that applies trapped vortex flame stabilization technology to mixed-flow combustor. Compared with the traditional mixed-flow combustor, the mixed-flow TVC has many advantages, such as complicated structure of the vortex flow field inside liner, large cooling area, significant local hot spots on the liner, and large wall temperature gradient. In this paper, for a mixed-flow TVC with inclined multi-hole cooling, the liner wall temperature of an annular test rig was examined in experiments. The effects of inlet temperature (T3), inlet Mach number (Ma) and fuel to air ratio (FAR) on the temperature of liner wall were obtained, which provided a valuable reference for understanding the distribution characteristics of liner wall temperature. The experiment results show that the highest temperature is found to be on the fore-wall of the cavity. When T3 and FAR are low, the highest wall temperature was obtained in injector plane. However, the wall temperature in the center plane between two adjacent injectors was higher than that in injector plane under the condition of high FAR and T3. With the increase of FAR and T3, the average wall temperature increases. Ma has a slight impact on the average wall temperature. In addition, this paper provides an effective reference for the design and improvement of the liner cooling structure of the combustor with many discontinuous small-area walls in the flow direction. It is difficult to form a continuous film, and cooling requirements can’t be achieved only by using inclined multi-hole cooling structure. Consideration needs to be given to other efficient cooling structures, or to the combination of multiple cooling structures.
PubDate: 2023-11-01
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- Experimental Study on Thermal Properties and Light-to-Thermal Conversion
Performance of Ionic Liquids Based Nanofluids-
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Abstract: Abstract As a new type of energy transport medium with high efficiency and high heat transfer performance, nanofluids have shown broad application prospects in the fields of thermodynamics, solar heat collection, microelectronics, thermal energy, and material science. The wide liquid range and environmental properties of ionic liquids have drawn ample attention to their application when used as a working fluid, especially as a base solvent of nanofluids. The ionic liquid-based nanofluids were prepared by a two-step method using 1-ethyl-3-methylimidazole trifluoroacetate ionic liquid as a base solvent and graphene oxide (GO) as a nanofiller. Thermophysical properties study reveals that the thermal conductivity could be enhanced by 3.0% with the addition of 0.05 wt% GO, and the viscosity and the specific heat capacity were also subject to study as a function of testing temperature and concentration of nanofiller. Additionally, the photothermal conversion efficiency of these nanofluids was studied comprehensively under different conditions. The results show that the photothermal conversion efficiency can reach 83% within an irradiation time of 6000 s and the highest temperature of the nanofluids is up to 105.89°C with a maximum photothermal conversion efficiency increase by 29%.
PubDate: 2023-11-01
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- Performance Assessment of a Novel Polygeneration System Based on the
Integration of Waste Plasma Gasification, Tire Pyrolysis, Gas Turbine,
Supercritical CO2 Cycle and Organic Rankine Cycle-
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Abstract: Abstract In this paper, a novel polygeneration system involving plasma gasifier, pyrolysis reactor, gas turbine (GT), supercritical CO2 (S-CO2) cycle, and organic Rankine cycle (ORC) has been developed. In the proposed scheme, the syngas is obtained by the gasification and the pyrolysis is first burned and drives the gas turbine for power generation, and then the resulting hot exhaust gas is applied to heat the working fluid for the supercritical CO2 cycle and the working fluid for the bottom organic Rankine cycle. In addition to the electrical output, the pyrolysis subsystem also produces pyrolysis oil and char. Accordingly, energy recovery is achieved while treating waste in a non-hazardous manner. The performance of the new scheme was examined by numerous methods, containing energy analysis, exergy analysis, and economic analysis. It is found that the net total energy output of the polygeneration system could attain 19.89 MW with a net total energy efficiency of 52.77%, and the total exergy efficiency of 50.14%. Besides, the dynamic payback period for the restoration of the proposed project is only 3.31 years, and the relative net present value of 77 552 640 USD can be achieved during its 20-year lifetime.
PubDate: 2023-10-12
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- Theoretical Insight into the Effect of Steam Temperature on Heavy
Oil/Steam Interface Behaviors Using Molecular Dynamics Simulation-
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Abstract: Abstract The interfacial behavior between heavy oil and steam is one of the vital pointers affecting the development efficiency of steam injection for heavy oil recovery. However, the underlying mechanisms of the interaction between heavy oil and steam at high temperature and pressure remain elusive. Herein, we have investigated the molecular-scale interactions on the interface between heavy oil droplet and steam phase at high temperatures (473 K, 498 K, 523 K, and 548 K) via molecular dynamics simulations. The results show that the interfacial thickness between heavy oil droplet and steam phase increases gradually with temperature, while the interfacial tension decreases constantly. Moreover, high temperature can damage hydrogen bonds, resulting in lower interaction energy between heavy oil droplet and steam phase. The radial distribution function results demonstrate that the interaction between heavy oil fractions and steam phase can be weakened by high temperature. Furthermore, the evolutions of interface are directly observed by the two-dimension density cloud maps at different temperatures, and the mean square displacement and self-diffusion coefficient demonstrate the evolution mechanism of heavy oil fractions and steam. In particular, the heavy oil/steam systems with asphaltenes at the interface are more likely to achieve high diffusivity and emulsifying capacity. This work provides a molecular-level insight for understanding the interfacial interaction mechanisms of heavy oil/steam systems during a steam injection process.
PubDate: 2023-09-26
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