For unshrouded blade tip, the high-temperature gas flows through the tip clearance by force of the lateral pressure difference. Thereby, the blade tip endures increasing thermal load. Furthermore, the conventional blade tip treatment cannot continuously provide protection for the deteriorating service environment. In the present study, aerothermal characteristics of the squealer blade tip with staggered ribs, partial squealer rim and different partial squealer rim thickness were investigated to explore the influences of ribbed-cavity tip on the tip heat transfer, leakage flow and turbine stage efficiency. The numerical results indicate that the ribbed-cavity tips are beneficial for the reduction of the blade tip thermal load and leakage flow. Among the present six blade tip designs, the minimal area-averaged heat transfer coefficient is obtained by the case with the staggered ribs and a deeper squealer rim, which is reduced by 31.41% relative to the squealer tip. Plus, the blade tip modification closer to leading edge or tip mid-chord region performs better than trailing edge in reducing the tip leakage flow.

Ice accretion on surfaces of the aircraft and engine is a serious threat to the flight safety. In this paper, a novel hot air anti-icing method is proposed based on the porous foam. Taking the NACA0012 airfoil as an example, the traditional thermal protection structure is proved to exist the deficiency in balancing the heat exchange caused by route loss of the heat. By dividing the hot chamber into multiple regions to fill with various foam metal, flow resistance characteristics and heat transfer characteristics for this protection mode are analyzed in order to derive the maximized benefit in anti-icing process. The calculation results reveal that, under the same condition, the region filled with foamed copper not only improves the temperature uniformity on the anti-icing area, but also achieves a better protection effect for enhancing heat transfer between the tube and the hot gas, averagely above 20°C higher than it without porous foam filling in surface temperature. Additionally, the minimum mass flow rate of the protection hot air is reduced by 16.7%. The gratifying efficiency of the porous filler in fortifying heat transfer confirms the potential of replacing the efficient but complex heat transfer design with simple structure filled with foam metal.

Understanding the correlation between the physical features of composite components and thermal conductive pathway is beneficial to optimizing the overall heat-transfer performance. Herein, we conduct numerical simulation to investigate the thermal conductivity and heat flux distributions of alumina (Al₂O₃)-filled composites. The finite element model was verified by both experimental data and theoretical models. The crucial factors include the influence of the interface thermal resistance, the intrinsic thermal conductivity of the matrix and Al₂O₃ filler, and the size effect of Al₂O₃ fillers were investigated. For single Al₂O₃-filled composites, the results indicate that increasing the intrinsic thermal conductivity of the matrix is conductive to bridge the Al₂O₃ pathway along heat-transfer direction, but there are very limited contributions by enhancing the intrinsic thermal conductivity of Al₂O₃ filler, tuning the size of Al₂O₃ filler, and reducing the interface thermal resistance. After introducing the multiscale fillers, it is found that the high thermal conductivity can be achieved by regulating their size matching effect. At the optimal binary ratio of 70:30 (40 μm:15 μm) and ternary ratio of 55:35:10 (40 μm:15 μm:10 μm), the heat-conduction network presents the dominant skeleton of large-sized filler and the bridging branch of small-sized fillers features, which facilitates the formation of a complete and continuous thermal conductive network. This study gives a practical guidance for the thermal conductive design of Al₂O₃-filled composites.

The influences of leading-edge tubercle amplitude on airfoil flow field have been analyzed at high angle of attack. The accuracy of a large eddy simulation (LES) research is validated through quantitative comparisons with corresponding experimental results. Then, a proper orthogonal decomposition (POD) analysis has been carried out based on the unsteady flow field and the fluid mechanisms of corresponding POD modes have been identified. Consequently, the influences of leading-edge tubercle amplitude have been uncovered. Since the streamwise vorticity is larger than that of small amplitude cases, the momentum transfer process at peaks is more obvious for large amplitude, leading to delayed flow separation. Both amplitude and wavelength play important roles in the generation of laminar separation bubble (LSB) at troughs. Moreover, the Karman vortex shedding process takes place at specific trough sections as pairs of periodic spatial structures exist in the dominant POD modes. The destruction of Karman vortex shedding process is strengthened along with the increase of amplitude.

A joint consideration of potential combustion and emission performance in spark-ignition engines is essential for designing gasoline fuel replacements and additives, for which the knowledge of the fuels’ characteristic properties forms the backbone. The aim of this study is to predict sooting tendency of fuel molecules for spark-ignition engine applications in terms of their yield sooting indexes (YSI). In conjunction with our previously developed database for gasoline compounds, which includes the physical and chemical properties, such as octane numbers, laminar burning velocity, and heat of vaporization, for more than 600 species, the identification of fuel replacements and additives can thus be performed jointly with respect to both their potential thermal efficiency benefits and emission formation characteristics in spark-ignition engines. For this purpose, a quantitative structure-property relationship (QSPR) model is developed to predict the YSI of fuel species by using artificial neural network (ANN) techniques with 21 well-selected functional group descriptors as input features. The model is trained and cross-validated with the YSI database reported by Yale University. It is then applied to estimate the YSI values of fuels available in the database for gasoline compounds and to explore the sensitivity of fuel’s sooting tendency on molecular groups. In addition, the correlation of YSI values with other properties available in the gasoline fuel database is examined to gain insights into the dependence of these properties. Finally, a selection of potential gasoline blending components is carried out exemplarily, by taking the fuels’ potential benefits in thermal engine efficiency and their soot formation characteristics jointly into account in terms of efficiency merit function and YSI, respectively.

The flow field at the inlet of compressors is generally encountered combined total pressure and swirl distortion for either aircraft engine with S-duct or gas turbine with lateral air intake. This inevitably deteriorates compressor aerodynamic performance, including not only the efficiency or pressure ratio but also the operation stability. In order to conquer this issue, appropriate measures such as integrating flow control techniques and modifying inlet or compressor design are of benefits. Due to this motivation, this article develops a full-annular two-dimensional (2D) and a partial-annular three-dimension (3D) optimization strategy for non-axisymmetric vane design. Firstly, two numerical simulation methods for evaluating performance of full-annular 2D vane and compressor with partial-annular 3D vane are developed. The swirl patterns at the inlet of a 1.5-stage axial compressor are analyzed and parametrized, and the parameterization is transferred to characterize the circumferential distribution of geometrical parameters of the vane profile. These approaches dramatically reduce computational simulation costs without violating the non-axisymmetric flow distortion patterns. Then various full-annular 2D sections at different radial locations are constructed as design space. The designed vane is reconstructed and 3D numerical simulations are performed to examine performance of the non-axisymmetric vane and the compressor with it. Also, partial annular 3D optimization is conducted for balancing compressor efficiency and stall margin. Results indicate that the designed non-axisymmetric vane based on full-annular optimization approach can decrease the vane total pressure loss under the considered inlet flow distortion, while those using partial-annular optimization achieve positive effects on compressor stall margin.

In this paper, to further improve thermodynamic performance of supercritical carbon dioxide cycle, simple/recompression transcritical carbon dioxide Brayton cycle (STBC/RTBC) and simple/recompression transcritical carbon dioxide Rankine cycle (STRC/RTRC) are proposed. Thermal and exergy performance analysis and optimization for the above four transcritical CO₂ cycles and simple/recompression supercritical cycle (SSBC/RSBC) are conducted. The effect of key thermodynamic parameters on those CO₂ cycle performance is studied. Results indicate that the improvements of thermodynamic performance of CO₂ cycle are obvious when transcritical Brayton and Rankine cycle are applied in it. Within the same range of optimization variables, the maximum thermal efficiency improvements of RTRC and RTBC are 4.98% and 3.6%, and maximum exergy efficiency improvements of RTRC and RTBC are 7.08% and 5.13% when compared with RSBC. Moreover, the thermodynamic performances of STBC and STRC are also outstanding than that of SSBC. This work provides a way to further improve the thermodynamic performance of CO₂ power cycle.

In this paper, a novel composite heat transfer enhancement technique comprised of louvered fins (LFs) and rectangular wing vortex generators (RWVGs) is proposed to improve the LF side thermal-hydraulic performance of louvered fin and flat tube heat exchangers (LFHEs). After validation of the LF side pressure drop ∆P and heat transfer coefficient h_LF of the baseline by experiments, the numerical method is applied to investigate the influential mechanisms of the RWVG parameters (the number N (7 to 15), attack angle β (30° to 90°), height H_VG (0.8 mm to 2 mm) and width W_VG (0.8 mm to 1.2 mm)) on the performance of the LFHE in the velocity range of 3 m/s to 10 m/s. Results show that thermal-hydraulic performance of the LFHE is significantly impacted by the RWVGs, and according to the performance evaluation criteria (PEC), the LFHE achieves its optimal thermal-hydraulic performance when N=7, β=45°, H_VG=1.8 mm and W_VG=1 mm. Compared to the baseline, the maximum, minimum and average increments of PEC for the optimal case are 13.85%, 4.67% and 8.39%, respectively.

Adding fins to a shell-and-tube phase change thermal storage is a simple and effective way to enhance the performance of the phase change heat storage unit, and the proper arrangement of the fins is essential to enhance the performance of the storage unit. To enhance the performance of the triplex-tube thermal storage unit, a novel V-shaped fin structure is presented in this paper. And the heat storage performance of the thermal storage system is studied by numerical simulation. Firstly, the performance of the triplex-tube thermal energy storage unit with different arrangements of V-shaped fins is investigated by a two-dimensional model and compared with the use of the traditional rectangular fin structure, and the optimal fin arrangement is derived. The results show that the V-shaped fins with the optimal arrangement can decrease the time for the PCM melting in the heat storage unit by 31.92% compared to the conventional rectangular fins. On this basis, the influence of fin angle and thickness on the heat storage unit was studied. Then, a three-dimensional model of the thermal storage unit was established. And the effect of the flow parameters (inlet temperature, inlet flow rate) of the heat transfer fluid (HTF) on its performance was discussed in detail. Finally, the stored energy analysis of the whole thermal storage unit is carried out.

As a simple and effective method of heat transfer enhancement, fins are widely used in latent heat storage systems. However, the choice of annular fins and longitudinal fins has always been controversial. In this paper, the melting process of phase change material (PCM) in annular fins and longitudinal fins latent heat storage units with the same volume is numerically simulated. To ensure the same thermal penetration, three-dimensional spaces occupied with fins are specially controlled to be the same. Combined with finned structures, the effects of natural convection (NC), placement mode and heat transfer fluid (HTF) inlet direction on the melting process are studied. The results show that the melting time in annular finned structure is always 10% less than that in longitudinal finned structure, which demonstrates the superior of the annular fins in the latent heat storage unit. The melting time is the shortest in vertical unit with annular fins and HTF inlet at the bottom. Additionally, the correlation formulas of the liquid fraction are proposed in the vertical unit with HTF inlet at the bottom.

Utilizing the phase change materials in different thermal storage applications attains valuable attention due to the fascinating thermal properties of these materials. The comprehension of the thermal behaviour of phase change materials during the melting and solidification is considered a significant priority in designing the shape of the different containers. In this review, analytical, computational and experimental investigations that address solidification/freezing of phase change materials within thermal energy storage systems are discussed. Emphasis is placed on the role of the shape of adopted containers encompassing planar, spherical, cylindrical and annular vessels. Energy storage for solar thermal applications, waste heat recovery, and thermal management of buildings/computing platforms/photovoltaics has been the topics that benefit from these investigations. For all container shapes, the freezing process is controlled initially by natural convection, and a high solidification rate is observed. Later, the conduction dominates the process, and the freezing rate declines. The temperature and flow of cooling heat transfer fluid affect the solidification process, but the impact of heat transfer fluid temperature is more significant than its flow rate. Also, the freezing time increases with the container’s size and amount of contained PCM. The aspect ratio of the planar and vertical cylindrical cavities substantially influences the discharging time and rate. In contrast, the orientation of the annular cavity has a lower impact on the discharging process.

Bunsen burner is a typical geometry for investigating the turbulence-flame interaction. In most experimental studies, only turbulence intensity u′ and integral scale l₀ are used to characterize the turbulent flow field, regardless of the perforation geometry of perforated plates. However, since the geometry influences the developing process and vortex broken, the plate geometry has to be considered when discussing the flame-turbulence interaction. In order to investigate conditions at the same l₀ and u′ using different geometries, large eddy simulation of CH₄/air flames with dynamic TF combustion model was performed. The model validation shows good agreement between Large Eddy Simulation (LES) and experimental results. In the non-reacting flows, the Vortex Stretching of circular-perforated plate condition is always larger than that of slot-perforated plate condition, which comes from the stresses in the flow fields to stretch the vorticity vector. In reacting flows, at the root of the flame, the Vortex Stretching plays a major role, and the total vorticity here of circular-perforated plate condition is still larger (53.8% and 300% larger than that of the slot-perforated plate at x/D=0 and x/D=2.5, respectively). More small-scale vortex in circular-perforated plate condition can affect and wrinkle the flame front to increase the Probability Density Function (PDF) at large curvatures. The 3D curvature distributions of both cases bias to negative values. The negative trend of curvatures at the instant flame front results from the Dilatation term. Also, the value of the Vortex Stretching and the Dilatation at the flame front of circular-perforated plate condition is obviously larger.

Barocaloric refrigeration technology, one of the caloric-effect refrigeration technologies, is drawing more and more attention. Neopentyl glycol (NPG) was reported to have a giant barocaloric effect, making it a potential barocaloric material. However, the high solid-solid (S-S) phase transition temperature and low thermal conductivity hinder the application of NPG in barocaloric refrigeration. This work lowers the S-S phase transition temperature and improves the thermal conductivity of the NPG-based barocaloric material. An NPG/TMP (TMP: Trimethylolpropane) binary system with an S-S phase transition temperature of 283.15 K is prepared, in which the mass ratio of TMP is 20%. Graphene is then added to the binary system to enhance thermal conductivity, and the optimal mass ratio of graphene was determined to be 5%. The thermal conductivity of this composite is 0.4 W/(m·K), increased by 110% compared to the binary system. To predict the effect of enhanced thermal conductivity on the cold-extraction process of the barocaloric refrigeration cycle, a numerical model is developed. The results show that the cold-extraction time of the barocaloric refrigeration cycle utilizing the composite with 5% graphene as the refrigerant is shortened by 50% compared with that using the binary system.

Dry reforming of methane (DRM) process has attracted much attention in recent years for the direct conversion of CH₄ and CO₂ into high-value-added syngas. The key for DRM was to develop catalysts with high activity and stability. In this study, LaNiO₃ was prepared by the sol-gel, co-precipitation, and hydro-thermal methods to explore the influence of preparation methods on the catalyst structure and DRM reaction performance. The regeneration properties of the used LaNiO₃ catalysts were also investigated under steam, CO₂, and air atmospheres, respectively. The results showed that LaNiO₃ prepared by sol-gel method showed the best DRM performance at 750°C. The DRM performance of the samples prepared by hydro-thermal method was inhibited at 750°C due to the residual of Na+ ions during the preparation process. The regeneration tests showed that none of the three atmospheres could restore LaNiO₃ perovskite phase in the samples, but they could eliminate the carbon deposits in the samples during the DRM reaction, so the samples could maintain stable DRM performance at different cycling stages.

Barocaloric refrigeration is regarded as one of the next-generation alternative refrigeration technology due to its environmental friendliness. In recent years, many researchers have been devoted to finding materials with colossal barocaloric effects, while neglecting the research on barocaloric refrigeration devices and thermodynamic cycles. Neopentyl glycol is regarded as one of the potential refrigerants for barocaloric refrigeration due to its giant isothermal entropy changes and relatively low operating pressure. To evaluate the performance of the barocaloric system using Neopentyl glycol, for the first time, this study establishes a thermodynamic cycle based on the metastable temperature-entropy diagram. The performance of the proposed system is investigated from the aspects of irreversibility, operating temperature range, and operating pressure, and optimized with finite-rate heat transfer. The guidance for the optimal design of the system is given by revealing the effect of the irreversibility in two isobaric processes. The results show that a COP of 8.8 can be achieved at a temperature span of 10 K when the system fully uses the phase transition region of Neopentyl glycol, while a COP of 3 can be achieved at a temperature span of 10 K when the system operates at room temperature. Furthermore, this study also shows that the system performance can be further improved through the modification of Neopentyl glycol, and some future development guidance is provided.

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.  

The heat transfer performance of ultra-thin flat heat pipes with #180 copper mesh wick was studied by numerical simulation for different heating powers. The length, width and height of the ultra-thin flat heat pipe are 80 mm, 8.5 mm and 1 mm, respectively. The temperature distribution and flow characteristics of ultra-thin flat heat pipes were simulated by coupling porous media model and user-defined function (UDF) in FLUENT. To validate the accuracy of the numerical model, the simulation results of the ultra-thin flat heat pipe are compared with the experimental data in predicting the evaporation section temperature. The numerical model has good accuracy for the one-dimensional heat transfer method of ultra-thin flat heat pipes. The velocity, pressure drop of the wick and total temperature difference have the same variation trend. With the increase of heating power, the temperature difference of ultra-thin flat heat pipes increases, and the pressure drop and the liquid velocity in the wick also increase.

Hydrogen is a type of clean energy which has the potential to replace the fossil energy for transportation, domestic and industrial applications. To expand the hydrogen production method and reduce the consumption of fossil energy, technologies of using renewable energy to generate hydrogen have been developed widely. Due to the advantages of widespread distribution and various hydrogen production methods, most of the research or review works focus on the solar and biomass energy hydrogen production systems. To achieve a comprehensive acknowledge on the development state of current renewable energy hydrogen production technology, a review on hydrogen production systems driven by solar, wind, biomass, geothermal, ocean and hydropower energy has been presented. The reaction process, energy efficiency, exergy efficiency, hydrogen production rate, economic and environmental performance of these systems have been evaluated. Based on the analysis of these different systems, the challenge and prospects of them are also analyzed.

Proton exchange membrane electrolysis cell (PEMEC) is one of the most promising methods to produce hydrogen at high purity and low power consumption. In this study, a three-dimensional non-isothermal model is used to simulate the cell performance of a typical PEMEC based on computational fluid dynamics (CFD) with the finite element method. Then, the model is used to investigate the distributions of current density, species concentration, and temperature at the membrane/catalyst (MEM/CL) interface. Also, the effects of operating conditions and design parameters on the polarization curve, specific electrical energy demand, and electrical cell efficiency are studied. The results show that the maximum distribution of current density, hydrogen concentration, oxygen concentration, and temperature occur beneath the core ribs and increase towards the channel outlet, while the maximum water concentration distribution happens under the channel and decreases towards the channel exit direction. The increase in gas diffusion layer (GDL) thickness reduces the uneven distribution of the contour at the MEM/CL interface. It is also found that increasing the operating temperature from 323 K to 363 K reduces the cell voltage and specific energy demand. The hydrogen ion diffusion degrades with increasing the cathode pressure, which increases the specific energy demand and reduces the electrical cell efficiency. Furthermore, increasing the thickness of the GDL and membrane rises the specific energy demand and lowers the electrical efficiency, but increasing GDL porosity reduces the specific electrical energy demand and improves the electrical cell efficiency; thus using a thin membrane and GDL is recommended.

Staged combustion of biomass is the most suitable thermo-chemical conversion for achieving lower gaseous emissions and higher fuel conversion rates. In a staged fixed bed combustion of biomass, combustion air is supplied in two stages. In the first stage, primary air is provided below the fuel, whereas in the later stage, secondary air is supplied in the freeboard region. The available literature on the effects of air staging (secondary air location) at a constant primary air flow rate on combustion characteristics in a batch-type fixed bed combustor is limited and hence warrants further investigations. This study resolves the effect of air staging, by varying the location of secondary air in the freeboard at five secondary to total air ratios in a batch-type fixed bed combustor. Results are reported for the effects of these controlled parameters on fuel conversion rate, overall gaseous emissions (CO₂, CO and NO_x) and temperature distributions. The fuel used throughout was densified hardwood pellets.
Results show that a primary freeboard length (distance between fuel bed top and secondary air injection) of 200 mm has higher fuel conversion rates and temperatures as well as lower CO emissions, at a secondary to total air ratio of 0.75 as compared to primary freeboard length of 300 mm. However, NO_x emissions were found to be lower for a primary freeboard length of 300 mm as compared to 200 mm. An increase in secondary to total air ratio from 0.33 to 0.75 resulted in higher freeboard temperatures and lower CO as well as NO_x emissions. The outcomes of this study will be helpful in the effective design of commercial scale biomass combustors for more efficient and environmentally friendly combustion.