The application of thermal diodes, which allow heat to flow more readily in one direction than the other, is an important way to reduce energy consumption in buildings and enhance the battery heat dissipation of electric vehicles. Depending on various factors including the specific design, materials used, and operating conditions, the convective thermal diode can exhibit the best thermal rectification effect in intended applications compared to the other  thermal diodes. In this study, a novel convective thermal diode with a wick was proposed based on the phase change heat transfer mechanism. This design takes advantage of both capillary forces provided by the wick and gravity to achieve enhanced unidirectional heat transfer performance for the designed convective thermal diode. The effect of the filling liquid ratio on the thermal performance of the thermal diode was experimentally investigated, which was in good agreement with the theoretical analysis. The research findings showed that with an optimal liquid filling ratio of 140%, the thermal diode with a wick can achieve a better thermal rectification ratio when subjected to a lower heating power, and the maximum thermal rectification ratio of 21.76 was experimentally achieved when the heating power of the thermal diode was 40 W.

With the advancement of micro machining technology, the high-heat-flux removal from miniature electronic devices and components has become an attractive topic. Flow boiling in micro-channels is an optimal form of heat transfer and has been widely employed in high-heat-flux cooling applications. This comprehensively-reviewed article focused on the available recent literatures of experimental investigation regarding the flow boiling heat transfer and unstable behaviors of the fluid with lower boiling point in micro-channels. The thermal-fluid characteristics and potential heat transfer mechanisms of low-boiling-point fluids flow boiling in different narrow passages were summarized and discussed. The literatures regarding the pressure drop and occurrence of the unstable phenomena existing in two-phase flow boiling process were also discussed. The emphasis was given to the heat transfer enhancement methods as well as instability elimination, and various methods such as modification of surface and channel flow geometries were considered. Some future researches in the field of micro-scale flow boiling were suggested.

Integrating a high proportion of intermittent renewable energy provides a solution for the higher peak-shaving capacity of coal-fired power plants. Oxy-fuel combustion is one of the most promising carbon reduction technologies for coal-fired power plants. This study has proposed a novel oxy-fuel power plant that is coupled with both liquid O₂ storage and cold energy recovery systems in order to adapt to the peak-shaving requirements. The liquid O₂ storage system uses cheap valley electricity to produce liquid O₂ for a later use in the peak period to enhance the peak-shaving capacity. Meanwhile, the cold energy recovery system has been introduced to recover the physical latent energy during the phase change of liquid O₂ to increase the power generation in the peak period. Technical economies of three power plants, i.e. a 330 MW (e) oxy-fuel power plant as reference (Case 1), the same power plant coupled with only liquid O₂ storage system (Case 2), and the same power plant coupled with both liquid O₂ storage and cold energy recovery systems (Case 3), have been analyzed and compared. Thermodynamic performance analysis indicates that the peaking capacity of Case 3 can reach the range of 106.03 to 294.22 MW (e), and the maximum peak-shaving coefficient can be as high as 2.77. Exergy analysis demonstrates that the gross exergy efficiency of Cases 2 and 3 reaches 32.18% and 33.57%, respectively, in the peak period, which are significantly higher than that of 26.70% in Case 1. Economic analysis shows that through selling the liquid O₂ and liquid CO₂, combined with carbon trading, the levelized cost of electricity (LCOE) of the three cases have been greatly reduced, with the lowest one of 30.90 USD/MWh shown in Case 3. For a comprehensive consideration, Case 3 can be considered a future reference of oxy-fuel power plant with the best thermodynamic and economic performance.

The low net efficiency of oxy-fuel circulating fluidized bed (CFB) combustion is mainly due to the addition of air separation unit (ASU) and carbon dioxide compression and purification unit (CPU). High oxygen concentration is one of the effective methods to improve the net efficiency of oxy-fuel combustion technology in CFB. In this research, a series of calculation and simulation were carried out based on Aspen Plus platform to provide valuable information for further investigation on the CFB oxy-fuel combustion system with high oxygen concentration (40%, 50%). A CFB oxy-fuel combustion system model with high oxygen concentration was established including ASU, CPU and CFB oxy-fuel combustion and heat exchange unit. Based on the simulation data, energy and exergy efficiency were analyzed to obtain the following results. The cross-sectional area of furnace and tail flue of 50% CFB oxy-fuel combustion boiler are 43% and 56% of the original size respectively, reducing the construction and investment cost effectively. With the increase of oxygen concentration, the net efficiency of power generation increased significantly, reaching 24.85% and increasing by 6.09% under the condition of 50% oxy-fuel combustion. The total exergy loss increases with the increase of oxygen concentration. In addition, the exergy loss of radiation heat transfer is far higher than convection heat transfer.

This study evaluates the effectiveness of phase change materials (PCMs) inside a storage tank of warm water for solar water heating (SWH) system through the theoretical simulation based on the experimental model of S. Canbazoglu et al. The model is explained by five fundamental equations for the calculation of various parameters like the effectiveness of PCMs, the mass of hot water, total heat content, and duration of charging. This study simulated eleven PCMs to analyze their effectiveness like Sodium hydrogen phosphate dodecahydrate (SHPD), OM 37, N-Eicosane (NE), Lauric acid (LA), Paraffin wax (PW), OM 48, Paraffin wax C_20-33 (PW-C20-33), Sodium acetate trihydrate (SAT), Palmitic acid (PA), Myristic acid (MA), and Stearic acid (SA). Among all PCMs, the SHPD has found the highest value of effectiveness factor of 3.27. So, it is the most recommended PCM for the storage tank of the SWH system. The study also includes the melt fraction analysis of all enumerated PCMs corresponding to container materials of stainless steel, glass, aluminum mixed, tin, aluminum, and copper. This melt fraction analysis is performed by making a coding program in the FORTRAN programming language. Through the analysis, copper container material is found to have high melting rate for all PCMs so it is superior to other container materials. 

The large-scale integration of new energy generation has put forward higher requirements for the peak-shaving capability of thermal power. The circulating fluidized bed (CFB) depends on the advantages of a wide load adjustment range and low cost of pollutant control to become a good peak shaving power supply. However, the large delay and inertia caused by its unique combustion mode make it very difficult to change the load quickly. To further understand the factors that affect the load change of CFB, and explore the method of increasing CFB load change rate, the load change experiment on the combustion side was carried out in the 0.1 MW CFB experiment platform. The influence law of bed material amount and fuel particle size on load change of CFB combustion side was revealed for the first time. The results indicated that the increase of bed material amount was beneficial to improve the load change rate on the combustion side of CFB and reduce the carbon content of fly ash, but had no obvious effect on NO_x emission. When the bed height at rest increased from 200 mm to 400 mm, the load change rate of the CFB combustion side load from 50% to 75% increased from 0.78%/min to 1.14%/min, and the carbon content of fly ash at 75% load decreased from 26.6% to 24.9%. In addition, the reduction of fuel particle size positively improved the load change rate on the combustion side of the CFB and reduced NO_x emission but had a negative effect on reducing the carbon content of fly ash. When the fuel particle size decreased from 0–1 mm to 0–0.12 mm, the load change rate of CFB combustion side load from 50% to 75% increased from 0.78%/min to 1.09%/min, and the NO_x emission and carbon content of fly ash at 75% load decreased from 349.5 mg/m³ to 194.1 mg/m³ and increased from 26.6% to 31.8%, respectively.

Pressurised oxy-fuel combustion (POFC) is a clean and efficient combustion technology with great potential. Due to the recycling of flue gas, the concentration of steam in the flue gas is higher than that of conventional combustion, which enriches the free radical pool in the flue gas and thus affects the emission of gaseous pollutants. Therefore, further research into the effect of high steam concentrations on NO_x emission mechanisms in POFC is necessary. In this work, a fixed-bed reactor was used to conduct combustion experiments of volatiles and combined with chemical kinetic models to study the NO release characteristics for different pressures and steam concentrations in an O₂/CO₂ atmosphere at 800°C/900°C temperature. The results of the study indicated that the volatile nitrogen comes from the pyrolysis of part of pyrrole, pyridine, and all quaternary nitrogen in coal. The increase in temperature promoted the formation of NO during combustion. Higher pressure affects the main reaction pathway for NO formation, promoting NO consumption by HCCO and C₂O groups while enhancing the overall NO reduction. Steam promoted NO consumption by NCO. In addition, steam increased the amount of H/OH groups during the reaction, which affected both NO formation and consumption. However, from the overall effect, the steam still inhibits the emission of NO.

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.

Using thermal models to describe the heat dissipation process of FCBGA is a significant topic in the field of packaging. However, the thermal resistance model considering the structure of each part of the chip is still ambiguous and rare, but it is quite desirable in engineering. In this work, we propose a detailed thermal resistance network model, and describe it by using thermal conduction resistance and thermal spreading resistance. For a striking FCBGA case, we calculated the thermal resistance of each part of the structure according to the temperature field simulated by COMSOL. The thermal resistance network can be used to predict the temperatures in the chip under different conditions. For example, when the power changes by 40%, the relative error of junction temperature prediction is only 0.24%. The function of the detailed thermal resistance network in evaluating the optimization space and determining the optimization direction is clarified. This work illustrates a potential thermal resistance analysis method for electronic devices such as FCBGA.

As the only controllable means of a micro gas turbine (MGT) combustor during unit operation, pilot fuel ratio (PFR) is the key to achieving stable combustion and low pollutant emission. This paper discusses the influence of PFR on the inner flow field structure and pollutant emissions. The steady-state three-dimensional RANS method with a 40-step reduced methane-air kinetics mechanism is used to study the reaction flow field and species field with PFR of 9.0%, 12.7%, 15.2% and 17.6%. Results show that, with the decrease in PFR, the axial velocity and temperature near the central axis of the combustion chamber show a tendency to decrease. A similar separation phenomenon occurred in the core pyrolysis reaction zone (measured by HCO) and oxidation zone (measured by OH), which is more conducive to promoting the oxidation of CO. The quantitative effect of the pilot flame on nitrogen oxides (NO_x) was separated by using inert gas instead of nitrogen in combustion air. It was found that the NO_x produced by the pilot flame under the operation condition with a PFR of 9.0% was 3.2×10^–6, accounting for 17.4% of the total NO_x emission, which was twice that of PFR.

This study is to utilize the heat-absorbing and releasing capabilities of phase change materials (PCM) to regulate the surface temperature fluctuations of batteries during charging and discharging. The goal is to keep the battery within the optimal operating temperature range. The impact of PCM thickness and phase change temperature on battery temperature is investigated by encircling a cylindrical battery with a PCM ring. To improve the thermal conductivity of PCM, expanded graphite (EG) is added to make a composite phase change material (CPCM), and the effects of various EG mass ratios on battery surface temperature and CPCM utilization level are investigated. The findings indicate that increasing PCM thickness effectively extends temperature control time, but its impact is limited. The difference in phase change temperature of PCM controls the battery temperature in different temperature ranges. Lower phase change temperatures are unsuitable for controlling battery temperature in high temperature environments. The addition of EG enhances the thermal conductivity of PCM, leading to further control of battery temperature. The results show that the addition of 6% (mass ratio) EG to CPCM extends the effective temperature control time by 11 min and improves by 28% compared to a single PCM. The CPCM utilization is also more satisfactory and achieved a balance between heat storage and thermal conductivity in a battery thermal management system (BTMS) based on PCM.

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 a_y=g should better be avoided for the sinusoidal channel printed circuit heat exchanger.

The operating principles of Circulating Fluidized Bed (CFB) boilers involve a significant amount of heat accumulation, which forms the thermal inertia of the boiler and hinders the improvement of its variable load response rate. This study aims to characterize the thermal inertia of CFB boilers by evaluating the change in the boiler’s heat accumulation corresponding to the change in unit power generation. The thermal inertia of a 330 MW CFB boiler was determined through the collection of operating data under four different operating conditions of 30%, 50%, 75%, and 100% load. The study proposes to substitute the existing refractory material with a metal grille to reduce the thermal inertia of the boiler. The effect of the metal grille on heat transfer was confirmed through verification on a 440 t/h CFB boiler, and its performance change and thermal inertia reduction were further predicted. The results indicate that over 50% of the total thermal inertia of CFB boilers originates from the refractory material. The use of metal grille in place of refractory material improved heat transfer in the furnace, resulting in a decrease of the furnace chamber temperature by 13°C in the 330 MW CFB boiler. This reduction of thermal inertia by 30%–35% will facilitate faster load lifting and lowering of the boiler, fulfilling the requirement for flexible peaking.

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%.

As an important component of the stirling-type pulse tube cryocooler (SPTC), an efficient phase shifter can significantly improve the cooling capacity. Compared to the common phase shifter, the active warm displacer (AWD) has a wider phase adjustment range and therefore can obtain a better phase relationship easily. Based on a two-stage thermal-coupled SPTC operating in the 20 K range, this paper studied the influence of the swept volume ratio between the compressor and displacer. The research found that the swept volume ratio changes the cooling capacity and efficiency of the cryocooler mainly by changing the phase difference between the pressure wave and the volume flow at the cold end. It was found from the results of the simulation and experiments that there is an optimal displacement of the displacer (Xd) of 2.5 mm and an optimal phase angle of 15° to obtain the highest cooling efficiency while the displacement of the compressor is constant. The cooling capacity at 20 K is 1.3 W while the input electrical power of the second stage compressor is 202 W, which indicates an overall relative Carnot efficiency (rCOP) of 0.055 in terms of input electrical power. In addition, due to the reasonable setting of precooling temperature and capacity, the swept volume ratio and phase at the maximum cooling capacity and maximum efficiency are consistent in this study. The research improves the understanding of phase shifters and has guiding significance for the optimization of the SPTC working below 20 K.

The heat storage performance of latent heat storage systems is not good due to the poor thermal conductivity of phase change materials. In this paper, a new type of pointer-shaped fins combining rectangular and triangular fins has been employed to numerically simulate the melting process in the heat storage tank, and the fin geometry parameter effects on heat storage performance have been studied. The results indicate that compared with the bare tube and the rectangular finned tank, the melting time of the phase change material in the pointer-shaped finned tank is reduced by 64.2% and 15.1%, respectively. The closer the tip of the triangular fin is to the hot wall, the better the heat transfer efficiency. The optimal height of the triangular fin is about 8 mm. Increasing the number of fins from 4 to 6 and from 6 to 8 reduces the melting time by 16.0% and 16.7% respectively. However, increasing the number of fins from 8 to 10 only reduces the melting time by 8.4%. When the fin dimensionless length is increased from 0.3 to 0.5 and from 0.5 to 0.7, the melting time is shortened by 17.5% and 13.0%. But the melting time is only reduced by 2.9% when the dimensionless fin length is increased from 0.7 to 0.9. For optimising the design of the thermal storage system, the results can provide a reference value.

Present work investigates the heat transfer and melting behaviour of phase change material (PCM) in six enclosures (enclosure-1 to 6) filled with paraffin wax. Proposed enclosures are equipped with distinct arrangements of the fins while keeping the fin’s surface area equal in each case. Comparative analysis has been presented to recognize the suitable fin arrangements that facilitate improved heat transfer and melting rate of the PCM. Left wall of the enclosure is maintained isothermal for the temperature values 335 K, 350 K and 365 K. Dimensionless length of the enclosure including fins is ranging between 0 and 1. Results have been illustrated through the estimation of important performance parameters such as energy absorbing capacity, melting rate, enhancement ratio, and Nusselt number. It has been found that melting time (to melt 100% of the PCM) is 60.5% less in enclosure-2 (with two fins of equal length) as compared to the enclosure-1, having no fins. Keeping the fin surface area equal, if the longer fin is placed below the shorter fin (enclosure-3), melting time is further decreased by 14.1% as compared to enclosure-2. However, among all the configurations, enclosure-6 with wire-mesh fin structure exhibits minimum melting time which is 68.4% less as compared to the enclosure-1. Based on the findings, it may be concluded that fins are the main driving agent in the enclosure to transfer the heat from heated wall to the PCM. Proper design and positioning of the fins improve the heat transfer rate followed by melting of the PCM in the entire area of the enclosure. Evolution of the favourable vortices and natural convection current in the enclosure accelerate the melting phenomenon and help to reduce charging time.

High energy consumption is a serious issue associated with in situ thermal desorption (TD) remediation of sites contaminated by petroleum hydrocarbons (PHs). The knowledge on the thermophysical properties of contaminated soil can help predict accurately the transient temperature distribution in a remediation site, for the purpose of energy conservation. However, such data are rarely reported for PH-contaminated soil. In this study, by taking diesel as a representative example for PHs, soil samples with constant dry bulk density but different diesel mass concentrations ranging from 0% to 20% were prepared, and the variations of their thermal conductivity, specific heat capacity and thermal diffusivity were measured and analyzed over a wide temperature range between 0°C and 120°C. It was found that the effect of diesel concentration on the thermal conductivity of soil is negligible when it is below 1%. When diesel concentration is below 10%, the thermal conductivity of soil increases with raising the temperature. However, when diesel concentration becomes above 10%, the change of the thermal conductivity of soil with temperature exhibits the opposite trend. This is mainly due to the competition between soil minerals and diesel, because the thermal conductivity of minerals increases with temperature, whereas the thermal conductivity of diesel decreases with temperature. The analysis results showed that, compared with temperature, the diesel concentration has more significant effects on soil thermal conductivity. Regardless of the diesel concentration, with the increase of temperature, the specific heat capacity of soil increases, while the thermal diffusivity of soil decreases. In addition, the results of a control experiment exhibited that the relative differences of the thermal conductivity of the soil samples containing the same concentration of both diesel and a pure alkane are all below 10%, indicating that the results obtained with diesel in this study can be extended to the family of PHs. A theoretical prediction model was proposed based on cubic fractal and thermal resistance analysis, which confirmed that diesel concentration does have a significant effect on soil thermal conductivity. For the sake of practical applications, a regression model with the diesel concentration as a primary parameter was also proposed.

Based on the COMSOL Multiphysics simulation software, this study carried out modeling and numerical simulation for the evaporation process of liquid metal lithium in the vacuum free molecular flow state. The motion of lithium atoms in the evaporation process was analyzed through a succession of studies. Based on the available experimental values of the saturated vapor pressure of liquid metal lithium, the relationship between saturated vapor pressure and temperature of liquid lithium in the range of 600 K–900 K was obtained. A two-dimensional symmetric model (3.5 mm×20 mm) was established to simulate the transient evaporation process of liquid lithium at wall temperatures of 750 K, 780 K, 800 K, 810 K, 825 K, and 850 K, respectively. The effects of temperature, the evaporation coefficient, back pressure, and length-to-diameter ratio on the evaporation process were studied; the variation trends and reasons of the molecular flux and the pressure during the evaporation process were analyzed. At the same time, the evaporation process under variable wall temperature conditions was simulated. This research made the evaporation process of liquid lithium in vacuum molecular flow clearer, and provided theoretical support for the space reactor and nuclear fusion related fields.

Using the efficient, space-saving, and flexible supercritical carbon dioxide (sCO₂) Brayton cycle is a promising approach for improving the performance of nuclear-powered ships. The purpose of this paper is to design and compare sCO₂ cycle power systems suitable for nuclear-powered ships. Considering the characteristics of nuclear-powered ships, this paper uses different indicators to comprehensively evaluate the efficiency, cost, volume, and partial load performance of several nuclear-powered sCO₂ cycles. Four load-following strategies are also designed and compared. The results show that the partial cooling cycle is most suitable for nuclear-powered ships because it offers both high thermal efficiency and low volume and cost, and can maintain relatively high thermal efficiency at partial loads. Additionally, the new load-following strategy that adjusts the turbine speed can keep the compressor away from the surge line, making the cycle more flexible and efficient compared to traditional inventory and turbine bypass strategies.

In this study, a composite powder capillary wick is prepared, manufactured by sintering copper powder and surface treated by low-temperature thermal oxidation. It is used to improve the performance of the capillary wick. The forced flow method and infrared imaging method are used to test the permeability and capillary performance of the samples. The effects of different oxidation temperatures on the performance of capillary wick are investigated. The experimental results show that the wetting performance of the oxidized samples is significantly enhanced. With the increase of oxidation temperature, the permeability decreases. The capillary height and velocity of the thermally oxidized samples are significantly higher than those of the untreated capillary wick. However, the oxidation temperature needs to be adjusted to obtain the best capillary performance. The highest capillary performance is found at oxidation temperature of 300°C, with an increase of 46% compared to the untreated ones. Comparisons with other composite wicks show that the sample with an oxidation temperature of 300°C has competitive capillary performance, making it a favorable alternative to two-phase heat transfer device. This study shows that combining low-temperature thermal oxidation technology with powder sintering is a convenient and effective method to improve the capillary performance of powder wicks.

The poor-reactivity anthracite urgently needs more ways for large-scale and high-quality utilization. Due to the advantage of good fuel adaptability, the circulating fluidized bed (CFB) gasification technology has the potential of high-quality utilization of anthracite. In this paper, one kind of anthracite from Shanxi province, China, was employed to be gasified in a pilot-scale CFB gasifier. It is found that at the operating temperature of 1049°C and oxygen concentration of 60.75%, the gas with a concentration of combustibles of 66% and a low heating value of 7.93 MJ/m³ (at about 25°C and 101.325 kPa) was produced in the CFB gasification process. However, the overall gasification efficiency was not desired because a large amount of gasification fly ash (GFA) escaped and its yield was up to 22%. In this case, the cold gas efficiency was below 48% and the carbon conversion ratio was only 62%. Further analysis reveals that the GFA was featured with a developed pore structure and the specific surface area (SBET) reached 277 m²/g. This indicates such GFA has a potential to use as activated carbon (AC) or AC precursor. Basis on this, steam activation experiments of the GFA produced were conducted to investigate the activation characteristics of GFA and thereby to determine its activation potential. Experimental results indicate that increasing temperature sharply accelerated the activation process, while did not impair the maximum activation effect. After activation, the SBET of GFA maximumly increased by 63%, reaching 452 m²/g. With the progress of activation, the pore structure of GFA presents a three-stage evolution process: development, dynamic balance, and collapse. Such a process can be divided and quantified according to the carbon loss. In order to achieve an optimal activation of GFA, the carbon loss shall be controlled at ~15%. This work provides a new scheme for high-quality utilization of anthracite.

Based on the fully three-dimensional (3-D) and two-dimensional (2-D) comprehensive CFD (Computational Fluid Dynamics) combustion models for a circulating fluidized bed boiler, a simplified 3-D computational domain considering the corrections of furnace side wall openings is proposed. It aims to compensate for the deficiencies of the large amount of computation in the fully 3-D model and improve the air and gas flow treatments at the openings in the simplified 2-D model. Three different computational domains, named as the fully 3-D model, simplified 3-D model and 2-D model, were implemented to perform a comparative CFD analysis in an ultra-supercritical circulating fluidized bed boiler including the hydrodynamics, penetration depth of secondary air, temperature and species distribution. The simulation results computed by the simplified 3-D model yield better agreement with the fully 3-D simulation results than those of the 2-D model. The simplified 3-D model is recommended as an alternative computational domain for the conventional 2-D model in the numerical simulation of large-scale circulating fluidized bed boiler.

The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct. Multiple shock waves are formed inside the duct at a shock Mach number of 1.75. The duct has an exit height of H, and the effect of duct resonance on multiple shock oscillations is investigated by attaching exit ducts of lengths 0H, 50H, and 150H. The downstream disturbance frequency varied from 10 Hz to 200 Hz to explore the oscillation characteristics of the multiple shock waves. The oscillatory response of shock waves under self-excited and forced oscillation conditions are analyzed in terms of wall static pressure, shock train leading-edge location, shock train length, and the size of the separation bubble. The extent of the initial shock location increases with an increase in exit duct length for the self-excited oscillation condition. The analysis of the shock train leading edge and the spectral analysis of wall static pressure variations are conducted. The variation in the shock train length is analyzed using the pressure ratio method for self-excited as well as forced oscillations. The RMS amplitude of the normalized shock train length (ζ_ST) increases with an increase in the exit duct length for the self-excited oscillation condition. When the downstream perturbation frequency is increased, ζ_ST is decreased for exit duct configurations. For all exit duct designs and downstream forcing frequencies, the size of the separation bubble grows and shrinks during the shock oscillations, demonstrating the dependence on duct resonance and forced oscillations.

The steam ejector is a crucial component in the waste heat recovery system. Its performance determines the amount of recovered heat and system efficiency. However, poor ejector performance has always been the main bottleneck for system applications. Therefore, this study proposes an optimization methodology to improve the steam ejector’s performance by utilizing computational fluid dynamics (CFD) techniques, response surface methodology (RSM), and genetic algorithm (GA). Firstly, a homogeneous equilibrium model (HEM) was established to simulate the two-phase flow in the steam ejector. Then, the orthogonal test was presented to the screening of the key decision variables that have a significant impact on the entrainment ratio (ER). Next, the RSM was used to fit a response surface regression model (RSRM). Meanwhile, the effect of the interaction of geometric parameters on the performance of the steam ejector was revealed. Finally, GA was employed to solve the RSRM’s global optimal ER value. The results show that the RSRM exhibits a good fit for ER (R²=0.997). After RSM and GA optimization, the maximum ejector efficiency is 27.94%, which is 48.38% higher than the initial ejector of 18.83%. Furthermore, the optimized ejector efficiency is increased by 46.4% on average under off-design conditions. Overall, the results reveal that the combination of CFD, RSM, and GA presents excellent reliability and feasibility in the optimization design of a two-phase steam ejector.

As the interaction between the combustor and the turbine in the aero-engine continues to increase, the film cooling design considering the combustor swirling outflow has become the research focus. The swirling inflow and high-temperature gas first affect the vane leading edge (LE). However, no practical improved solution for the LE cooling design has been proposed considering the combustor swirling outflow. In this paper, the improved scheme of showerhead cooling is carried out around the two ways of adopting the laid-back-fan-shaped hole and reducing the coolant outflow angle. The film cooling effectiveness (η) and the coolant flow state are obtained by PSP (pressure-sensitive-paint) and numerical simulation methods, respectively. The research results show that the swirling inflow increases the film distribution inhomogeneity by imposing the radial pressure gradient on the vane to make the film excessively gather in some positions. The showerhead film cooling adopts the laid-back-fan-shaped hole to reduce the momentum when the coolant flows out. Although this cooling scheme improves the film attachment and increases the surface-averaged film cooling effectiveness (η_sur) by as much as 15.4%, the film distribution inhomogeneity increases. After reducing the coolant outlet angle, the wall-tangential velocity of the coolant increases, and the wall-normal velocity decreases. Under the swirl intake condition, both η and the film distribution uniformity are significantly increased, and the growth of η_sur is up to 16.5%. This paper investigates two improved schemes to improve the showerhead cooling under the swirl intake condition to provide a reference for the vane cooling design.

Post-combustion technology of circulating fluidized bed can largely reduce the emission of nitrogen oxides (NO_x) in the process of combustion and succeed in meeting the ultra-low NO_x standard for some fuels like Shenmu coal. Exploring the potential of synergistic control of the emissions of NO_x and sulphur dioxide (SO₂) under post-combustion technology has become a direction that needs further study. The experiments were conducted on a 0.1 MW (thermal) circulating fluidized bed (CFB) test platform, composed of a CFB main combustor and post-combustion chamber (PCC). The paper focuses on the effects of air distribution ratio and temperature in CFB and limestone addition on NO_x and SO₂ emissions. The experimental results showed that compared with traditional CFB combustion, post-combustion technology can reduce NO_x emission largely, but lead to a slight increase in SO₂ emission. The higher SO2 emissions at post-combustion can lead to less NO_x emission. With the decrease in λ_CFB, NOx emission first decreased and then increased; by contrast, SO₂ emission with λ_CFB first increased and then decreased. Under post-combustion, when λCFB was 0.9, NO_x emission was the minimum, while the SO₂ emission was the largest. Combustion temperature and limestone addition has less adverse effects on NO_x emission under post-combustion, compared with traditional CFB combustion. Limestone injection into the furnace is applicable under post-combustion, and the sulfur removal efficiency under post-combustion is very high, almost equivalent to that under traditional combustion.

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.

This paper experimentally studied the effect of CO₂ opposing multiple jets on the thermoacoustic instability and NO_x 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 NO_x emissions show a reverse trend with the increase of open area ratio on the whole, and the optimal jet flow rate range is 1–4 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%. NO_x 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 NO_x emissions, which could be a design reference for constructing a safer and cleaner combustor.

With the advantages of high efficiency and compact structure, supercritical carbon dioxide (sCO₂) Brayton cycles have bright prospects for development in energy conversion field. As one of the core components of the power cycle, the centrifugal compressor tends to operate near the critical point (304.13 K, 7.3773 MPa). Normally, the compressor efficiency increases as the inlet temperature decreases. When the inlet temperature is close to the critical point, the density increases sharply as the temperature decreases, which results in quickly decreasing of volume flow rate and efficiency reducing. The flow loss mechanism of the sCO₂ compressor operating at low flow rate is studied in this paper. Computational fluid dynamics (CFD) simulations for sCO₂ compressor were carried out at various inlet temperatures and various mass flow rates. When the sCO₂ compressor operates at low volume flow rate, the flow loss is generated mainly on the suction side near the trailing edge of the blade. The flow loss is related to the counterclockwise vortexes generated on the suction side of the main blade. The vortexes are caused by the flow separation in the downstream region of the impeller passage, which is different from air compressors operating at low flow rates. The reason for this flow separation is that the effect of Coriolis force is especially severe for the sCO₂ fluid, compared to the viscous force and inertial force. At lower flow rates, with the stronger effect of Coriolis force, the direction of relative flow velocity deviates from the direction of radius, resulting in its lower radial component. The lower radial relative flow velocity leads to severe flow separation on the suction side near the trailing edge of the main blade.

Hydrogen is an attractive energy carrier due to the high conversion efficiency and low pollutant emission. Chemical looping hydrogen production (CLHP) is an available way for producing high purity hydrogen with relatively low penalty energy and CO₂ is captured simultaneously. Three reactors are usually contained for CLHP system including air reactor (AR), fuel reactor (FR) and steam reactor (SR). In current work, we focus on the performance of CLHP system, which is the basement for operation and design. Numerical simulations are carried out for analyzing the flow behavior and the numerical structure is built according to the experimental unit constructed at Southeast University, China. Results show that the operation of L-valve influences most the solid circulating rate of system and particles pass L-valve easily with large aeration rate. Mass distribution results indicate that fuel reactor has the capacity for particles storage. Increase of gas inlet rate of steam reactor leads to more particles leave steam reactor and accumulate into fuel reactor. L-valve can prevent the gas leakage between reactors and it will be adopted for reactive unit. Combining the operation of fuel reactor and L-valve, the system can reach steady state and get the regulating ability.

The co-combustion of biomass and coal can positively impact the environment and reduce the cost of power generation. However, biomass fuels have many limitations. Circulating fluidized bed (CFB) preheating combustion is suitable for co-combusting coal and biomass because of better fuel adaptability. In the cement industry, fuel combustion and raw meal decomposition in precalciners affect cement quality and cause pollutant emissions. The preheating combustion method used in precalciners can improve combustion performance and reduce NO_x emissions. This study investigated the preheating characteristics of a coal-biomass mixed fuel in a cement precalciner. The effects of load, biomass type, and biomass proportion on the preheated fuel and the conditions of the CFB were investigated. The results indicated that a lower load reduces the combustible components in gaseous and solid preheated fuels. However, due to the gas volume remains constant under different loads, a lower load also increases temperature and intensifies the reaction. The carbon chain and microscopic structural activities of preheated fuels are considerably enhanced, facilitating their combustion in precalciners and reducing nitrogen oxides in rotary kilns. Furthermore, adding biomass can improve the reactivity of a fuel subjected to preheating. Thus, biomass fuels (e.g., rice husks) exhibit high combustion efficiency, and thus high energy utilization. The present study achieved better pore structure and molecular activity using preheated fuel from a CFB preheater. In addition, the improvement of pore structure and molecular activity increases with the proportion of the biomass.

To guide the application of gasification agent staging in circulating fluidized bed (CFB) gasifiers, a cold model test was implemented to study the effects of air staging on the operation of the CFB system. The results show that the re-entrainment of the solid in the downward solid flow by the secondary air jet reduces the back-mixing of solid into the dense phase zone and increases the total entrainment rate. The uniformity of axial solid holdup profile in the riser is improved by air staging. With increasing secondary air ratio, the solid concentration in the dense and dilute phase zones increases because the solid in the standpipe is transferred into the riser. After air staging, the pressure drop of the cyclone significantly increases, which results from the disturbance of the inside flow field and the increase in inlet solid concentration. Within the experimental range, the failure of the system appears as gas leakage in the standpipe. This failure can be understood as the mismatch of the mass balance and pressure balance of the system after air staging. Therefore, the results also provide guidance for the matching design of key components for the implementation of gasification agent staging.

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.  

Heat storage properties of phase change materials (PCMs) are essential characteristics that perform a key role in thermal heat energy storage systems. The thermal properties of PCMs can be improved by developing metal foam/PCM composites. The addition of metal foam in PCMs has a significant effect on the thermal characteristics of PCMs. In this paper, the heat storage properties of two different metal foam/PCM composites were experimentally examined. The behavior of paraffin in metal foam (copper and iron-nickel)/paraffin composites concerning pure paraffin at a constant heat flux of 1000 W/m² in three directions simultaneously (x, y, and z) was studied. Paraffin was infiltrated into copper and iron-nickel foams to develop composite materials which resulted in enhancing the thermal conductivity of the paraffin. A comparative analysis is made on the heat storage properties of paraffin in copper and iron-nickel foams/paraffin composites. Inner temperature distribution during the phase transition process is experimentally evaluated. This comparison indicates that temperature uniformity in copper foam/paraffin composite is better than in iron-nickel foam/paraffin composite and pure paraffin at the same heat flux. Experimental results show that at heat flux of 1000 W/m2, the heat storage time for copper foam/paraffin composite is 20.63% of that of iron-nickel foam/paraffin composite.

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) which 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%:19.5%, mass ratio) 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.