Air Convection Research Articles

Study on Shutter Heating Performance of Gas Turbine Intake System

Abstract Aiming at the anti-icing and de-icing requirements of gas turbine intake system, study the heating performance of a typical shutter vane, and compares and analyzes the influence of different ambient temperature and different electrothermal pipe heat generation rate on vane temperature distribution and heat transfer characteristics. The results show that the air convection at different positions on the blade surface of the louver leads to the difference in the temperature distribution of the upper and lower surfaces of the blade, as well as the leading edge and trailing edge of the blade, and the leading edge of the blade, as the area with the lowest overall temperature distribution of the blade, should be focused on in the design of anti-icing and de-icing systems. Increasing the heat production rate of the electric heating tube, there is more heat flow near the midline of the blade, which makes the temperature rise at this position the highest, and it is necessary to pay attention to the energy waste and blade damage caused by local overheating of the blade. Therefore, when the ambient temperature increases from 245.15 K to 318.15 K, the leaf temperature increases from 248.73 K to 322.74 K, and the temperature rise also increases from 3.58 K to 4.59 K. The electrothermal technology can be used to the anti-icing and de-icing of the intake system shutters on the basis of choosing the heat generation rate of the electrothermal tube reasonably.

Drying of avocado peels using carbonation-ultrasonication as pretreatment: energy consumption, antioxidant capacity and rheological properties

Fruit processing by-products, especially peels are underused and mostly discarded as waste. The aim of this study was to assess the effect of ultrasonication (US) combined with carbonation (CUS) on the convective drying process of avocado peels at different temperatures, adding value to this waste. For this, the avocado peels were treated with dry ice for 15 min and subjected to US (400W/10 min, 30°C) before convective air drying (50-70°C). The energy consumption, antioxidant capacity, water adsorption isotherms, rehydration rate, and dynamic rheology of dried avocado peels pretreated by CUS were compared with a control process (without pretreatment) and only US pretreatment. The combined treatment (CUS70) resulted in a 2.6-fold reduction in drying time and a 2.3-fold decrease in energy consumption, with CO2 preserving bioactive compounds and antioxidant capacity after the drying process. Differences were also observed in the rehydration capacity of the samples (CUS), with an increased water absorption capacity, along with a reduction in the viscoelastic properties of the peels. The results present new perspectives for the application of CUS in the food industry, paving the way for the development of creative, innovative, and simple approaches for the management and recycling of agri-food waste, with the potential to extend this knowledge to new food matrices.

Enhancement of the Elastocaloric Performance of Natural Rubber by Forced Air Convection

Enhancement of the Elastocaloric Performance of Natural Rubber by Forced Air Convection

Initiation of prefrontal convection within a Northeast China cold vortex: The roles of elevated front and dry air intrusion

AbstractConvective initiation ahead of a surface cold front within the Northeast China cold vortex of June 1, 2021, is investigated using observations and a convection‐permitting simulation. The initiation of the convection is elevated without identifiable surface mesoscale forcing. Air feeding the initial convective cells originates from at least 1 km above the ground where parcel‐based convective available potential energy is sufficiently large. An elevated front with large equivalent potential temperature gradient and flow convergence across is primarily responsible for the initiation of elevated convection and later organization into a deep convective line. The elevated front is similar to the upper cold front within extratropic cyclones studied elsewhere, but its altitude is lower in this case. Backward‐trajectory analysis of air parcels on the cold side of the elevated front shows that dry air intrusion reinforces the elevated front by increasing the equivalent potential temperature gradient and moment convergence across the front. The convergence forcing combined with access to convective unstable air at the leading edge of the westerly flows east of the elevated front causes the initiation of convection. The development and spreading of a surface cold pool help push the convective line eastward away from the surface cold front located to the west. Orographic gravity waves provide additional forcing so that convection cells are initiated first at the upward branches of the gravity waves, but the overall organization of initial cells into a solid convective line is controlled mainly by mesoscale structures associated with the elevated front.

A combined experimental-mathematical study on the kinetics of dry ice sublimation under different airflow velocities and blowing modes

The sublimation rate of dry ice, crucial for its cooling performance, is typically influenced by environmental temperature, pressure, and specific surface area. However, the effect of wind speed under forced air convection is not well understood, and current sublimation kinetic models inadequately capture this influence, leading to discrepancies between simulations and experiments. This study examines the sublimation kinetics of static dry ice particles under varying wind speeds and blowing modes. A mathematical model was developed to determine the sublimation kinetic parameters by integrating the Clausius-Clapeyron equation, mass transfer theory, and hybrid particle swarm optimization (HPSO) algorithm. These parameters were then used to create a cooling model for a small insulated box, and the results were validated against experimental data. The findings show that increasing wind speed enhances the sublimation rate of dry ice, with upward-blowing conditions resulting in higher rates than side-blowing conditions. The model’s predictions closely match experimental data, with a maximum mass change deviation of less than 3 % and a maximum temperature deviation of less than 4 °C, demonstrating high reliability.

A Validated Thermal Computational Fluid Dynamics Model of Wine Warming in a Glass

Oenophiles are aware that the temperature at the time of drinking can profoundly shape wine’s sensory attributes. Wine is usually served and drunk below room temperature but warms up after pouring due to heat exchange with warmer surroundings. This study investigates how quickly wine warms up in a wine glass and identifies the relevant heating effects. A numerical simulation using conjugate heat transfer is established, representing the complex multi-physical process. Experiments are conducted to validate the simulation. It is shown that the simulation must take into account thermal conduction, convection, and even radiation to provide accurate results. Without simulating radiation and convection of the room air, the predicted temperature is off by 66.3% or 3.3 °C. As warming is independent of the alcohol content, the simulation results are valid for non-sparkling wine types with moderate sugar levels within the considered configuration. A parameter study investigated the temperature increase over time depending on the ambient temperature and the initial wine temperature for 150 mL wine in a medium-sized red wine glass. The results can provide information on preparing a wine to obtain the desired drinking temperature.

Mechanism of Wind and Buoyancy Driving on Ventilation and Pollutant Transport in an Idealized Urban Street Canyon

The mechanisms underlying the effects of wind and buoyancy on ventilation in urban street canyons are unclear. This study investigated the effects of facade heating on ventilation and pollutant transport in an idealized street canyon with a 1.67 aspect ratio through computational fluid dynamics simulations. The dispersion pattern of discharged hot pollutants was also studied. A primary recirculation was observed when facade heating was not applied; this recirculation was promoted in leeward-wall and ground heating cases. However, the recirculation was bifurcated into two recirculations in windward-wall heating cases, restricting ventilation. Enhanced recirculation increased the ventilation and decreased the pollution level; by contrast, air pollution increased considerably when the recirculation was bifurcated and ventilation was restricted. In the hot-pollutant case, similar results to those in the ground-heating case were observed. The hot discharged pollutant enhanced ventilation, reducing pollution. The pollutant transport mechanism was determined through an analysis of pollutant fluxes. For the one-recirculation pattern, air convection transported the pollutant from the ground level to the top boundary, and turbulent diffusion then caused pollutant removal. For the two-recirculation pattern, turbulent diffusion contributed substantially to pollutant transport both in the junction between the recirculations and through the top boundary of the street canyon.

Изменение состава пектиновых веществ при замораживании и хранении растительной продукции

To keep up with the growing demand, producers of frozen plant products have to develop new freezing technologies that would preserve the sensory and biological properties of fruits and vegetables. Pectins are important structural and moisturebinding components of plant cells that improve their stability at high and low temperatures. The research objective was to study the effect of blanching and various freezing methods on the composition of pectin substances during long-term storage of fruits and vegetables. The research featured scorzonera, salsify, kohlrabi, apples, and plums. The freezing modes included two temperature modes (–24 and –35°C) and three freezing methods, i.e., blanching, air-freezing represented by natural air-freezing, artificial convection, and fluidization, and immersion in a mix of water, ethyl alcohol, sucrose, and sodium chloride. The frozen samples were stored in sealed bags at –18°C for 7–12 months. The water-soluble pectin, intermediate fraction, and protopectin obtained by extraction were determined using the colorimetric carbazole method. The qu alitative analysis relied on infrared spectroscopy. Blanching reduced the pectin content by 2–10% in vegetables and by 18–21% in apples. Fluidization and immersion freezing had the least damaging effect on pectins. Air-freezing with natural convection caused the greatest damage to protopectin. During storage, the maximal loss of pectins (66%) occurred in the salsify sample subjected to natural air convection at –24°C. The least damage (9%) was detected in the kohlrabi sample frozen at –24°C in ice environment. A higher moisture content in the native state correlated with minimal losses of pectins by the end of refrigerated storage. The research also included identification of absorption bands for pectic substances in fro zen scorzonera and salsify. In this study, pectin content depended on moisture content in tissues, blanching process, and freezing method. All frozen samples demonstrated losses of protopectin and an increase in the intermediate fraction. An intense freezing process had a positive effect on the pectin content during long-term storage. However, after six months of storage, the samples demonstrated significant fractional changes and pectin losses.

Experimental study of thermoconcentration convection in air–water and air–undecane mixtures

A quantitative experimental comparison was conducted between thermal convection in dry air and thermoconcentration convection in two gas mixtures: air–water vapor and air–undecane vapor, within the temperature range of 0–80 °C at normal atmospheric pressure. Convection in these mixtures is driven by temperature and concentration gradients of water (or undecane) vapor in the air. The stationary thermoconcentration convection is accompanied by continuous phase transitions of the fluids. The quantitative results of the experiments are represented in terms of the Nusselt number Nu and the effective Rayleigh number RaE, which is the sum of the thermal RaT and concentration RaC Rayleigh numbers. Quantitative laboratory measurements were performed using the thermocouple method and were supplemented with qualitative data from visual monitoring of transparent fluid flows using holographic interferometry. The cubic and quadratic temperature dependencies of RaCRaT−1 were determined experimentally for moist air and for the air–undecane vapor mixture, respectively. The significant role of moisture phase transitions in air convection is established. Neglecting these effects at 25 °C and using the ordinary RaT instead of actual RaE would result in an error exceeding 30%. At 38 °C, this error would increase to nearly 100%. At around 80 °C, thermoconcentration convection becomes almost entirely concentration-driven, as the high molecular disordered thermal motion is suppressed by the ordered convective motion generated by evaporation and condensation of water on the opposite heat exchangers of the convective cell.

Inactivation kinetics of Bacillus cereus and Aspergillus niger spores in dehydrated onion shreds after pulsed light and infrared treatments

Fresh onions are dehydrated to increase their shelf-life. Primarily, open dehydration techniques like solar dehydration come with the problem of contamination through natural air convection. A solar conduction dryer that uses conduction, convection, and radiation for dehydration of food samples is exploited in this study. The food samples are often contaminated by Bacillus and Aspergillus species spores. As a remedy, pulsed light treatment as a non-thermal technology and infrared treatment as a thermal technology are studied and compared. Bacillus cereus and Aspergillus niger spores are chosen as a representative of bacterial and fungal contamination in onions. Dehydrated onion shreds with varying water activities (0.4, 0.5, 0.6) were treated. The spore inactivation was best described by Weibull model as compared with first-order model. Scanning electron microscopy images of the microbial cells showed surface distortions on the bacterial and fungal spores. The effect of the treatment technologies on the colour, flavour (thiosulphinate and pyruvic acid concentration), total phenolic and flavonoid content, and ascorbic acid concentration are compared. Overall, pulsed light treatment showed promising inactivation with a maximum log reduction of 4.5 log B. cereus spores·g−1 and 3.1 log A. niger spores·g−1 at 2.131 J·cm−2 in samples with water activity 0.6. The inactivation rate increased with an increase in water activity. The colour was better retained in pulsed light treated samples. The thiosulphinate content (9.24 μmol·g−1), total phenolics (0.268 mg GAE·g−1), and flavonoid content (0.344 mg QE·g−1) in the sample were improved upon pulsed light exposure.Graphical

Experimental study on thermal insulation mortar with normal bearing capacity and its mesoscopic characteristics analysis

Low strength limits the application potential of thermal insulation concrete in high-temperature underground engineering. However, current research on enhancement methods for thermal insulation concrete is relatively limited, and there is a lack of appropriate evaluation indicators, which results in significant room for improvement in its overall performance. To address this issue, this paper develops a load-bearing and thermal insulation mortar (LBTIM) with both thermal insulation and load-bearing capabilities: based on M20 mortar, low-thermal-conductivity materials (aerogel, coal gangue, fly ash) and reinforcing materials (silica fume, basalt fiber, polypropylene fiber) were added. Orthogonal experiments with 6 factors at 5 levels and 6 factors at 3 levels were designed to investigate the thermal conductivity and uniaxial compressive strength of different material ratios. Subsequently, the "strength-to-thermal conductivity ratio" (RST) was defined, and an intensity-thermal conductivity scatter plot was drawn as an evaluation indicator. Based on the experimental results, the ratio of LBTIM was successfully developed and optimized, and its stability was verified through experimental replication. The optimal ratio of LBTIM was determined as follows: aerogel 0.26 %, silica fume 3.35 %, fly ash 7.06 %, coal gangue 30 %, basalt fiber 0.05 %, and polypropylene fiber 0.45 %. Experimental results showed that its thermal conductivity was approximately 0.8 W/m·K, and its uniaxial compressive strength reached 17 MPa. The strength-to-thermal conductivity ratio was improved by 60.7 % compared to M20 mortar. Furthermore, near-distance imaging and SEM tests revealed the mesoscopic mechanism of LBTIM: the high porosity and the formation of an effective porous shear-resistant structure in LBTIM significantly reduced internal air convection. Combined with the externally added porous materials, this effectively blocked the large heat flow channels within the mortar, thereby significantly reducing the thermal conductivity. Meanwhile, the internal porous shear-resistant structure and the reinforcing fiber materials jointly ensured the good load-bearing capacity and stability of LBTIM, providing an important reference solution for addressing the load-bearing and thermal insulation issues in high-temperature tunnels.

3D structural-engineering evaporator integrating light-space-heat omnibearing regulation

Interfacial solar evaporators designed with sophisticated 3D structure hold the potentiality for ameliorating the evaporation rate through expanding the surface area for evaporation, facilitating water movement, and bolstering air convection. However, the most current 3D evaporators are stalemated of constrained light absorption, circumscribed evaporative surface or thermal dissipation which collectively result in the curtailment of evaporation rate escalation. In this work, an omnibearing convergence of new cup-like 3D solar steam generator (C-3D SSG) based on MoS2/C and PVA materials with integrated coordination of light-space-heat is constructed. The innovative cup-like structural design of C-3D SSG successfully embodies the convergence of light, space, and heat management through the strategic integration of photothermal materials (PTM), substrate materials, and evaporative elements across multiple scales, demonstrating a compelling advancement in light absorption, copious heat diffusion space and prodigious energy-harvesting zone and water evaporation rate enhancement. The omnibearing regulation attains a premium evaporation rate of 3.89 kg m-2h−1 under 1 Sun illumination with recycle energy of 1.71 W. By incorporating the C-3D SSG for practical application, it can function as an evaporator within a cup, thereby enhancing its practical utility. And C-3D SSG with panoramic convergence provides a broad range of research avenues and methodologies for addressing the water crisis and the development of ISSG technology.

Changes in flavor profile of vegetable seasonings by innovative drying technologies: A review.

Seasonings like garlic, ginger, and scallion provide spicy and masking flavor or aroma in vegetables. However, the method or technique used for drying these spices can affect the flavor profile. Therefore, this review focuses on vegetable seasonings like ginger, garlic, and scallion, the characteristic flavor of fresh and dehydrated vegetable seasoning, and how drying methods (freeze-drying [FD], convective hot air drying [HAD], infrared drying, microwave drying [MW]), and other recent dryers (swirling fluidized bed [SFB], pulsed-vacuum dryer, relative humidity-convective dryer, etc.) affect the flavor profile of the common vegetable seasonings. HAD increases α-zingiberene, reduces gingerol, and forms β-citral and citral in fresh ginger. FD increased sesquiterpenes, retained terpenoids, sulfides, and other volatiles in fresh ginger, and did not produce new volatile compounds (VOCs) in garlic. SFB drying better preserves 6-gingerol than FD and HAD. MW increases trisulfides and cyclic sulfur compounds in garlic. In general, drying, especially thermal drying reduces the VOCs in fresh garlic, ginger, and scallion and causes the formation of new VOCs.

Performance Characteristics of a Free-Breathing Polymer Electrolyte Fuel Cell with Various Channel Shapes

This study utilized a small free-breathing fuel cell, with an active area of 4 cm2 (2 cm x 2cm), and channel cathodes with various channel shapes, to experimentally investigate the effect of channel structure on cell performance, to numerically analyze the natural convection air flow in channels, and to compare with the results of performance characterisitics. The results indicated that, compared with a conventional cathode separator with four straight channels (with a width of 3 mm, a depth of 3 mm, and a rib width of 2 mm), cell performance was improved by eliminating some of the channel ribs and increasing the opening ratio, up to a point. A separator with 2 mm square ribs rotated by 45° further improved cell performance. However, when the opening ratio exceeded 72% with a straight center rib of 2 mm width, cell performance leveled off. The analysis results revealed that separators with modified channels promoted natural convection.

Experimental and Numerical Investigation for Optimization of a Hybrid Battery Thermal Management System based on PCM and Air Convection

Abstract This work presents the design and optimization of a phase change material (PCM) based hybrid battery thermal management system (HBTMS). In the first stage, experiments are performed to measure the battery cell temperatures under various charge rates with and without the usage of PCM. Thereafter, a numerical model is developed to conduct a parametric study on the effect of thickness of PCM layer around the battery cell. The maximum cell temperature (36.35°) and thermal nonuniformity are within the safe range for the PCM thicknesses of 6 to 12 mm. In the second stage, a parametric study is conducted in the 6S1P battery module to optimize the spacing between the cells at constant inlet velocity. The maximum temperature is within the optimal range when the cell spacing is 10 mm. At the constant cell spacing of 10 mm, increase in inlet velocities from 0.25 m/s to 2.5 m/s gradually improves the thermal non-uniformity. The maximum temperature and thermal non-uniformity for 6S1P battery module is found to be 42.07° and 1.17° respectively. In the third stage, 6S1P battery module is optimized for PCM thickness, cell spacing and inlet air velocity. It is found that effective thermal management is possible with PCM based HBTMS at low airflow rate of up to 1.5 m/s. The optimized PCM based HBTMS shows 46.59% and 40% reductions in PCM mass and air flow rate respectively.

Effects of corrugation on convective heat transfer and power generation in a wavy walled triangular cavity equipped with inclined elastic fin and piezo-energy harvester assembly

Piezoelectric energy harvesters are one of the energy conversion technologies that can be used to convert a variety of external sources, including wind, fluid motion, and vibrations, into electrical energy. This work suggests a novel wall corrugation design in addition to an elastic fin piezo assembly arrangement for power generation and thermal management in a triangular cavity during turbulent forced convection of air. Using the finite element method with ALE, the analysis is conducted for different values of fin inclination (γ between 0 and 60), corrugation amplitude (Af between 0.01H and 0.06H), corrugation frequency (Nf between 1 and 20) and fin distance from the mid-point of the inclined wall in wall direction. The average Nusselt number (Nu) and generated power (PW) show a non-linear increasing trend with increasing fin tilt. Average Nu increment factor becomes 5.17 with the highest fin inclination while the power increments become 11.6 and 4.46 when rising inclination from 30 to 45 and from 45 to 60. The generated power rises with higher corrugation amplitude and wave number. However, increasing the wave number results in thermal performance degradation. Increment of average Nu becomes 1.17 with highest corrugation amplitude while it declines by a factor of 10.3 at the highest wave number. Power enhancement factors of 5.73 and 2.32 are obtained by increasing the corrugation amplitude from Af = 0.0714H to Af = 0.1786H and from Af = 0.1786H to Af = 0.2143H. When fin positions sf = 0.7143H and sf = -0.7143H are compared with the case of fin location at sf = 0, the power increment factors become 12.27 and 4.76, respectively. For the power produced by the piezo device, a polynomial type correlation is suggested by adjusting the parameters of the corrugated wall.

Thermal Stress Analysis of Compact Heat Exchanger Produced by Additive Manufacturing

Abstract Compact heat exchangers are renowned for their high heat transfer rates and efficiency, achieved by incorporating mini and micro-channels in their core design. However, operating under conditions of high-pressure fluctuations and significant temperature differences between hot and cold streams can potentially induce fatigue failure. To the best of our knowledge, this study represents the first investigation into the thermal stresses experienced by heat exchanger samples manufactured by selective laser melting technology, focusing on circular channels. Experiments were conducted using hot water in the inner channel, while the remaining channels and the sample surface were subjected to natural convection in ambient air. Strain gauges, thermocouples, and RTDs were employed to measure strain and temperature variations over time. These data were utilized as inputs for a numerical model based on finite element method. The strain measurements were compared with those obtained from the numerical model, revealing an average difference of approximately 20%. Lastly, a thermal fatigue analysis based on the maximum equivalent stresses predicted by the numerical model is presented. The evaluation considered both S-N curves: outlined in the ASME standard and the one obtained with specimens produced through selective laser melting. In the case of circular channels manufactured through additive manufacturing evaluated in this work, thermal stresses alone are insufficient to cause component failure due to fatigue. However, significant pressure cycles superimposed on the model can reverse this situation, making the combined effect of thermal and mechanical stresses influential in determining the component's fatigue behavior.

Biomimetic heat-localized and solar absorption-enhanced hollow structural nanofibrous membrane for clean water production from saline water and dye wastewater

The rational design of material structures can be an effective approach to enhance the performance of solar-driven clean water production. In this study, a hollow structural nanofibrous membrane was developed by mimicking the hollow structure of polar bear hair using coaxial electrospinning. The shell layer consisted of carbon nanoparticles (C NPs) decorated CuO nanosheets (C@CuO), that exhibited photothermal conversion capacity. Meanwhile, the core layer containing hydrophilic polyvinylpyrrolidone (PVP) was eliminated to generate the hollow structure. The C NPs enhanced the membrane’s light absorption to increase thermal energy harvesting, while the CuO nanosheets improved the membrane’s wettability enhancing the water supply. Furthermore, the hollow structure limited air convection, prevented heat conduction, and minimized heat radiation, enabling heat localization to be achieved inside the membrane to suppress heat loss during evaporation. For 3.5 wt% saline water and actual dye wastewater, the C@CuO nanofibrous membrane achieved high evaporation rates of 1.36 kg·m−2·h−1 and 1.31 kg·m−2·h−1, respectively, under 1 sun illumination. Moreover, even after continuous 6-h evaporation tests, the evaporation rate of the C@CuO membrane remained virtually unchanged, highlighting its long-term stability with regard to salt resistance in real-world applications. Additionally, the remarkable flexibility of the C@CuO membrane offers convenience during operation and guarantees dimensional stability when it is subjected to external stresses. These discoveries should inspire subsequent research on developing delicate architectural materials and exploring their potential applications in various fields, including energy generation, clean water production, and thermal insulation.

Mathematical modeling of blanch-assisted drying of drumstick leaves (Moringa oleifera) in convective hot air system

Studies were conducted to investigate the drying characteristics and kinetics of pre-drying treated leaves of Moringa oleifera using a hot air oven at 50, 60 and 70 °C. The equilibrium moisture content (Me), moisture ratio (MR) and drying time decreased, whereas the drying rate increased with the increase in temperature from 50 to 70 °C. The blanching of the leaves in 0.5 % KMS and 0.1 % NaHCO3 was at par and took less drying time to reach Me than other pre-drying treatments. Minimum MR was attained in 6.5, 7.0 and 7.5 h in leaves blanched with 0.5 % KMS and 0.5 % NaHSO3 solutions, while in unblanched leaves it was obtained in 7.0, 8.0 and 9.5 h at 50, 60, and 70 °C, respectively. The drying rate was higher in 0.5 % KMS pre-drying treatment than the other pre-drying treatments, and the lowest was in unblanched leaves. Among the models, the Midilli–Kucuk model was adjudged as the best fit with highest R2, lowest reduced χ2 and the least RMSE. The effective diffusivity of moisture (Deff) increased while energy consumption (Ec) and specific energy consumption (SEC) of leaves decreased with increasing temperatures from 50 to 70 °C. Blanching with 0.5 % KMS solution had the highest Deff, while, in unblanched leaves, the results were reversed. The leaves blanched with 0.5 % KMS and 0.1 % NaHCO3 solutions required the lowest Ec and SEC while the unblanched leaves had the highest values.

Experimental study on energy storage characteristics of packed bed using different solid materials

The packed bed energy storage system can solve the mismatch between solar energy supply and demand at a low cost. The physical properties of storage materials have a decisive impact on the performance of storage systems. Different scenarios may require different storage materials. Studying the impact of storage materials on storage characteristics is crucial. However, the comparative analysis and research on different TES materials are focused on characterization and numerical simulation but less on packed bed TES experiments. This paper evaluates the thermal durabilities of three materials, including sintered ore particles, alumina balls, and rock particles, through thermal cycling tests. Through packed bed heat storage experiments, the energy storage characteristics and thermocline evolution characteristics of three beds under different operating conditions are compared and analyzed. The results indicate that all materials exhibit excellent thermal durabilities. A larger bed voidage and smaller bed heat capacity are beneficial for thermal diffusion in the bed. When reverse charging, the natural convection of air in the bed enhances the convective heat transfer effect, resulting in a higher charging power. The existence of natural convection promotes the mixing of cold air and hot air in the tank, increases the irreversibility of the process, and leads to a significantly lower efficiency in reverse flow compared to that in forward flow. When changing the airflow direction, the system overall exergy efficiencies of SOP, alumina, and rock bed decrease from 74.1 %, 72.4 %, and 77.2 % to 47.0 %, 39.9 %, and 45.8 %, respectively. Regardless of the airflow direction, the smaller the bed voidage and the larger the bed heat capacity, the better the maintenance characteristics of the thermocline.