Journal of Thermal Analysis and Calorimetry最新文献

The steady and incompressible two-dimensional flow of a hybrid nanofluid across a porous stretchable sheet is numerically analyzed in this study. To create a hybrid combination, copper (Cu) and alumina (Al2O3) nanoparticles are merged in water, which is regarded as the host fluid. The effects of suction, magnetic fields, porous media, thermophoresis, chemical reactions, Brownian motion, and activation energy have used in this work. Additionally, the molar concentration, velocity, and thermal slip constraints are used in this study. PDEs are used to illustrate the mathematical model, and with the use of suitable similarity variables, they are transformed into ODEs. After that, the transformed ODEs are numerically solved and verified using those reference studies. The velocity profile was observed to decrease with the increasing solid volume fractions of copper and alumina nanoparticles, as well as with higher magnetic, velocity slip, and porosity factors. Skin friction increased with the influence of porosity, magnetic, and suction factors, but decreased with the velocity slip factor. The temperature slip factor led to a reduction in the temperature profile, while higher solid volume fractions of copper and alumina nanoparticles, along with Brownian motion, thermophoresis, and magnetic factors, expressively enhanced it. The rate of heat transfer increased with radiation, Eckert number, Brownian motion, and thermophoresis effects, but decreased with the thermal slip factor. Furthermore, Brownian motion and the concentration slip factor reduced the mass transfer rate, whereas the Schmidt number, thermophoresis, and chemical reaction factors amplified it.

Enhancement in the heat transfer rate of the heat-exchanging fluid can significantly improve the efficiency of a thermal system. Nanofluids have emerged out to be a new promising fluid because of their unique heat-exchanging ability. However, most existing studies are restricted to single-component ferrofluids with limited control over thermal performance. To address this limitation, the present study experimentally investigates the parametric impact and tunability of the heat transfer coefficient (HTC) of a Fe₃O₄–Ag hybrid nanofluid, engineered to exploit the high thermal conductivity of silver nanoparticles and the magnetic responsiveness of magnetite nanoparticles. The experiments explore the influence of varying frequency (50–1 kHz) and field intensity of an alternating magnetic field (0–2.4 mT) on the heat transfer rate. Additionally, the effect of nanoparticles concentration (0.25–1 mass%) on HTC is analyzed. Results demonstrate that the HTC is highly susceptible to magnetic field parameters, exhibiting up to a 67.5% enhancement at a field intensity of 2.4 mT compared to the base fluid. To further optimize thermal regulation, a split-range fuzzy logic controller (FLC) is implemented to dynamically control fluid temperature by adjusting magnetic field strength and frequency. The FLC-based system achieves comparable cooling performance to the uncontrolled case while reducing heater energy consumption by 2.1% and electromagnetic energy input by 31.8%. The Fe₃O₄–Ag ferrofluid and control scheme establish a foundation for smart, magnetically tunable thermal management systems applicable to solar thermal devices and advanced heat exchangers.

This present investigation reports the measurement of thermally stimulated discharge current and contact angle to understand the role of surface properties in thermal relaxation in nanocomposite samples. The polysulfone (PSF)–ZnO nanocomposites thin film of thickness 40 µm was prepared by a solution-mixing method. TSDC is not only used to study the fine structure of polymeric materials, but it is an important technique for fine structure investigation of both solid polymers and additives of PSF nanocomposites, which were recorded at room temperature and 60 °C with different values of DC field. The nature of relaxation mechanisms in PSF nanocomposite was observed by the measurement of discharge current after polarization by DC field. The single relaxation peak was observed at around 180 °C. The high-temperature peak is associated with MWS relaxation mechanism. The PSF nanocomposite had mass ratio proportion of 3, 5, and 10 where the comparison of surface properties was made between the nanocomposites and the pure PSF.

Lignocellulosic biomass (LC) is a non-food-competing resource that can be converted into valuable products via pyrolysis. However, its complex polymeric structure makes this process challenging. Acetylation is a promising chemical treatment to enhance the efficiency of biomass pyrolysis. Furthermore, thermogravimetric analysis (TG) is a simple and low-cost technique that can be used to simulate pyrolysis, although dynamic TG curves may not be appropriate for LC. This work investigated the effects of acetylation on the chemical composition, thermal behavior, and catalytic thermo-degradation of three types of LC (wood sawdust, coconut husk, and cow manure). Acetylation was performed using acetic anhydride and sulfuric acid under microwave irradiation, and catalytic thermo-degradation was investigated by dynamic and isothermal TG analysis. Acetylation enhanced carbon content and total mass loss while decreasing residual mass in all biomass types. Interestingly, isothermal TG analysis revealed improved interaction between the catalyst and LC, surpassing dynamic analysis in catalytic thermo-degradation. Remarkably, the isothermal TG analysis showed greater mass loss in the presence of the catalyst. The combined effect of acetylation and the catalyst increased biomass thermo-degradation by 4.5% at 523 K compared to raw biomass. This suggests that acetylation combined with catalytic thermo-degradation can enhance the pyrolytic conversion of lignocellulosic biomass, with efficiency evaluated through isothermal TG analysis.

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One way to amend the heat transfer process in heat exchangers is to add substances with high thermal conductivity (TC) to the base fluid. The usage of nanofluids (NFs) in energy systems is rapidly growing. This study investigates the TC of graphene oxide (GO)–Al₂O₃/(50% ethylene glycol (EG) and 50% water) NF at temperatures T = 25–50 °C and the volume fraction of nanoparticles (φ = 0.1–1.6%). The two-step technique was applied to create the samples. The results show raising the φ from φ = 0.1 to 1.6%, the temperature from 25 to 50 °C, and the TC by 38%. The maximum increase in TC occurred at φ = 1.6%. Finally, the experimental equation is provided for estimating the TC of the generated NF over T and φ. The study reveals a MOD of 1.75%, indicating its accuracy. In addition, the proposed equation and experimental results were compared with the Li and Peterson model, which were in good agreement with the second equation presented by Li and Peterson.

This study explores the enhancement of phase change material (PCM) melting performance within a double-tube heat exchanger, a key factor in improving thermal energy storage and transfer efficiency. Optimizing PCM melting behavior is essential for efficient thermal management and sustainable energy applications. In this research, a novel double-tube energy storage system with twisted tape inserts is analyzed numerically, with findings validated through experimental data. The system utilizes twisted tapes with three pitch lengths (60 mm, 80 mm, and 100 mm) to investigate their impact on melting rates. The numerical results reveal significant improvements in charging time, with reductions of 34%, 46%, and 53% for twisted tapes with pitch lengths of 100 mm, 80 mm, and 60 mm, respectively, compared to a plain tube. The average PCM temperature shows a 13.7% increase with the 60-mm pitch length twisted tape. Furthermore, the system achieves a total energy storage of 260 kJ kg⁻¹ in just 120 min with the twisted tape insert (60 mm pitch length), in contrast to 250 kJ kg^-1 over 240 min in a plain tube setup. Temperature contours along the axial and radial directions indicate elevated temperatures near the twisted tape surface, promoting a higher melting fraction and accelerating the complete melting process. These findings underscore the potential of twisted tape inserts to significantly improve PCM-based thermal energy storage, offering promising applications in sustainable energy systems.

This study presents a computational investigation of various minichannel configurations to enhance heat transfer for battery surface cooling in electric and hybrid electric vehicles. Nanofluids and rib structures are incorporated to achieve improved thermal performance. Copper oxide (CuO)/water nanofluid is employed as the coolant, while ribs are introduced to disturb the boundary layer and generate eddies, thereby intensifying convective heat transfer. Magnetic fields are further applied to promote eddy formation and augment the overall heat transfer rate. To determine the optimal configuration, the Nusselt number (Nu), friction factor (f), Colburn j-factor, and thermal enhancement factor (TEF) are evaluated using empirical correlations. The upstream staggered ribbed configuration demonstrates a 136.036% increase in Nu and a 136.045% rise in the Colburn j-factor compared with a plain channel using water as the base fluid. The corresponding TEF value of 1.92 confirms its superior heat transfer performance. The findings establish that the integration of ribs, magnetic fields, and nanofluid coolants offers a promising approach for enhancing thermal management and extending battery life in electric vehicle applications.

Efficient recovery of high-grade waste heat from solid oxide fuel cells (SOFCs) is crucial for enhancing energy utilization and environmental performance. This study addresses this challenge by proposing an advanced SOFC-based cogeneration system that integrates a gas turbine (GT), a recuperated regenerative organic Rankine cycle (RRORC), and a water heater for simultaneous power and hot water production. A comprehensive thermodynamic, economic, and environmental assessment was conducted using a detailed computational model to evaluate system performance and feasibility. The results indicate that incorporating the RRORC with the SOFC-GT system enhances exergy efficiency by 9.56%, while the inclusion of a water heater further raises the improvement to 11.14%. The overall energy efficiency increased by 30.76% with only an 11.16% rise in total cost, and CO_₂ emissions were reduced by 23.49% compared to the conventional SOFC-GT system. These findings demonstrate that the proposed configuration effectively harnesses SOFC waste heat for improved energy recovery and sustainability. The novelty of this work lies in the integration of a RRORC and a water heating subsystem with the SOFC-GT cycle, extending the efficiency and environmental advantages beyond previously reported hybrid configurations.

Flaxseed gum (FSG) comprises neutral and acidic polysaccharides. Research shows that flaxseed gums with high arabinoxylan concentration have shear thinning and weak gel-like properties, whereas those with high acidic monosaccharides have decreased rheology. FT-IR and DSC tests described a bio-PCM composite made from flaxseed gum and fatty acid anhydrides. The study examined how fatty acid type affects bio-synthesized composite materials made from flaxseeds and various fatty acids with and without octadecane as phase transition materials. In the final composite structure, the fatty acid backbone lengthened, increasing the host material’s latent heat. As phase transition material, 20% octadecane yielded best results. Polymer-based materials (PCM) are used to make bio-synthesized composite materials from flaxseeds and stearic acid. Latent heat of host materials increases with PCM content, optimum at 20% octadecane. The treated cotton cloth regulates temperature better than the untreated. The study shows that PCM composite material treatment creates a homogenous thin coating on cotton fiber surfaces, improving thermal characteristics and heat retention.

This study experimentally demonstrates that enhancing solar absorptance and heat transfer in a single-pass solar air collector can be achieved through a coating of reduced graphene oxide-doped black paint. The introduction of carbon-based nanoparticles results in an augmented thermal conductivity in a turpentine-oil nanofluid. Subsequently, a homogeneous blend of the thermally modified turpentine oil with the black paint is coated onto the absorber plate, resulting in a consequent increase in absorptance across the incident solar spectrum. In this regard, two different solar air collectors were fabricated, namely (i) a single-pass flat plate SAC with BP coating and (ii) a single-pass flat plate SAC with rGO-doped BP coating as surface coating. The thermal performance of both solar air collectors was evaluated across a range of airflow rates. Data obtained during the experiments demonstrated that the collector with the surface coating exhibited superior thermal response: specifically, higher absorber temperatures, increased exit air temperatures, and an improved temperature difference between the exit and inlet air streams. However, the increase in the flow rate of air through the rectangular channel decreases the absorber, exit air temperature, and temperature difference between the exit and inlet of the rectangular channel. Furthermore, the results also showed that at the higher flow rate of air through the channel, the Nusselt number and the heat transfer coefficient increase from coated and uncoated absorber plates. From the experimental results, the average daily efficiency of the single-pass SAC with BP coating ranged from 30.12 to 67.2% for a flow rate of 0.01 to 0.03 kg s⁻¹. However, with surface coating and improved surface roughness, the daily efficiency increased to 34.6 to 79.5%. Furthermore, in this study, a response surface methodology is employed to optimize the exit, absorber temperature, and the change in temperature between exit and inlet, considering the impact of solar radiation, ambient temperature, and concentration of nanoparticles. Moreover, the correlations are expressed in the form of a quadratic function.