Journal of Thermal Analysis and Calorimetry最新文献

Pool boiling is extremely effective in dissipating high heat flux at relatively low surface superheat temperatures, making it a key focus in two-phase heat transfer research and valuable for numerous thermal management applications. In the current research, the pool boiling heat transfer performance of a multi-walled carbon nanotubes (MWCNTs) porous coated surface was investigated in deionized water at saturated and atmospheric pressure state. A two-step electrochemical deposition method involving high current density for a short period (coating phase) and low current density for longer period (bonding strength phase) was used to obtain the MWCNTs porous coating. The different wettability characteristics of the surface were prepared by varying the current density to explore the surface wettability effect on boiling performance. The MWCNTs surface showed a prior onset of nucleate boiling with a maximum reduction of 37.58% in comparison with the plain surface. The coated surfaces yielded a high heat flux at lower wall superheat than the bare copper surface. The critical heat flux of MWCNTs coated surface was much higher and thereby exhibited a greater safety margin by a maximum increase of 108.5%. The heat transfer coefficient of the MWCNTs surface surpassed the bare surface across entire heat flux, representing a maximum enhancement of 113.85%. An increase in current density during the coating phase increased the hydrogen bubble evolution, leading to a greater porosity. This increased porosity contributed to higher surface roughness and improved wettability, ultimately resulting in an increased nucleation sites density and bubble release frequency.

Nanofluids have facilitated the improvement of several current thermal application performances. The improved working fluids possess remarkable thermophysical qualities, rendering them superior alternatives to conventional working fluids. Conversely, MXenes have been demonstrated in the literature to possess the highest thermal conductivity compared to all other nanoscale materials. Consequently, when these materials are uniformly distributed in a base fluid, the resultant suspension is expected to achieve significantly greater effective thermal conductivity than its equivalent. Despite this fact, challenges remain regarding these fluids. The primary limitation is the dispersion stability of nanoparticles, which can result in the deterioration of the nanofluid’s advantageous features over time, ultimately leading to a loss of effectiveness. This paper is devoted to a comprehensive review of MXene nanofluids and their application in thermal systems common in the energy sector. This paper initially examines the synthesis methods of MXene and elucidates the production techniques for nanofluids. The stability and thermal conductivity of MXene nanofluid were examined. Furthermore, the thermophysical characteristics and thermal applications of MXene nanofluid are also examined. Finally, the issues associated with MXene nanofluid and the existing gaps in scientific understanding are presented to establish future research directions.

The high-speed motorized spindle is the fundamental component of computerized numerical control (CNC) machine tools. During the working process, the components within the motorized spindle exhibit varying degrees of thermal elongation due to differing coefficients of thermal expansion, which in turn lead to the generation of thermal errors. Thermal error is a crucial determinant of the motorized spindle’s machining precision. With the continuous improvement of industrial automation levels and the increasing complexity of machining requirements, controlling thermal error has emerged as a critical focus in the study of motorized spindles. Unlike previous reviews, which typically focused solely on one aspect of thermal error control, this paper proposes a comprehensive and systematic review framework that integrates the analysis of three key technologies: motorized spindle cooling technology, thermal error compensation technology, and motorized spindle materials. This integrated approach offers a comprehensive perspective on thermal error control, highlighting the respective strengths and limitations of various technologies. Firstly, the cooling technology for the motorized spindle is categorized and analyzed. Secondly, the key steps of thermal error compensation technology are explored. The impact of various materials on the performance of motorized spindles is then discussed. The novelty of this review lies in its integration and comparative analysis of recent advances across these three domains, alongside a critical examination of their respective strengths, weaknesses, and applicability, thereby illuminating the combined impact of these diverse technologies. Finally, the analysis summarizes the shortcomings of thermal error control technology at this stage, outlines the outlook, and elaborates on the future research direction, offering theoretical guidance and technical assistance for the advancement of thermal error control technology in high-speed motorized spindles, thereby enhancing the precision machining capabilities of CNC machine tools.

Renewable energy technologies, including Solar Chimney Power Plants (SCPP), harness natural resources to produce clean energy. SCPPs use solar energy to heat air, generating an upward flow that drives turbines to produce electricity. This study, conducted at the University of Ouargla, Algeria, explores design improvements to enhance SCPP performance. The study found that a collector opening height of 0.05 m provided the highest efficiency, achieving an air velocity of 5.8 m s⁻¹ and a maximum collector temperature of 68.3 °C, with a temperature difference of 51.2 °C relative to the ambient air. In comparison, opening heights of 0.15 m and 0.20 m resulted in lower airflow velocities of 4.2 m s⁻¹ and 3.8 m s⁻¹, respectively, causing heat loss. The use of a curved junction between the collector and chimney improved airflow, reaching 6.7 m s⁻¹ at the chimney entrance, outperforming straight junctions. Incorporating an air guide further enhanced airflow, with a peak velocity of 6.7 m s⁻¹ for a guide height of 1.0 m. The innovative helical collector design extended the airflow path to 10 m, improving energy output. When combined with an air guide, the helical collector system achieved the highest air velocity of 7.2 m s⁻¹. These findings demonstrate that thoughtful structural enhancements significantly boost SCPP performance.

The work applies an imaging-based approach to evaluate the degradation of concrete subject to high-temperature conditions, providing information on non-destructive assessment methodologies based on colour characteristics. Specifically, it investigates the potential of using the hue, saturation, and intensity (HSI) colour space to quantify the thermal deterioration of ordinary Portland cement concrete (OPCC) of M30 grade, multi-component binder-based cement concrete (MBCC), and fibre-reinforced multi-component binder-based cement concrete (FRMBCC). Concrete cube specimens of OPCC, MBCC, and FRMBCC are cured for 28 days and exposed to various temperatures like ambient room temperature, 100 °C, 400 °C, 600 °C, and 800 °C. These specimens are photographed under medium light indoor (MLI) lighting conditions for analysis. Digital images of the concrete surfaces are captured and analyzed using ImageJ software to extract RGB values, then converted into HSI colour parameters. The compressive strength of the specimens is evaluated at different temperature exposures to establish correlations between the HSI values and the residual compressive strength. The results demonstrate that the hue parameter exhibits strong correlations with residual compressive strength for OPCC and MBCC, while FRMBCC showed a moderate correlation. The saturation parameter displayed a moderate correlation for OPCC, MBCC, and FRMBCC. The intensity parameter displayed an excellent correlation for OPCC and a reasonably moderate correlation for MBCC and FRMBCC. The study demonstrates the application of the hue–saturation–intensity (HSI) colour space for evaluating concrete deterioration, with different concrete types showing varying levels of fit between data points and polynomial curves. These findings support imaging-based non-destructive evaluation techniques for assessing the condition of concrete structures based on their colour attributes, which could lead to more efficient and cost-effective inspection and maintenance practices.

This research accounts bioconvection influence in convectively heated magnetized couple-stress material confined by cylindrical stratified regime. The mathematical modeling includes Brownian diffusive together with thermophoretic aspects, while suspension stability is ensured by considering bioconvection features owing to gyrotactic microorganisms. Robin-type thermosolutal conditions are deployed to elaborate heat–mass transmission at the magnetized cylindrical surface subject to suction/injection (wall transpiration). The investigation further considers radiation impact in energy expression. The governing mathematical (partial differential) expressions are transmuted into nonlinear ordinary differential equations (ODEs) by implementing apposite variables. These ODEs are computed analytically by utilizing homotopy scheme, assuring convergence via selection of suitable auxiliary variables. The influences of key variables on non-dimensional profiles are systematically scrutinized. The velocity exhibits an increasing trend when curvature, mixed convection and injection parameters are escalated. However, it demonstrates opposite behavior when Reynolds number, Hartman number, couple stress, and bioconvection variables are increased. The outcomes provide valuable perception into nanofluidic transportation in state-of-the-art coating technologies, bio-microsystems, and thermal energy mechanisms where magnetized nanomaterials are considered subject to bioconvection phenomena.

Polymeric heat exchangers are alternatives to traditionally made steel heat exchangers to reduce corrosion and increase longevity. Chemical industries typically employ polymer-based heat exchangers to heat and cool concentrated acids as well as alkaline solutions. Primarily, polyethylene terephthalate glycol (PETG) exhibits excellent chemical inertness and is resistant to corrosion, thereby reducing the fouling factor. However, it has low thermal conductivity. This work enables the fused deposition additive manufacturing (AM) technique to produce PETG-based polymer heat exchangers (PHE) with gyroid structures to achieve a high heat transfer rate by reducing the wall thickness and increasing the surface area of the material. By varying the process parameters, such as volume flow rate and the geometry of the heat exchanger, the heat transfer coefficient (HTC) is enhanced by 287.81% at 1 lpm compared to conventional double pipe heat exchangers. On comparing the effectiveness of the proposed heat exchanger with the conventional one, the enhancement is 240.37% at 1 lpm. Validation studies using CFD were also done and compared with experimental results, which are found to be in agreement. Hot fluid temperature drops by 16 °C. The thermal enhancement factor of the proposed heat exchanger is also very high (3.40) when compared to the other exchangers. This leads to the compactification of the heat exchanger.

Mixing ethanol into pure diesel fuel has significant promise for enhancing engine performance and reducing hazardous emissions in Compression Ignition Engines (CIEs). A comprehensive numerical analysis using a well-validated single-cylinder, water-cooled CIE model to evaluate the impact of ethanol–diesel blends at different ratios (0%, 5%, 10%, 15%, and 20%) on performance and emission has been carried out in this study. The analyzed key parameters include temperature, pressure of the cylinder, rate of heat release, and gas temperature at exhaust and emissions of pollutants, including NOx, soot, CO, CO₂, and others. Findings indicate that a 5% ethanol blend provides excellent improvements, significantly improving combustion efficiency and lowering exhaust gas temperature while maintaining emission quality. Although these higher blends reduce the overall advantages of lower emissions, these emissions are much lower compared to pure diesel combustion, with a 20% blend resulting in a 91.7% decrease in NOx emissions. Blending ethanol up to 20% shows significant potential for improving performance and reducing emissions in CIEs, with a 5% blend exhibiting the lowest emission characteristics with acceptable performance characteristics.

In modern eons, improving the thermal conductivity of conventional liquids has become a significant challenge in various nanotechnology applications. The present study tackles this issue by investigating how nanolayers contribute to enhancing the heat transfer capability of base fluids. For this, we considered the flow over a curved stagnation region and suspended the base liquid with sphere and cylinder-shaped magnetite (Fe₃O₄) nanoparticles. To calculate the augmented thermal conductivity, we considered the nanolayer formed around the sphere and cylinder-shaped nanometer-sized particles and discussed it in detail with the help of simultaneous outcomes. We also considered the magnetic field, radiative, Ohmic heating, and uneven temperature sink/source effects for physical relevance and modeled the problem accordingly. The computational outcomes of flow and thermal fields are obtained using the bvp5c MATLAB technique. The nanolayer formed around the nanoparticles has a significant impact on the momentum and thermal boundary layers. Additionally, the nanolayer formed around spherical-shaped nanoparticles exhibited a significant increase in the heat transport rate compared to that formed around cylindrical-shaped nanoparticles. This study applies to solar energy generation through nano-coating.

The temperature rise caused by shear action during melting for high molecular polymer is widespread and difficult to control, especially for the co-rotating twin-screw extrusion (CRTSE) process. Considering the very small gap between the screw and the barrel, it is difficult to in-line measure and control the value of materials’ temperature along the extrusion direction. Consequently, a co-rotating twin-rotor mixing apparatus with a high-precision temperature sensor is employed to explore the temperature variation of polyethylene (PE) with different average molecular weights (M_w) from solid to melt, similar with the CRTSE process, but the material will not be conveyed forward. The experiment’s result indicates that a higher rotor speed and a lower meshing clearance result in a higher temperature rise. Meanwhile, unexpectedly, an interesting experimental phenomenon is observed: the temperature rise caused by shear action in high-viscosity PE increases with the rotor speed, while it enlarges initially and then stabilizes in low-viscosity PE as the increased rotor speed. Therefore, it is speculated that the temperature rise during the processing strongly depends on the viscosity. Simulation studies based on Ludovic software by actively varying the consistency index and power-law exponent confirm the correctness of the experimental conjecture under a wider screw speed and viscosity range. This study has theoretical and practical implications for a deeper understanding of the temperature rise caused by shear action in polymeric materials during extrusion.