Journal of Thermal Analysis and Calorimetry最新文献

The roof is the building envelope component most exposed to climatic conditions, making it a major contributor to the overall thermal load in hot regions. Optimizing the thermal performance of hollow block roofs can therefore significantly reduce the energy required for cooling buildings. This study examines the thermal performance of hollow block roofs commonly used in Moroccan construction. A dynamic model accounting for heat transfer modes was used for the analysis. Time lag, decrement factor, and internal surface temperature fluctuations were used to assess the thermal behavior. Additionally, energy consumption comparisons were made between Type A and Type B roofs. The results show that Type B reduces the peak interior surface temperature by 8 °C, delays heat transfer from the external environment by about 2 h, and decreases the decrement factor by approximately 33%. Moreover, Type B achieves energy savings of up to 21%, confirming its effectiveness in improving energy efficiency and enhancing thermal comfort in buildings located in hot climates.

The article presents the research results on identifying mechanisms and the intensity of corrosion processes occurring in the low-emission OP-430 boiler using a new internally cooled three-material diagnostic probe. This probe was located at the height of the low-emission burners in the evaporator combustion chamber. It included three cooled pipes made of P265GH, 16Mo3 and 10CrMo9-10 steel and the exposure time in actual boiler operating conditions lasted 120 h. After removing the probe, microstructural analyses were taken from the areas directly adjacent to the evaporator wall, the place most exposed to low-emission corrosion. The second sample was taken from the probe's tip, approximately 450–500 mm from the evaporator wall, characterized by a completely different exhaust gas temperature and composition of the working atmosphere. The scope of the research included the chemical and phase composition analysis of ash deposits and microstructural aspects of corrosion processes occurring in the analysed materials. Differences were found in the corrosion behaviour and intensity of the tested materials regarding their type and sample location, which confirm the practical usefulness of the proposed new construction of diagnostic multi-material probes.

Photovoltaic/thermal (PV/T) systems with integrated cooling mechanisms have gained significant attention due to their ability to enhance both electrical and thermal performance. Excessive heat accumulation in photovoltaic (PV) panels reduces their efficiency, making efficient cooling strategies essential. In this study, a novel PV/T system utilizing a water storage cooling system with a clay pot was investigated. The cooling mechanism was integrated through a heat exchanger section, utilizing coconut husk and a heat exchanger pipe at the backside of the panel to improve heat dissipation. Two PV panel setups were tested: one as a reference panel and the other with the water storage cooling system. The results showed that the electrical efficiency of the reference PV panel reached 14.97%, while the PV/T system with water storage cooling achieved an improved efficiency of 17.61%. Additionally, the thermal efficiency of the PV/T system with water storage cooling was found to be 72.43%, significantly enhancing overall energy utilization. Furthermore, the energy payback time (EPBT) for the reference PV panel and the PV/T system with water storage cooling was determined to be 1.4 years and 1.2 years, respectively, demonstrating improved economic feasibility. The study concludes that the proposed PV/T system with a water storage cooling mechanism not only enhances electrical and thermal efficiency but also offers an environmentally sustainable and cost-effective alternative to conventional PV systems without cooling.

This review presents a critical discussion of nanofluid application in pulsating heat pipes (PHPs), which is a gap in the literature of thermal management research. It also provides a unique structure of the literature and presents a comparative evaluation of mono-nanofluids (e.g., Cu, Ag, graphene) and hybrid nanofluids, which was not fully done in previous reviews. The integrated results indicate that nanofluids significantly increase PHP efficiency, and the improvements obtained are measurable in the form of heat transfer enhancement rates of up to 69.7, thermal resistance reduction rates of 34–57 and reduction of the startup time to up to 58. More importantly, hybrid nanofluids are depicted to possess better thermophysical characteristics and performance as compared to their mono-type counterparts in different conditions due to the effects of synergies. The research also encapsulates key issues, including, the stability and economic feasibility of nanoparticles, and translates the same to a strategic plan of future endeavors. The roadmap focuses on the research on new nanomaterials, improved methods of dispersion and application-oriented optimization to fill the gap between the laboratory potential and application of nanofluid-charged PHPs to high-need sectors, such as electronics cooling and electric vehicle batteries thermal management.

Double-diffusive convection within a partially porous medium constitutes a complex coupling phenomenon, where boundary conditions at the interface between porous and free zones play a key role. As a part of this research, we have numerically modeled the double-diffusive convection of a nanofluid (Cu-(H_{2}O)) circulating in a partially porous annular space between two coaxial cylinders, reproducing realistic configurations, in which we looked into the contribution of putting discret hot cells in the inner cylinder in order to control all the cavity and minimize the size of the hot source. In addition, we tried to use recent and experimental models of Corcione to better understand the heat and mass transfer processes. The inner cylinder is associated with a higher nanoparticles concentration. In contrast, the external cylinder is maintained at a uniform cold temperature, corresponding to a region with a lower nanoparticles concentration. However, the base walls are designed to be impermeable and adiabatic. Then, to solve the system of nonlinear and coupled conservation equations, we used a method based on the vorticity-stream function, combined with a finite-difference scheme. The numerical results represented by the streamlines, isotherms, isoconcentrations, and Nusselt and Sherwood numbers highlight the critical influence on some control parameters like the Rayleigh number, Darcy number, buoyancy ratio forces, the aspect ratio number, and nanoparticle concentration. For instance, the average Nusselt number increases by about 242(%) and 177(%) when the Rayleigh number rises from (10^{4}) to (10^{6}) for aspect ratios of 0.5 and 3, respectively, while the Sherwood number improves by nearly 50(%) as the aspect ratio decreases from 3 to 0.5. In addition, the thermal and mass transfer rates increase by approximately 102(%) and 196(%) when the Darcy number rises from (10^{-5}) to (10^{-1}) simultaneously with a reduction in the aspect ratio from 3 to 0.5, which underlines the pronounced effect of permeability and geometry on the transport process.

During long-term storage of solid rocket engines, plasticizers will gradually migrate out of the propellant and enter the insulation layer. In order to analyze the deterioration of thermal insulation and flame resistance properties of the insulation layer, the thermal decomposition mechanism of NBR insulation containing the mixture of bis(2,2-dinitropropyl) formal/acetal (BDNPF/A) plasticizers is studied by combining ignition experiment and molecular dynamics method. Firstly, the density and thermal decomposition temperature of the molecular models are verified to be consistent with the experimental results. Then, through the X-ray micro-computed tomography (micro-CT) technology and morphological analysis of molecular models, it is determined that there is a phenomenon of phase separation between BDNPF/A and NBR components, and the gas decomposed in BDNPF/A component results in the formation of a porous structure in the insulation film. Finally, the molecular simulation results show that the primary thermal decomposition product of the nitrile butadiene rubber (NBR) insulation film containing BDNPF/A is nitrogen oxides, and the primary decomposition pathway is nitrous acid elimination (NAE). However, the decomposition pathway of NO₂ radical homolysis can only occur at low concentration of BDNPF/A and is more significant at high temperatures.

The Earth Air Heat Exchanger (EAHE) is an efficient and sustainable thermal energy system designed to meet the heating and cooling requirements of buildings by utilizing the renewable energy potential of the earth. By reducing dependency on conventional energy sources, EAHE systems contribute to minimizing greenhouse gas emissions and mitigating environmental degradation. This paper presents a comprehensive review of exergy analysis conducted on EAHE systems, highlighting their thermodynamic efficiency and potential for integration with other renewable energy technologies. A systematic evaluation of existing studies has been performed, and the key findings have been compiled in a structured manner. The impact of various design and operational parameters, such as pipe length, pipe diameter, air velocity (mass flow rates), ambient conditions, and soil properties, on the exergetic efficiency of EAHE systems has been critically examined. This review also discusses different methodologies used for exergy assessment and their implications for optimizing system performance. This study emphasizes the importance of exergy analysis in enhancing the overall efficiency of EAHE systems, thereby promoting energy conservation and sustainability. The insights presented in this paper will be valuable for researchers, engineers, and policymakers interested in the design, modeling, and performance evaluation of EAHE systems for energy-efficient building applications.

Solar air heaters (SAHs) are prone to lower thermal efficiency owing to the reduced heat transfer coefficient (HTC) between traditional absorber plates and the working fluid (air). Mitigate this challenge by employing shot blasting on a trapezoidal profile absorber coupled with surface-modified encapsulation tubes containing organic phase change material (OPCM). This study assesses four different configurations, namely (i) trapezoidal profile SAH (TAPSAH), (ii) TAP with shot blasting (TAPSB), comprising OM 49 (6 tubes), (iii) TAPSB, including OM 49 (8 tubes), and (iv) TAPSB, including 10 tubes. Shot blasting expertise modifies the absorber plate’s boundary layer thickness, improving its absorption capacity. In this study, OM 49 was selected as the OPCM. The supreme average thermal efficiencies for configuration 4 (TAPSAH with 10 tubes) were detected at 61.41% and the highest average exergy efficiency of 2.894% with a flow rate (MR) of 0.045 kg s⁻¹. TAPSAH with 10 tubes has attained the highest average “Nu” value of 25.41 at an operated flow rate of 0.045 kg s⁻¹, implying its outstanding convective heat transfer compared with the other configurations. The maximal thermal augmentation index (ϕ) of 1.483 was recorded for OPCM when employing 10 tubes at an MR of 0.045 kg s⁻¹. The outcomes specified a significant advancement in performance under forced convection mode (FCM), with the mean drying efficiency reaching 18.25% compared to 14.43% under natural convection mode (NCM), with an enhancement of 26.51%. The drying models for FCM and NCM reveal an outstanding fit to the data, as shown by R² values of 0.9841 and 0.9818, based on linear regression analysis.

Hydromagnetic fluid flows experience the drag due to the porous medium and the Lorentz force. Porous medium and magnetic field affect fluid flows and hence the transfer of heat in the fluids. Viscoplastic fluids are encountered in several engineering applications and, therefore, have the potential to be studied. The flow of viscoplastic fluid and heat transfer are modeled by considering the magnetic field and the Darcy-Forchheimer porous medium. The basic conservation laws provide a set of PDEs, and the no-slip theory provides a set of boundary conditions. Due to the development of boundary layer flow, boundary layer approximations are used for the simplification of PDEs, which are further transformed into a system of ODEs. The system of ODEs with boundary conditions is numerically solved using the finite element method (FEM). Mesh analysis is performed, and convergence is ensured. Numerical solutions are further used for studying the dynamics of the Nusselt number and the skin friction coefficient. Darcy-Forchheimer porous medium has an increasing effect on the temperature of the hybrid nano-viscoplastic fluid. This increasing effects on temperature of hybrid nanofluid is greater than on the temperature of the mono nano-viscoplastic fluid. The viscoelasticity has a significant increasing effect on the velocity of the fluid. Thus, fluids exhibiting higher yield stress experience a higher effect of boundary. The Darcy-Forchheimer porous medium is responsible for lowering the rate of transfer of heat from the heated surface to the fluid. It is also noted that the Nusselt number decreases when the resistive force of the porous medium increases, because convective transport of heat becomes slow due to decrease in the velocity.

Additive manufacturing enables the production of complex geometries that are not feasible with conventional methods, offering significant potential for lightweight and efficient heat exchangers. This study investigates the hydraulic and thermal performance of a conventional unmanned aerial vehicle (UAV) fuel heat exchanger through both experimental measurements and computational fluid dynamics (CFD) simulations. Experimental tests were conducted at air velocities of 4–6 m s⁻¹ to evaluate pressure drop and heat transfer characteristics. A validated CFD model was then used to explore alternative fin geometries optimized for additive manufacturing. Among the tested designs, the SD hole fin type demonstrated superior thermal performance with reduced mass. The optimized heat exchanger, featuring an integrated air hood and flow-directing plates, achieved a 6% improvement in heat transfer while reducing mass by approximately 200 g, corresponding to a 30% reduction compared to the existing cooler. The results highlight the potential of additive manufacturing to enhance both performance and mass efficiency in UAV thermal management systems.