Pentamode metamaterials, characterized by their near-zero shear modulus and high bulk modulus, have attracted solid interest due to their unique ability to mimic fluid-like behaviour. Pentamode metamaterials have driven by improvements in computational design, material selection and advanced manufacturing techniques, especially additive manufacturing. As a comprehensive review article specificially addressing pentamode metamaterials produced by additive manufacturing, this review systematically represents the theoretical foundations, essential design concepts, and main parameters, including the high bulk-to-shear modulus ratio that presents fluidic behaviour. Recent advancements in manufacturing methods such as selective laser melting, direct laser writing, and hybrid fabrication processes are also discussed, along with their impact on achieving precise lattice geometries. Extensive analysis of acoustic and mechanical applications reveals pentamode metamaterials’ versatility in acoustic cloaking, wave scattering reduction, vibration isolation, shock absorption and tunable stiffness devices. Despite intensive progress, challenges such as scalability, precision of manufacturing, and material optimization continue to emerge. This systematic review concludes by highlighting future research opportunities, emphasizing hybrid material usage, computational optimization, and real-world applications, enhancing the transformative potential of pentamode metamaterials in acoustic and mechanical applications.
Phase Change Materials (PCMs) have excellent energy density and reliable temperature control which enables them to store thermal energy with a prominent efficiency. But, challenges like low thermal stability, phase separation, leakage during phase transition, and low thermal conductivity limit their broader use in thermal energy storage (TES) systems. The development of PCM composites, enabled by integrating PCMs with nanomaterials, mitigates the problem of low thermal conductivity; however, a low thermal stability issue persists. To tackle this issue, the strong tendency of nanoparticles to form robust intermolecular bonds with PCMs is addressed by combining nanoparticles with PCMs. Consequently, review provides a comprehensive analysis of TES and the classification of PCMs, highlighting specific enhancements in thermal and mechanical properties achieved through the use of hybrid and other nanomaterials. These enhancements, including increased thermal conductivity, mechanical robustness, and shape stability, lead to more efficient heat transfer and improved thermal performance in TES systems, thereby addressing thermal stability issues that degrade after multiple thermal cycles. Additionally, the review examines the preparation methods of PCM composites by dispersing various hybrid nanomaterials and bio-derived carbonaceous substances. Authors observed that maximum augmentation in thermal conductivity of a hybrid PCMs is 900 %. Moreover, emerging applications based on the thermos-mechanical properties of the PCMs are comprehensively discussed. At last, the limitations of hybrid particle-dispersed PCM composites are evaluated, along with current challenges and future research prospects.
Wavy fin heat sinks offer significant potential for thermal management due to their enhanced surface area compared to conventional straight-fin designs. However, the effect of surface area on thermal resistance is not straightforward since thermal resistance depends on the inverse product of surface area and the convective heat transfer coefficient. This study investigates the relationship between surface area, convective heat transfer coefficient, and thermal resistance for wavy fin heat sinks under natural convection. Experimental tests were conducted on a l parallel-fin heat sink (HS1) and a wavy-fin heat sink (HS2) using a polyimide heater supplying 4 W of input power. Thermal resistance is determined from steady-state temperature measurements using three thermocouples located at the heat sink base. Despite having an approximately 10% greater surface area, HS2 exhibited a thermal resistance of 14.85 K/W, about 4.7% higher than HS1 (14.19 K/W). This highlights that increased area alone does not guarantee improved performance. This is attributed to a lower convective heat transfer coefficient (8.38 vs. 9.71 Wm⁻²K⁻¹) caused by restricted airflow within the wavy fin channels. Three-dimensional steady state computational fluid dynamics simulations on four cross-cut variants of HS2 are performed to investigate the effect of geometric modifications on the convective heat transfer performance. The HS2B showed a reducing thermal resistance by up to 3% (5.57 K/W) while slightly decreasing surface area compared to HS2(16.21 K/W). These results demonstrate that effective heat sink design under natural convection requires the balancing surface area and convective heat transfer coefficient.
One of the most essential processes in manufacturing is continuous operations without any downtime. The Energy Balanced Hybrid Flow Shop Scheduling Problem (EMBHFSP) is an interesting study as it provides huge impact on machine effectiveness while balancing between minimizing completion time and energy consumption. Limited study has focused on hybrid flow shops (HFS) with a concentration on energy-machine balanced production. This paper aims to develop a computational model and evaluate the exploration effectiveness of Differential Evolution in optimizing the EMBHFSP. The most popular as well as latest optimization algorithms including Simulated Annealing, Grey Wolf Optimization, Henry Gas Solubility Optimization, Harmony Search, Imperialist Competitive Algorithm, Multi-verse Optimizer, and Thermal Exchange Optimization were evaluated against Differential Evolution utilizing the EMBHFSP model across 20 Optimization repetitions. The experimental results indicate that the Differential evolution algorithm surpassed others by 45% in mean fitness value and exhibited a 67.5% enhancement in standard deviation across all benchmark problems. In addition, a case study was performed in a manufacturing facility to validate the applicability of the model. Three different scheduling solutions, optimizing makespan, energy balance and machine utilization balance are generated using differential evolution. The results show the ability of the model to solve trade-offs between efficiency of production and sustainability in real industrial environments.
Detonation combustion modes offer potential benefit over deflagration-based combustion due to rapid heat release and pressure-gain characteristics. A small-scale rotating detonation engine (RDE) is a compact detonation-based device capable of continuous and high-frequency operation. Small-scale RDEs are promising for propulsion related and laboratory-scale applications, especially for compact operation under low flow-rate conditions. In the present study, wave propagation behaviour in a small-scale RDE running on methane–oxygen was investigated experimentally using high-speed imaging. The combustor annulus had an inner diameter and outer diameter of 38 mm and 46 mm, respectively. The operating conditions were varied over equivalence ratios (φ = 0.8–1.2) and total mass flow rates (ṁtotal = 3.8, 4.0, and 4.2 g/s). The high-speed image sequences showed alternating single-wave and dual-wave propagation modes within the RDE annulus under the tested conditions. The wave propagation velocity and wave propagation frequency were determined from the recorded image sequences. The average wave propagation velocity was found to be significantly lower than the ideal Chapman–Jouguet value, indicating non-ideal wave behaviour under the present low flow rate operating conditions. Overall, the results provide useful insight into the propagation characteristics of a small-scale RDE operating with methane–oxygen mixtures at very low total mass flow rates.
