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This study aims to prepare a stable caprylic acid (CA) and cetyl alcohol (CAL) organic binary mixture as a solid–liquid phase change material (PCM) with a phase transition temperature in the range for exotic chilled refrigeration. A detailed study was carried out on the thermo-physical properties, thermal reliability and corrosion analysis of the prepared binary mixture. The result showed that the binary mixture of caprylic acid–cetyl alcohol (CA–CAL) with a eutectic point at 85:15 molar mass ratio is suitable for medium-range refrigeration application. The determined onset melting/freezing temperature with differential scanning calorimetry (DSC) was 10 °C/8.9 ± 0.1 °C with a phase transition enthalpy of 154.1/153.3 ± 1% J/g. The binary mixture thermal conductivity measured in the solid phase (at 0 °C) and liquid phase (at 20 °C) was (0.288 ± 0.028) and (0.156 ± 0.007) W/(m⋅K), respectively. Moreover, the thermal reliability test result of the prepared binary mixture under accelerated thermal cycling for 500 melting/freezing cycles showed a maximum of 10.1% deviation in thermal properties, which was in the acceptable range for organic binary PCM. The prepared PCM was found to be compatible with stainless steel and aluminum over an extended period of time, based on corrosion tests conducted on aluminum, copper and stainless steel over a period of 84 days. According to this study, the binary combination CA–CAL as PCM is a potential candidate for cold chain food transportation, supermarket cold cabinets, and other refrigeration applications.

Two-phase ejectors are highly useful devices because they can recover and use the energy lost in the expansion process of the refrigeration cycle. However, in a small-sized household refrigeration cycle, a modified ejector cycle is required due to the low operating pressure and mass flow rate. In this study, a dual evaporator ejector cycle (DEEC), which is advantageous for household refrigeration, was applied. In the DEEC, unlike the conventional ejector cycle, the motive nozzle exit position (NXP) considerably affects the cycle performance. The objective of this study was to optimize the NXP of a DEEC for a household refrigeration cycle with low-pressure refrigerants via an artificial neural network (ANN) model. Using the developed model, the DEEC pressure lifting ratio and coefficient of performance (COP) were analyzed under various operating and ejector geometry conditions. Moreover, the optimal NXP of a small-sized household DEEC was proposed using the developed correlation to achieve maximum performance under different operating conditions. The COP of the DEEC with the optimized NXP is 2.3% and 8.4% higher than those of the DEEC with the conventional NXP and the baseline cycle, respectively. These results validate the ANN model used for optimization and serve as design guidelines for obtaining optimized NXPs and cycle performance with increased energy efficiency.

This paper presents a novel numerical model for “effective thermal conductivity” designed to address the limitations of previous models, which required different constants for each distinct shape. The constants C and m incorporates the natural convection effect through the Rayleigh number (CRam), obviating the need to solve velocity equations such as those for continuity and momentum. Notably, this model is applicable to a wide range of phase change materials (PCMs) using the same constants. Prior investigations predominantly focused on spherical capsule shapes and specific PCMs with varying C and m constants. The present study extends the limitations from spherical to cylindrical, square and rectangular shapes. The PCMs evaluated includes pure paraffins ranging from C14 to C33, all assessed using constant values for the C and m. Initially, the proposed model for effective thermal conductivity, along with the constrained model accounting for natural convection, was verified against experimental data for C18 alkane, achieving a root mean square error of 0.0177 with experimental and 0.0077 with constrained model. Subsequently, the present model's validity was affirmed against a reference constrained model across a wide range of alkanes. Simulations were carried out for both cylindrical and square shapes. For rectangular configurations, the aspect ratio was incorporated into the Rayleigh number to account the effects of both vertical and horizontal orientations.

Thermo-resistant nanoalloys are a new class of materials that combine high-temperature refractory compounds (such as carbides, nitrides, borides, and oxides) with nanoscale particles of metals, ceramics, or carbon. These composites exhibit remarkable thermal stability and anti-ablation/oxidation properties, making them highly attractive for various high-temperature applications in aerospace, energy, and high-temperature manufacturing. Despite their potential, the fabrication of these materials is challenging due to their complex synthesis and processing. Many researchers have summarized the challenges and suggested solutions to produce high-density, superior physicochemical properties of nano refractory materials for specific applications. Thus, in view of these perspectives, the present review provides an overview of the production criteria, processing, and synthetic routes for producing high-temperature nano refractory material composites with exceptional thermal and anti-ablation/oxidation properties. The review also highlights the challenges encountered by researchers and their solutions for fabricating these materials. Potential applications of high temperature refractory materials are found in various industries, such as refractory ceramics, high-temperature components in wear resistant, neutron shielding, and high power-density microelectronics manufacturing to name a few.

A numerical analysis is conducted for both the outward and inward phase change (melting/solidification) processes in a horizontal shell-and-tube-type latent thermal energy storage (LTES) system filled with an n-eicosane phase change material. The analysis includes—for the first time—direct comparisons of the effects of heat transfer enhancement (HTE) methods on the solidification and melting processes, considering five parameters (with three levels for each) and at four phase change stages (70 %, 80 %, 90 %, and 100 %). The HTE, defined by the reduction in the overall phase change time, was found to differ between melting and solidification. In certain situations, the HTE method induces a smaller improvement in melting but a significant deterioration in solidification. The solidification-to-melting-time ratios (SMTRs) for all analysis cases are compared to clearly identify the common HTE methods between the melting and solidification processes. Maximal SMTR values of 11 and 10.85 (corresponding to the worst cases) were observed at the maximal tube eccentricity during the outward phase change and at the maximal tube diameter during the inward phase change, respectively. This research should aid engineers in designing novel technologies capable of efficiently and safely storing thermal energy.

We examined how the outer shape of a cylindrical capsule, and the quantity of super-cooling, influenced the charging performance of a phase change material (water). The numerical method was validated using previous research and showed good agreement. Higher amplitude of roughness of the capsule shape was affirmed to affect solidification performance with or without super-cooling. The capsule with higher amplitude had an advantage in solidification performance, not only by increasing the heat transfer rate inside the capsule but also by reducing the quantity of super-cooling. Small super-cooling (∆TSmooth Surface = 4 °C) shows less impact (only 1%), while large super-cooling (∆TSmooth Surface = 8 °C) shows a prominent impact (10%) on the delay of solidification time. Typical results with no super-cooling and with super-cooling (∆TSmooth Surface = 8 °C) showed 10% and 15% shorter solidification time, respectively, for optimal shape with n = 6 compared to a matching smooth capsule (n = 0).