Natural Convection within Inversed T-Shaped Enclosure Filled by Nano-Enhanced Phase Change Material: Numerical Investigation

Heat Transfer and Fluids Properties of Nanofluids

As it is popular research field, extensive research has been performed in various areas of nanofluids, and most of the studies have demonstrated significant enhancements in their thermophysical properties and thermal transport performance compared to those of conventional thermal fluids. However, there have been unanimous conclusions regarding such enhancements and their underlying mechanisms. Nanofluids' potential and thermal applications mainly depend on their convective and boiling heat transfer performances, which are also not unbiased in the literature. On top of this, a major challenge with nanofluids is obtaining sustainable stability and persistent properties over a long duration. All these issues are very crucial for nanofluids' development and applications, and a lot of research in these areas has been conducted in recent years. Thus, this Special Issue, featuring a dozen of high-quality research and reviews on different types of nanofluids and their important topics related to thermophysical and electrical properties as well as convective and boiling heat transfer characteristics, is of great significance for the progress and real-world applications of this new class of fluids.

Convective Heat Transfer of a Pseudoplastic Nanosuspension within a Chamber with Two Heated Wall Sections of Various Heat Fluxes

Cooling of heat-generating elements in different engineering fields is a very important and crucial topic. The present research is devoted to numerical analysis of thermogravitational convection of a pseudoplastic nanosuspension in a chamber with two heated bottom wall sections of various heat fluxes and isothermally cooling vertical walls. A mathematical model formulated employing the time-dependent Oberbeck–Boussinesq equations with non-primitive variables has been worked out by the finite difference technique. It has been revealed that a mixture of 1% carboxymethylcellulose with water can be the most effective medium to cool the heat-generating elements. At the same time, aluminum oxide nano-sized solid particles have a more essential cooling impact on the heated sections.

Heat Transfer in an Inclined Rectangular Cavity Filled with Hybrid Nanofluid Attached to a Vertical Heated Wall Integrated with PCM: An Experimental Study

In this paper, natural convective heat transfer in a rectangular cavity filled with (50% CuO-50% Al2O3)/water hybrid nanofluids connected to a wall containing a phase change material (PCM) has been experimentally investigated. The vertical walls were heated at varying temperatures while the horizontal walls were kept adiabatic. The considered parameters were the concentration of hybrid nanomaterial (Φ = 0.03, 0.05), the cavity inclination angle (θ = 0°, 30°, 45°), and the temperature difference between the hot and cold sides (∆T = 10, 15, 20 °C). The results have been validated and agree well with previously published papers. Furthermore, the main results stated that when the nanomaterial concentration increased, the heat transfer rate by free convection also increased. By increasing the natural convection flows via high temperature, symmetrical vortexes may appear near the heated wall. It also found that the PCM can potentially reduce the temperature of the hot side by up to 22% due to its high absorbability and heat storage. Furthermore, the inclusion of hybrid nanofluids in addition to the PCM enhanced its efficiency in heat storage and, therefore, its capacity to cool the hot side. Moreover, the influence of the inclination cavity enhanced the heat transfer, where θ = 30° was the optimal angle in terms of thermal conductivity.

2D MHD Mixed Convection in a Zigzag Trapezoidal Thermal Energy Storage System Using NEPCM

In a magnetic field, two-dimensional (2D) mixed convection is investigated within a zigzagged trapezoidal chamber. The lower side of the trapezoidal chamber is irregular, in particular, a zigzagged wall with different zigzag numbers N. The fluid particles move in the room due to the motion of the upper wall, while the porosity-enthalpy approach represents the melting process. The thermal parameters of the fluid are enhanced by what is called a nano-encapsulated phase change material (NEPCM) consisting of polyurethane as the shell and a nonadecane as the core, while water is used as the base fluid. In order to treat the governing equations, the well-known Galerkin finite element method (GFEM) is applied. In addition, the heat transfer (HT) irreversibility and the fluid friction (FF) irreversibility are compared in terms of the average Bejan number. The main results show that the melt band curve behaves parabolically at smaller values of Reynolds number (Re) and larger values of Hartmann number (Ha). Moreover, minimizing the wave number is better in order to obtain a higher heat transfer rate.

Enhancing the Melting Process of Shell-and-Tube PCM Thermal Energy Storage Unit Using Modified Tube Design

Recently, phase change materials (PCMs) have gained great attention from engineers and researchers due to their exceptional properties for thermal energy storing, which would effectively aid in reducing carbon footprint and support the global transition of using renewable energy. The current research attempts to enhance the thermal performance of a shell-and-tube heat exchanger by means of using PCM and a modified tube design. The enthalpy-porosity method is employed for modelling the phase change. Paraffin wax is treated as PCM and poured within the annulus; the annulus comprises a circular shell and a fined wavy (trefoil-shaped) tube. In addition, copper nanoparticles are incorporated with the base PCM to enhance the thermal conductivity and melting rate. Effects of many factors, including nanoparticle concentration, the orientation of the interior wavy tube, and the fin length, were examined. Results obtained from the current model imply that Cu nanoparticles added to PCM materials improve thermal and melting properties while reducing entropy formation. The highest results (27% decrease in melting time) are obtained when a concentration of nanoparticles of 8% is used. Additionally, the fins' location is critical because fins with 45° inclination could achieve a 50% expedition in the melting process.