Sharif Digital Repository

Improving the discharge process of phase change materials (PCMs) is of great importance and can be effective for thermal energy storage (TES) systems. In this research, the direct-contact method for acetone droplet on molten paraffin is optimized to enhance the efficiency of the discharge process of PCMs and TES systems working with intermediate boiling fluid (IBF). In order to improve the storage rate and increase the freezing rate in the system, the NSGA-II algorithm is used. When the acetone droplet hits, owing to its low boiling point relative to the temperature of molten paraffin, the acetone evaporates, causing the creation of solidified paraffin area. The main goal of the current... 

The boiling of a fluid dripping on the surface of molten phase-change materials provides an efficient means for heat exchange or cooling of the melt. For the first time, in this study, the impact of acetone drops onto molten paraffin as a direct-contact solidification method is experimentally investigated to get a better insight into the interaction between the drop boiling and the heat extraction process from the phase change materials during impact. As the acetone drop impacts the molten paraffin surface, acetone starts to boil, and a portion of molten paraffin is solidified. Four impact Weber numbers (corresponding to heights of 10, 20, 30, and 40 cm) for the acetone drop and six surface... 

The low melting and solidification rates of phase change materials (PCM), which traces back to their low thermal conductivity coefficient, has led the application of these materials to face limitations. This paper aims to explore the effectiveness of a novel method called intermediate boiling fluid (IBF) in speeding up the energy storage and transfer processes in PCMs during a complete charging-discharging cycle. Throughout this novel technique, paraffin and acetone are utilized as PCM and IBF, respectively. In the solidification process, there is no direct contact between the cold source and the molten paraffin, while acetone, as an intermediate fluid, is being boiled via absorbing... 

The present article aims to investigate the Graetz-Nusselt problem for blood as a non-Newtonian fluid obeying the power-law constitutive equation and flowing inside the axisymmetric tube subjected to non-uniform surface heat flux. After the flow field is determined by solving the continuity and the momentum equations, the energy equation is handled by employing the separation of variables method. The resulting Eigen functions and Eigen values are numerically calculated using MATLAB built-in solver BVP4C. The analysis is first conducted for the situation of constant heat flux and subsequently generalized to apply to the case of sinusoidal variation of wall heat flux along the tube length,... 

Embracing an interaction between the phase change material (PCM) and the droplets of a heat transfer fluid, the direct contact (DC) method suggests a cutting-edge solution for expediting the phase change rates of PCMs in thermal energy storage (TES) units. In the direct contact TES configuration, when impacting the molten PCM pool, droplets evaporate, provoking the formation of a solidified PCM area (A). Then, they reduce the created solid temperature, leading to a minimum temperature value (T min). As a novelty, this research intends to maximize A and minimize T min since augmenting A expedites the discharge rate, and by lowering T min, the generated solid is preserved longer, resulting in... 

The mixed convective heat transfer in a two-dimensional enclosure containing ethylene glycol-water mixture-based MoS2 nanofluid in the presence of magnetic field and thermal radiation is evaluated, adopting Galerkin standard finite element method. The Boussinesq approximation is applied to simulate natural convection. The partial differential governing equations with the appropriate boundary conditions are numerically handled using FlexPDE software. In order to validate the implemented numerical method, results were compared against outcomes obtained from the previous studies. Afterward, the influences of key indicators such as Hartmann number (Ha), Radiation parameter (Rd), Volume fraction... 

The current research attempts to illustrate results of a reliable 3-D numerical simulation to scrutinize the charging process of paraffin as the phase change material (PCM) in an innovative heat exchanger called double spirally coiled tube heat exchanger (DSCTHE) with two separated paths. The water as a heat-transfer fluid (HTF) streams through the double spiral tubes embedded throughout the latent thermal energy storage (LTES) system. The PCM melting characteristics under three different geometries are investigated. After validating the proposed numerical simulation model, the impacts of operational and geometrical factors including inlet temperature of HTF and radius of the inner spiral... 

In this paper, a comprehensive analytical study is performed to assess the lycopodium-diesel dual-fuel combustion system in counter-flow premixed configuration. The system is modeled as multiple zones that are coupled together via proper boundary and jump conditions on interfaces. According to the respective reaction and transport phenomena in these zones, conservation equations of mass and energy are derived, non-dimensionalized, and solved by Matlab and Mathematica in an analytical way. The porosity of lycopodium particles and the thermal radiation from the reaction zone and the post-flame zones into the preheating zone are considered, in order to improve the realism and accuracy of the...