M. Rahimi

Bio: M. Rahimi is an academic researcher from Golestan University. The author has contributed to research in topics: Phase-change material & Heat transfer. The author has an hindex of 16, co-authored 26 publications receiving 867 citations. Previous affiliations of M. Rahimi include University of Mazandaran.

Thermal analysis of PCM containing heat exchanger enhanced with normal annular fines

Abstract: . In this study, the effect of fins' height and Stefan number on performance of a shell and tube heat exchanger which contains a phase change material is investigated numerically and experimentally. Melting time, solidification time, liquid mass fraction, melting and solidification front and temperature distribution in different directions (longitudinal, radial and angular) are among criteria for the heat exchangers' comparison. In order to generalize the comparison, melting and solidification fronts are studied for different sections of the shell, fin section and mid-section, for different fins' height during charging and discharging processes. The results show that, these two parameters play important roles in the heat exchanger performance. Increasing Stefan number, the melting time reduces; which exhibits a descending trend in rate when the fins are heightened. In addition, investigating both processes, it can be figured out that increasing fins' height influences the solidification time more significantly than melting.

Heat transfer enhancement of phase change materials for thermal energy storage applications: A critical review

Abstract: This paper presents a state-of-the-art review on various techniques of heat transfer enhancement in latent heat thermal energy storage (LHTES) systems. Heat transfer enhancement in LHTES systems can be achieved through either geometric configuration and/or thermal conductivity enhancement. The use of extended surfaces such as fins or heat pipes is a common technique for heat transfer enhancement in LHTES systems and therefore, reviewed in details in this paper. Next, we studied the thermal conductivity enhancement techniques, which include the use of porous materials, nanoparticles with high thermal conductivity, and low-density materials. Finally, studies involving combined techniques for heat transfer enhancement are reviewed in the paper. The paper discusses research gaps in the methods of heat transfer enhancement for LHTES systems and proposed some recommendations.

A review of phase change material and performance enhancement method for latent heat storage system

Abstract: Latent heat storage (LHS) is considered as the most promising technique for thermal energy storage, due to its high energy storage density and nearly constant working temperature. However, the lower thermal conductivity of the phase change material (PCM) used in LHS system seriously weakens thermal energy charging and discharging rates. In order to improve the thermal performance of LHS system, a lot of research on performance enhancement have been carried out. This review paper will concern on the development of PCMs and performance enhancement methods for LHS system in the last decade. The available enhancement methods can be classified into three categories: using high thermal conductivity additives and porous media to enhance PCM thermal conductivity, using finned tubes and encapsulated PCMs to extend heat transfer surface, using multistage or cascaded LHS technique and thermodynamic optimization to improving the heat transfer uniformity. The comparative reviews on PCMs, corresponding performance enhancement methods and their characteristics are presented in present paper. That will help in selecting reliable PCMs and matching suitable performance enhancement method to achieve the best thermal performance for PCM based LHS system. In addition, the research gaps in performance enhancement techniques for LHS systems are also discussed and some recommendations for future research are proposed.

Melting and convection of phase change materials in different shape containers: A review

Abstract: A review of analytical, numerical and experimental investigations of melting and ensuing convection of phase change materials within enclosures with different shapes commonly used for thermal energy storage is presented. The common shapes of the containers being rectangular cavities, spherical capsules, tubes or cylinders (vertical and horizontal depending on orientation of gravity) and annular cavities are covered. Studies focusing on melting within rectangular cavities are categorized into two groups. The first one is melting due to isothermal heating on one or more boundaries, whereas the second is the constant heat flux-assisted melting. Moreover, constrained and unconstrained melting in both spherical and horizontal cylindrical containers were discussed. The effects of the concentric geometry and location of the heating source on melting in horizontal annular spaces are presented. The review concentrated on elucidating the heat transfer mechanisms (conduction and convection) during the multiple stages of the melting process and the effects of these mechanisms on the liquid–solid interface shape and its progress, melting rate, charging time of the storage system, etc. The strength of buoyancy driven-convection varies greatly with the dimensionless Rayleigh or Stefan numbers and depends somewhat on the location of heat source and imposed boundary condition. High dimensionless numbers and/or side position of the heat source ensure the dominant role of natural convection melting, otherwise conduction will be responsible for major melting within the container. Furthermore, the geometrical parameters such as the aspect ratio in rectangular containers and vertical cylindrical ones, diameter or radius in spherical capsules and horizontal cylindrical vessels, and eccentricity in annular cavities are reviewed. In addition, the parameters affecting the thermal behavior of the melting process in various enclosures, i.e. the Nusselt, Rayleigh, Stefan, Prandtl and Fourier numbers and are reviewed.