PCM in Shell and Tube Finned Heat Exchanger CFD Simulation

Description

The present problem simulates the performance of Phase Change Material (PCM) inside a shell and tube finned heat exchanger by ANSYS Fluent software. We perform this CFD project and investigate it by CFD analysis.

Thermal energy storage in PCM is achieved during the process of the phase change (solid phase to liquid or vice versa); So that when the phase changes from solid to liquid, it absorbs heat from the environment, and when the phase changes from liquid to solid, it returns heat to the environment.

These phase-change materials have various melting or freezing temperatures and are used in cooling and heating systems. For example, these materials received ambient heat on a hot day as latent heat and melted, then returned to the environment by changing the phase and freezing process on a cold night.

The shell is designed as a cylindrical tank carrying phase change materials, and these PCMs are evenly distributed inside the tank. Since the PCMs of the present model are based on the phase change between the liquid and solid phases, the solidification and melting model has been used for the current simulation.

Because the simulation process is time-consuming, the simulation process is performed in a time interval of 880 s with a time step of the 1200s.

The current model is designed in three dimensions using Design Modeler software.

The meshing of the present model has been done using ANSYS Meshing software. The mesh type is unstructured, and the element number is 2989887.

PCM in Shell and Tube Methodology

In the current modeling, the phase change materials are paraffin material with a density equal to 750 kg.m-3, a specific heat capacity of 2000 j.kg-1.K-1, thermal conductivity equal to 0.2 W/m.K  and viscosity equal to 0.008 kg/m.s.

To define the Solidification & Melting model, the maximum temperature at which only the liquid phase prevails (T_solidus) is 314.15 K, the minimum temperature at which only the liquid phase is dominant (T_liquidus) is 317.15 K, and the latent heat of solvent melting at which is pure solvent melting heat is equivalent to 255000 j/kg.

Inside the tank, a 0.001 m thick copper pipe is routed through a winding path, which is responsible for heat transfer and, consequently, the occurrence of phase change of PCM.

The water flow with a mass flow of 1.4973 kg/s and a temperature of 325.15 K is considered inside this pipe. Also, cross-shaped fins inside the tank in the pipe path are made of copper.

PCM in Shell and TubeConclusion

At the end of the solution process, two-dimensional contours related to the temperature and mass fraction of the liquid are obtained. These contours are obtained during the last second of the simulation process, the 1200s.

The contours show well that with the passage of time and the melting of the PCM material, the heat transfer has taken place well, and the temperature in the center of the tubes has risen.