Phase Change Material in a Glass-Coated Circular Chamber

Description

PCM Project Description

The present problem simulates the performance of phase change material in a circular chamber with a glass cover. This PCM is evenly distributed inside the chamber. Due to the fact that the nature of the PCMs of the present model is based on the phase change between solid and liquid phases, solidification and melting model has been used for the simulation. PCMs are materials with inorganic or organic compounds that are capable of absorbing and storing large amounts of latent thermal energy.

Thermal energy storage in these materials is achieved during the phase change process (solid phase to liquid or vice versa); So that when the phase changes from solid to liquid, they absorb heat from the environment and when the phase changes from liquid to solid, they return the heat to the environment. Of course, latent heat in phase change materials is obtained from three modes of solid-solid, solid-liquid and solid-gas phase change; But since in the solid-gas state, a lot of heat or pressure is required and the solid-solid state is very slow, so most phase change materials are in the solid-liquid state.

These phase change materials have different melting or freezing temperatures. Therefore PCM is used in heating and cooling systems; For example, these materials receive ambient heat on a hot day in the form of latent heat and melt, and then, in the cool air of the night, return the heat to the environment again, by changing the phase and solidification process. For the present modeling, a glass coating around the chamber containing phase change material with a constant temperature of 338.15 K has been used, which is responsible for transferring heat to the phase change material.

This PCM is in the initial state of simulation at 332.15 K. To use the solidification and melting model, the maximum temperature at which only the solid phase exists (Tsolidus), the minimum temperature at which only the liquid phase exists (Tliquidus), and the latent heat of solvent melting in the pure state (Pure solvent melting) must be used. Because the simulation process is transient, the simulation process is performed in a time interval of 250 minutes (15,000 seconds) with a time step of 600 s.

2500	787.5	density (kg.m-3)
840	15900	specific heat (j.kg-1.K-1)
0.8	0.2	thermal conductivity (W.m-1.K-1)
–	0.062	viscosity (kg.m-1.s-1)
–	332.15	solidus temperature (K)
–	333.15	liquidus temperature (K)
–	300000	pure solvent melting heat (j.kg-1)

Geometry & Mesh

The 2-D geometry of the model is designed using Design Modeler software. The present model includes a circle with an outer radius of 0.0335 m and an inner radius of 0.032 m. The following figure shows a view of the geometry.

The meshing of the model has been done using ANSYS Meshing software and the mesh type is unstructured. The element number is 4797. The following figure shows the mesh.

PCM CFD Simulation Setting

To simulate the present model, several assumptions are considered:

• We perform a pressure-based solver.
• The simulation is transient. Because the purpose of the problem is to study the behavior of PCM over time.
• The gravity effect on the fluid is equal to -9.81 m.s-2 along the z-axis.

A summary of the defining steps of the problem and its solution is given in the following table:

Models (PCM)
k-epsilon	Viscous model
Standard	k-epsilon model
Standard wall function	near wall treatment
on			Energy
Solidification/Melting model			Solidification & Melting
100000	Mushy zone parameter
on			energy
Boundary conditions (PCM)
Wall	Outer Wall
338.15 K	temperature
Wall	Inner Wall
coupled	thermal condition
Solution Methods (PCM)
SIMPLE			Pressure-velocity coupling
Second order	pressure		Spatial discretization
Second order upwind	momentum
Second order upwind	energy
First order upwind	turbulent kinetic energy
First-order upwind	turbulent dissipation rate
Initialization (PCM)
Standard	Initialization method
0 Pa	gauge pressure
0 m.s-1	velocity (x,y)
332.15 K	temperature

PCM Results

At the end of the solution process, liquid mass fraction and temperature contours were obtained at different times with intervals of 40 minutes. Also, a graph of changes in the amount of liquid mass fraction over time is obtained.

All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.