PCM Melting in Triplex Tube with Internal–External Fins
The simulation is based on the data in the reference article “Enhance heat transfer for PCM melting in triplex tube with internal–external fins“, and the results are compared and validated with the results in the paper.
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Paper Description (PCM)
The present problem simulates the process of melting of phase change materials inside a finned tube using ANSYS Fluent software. The simulation is based on the data in the reference article [Enhance heat transfer for PCM melting in triplex tube with internal–external fins], and the results are compared and validated with the results in the paper. This simulation is performed in two dimensions and hence, only a hollow circular section of the pipe is modeled.
The pipe has four rows of outer fins connected to the inner diameter wall of the pipe and four rows of inner fins connected to the outer diameter wall of the pipe; So that the material of these inner and outer walls as well as their fins is made of copper. Inside the tube, the phase change material is RT-82.
So that it has an initial density of 770 kg.m-3 in boussinesq mode, specific heat capacity equal to 2000 j.kg-1.K-1 and thermal conductivity equal to 0.2 Wm-1.K-1 and viscosity equal to 0.03499 kg .m-1.s-1. Since the aim of the present work is to investigate the changes of solid and liquid phases due to the phenomenon of melting and freezing over time, the solidification and melting model has been used.
To define the solidification and melting model, the maximum temperature at which only the liquid phase prevails (Tsolidus) is equal to 70℃ and the minimum temperature at which only the liquid phase is dominant (Tliquidus) is equal to 82℃ and the latent heat of solvent melting in the pure state (pure solvent melting heat) is equivalent to 176000 j.kg-1. The inner wall of the tube and its outer fins, and also the outer wall of the tube and its inner fins have a constant temperature equal to 90℃; While the phase change material inside the tube has an initial temperature of 27℃.
Geometry & Mesh
The present model is designed in two dimensions using Design Modeler software. The model consists of a circular cross section of a pipe that has four rows of outer fins on the inner wall of the tube and also four rows of inner fins on the outer wall of the tube.
The meshing of the model has been done using ANSYS Meshing software and the mesh type is structured. The element number is 17856. The following figure shows the mesh.
PCM CFD Simulation
To simulate the present model, several assumptions are considered:
- We perform a pressure-based solver.
- The simulation is unsteady. Because the aim of the present work is to investigate the process of melting the phase change material inside the tube over time.
- The gravity effect on the fluid is equal to -9.81 m.s-2 along the Y-axis.
A summary of the defining steps of the problem and its solution is given in the following table:
|Solidification & Melting Model||On|
|Mushy zone parameter||100000|
|Wall with internal fins||Wall|
|Wall with external fins||Wall|
|momentum||second order upwind|
|energy||second order upwind|
|gauge pressure||0 Pascal|
|x-velocity & y-velocity||0 m.s-1|
At the end of the simulation process, the results of the present work were compared with the results in the paper. For this purpose, the diagrams in Figures 7 and 13 of the paper are used, which are related to changes in the average temperature of phase change materials over time and changes in the liquid mass fraction resulting from the melting process over time, respectively. The present work is related to the state of the paper in which the phase change materials are simultaneously affected by the inner fins and the outer fins.
Comparison of the results of the present work with the results of the article is shown in following figures.
Also, after the solution process, two-dimensional contours related to pressure and temperature as well as the liquid mass fraction resulting from the melting process are obtained. Because the simulation process is transient, the results of the present work are taken at different times of the output simulation.
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.