PCM Solar Collector CFD Simulation by ANSYS Fluent Training
The present problem simulates heat transfer within a solar collector with phase change material using ANSYS Fluent software.
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The present problem simulates heat transfer within a PCM solar collector using ANSYS Fluent software. The current model consists of a U-shaped tube that carries water flow. Around this U-shaped tube, a cylindrical space is used, composed of phase change material (PCM). Around this space for phase change materials, three layers are placed in a cylindrical shape. Its first layer is a solid body made of aluminum and is defined as a heat-absorbing layer caused by solar radiation. There is a layer of the air gap in the next layer and then a layer of glass. This system’s functional mechanism is that the heat caused by sunlight passes through the glass layer and heats the air layer.
This heat is transferred to the absorbent layer to absorb heat in this layer. This heat is transferred to space with phase change materials to cause a phase change in these materials. Based on the phase change in the particular layer of phase change materials, it is possible to create cooling or heating in the U-shaped tube. Phase change materials act based on their latent heat, i.e., heat absorbed or lost during the phase change. During the day when the air is warm, and there is sunlight, these materials receive the sun’s heat through the absorber layer, and part of this heat is spent on the phase change or the same process of melting in these materials. These phase change materials can store this latent heat from the melting process.
Then, during cold weather (night), these PCMs return the latent heat stored in the environment to the surrounding environment by changing the phase, i.e., the freezing (solidification) process, thus heating the water flow inside the U-shaped tube in cold weather. The solidification and melting model is used to define the PCM material. Definition PCM material with density equal to 910 kg.m-3, specific heat capacity equal to 2100 j.kg-1K-1, thermal conductivity equal to 0.5 Wm-1.K-1 and viscosity equal to 0.0273 kg.m-1 .s-1. Also, the maximum temperature at which the solid phase temperature is (solidus temperature) is 302 K. The minimum temperature at which the liquid phase is dominant (liquidus temperature) is 310 K.
The latent heat of melting of the pure solvent melting heat is defined as 178000 j.kg-1. The radiation model is used to define radiant heat transfer and solar radiation. The radiation process is described as discrete ordinate or DO. This model is used for cases where the radiation heat transfer equations are solved for a discrete number of finite solid angles. This radiation model is suitable for transparent environments, glossy screens such as mirrors, wave-dependent transmission, light scattering modes, etc. Also, to apply solar radiation, solar ray tracing mode has been activated.
Then items such as longitude and latitude of the place under sunlight, date and time of radiation, solar radiation directions, direct radiation intensity, and scattering radiation intensity should be adjusted.
PCM Solar Collector Geometry & Mesh
The present model is designed in three dimensions using Design Modeler software. A U-shaped pipe is two parallel pipes that carry water flow. A cylindrical layer having phase change material is located around this tube. A layer of an aluminum absorbent tube in an incomplete cylinder is located around this fluid. A layer of air space in the form of an incomplete cylinder is around this aluminum tube. Finally, there is a layer of glass in an incomplete cylinder around this air space.
We carry out the model’s meshing using ANSYS Meshing software, and the mesh type is structured. The element number is 969866 . The following figure shows the mesh.
PCM Solar Collector CFD Simulation
We consider several assumptions to simulate the present model:
- We perform a pressure-based solver.
- The simulation is steady.
- The gravity effect on the fluid is ignored.
The following table represents a summary of the defining steps of the problem and its solution:
|Models (PCM Solar Collector)
|Radiation Model||Discrete Ordinates|
|solar load||solar ray tracing|
|number of Eulerian phases||2 (water & air)|
|direct solar irradiation||1000 W.m-2|
|diffuse solar irradiation||0 W.m-2|
|Boundary conditions (PCM Solar Collector)
|velocity magnitude||0.1 m.s-1|
|gauge pressure||0 pascal|
|Wall of U-type (between fluids & PCM)||Wall|
|(PCM Solar Collector)||thermal condition||coupled|
|Wall (between air & glass)||Wall|
|Wall (between absorber & air)|
|(PCM Solar Collector)||thermal condition||convection|
|heat transfer coefficient||12.7 W.m-2.K-1|
|free stream temperature||300 K|
|direct irradiation||0 W.m-2|
|diffuse irradiation||666 W.m-2|
|wall motion||stationary wall|
|heat flux||0 W.m-2|
|Methods (PCM Solar Collector)
|Pressure||body force weighted|
|momentum||second order upwind|
|energy||second order upwind|
|discrete ordinates||first order upwind|
|Initialization (PCM Solar Collector)
|gauge pressure||0 pascal|
|velocity (x,y,z)||0 m.s-1|
Results & Discussions
At the end of the solution process, three-dimensional and two-dimensional contours related to the pressure, velocity, temperature, and mass fraction of the produced liquid are obtained from the phase change material. The images show that the central cylindrical medium carrying the phase change material has more phase change and, as a result, the melting process and more liquid production. It is also clear from the images that heat is transferred to the U-shaped tube.
There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.