Description

The present problem simulates heat transfer within a PCM solar collector using ANSYS Fluent software. We perform this CFD project and investigate it by CFD analysis.

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 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. 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.

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 present model is designed in two 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.

An aluminum absorbent tube layer 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.

The meshing of the model has been done using ANSYS Meshing software, and the mesh type is structured. The element number is 969866.

PCM Solar Collector Methodology

The solidification and melting model is used in this simulation to define phase change materials. The PCM material is defined to have a density equal to 910 kg.m-3, specific heat capacity equal to 2100 j/kgK, thermal conductivity equal to 0.5 W/mK and viscosity equal to 0.0273 kg.m-1 .s-1.

Also, the maximum temperature at the solid phase temperature (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. 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, solar ray tracing mode has been activated to apply solar radiation. 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.

Moreover, the laminar model and energy equation are enabled to solve fluid equations and calculate temperature change within the domain.

PCM Solar Collector Conclusion

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 PCM medium inside the central cylindrical has changed phase and, as a result, liquid has been produced in that region. It is also clear from the images that heat is transferred to the U-shaped tube when its inlet and outlet temperature are compared.