Solar Heat Exchanger, ANSYS Fluent CFD Simulation Training
The present problem simulates a solar heat exchanger using ANSYS Fluent software.
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The present problem simulates a solar heat exchanger using ANSYS Fluent software. This system consists of two parts; So that the water flow moves in the central part of the heat exchanger and the air flow is in the gap installed in the front plate of the heat exchanger. The water flow enters the heat exchanger at a speed of 4 m.s-1 and a temperature of 30 ° C and leaves the heat exchanger at atmospheric pressure. The heat exchanger absorber wall is exposed to solar radiation and absorbs heat through radiant heat transfer. This means that the air gap temperature in front of the absorber plate rises as the sun heats up.
This increase in air temperature causes heat to be transferred to the absorber plate, and subsequently, heat is transferred from the absorber plate to the water flow inside the heat exchanger. Therefore, the water flow inside the system increases with the temperature received by the absorber plate. Also, to enhance heat transfer, several rows of inner walls are designed as a barrier inside the heat exchanger to prolong the flow of water and increase the chance of contact with the absorber plate. To define radiant heat transfer, the radiation model is used and the defined radiation model is discrete ordinates (DO). Also, solar ray tracing model has been used to apply solar load on the heat exchanger.
The amount of direct solar radiation is defined as 1150 W.m-2 and the amount of diffuse solar radiation is defined as 80 W.m-2 and the direction of the sun’s rays is defined perpendicular to the absorber plane.
Solar Heat Exchanger Geometry & Mesh
The present model is designed in three dimensions using Design Modeler software. The model is related to a heat exchanger that consists of a central part for the water flow and a special space for air. The inlet and outlet of the water flow are located on the side wall of the heat exchanger and there are several rows of barriers inside the water flow space, which are specially designed to guide the water flow.
We carry out the model’s meshing using ANSYS Meshing software, and the mesh type is structured. The element number is 304200. The following figure shows the mesh.
Solar Heat Exchanger 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:
|near wall treatment||standard wall functions|
|Radiation Model||Discrete Ordinates|
|solar model||solar ray tracing|
|direct solar irradiation||1150 W.m-2|
|diffuse solar irradiation||80 W.m-2|
|velocity magnitude||4 m.s-1|
|gauge pressure||0 pascal|
|wall motion||stationary wall|
|Inner & Outer Walls||Wall|
|wall motion||stationary wall|
|heat flux||0 W.m-2|
|momentum||second order upwind|
|turbulent kinetic energy||second order upwind|
|turbulent dissipation rate||second order upwind|
|energy||first order upwind|
|discrete ordinates||first order upwind|
|gauge pressure||0 Pascal|
|y-velocity & z-velocity||0 m.s-1|
Results & Discussions
At the end of the solution process, two-dimensional and three-dimensional contours related to pressure, speed and temperature are obtained. The results show that the water flow temperature increases from the inlet section to the outlet section. These temperature changes indicate that the radiant heat transfer and the effect of the solar beam charge are completely applied to the heat exchanger absorber plate and, consequently, to the water flow.
There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.