Radiator Thermal Performance with Fans, Validation

Radiator Thermal Performance with Fans, Paper Numerical Validation, ANSYS Fluent Tutorial

The present problem concerns heat transfer and airflow simulation around a radiator. The present simulation is based on the reference article “CFD Study on Thermal Performance of Radiators in a Power Transformer: Effect of Blowing Direction and Offset of Fans” using ANSYS Fluent software.

Also, the current CFD simulation results are compared and validated with the results of the reference paper. This radiator has three fans for transmitting airflow in the horizontal direction. This radiator consists of several rows of fins and aluminum plates that increase the heat transfer rate.

The present modeling has been done in three dimensions using Design Modeler software. The model consists of three main parts: the radiator body, fans, and the surrounding space.

The radiator consists of four sections, each consisting of fourteen rows of plate fins and two hot water transfer pipes at the top and bottom of the radiators.

Also, three fans have been used to create airflow next to the body of the radiators; The location of the fans in the model of horizontal radiators is on the left side of the radiator and creates airflow in the horizontal direction.

The meshing of the present model has been done using ANSYS Meshing software, and the mesh type is unstructured. Also, according to the physics of the problem and the need for heat transfer between the radiator fins and the airflow, the INFLATION boundary layer mesh is used on the surfaces of the radiator walls.

Also, the FACE SIZING command on the wall surfaces of the radiator fins is used to increase the mesh accuracy. The element number is equal to 4683472.

Radiator Methodology

Hot water flows through the upper and lower pipes of the radiator and its middle fins; In fact, it is assumed that all the walls of the pipes and radiator fins have determined temperatures at different points.

Therefore, the temperature profile depends on the height of the radiator plates. The TEMPERATURE boundary condition applying a UDF is used to define this temperature profile.

This temperature profile of the plates on which the UDF is written is obtained in such a way that the temperature of the hot water entering the radiator from the upper part is initially assumed to be 366.15 K, which after flowing into the pipes and downward moving, heat exchange with the ambient airflow, and reaches its lowest temperature value of 353.15 K in the lower part.

These temperature changes are mainly due to the movement of the flow in the vertical direction. The mentioned UDF is written linearly in the form 346.15 + 5 * y. Also, to apply the effect of the fans, the Fan boundary condition is used in the plates located in the middle of the side of the radiator.

Since the input flow to these fans is in the horizontal direction, the rotational speed around the x-axis is considered. The flow in the fans is assumed to be suction by default, but in this model, the fan flow must be blowing, so Reverse Fan Direction is activated to change the airflow direction in the fan.

Also, the amount of pressure jump for each fan is defined as a polynomial pressure function in terms of velocity; Thus, the polynomial function has two coefficients equal to 80 and -10.

Radiator Conclusion

At the end of the solution process, we calculate the net heat loss rate from the radiator plates to the airflow and compare it with the reference paper for Validation. To make this comparison, we use Figure 5 of the article and the ONAF mode (with forced convection heat transfer). We can assume that the rate of heat loss from the radiator body to the surroundings is equal to the air temperature difference between the inlet and outlet. Thus, by using the Report and selecting the Total Heat Transfer Rate option from the Flux Report section, we can calculate the difference in heat transfer rate between the input and output boundaries.

Also, after the completion of the solution process, we obtain two-dimensional and three-dimensional contours of temperature, velocity, and pressure, as well as three-dimensional path lines and velocity vectors.