Laminar Flow Heat Transfer in U-Bend, Paper Validation

Laminar Flow and Heat Transfer in U-Bend, Paper Numerical Validation, CFD Simulation by ANSYS Fluent

The present problem simulates the fluid flow inside a tube with a U-shaped bend by ANSYS Fluent software. The simulation was performed and validated according to the reference article “Laminar flow and heat transfer in U-bends: The effect of secondary flows in ducts with partial and full curvature.”

The fluid defined inside the tube was therminol; Its properties include density equal to 793.9 kg/m3, specific heat capacity equal to 2315 j/kg.K, thermal conductivity equal to 0.116 W/m.K and viscosity equal to 0.00173 kg/m.s.

According to the paper, the simulation has been done in different Reynolds numbers. The present simulation has been done in Reynolds number 1000. According to the formula related to the Reynolds number in the paper, the inlet velocity in the pipe is equal to 0.21791 m/s.

The present 3-D model is drawn using Design Modeler software. This model consists of a tube consisting of a bend. This bend is in the form of two knees connected. The pipe diameter is 0.01m, and the radius of curvature of each elbow is 0.015m.

The meshing has been done using ANSYS Meshing software, and the mesh type is structured. The element number is 2268000.

U-bend Methodology

In this model, the thermal boundary condition on the pipe wall is used; So that a constant heat flux of 1156 W/m2.K is defined on the pipe wall.

U-bend Conclusion

The purpose of the present problem is to investigate the behavior of the flowing fluid in the pipe and its heat transfer in the passage through the pipe bend. At the end of the solution process, the results are compared and validated with the results of the reference article.

First, the results related to the amount of fluid temperature on the pipe’s inner wall and its bending are validated. This validation is performed according to the diagram in Figure 14-b of the article.

For this purpose, a graph of temperature changes in the position of the pipe’s inner wall is drawn. Temperature and position are dimensionless, and the related formulas are presented in the article. The following figure shows a graph of dimensionless temperature changes in dimensionless position.

Then the Nusselt number is investigated in different sections of pipe bending. For this purpose, the value of the Nusselt number, according to the formula in the article, in five different sections (P1, P2, P3, P4, and P5) has been obtained, and its ratio to the value of the Nusselt number in section P1 has been calculated.

These resulting numbers are validated with the values of the dimensionless Nusselt number in the mentioned sections according to the diagram in Figure 19-b. The following table shows the values of the Nusselt number ratio at different sections of the pipe bend.