Flow through a Tube with U-Bend: Smooth vs. Rough Walls - Simulation Example


Heat exchangers are devices used to exchange heat between different fluids separated by solid walls to prevent mixing. They are employed in a wide variety of heating and cooling applications such as refrigeration, petroleum refineries, process industries, chemical plants and power plants. One common type of heat exchanger is the double-pipe heat exchanger. As the name suggests, there are two concentric pipes in the double-pipe heat exchanger — one outside and one inside. The outer pipe is called the shell side and the inner one is called the tube side.

The fluid flow in the double-pipe heat exchanger is generally pressure driven. A pump generates favorable driving pressure, and this pressure must overcome the major and minor losses experienced by the flowing fluid. Apart from parameters like the pipe diameter, the mass flow rate of the fluid and fluid properties such as density and viscosity, these losses are also dependent on the surface roughness of the pipe walls. Because of the flow conditions and high-temperature environments, it is common for  smooth pipe walls to corrode over time and become rough. In this simulation example, we will learn about the impact of wall roughness on the major and minor losses in the tube-side flow through a double-pipe heat exchanger.


In this simulation example, we will learn to simulate the fluid flow on the tube side of the double-pipe heat exchanger. The pipe on the tube side generally forms a U-shape. We will use Ansys Fluent to simulate the flow through this single U-bend and compare the major and minor losses between pipes with smooth and rough walls. The working fluid is water and the flow velocity is 1.5 m/s.


Download the Mesh file required for setting up the simulation and associated Case & Data files here. Follow the instructions below to set up this simulation in Ansys Fluent starting with the Mesh file. In case you face any issues setting up or running the simulation, refer to the corresponding initial and final Case and Data files.

Alternate video link.

Results & Discussion

Let’s now take a look at the impact of surface wall roughness on the major and minor losses in the tube.