Secondary flow

Secondary flow happens when you move something around, like water or air, in a pipe or a tube. Think of it like this - imagine a straw. When you blow air through a straw, the air moves in a straight line from your mouth through the straw and out the other end. But what happens if you move the straw around while blowing air through it? The air starts to move in different directions - up and down, side to side and round in circles. This is what we call secondary flow.

In a pipe, secondary flow happens because of the way liquid or gas moves across a curved pipe or around objects in the pipe. Just like with the straw, the movement of the liquid or gas produces swirling, circular motion that creates secondary flow.

Now let's take an example of how secondary flow can cause problems. Imagine you are trying to pipe water into a building through a curved pipe. The water is moving in a straight line, but when it hits the curve, it starts to move in different directions. This creates turbulence and pressure changes that can cause the water to slow down, which means that less water will reach the building. Additionally, the turbulence can cause the formation of sediment build-up, which can cause the pipes to clog over time.

So, secondary flow is a process that makes things move in different directions, and it can cause problems in pipes and tubes when trying to move liquids or gases around, like water or air.