Consider large scale solar plants that rely on focused solar energy from an array of heliostats onto the receiver sitting atop a tower. Inside the solar receiver, a working fluid is heated to be used in the thermal powerplant cycle. As the receiver operates at a very high temperature, it loses energy by convection and radiation to the ambient atmosphere. The wind flow in the vicinity of the receiver leads to a complex flow field and the boundary layer regions are characterized as mixed convection–flow with a horizontal inertial force and a vertical buoyant force.
This is just one example of many engineering applications that involve convective heat transfer via forced convection, along with natural convection currents that set up in the flow because of existing density gradients. In such situations, the natural convection can either assist or oppose the heat transfer resulting from forced convection. This is known as mixed convection.
But how do we know when to include natural convection in the overall heat transfer analysis? Another important question in designing such applications is “when does a laminar natural convection boundary layer transition to a turbulent one?”
Let’s find out answers to these questions!
Here are the handouts for this lesson.