You might think that they are designed to help the blade to cut more efficiently through the air. This isn’t strictly true. The dimples don’t make the blade more aerodynamic. Instead, they decrease pressure drag, contributing to the fan’s overall performance. This is how it works.

When air moves over the curved surface of the fan blade, it changes speed. A thin layer of air forms close to the surface, caused by the friction between the blade and the air. 

This layer of air is known as a boundary layer and it slows down the air passing over the blade. Other examples of boundary layers include air passing over an airplane wing or water flowing over the hydrofoil of a ship. A boundary layer also forms around a golf ball when it is in flight. 

The dimples on the fan blade are designed to disrupt the flow of air within the boundary layer. Without the dimples, a thick boundary layer can form, creating a large wake behind the back of the blade. This is what creates the drag. 

The dimples act as a vortex generator, breaking up the boundary layer by creating turbulence. This smooths out the air flow, moving it further away from the back of the blade. The result is a smaller wake and a reduction in drag.

In a golf ball, the turbulence created by the dimples mixes the air in the boundary layer with the surrounding air. This allows more of the ball’s kinetic energy to be retained, allowing it to fly further. 

You might think that there would be an increase in friction across the surface of the ball – and you would be right. However, the increase in friction is quite small while the reduction in pressure drag is significant. Overall, there is a large increase in efficiency. 

Compared to a golf ball, the dimples on a Unada fan make a negligible direct impact. A fan is not a sphere having to cut through the air. It is already a streamlined shape designed to rotate at 2400 rpm. As such the disruption of the boundary layer by the dimples makes only a tiny contribution. It's why you won't find dimples on a Formula One car either. 

Designing a highly-efficient refrigeration fan involves many interrelated factors. Unada's design team analyse every factor in this complex system using computational fluid dynamics, adjusting each one in turn to see the effect on other elements. 

Adding the dimples helps improve stability in the system as a whole, making it possible to adjust and improve other fan parameters, such as the size of the blade or its pitch, which have a much larger contribution to the fan's overall efficiency.