Explanation:

Introduction:
Fins are used in various heat transfer applications to increase the heat transfer rate from a surface. They are typically thin, elongated structures attached to a surface and are designed to enhance heat transfer by increasing the effective surface area.

Increased Surface Area:
The primary purpose of using fins is to increase the effective surface area of the system. By adding fins to a surface, the total area available for heat transfer is increased. This results in a larger contact area for the fluid or medium surrounding the surface, allowing for more efficient heat transfer.

Heat Conduction:
Fins rely on heat conduction to transfer heat from the surface to the surrounding fluid or medium. As heat is conducted through the fins, it is gradually dissipated to the surroundings, thereby reducing the temperature of the surface. The temperature gradient along the fin length drives the heat transfer process.

Convection Heat Transfer:
The increased surface area provided by the fins enhances the convective heat transfer process. Convective heat transfer occurs when a fluid or medium flows over the surface and carries away the heat. The larger surface area allows for a greater interaction between the fluid and the fin surface, resulting in improved convective heat transfer.

Heat Transfer Coefficient:
The convective heat transfer coefficient is a measure of the efficiency of heat transfer between a surface and a fluid. While fins do not directly increase the convective heat transfer coefficient, they indirectly improve it by increasing the surface area available for convective heat transfer. The convective heat transfer coefficient depends on various factors such as fluid properties, flow conditions, and surface characteristics.

Conclusion:
In summary, fins are used to increase the heat transfer from a surface primarily by increasing the effective surface area. This leads to enhanced convective heat transfer and improved overall heat transfer performance. The other options mentioned in the question, such as increasing the temperature difference or convective heat transfer coefficient, are not directly related to the function of fins in heat transfer applications. Therefore, the correct answer is option 'B' - increasing the effective surface area.